Question:

I am interested in converting my hot tub to passive solar water heater plans rhodale solar heating.

passive solar water heater plans rhodale I just got some mail from Eagle Pools, a local spa dealer who say “Heating elements are the #1 reason for spa failures in the spa industry.” I will call them again and suggest solar heating. They usually get defensive and tell me spa heating only costs pennies a day. I have a good south roof to use. passive solar water heater plans rhodale ANy idea how many feet of tubeing I need, or any other ideas.

Is the hot tub indoors or outdoors? You might make a simple solar air heater on the south side of an outdoor version.passive solar water heater plans rhodale  Year-round use and the higher-than- swimming-pool-temp argue against covering the roof with two layers of UV-poly film and trickling water between them. Plus, you need so little heat. The Hot tube is 7X7 and holds about 400 gals. passive solar water heater plans rhodale

Four feet tall, with 112 ft^2 of walls and a 49 ft^2 cover, and R20 insulation, eg 4″ of beadboard, and a thermal conductance of 161ft^2/R20 = 8 Btu/F-hr? With 104 F water inside and 36 F air outside, so it needs (104-36)8 = 544 Btu/hour to stay warm, where I live, in December? That’s 13K Btu/day or about 4 kWh or 40 cents a day… Please remember that most hot tubs are used in the evening – usually after the sun has gone down.

OK. And let’s assume that the tub isn’t used all that often, that the cover is mostly in place in the winter. If you blow air into the hot tub it is going to cool off very rapidly -

Why blow air into the tub? And if it loses 544 Btu/hr, and the water weighs 3200 pounds, it will lose 544/3200 = 0.17 F degrees per hour, no? How about circulating a little sun-warmed air under the hot tub, once in a while? And using a bigger hot tub, or passive solar water heater plans rhodale one with more insulation. A 7×7x4′ tall hot tub will hold about 12K pounds of water. Surround it with R40 insulation, and it will only lose 6.5K Btu/day, cooling off 0.5 F per day–4 days, 2 degrees. and you are going to need a “on-demand” heater -eg: natural gas or electric to keep the tub warm.

Really? Well, most people like precise hot tub temperature control: 103 F seems very cold, and 105 seems very warm. We can’t store much solar heat for a cloudy week in that kind of temperature swing. We could store 6.5K Btu per day for 5 days in 1300 pounds of water cooling from 130 F to 105 F. In 3 plastic 55 gallon drums full of water,passive solar water heater plans rhodale  sitting inside a strawbale skirt? If the tub is built on a 4′ pedestal, this could be a completely passive system. Were we concerned that the drum surface be insufficient, 25 ft^2 each, compared to 28 ft^2 of solar glazing, we might use 32 5 gallon plastic paint or drywall compound buckets with lids, or 300 2 liter soda bottles. The tub enclosure might have a dark insulated south wall with a single layer of polycarbonate plastic on the outside, over an air gap, and a small PV fan, to collect about 20K Btu/day of sun, or a third more, if there’s a reflective surface on the ground in front, eg a shallow frozen reflecting pool, used for water replenishment and treatment, vs chemicals. No insulation under the tub, and a small PV/battery-powered fan that circulates a little warm air under the tub on a cloudy day. If the tub bottom were 6′ square, and the fan moved air at 6 mph with a 1 F delta T, the surface air film thermal conductance of the tub bottom would be about (2+6/2)36ft^2 = 180 Btu/F-hr, so 544 = 1F(180)cfm, roughly, so we would need a 3 cfm fan, or in a more passive version with slightly less accurate temperature control, a damper with a bimetallic spring, like the $12 Leslie-Locke FV-1B automatic foundation vent from Home Depot. Solar can work, but it has its’ limitations, it is usually not installed as the only heater for a hot tub (or Spa).

What we usually do is use oil to heat water, and bomb Iraq when the oil price threatens to go up. I suppose we could use gas or electricity instead, but have you noticed the sun? passive solar water heater plans rhodaleI am interested in converting my hot tub to solar heating. Nice I just got some mail from Eagle Pools, a local spa dealer who say “Heating elements are the #1 reason for spa failures in the spa industry.” I will call them again and suggest solar heating. They usually get defensive and tell me spa heating only costs pennies a day. I have a good south roof to use. ANy idea how many feet of tubeing I need, or any other ideas. Is the hot tub indoors or outdoors? You might make a simple solar air heater on the south side of an outdoor version. Year-round use and the higher-than- swimming-pool-temp argue against covering the roof with two layers of UV-poly film and trickling water between them. Plus, you need so little heat. The Hot tube is 7X7 and holds about 400 gals. Four feet tall, with 112 ft^2 of walls and a 49 ft^2 cover, and R20 insulation, eg 4″ of beadboard, and a thermal conductance of 161ft^2/R20 = 8 Btu/F-hr? With 104 F water inside and 36 F air outside, so it needs (104-36)8 = 544 Btu/hour to stay warm, where I live, in December? That’s 13K Btu/day or about 4 kWh or 40 cents a day…

Note: that the spa above could only be about two feet deep, if it hold only 400 gallons. Please remember that most hot tubs are used in the evening – usually after the sun has gone down.

The point is that you are going to need to store the heat for use later, rather than heat the spa with solar directly “on demand”. Storage systems are cumbersome (at best) and expensive and ineffective at worst. OK. And let’s assume that the tub isn’t used all that often, that the cover is mostly in place in the winter. If you blow air into the hot tub it is going to cool off very rapidly – passive solar water heater plans rhodale

Most spas and hot tubs have air blowers to create the physical sensations craved by the owners. Unfortunately this increases evapouration dramatically and cools the spa off rapidly. Why blow air into the tub? And if it loses 544 Btu/hr, and the water weighs 3200 pounds, it will lose 544/3200 = 0.17 F degrees per hour, no? How about circulating a little sun-warmed air under the hot tub, once in a while? And using a bigger hot tub, or one with more insulation. A 7×7x4′ tall hot tub will hold about 12K pounds of water. Surround it with R40 insulation, and it will only lose 6.5K Btu/day, cooling off 0.5 F per day–4 days, 2 degrees. and you are going to need a “on-demand” heater -eg: natural gas or electric to keep the tub warm. Really? Well, most people like precise hot tub temperature control: 103 F seems very cold, and 105 seems very warm. We can’t store much solar heat for a cloudy week in that kind of temperature swing.

This is exactly my point. People don’t want a system that causes variations in the spa temp. A direct solar water heater WILL cause this to happen. passive solar water heater plans rhodale-We could store 6.5K Btu per day for 5 days in 1300 pounds of water cooling from 130 F to 105 F. In 3 plastic 55 gallon drums full of water, sitting inside a strawbale skirt? If the tub is built on a 4′ pedestal, this could be a completely passive system. Were we concerned that the drum surface be insufficient, 25 ft^2 each, compared to 28 ft^2 of solar glazing, we might use 32 5 gallon plastic paint or drywall compound buckets with lids, or 300 2 liter soda bottles. The tub enclosure might have a dark insulated south wall with a single layer of polycarbonate plastic on the outside, over an air gap, and a small PV fan, to collect about 20K Btu/day of sun, or a third more, if there’s a reflective surface on the ground in front, eg a shallow frozen reflecting pool, used for water replenishment and treatment, vs chemicals. No insulation under the tub, and a small PV/battery-powered fan that circulates a little warm air under the tub on a cloudy day. If the tub bottom were 6′ square, and the fan moved air at 6 mph with a 1 F delta T, the surface air film thermal conductance of the tub bottom would be about (2+6/2)36ft^2 = 180 Btu/F-hr, so 544 = 1F(180)cfm, roughly, so we would need a 3 cfm fan, or in a more passive version with slightly less accurate temperature control, a damper with a bimetallic spring, like the $12 Leslie-Locke FV-1B automatic foundation vent from Home Depot. Solar can work, but it has its’ limitations, it is usually not installed as the only heater for a hot tub (or Spa). What we usually do is use oil to heat water, and bomb Iraq when the oil price threatens to go up. I suppose we could use gas or electricity instead, but have you noticed the sun? Nick

I revel in the sun. I also refuse to install systems that can’t or won’t work. If you made a living from this type of business, you would quickly realize what is practical and cost-effective, rather than what can technically be done if you have enough space, time and money. Andrew McKegney C.E.T.passive solar water heater plans rhodale

Response:

If you blow air into the hot tub it is going to cool off very rapidly – Most spas and hot tubs have air blowers to create the physical sensations craved by the owners. Unfortunately this increases evapouration dramatically and cools the spa off rapidly.

Perhaps they should not have air blowers. Perhaps this is an undesirable energy-wasting craving, unhealthy for the earth and the pocketbook. Consider Japanese hot tubs. Should this craving be more sparingly indulged? How many cfm are needed to satisfy this craving? How much heat does 1 cfm remove from the tub? How much power does the air pump need to move 1 cfm? Where are the spa heating professionals who know how to use numbers, when you need them? Please remember that most hot tubs are used in the evening – usually after the sun has gone down. The point is that you are going to need to store the heat for use later, rather than heat the spa with solar directly “on demand”. passive solar water heater plans rhodale

As I recall, we figured the cooling rate for a well-coverd tub like this might be 0.2 degrees F per hour. So the point is, at that rate, why worry about the amount of time between day and evening? Storage systems are cumbersome (at best) and expensive and ineffective at worst.

How does this sound? Telephones are cumbersome (at best) and expensive and ineffective at worst.

I used to work for Western Union, a status-quo company whose president told Alexander Graham Bell that his invention was preposterously expensive (he wanted $8,000) and useless… “Why would anyone use this ‘telephone,’” he said, “if they could simply send a telegram?” When I worked there, one major corporate goal was to “Exploit the world of data communications, at 50 baud and below.” Western Union is bankrupt now. This storage system does use a lot of space. But there may be lots of empty space under the tub, inside the enclosure. This could be smaller with an extremely efficient heat pump, like a small jet engine… Compress and heat some warm air from the storage compartment using a fan, make it flow past the tub bottom to lose heat, and despin the air with another fan attached to the first by a shaft, to partially power the first fan. This might also make the solar air heater more efficient. If you made a living from this type of business, you would quickly realize what is practical and cost-effective, rather than what can technically be done if you have enough space, time and money.

I might just get lazy and sell what I can. But that’s not my job. Nick       Noone is exempt from occasionally uttering nonsense.       The misfortune is to do so solemnly.      –Moliere

Response:

If you blow air into the hot tub it is going to cool off very rapidly – Most spas and hot tubs have air blowers to create the physical sensations craved by the owners. Unfortunately this increases evapouration dramatically and cools the spa off rapidly. Perhaps they should not have air blowers. Perhaps this is an undesirable energy-wasting craving, unhealthy for the earth and the pocketbook. Consider Japanese hot tubs. Should this craving be more sparingly indulged? How many cfm are needed to satisfy this craving? How much heat does 1 cfm remove from the tub? How much power does the air pump need to move 1 cfm? Where are the spa heating professionals who know how to use numbers, when you need them?

“Perhaps they should not have air blowers.” Well, perhaps they should outlaw hot-tubs and spas all-together!! They are a fact of life and wishing they away is not going to change that reality. I do’t have the numbers but I suspect the ratings on the spa blowers are close to 100 cfm. That’s using cold air with continuous operation for 10-20 minutes. Please remember that most hot tubs are used in the evening – usually after the sun has gone down. The point is that you are going to need to store the heat for use later, rather than heat the spa with solar directly “on demand”. As I recall, we figured the cooling rate for a well-coverd tub like this might be 0.2 degrees F per hour. So the point is, at that rate, why worry about the amount of time between day and evening?

The time of USE is the problem. There will be no solar energy available (unless it is stored somewhere) when the spa is in use -ie after the sun has gone down! Storage systems are cumbersome (at best) and expensive and ineffective at worst. How does this sound? Telephones are cumbersome (at best) and expensive and ineffective at worst. I used to work for Western Union, a status-quo company whose president told Alexander Graham Bell that his invention was preposterously expensive (he wanted $8,000) and useless… “Why would anyone use this ‘telephone,’” he said, “if they could simply send a telegram?” When I worked there, one major corporate goal was to “Exploit the world of data communications, at 50 baud and below.” Western Union is bankrupt now.

Your point with this? This storage system does use a lot of space. But there may be lots of empty space under the tub, inside the enclosure.

Very unlikely. Most tubs I’ve seen are shoehorned into an existing space.  This could be smaller with an extremely efficient heat pump, like a small jet engine… Compress and heat some warm air from the storage compartment using a fan, make it flow past the tub bottom to lose heat, and despin the air with another fan attached to the first by a shaft, to partially power the first fan. This might also make the solar air heater more efficient.

Again with the jet engines! I still think a small nuclear reactor would be a better option! If you made a living from this type of business, you would quickly realize what is practical and cost-effective, rather than what can technically be done if you have enough space, time and money. I might just get lazy and sell what I can. But that’s not my job.

Sorry for you. I don’t sell what I can, I only sell what works, that is my job. Andy      No one is exempt from occasionally uttering nonsense.      The misfortune is to do so solemnly.      –Moliere

This is very true. Please look in a mirror.

Response:

If you blow air into the hot tub it is going to cool off very rapidly – Most spas and hot tubs have air blowers to create the physical sensations craved by the owners. Unfortunately this increases evapouration dramatically and cools the spa off rapidly.

no u here… Hmmm. Mebbie he’s English, not just ignorant… Perhaps they should not have air blowers. Perhaps this is an undesirable energy-wasting craving, unhealthy for the earth and the pocketbook. Consider Japanese hot tubs. Should this craving be more sparingly indulged? How many cfm are needed to satisfy this craving? How much heat does 1 cfm remove from the tub? How much power does the air pump need to move 1 cfm? Where are the spa heating professionals who know how to use numbers, when you need them? “Perhaps they should not have air blowers.” Well, perhaps they should outlaw hot-tubs and spas all-together!!

I wouldn’t say so. They are a fact of life and wishing they away is not going to change that reality.

Is it OK to question their design, and energy efficiency, and where that energy comes from? I do’t have the numbers but I suspect the ratings on the spa blowers are close to 100 cfm. That’s using cold air with continuous operation for 10-20 minutes.

Well, perhaps that’s a small energy crime. The hot tub blower in the Grainger catalog uses 35 cfm and 700 watts. Perhaps you can tell us how much heat that removes from the tub, as 70F room air is raised to 104 F and saturated with humidity. No big deal if it’s indoors, I guess. Please remember that most hot tubs are used in the evening – usually after the sun has gone down. The point is that you are going to need to store the heat for use later, rather than heat the spa with solar directly “on demand”. As I recall, we figured the cooling rate for a well-coverd tub like this might be 0.2 degrees F per hour. So the point is, at that rate, why worry about the amount of time between day and evening? The time of USE is the problem. There will be no solar energy available (unless it is stored somewhere) when the spa is in use -ie after the sun has gone down!

Recall the tub temp decreases by 0.2 F per hour? I’m beginning to suspect you are an idiot, Andy. This storage system does use a lot of space. But there may be lots of empty space under the tub, inside the enclosure. Very unlikely. Most tubs I’ve seen are shoehorned into an existing space.

Seems like what matters is what’s under the tub, not what’s around it. This could be smaller with an extremely efficient heat pump, like a small jet engine… Compress and heat some warm air from the storage compartment using a fan, make it flow past the tub bottom to lose heat, and despin the air with another fan attached to the first by a shaft, to partially power the first fan. This might also make the solar air heater more efficient. Again with the jet engines! I still think a small nuclear reactor would be a better option!

Chacun a son chauffage. Nick It’s a snap to save energy in this country. As soon as more people become involved in the basic math of heat transfer and get a gut-level, as well as intellectual, grasp on how a house works, solution after solution will appear.                                           Tom Smith

Response:

If you blow air into the hot tub it is going to cool off very rapidly – Most spas and hot tubs have air blowers to create the physical sensations craved by the owners. Unfortunately this increases evapouration dramatically and cools the spa off rapidly.     no u here… Hmmm. Mebbie he’s English, not just ignorant…

I’m not an ignorant American. Perhaps they should not have air blowers. Perhaps this is an undesirable energy-wasting craving, unhealthy for the earth and the pocketbook. Consider Japanese hot tubs. Should this craving be more sparingly indulged? How many cfm are needed to satisfy this craving? How much heat does 1 cfm remove from the tub? How much power does the air pump need to move 1 cfm? Where are the spa heating professionals who know how to use numbers, when you need them? “Perhaps they should not have air blowers.” Well, perhaps they should outlaw hot-tubs and spas all-together!! I wouldn’t say so. They are a fact of life and wishing they away is not going to change that reality. Is it OK to question their design, and energy efficiency, and where that energy comes from?

Sure. Not that it is going to make a bit of difference to the industry. I do’t have the numbers but I suspect the ratings on the spa blowers are close to 100 cfm. That’s using cold air with continuous operation for 10-20 minutes. Well, perhaps that’s a small energy crime. The hot tub blower in the Grainger catalog uses 35 cfm and 700 watts. Perhaps you can tell us how much heat that removes from the tub, as 70F room air is raised to 104 F and saturated with humidity. No big deal if it’s indoors, I guess.

It’s a big deal because a tremendous amount of heat is lot to evapouration, and the humidity in the room must be dealt with. (if indoors). Please remember that most hot tubs are used in the evening – usually after the sun has gone down. The point is that you are going to need to store the heat for use later, rather than heat the spa with solar directly “on demand”. As I recall, we figured the cooling rate for a well-coverd tub like this might be 0.2 degrees F per hour. So the point is, at that rate, why worry about the amount of time between day and evening? The time of USE is the problem. There will be no solar energy available (unless it is stored somewhere) when the spa is in use -ie after the sun has gone down! Recall the tub temp decreases by 0.2 F per hour? I’m beginning to suspect you are an idiot, Andy.

Im not worried about the heat loss when the spa is unused and covered!!!! There is practically none! It’s when the spa is being USED!!!! How many times do I have to say this!!! It’s you that is the idiot, Nick!!! This storage system does use a lot of space. But there may be lots of empty space under the tub, inside the enclosure. Very unlikely. Most tubs I’ve seen are shoehorned into an existing space. Seems like what matters is what’s under the tub, not what’s around it.

You obviously have NO IDEA how spas and hot tubs are made and installed in 95 + % of the installations. If people have bags of money, or if the tubs are for commercial applications, it is possible there would be space for a solar heat storage tank. BUT, in those instances 1.) those with money probably wouldn’t care what it costs to heat the tub while they use it ie: no market to sell a solar system and 2.) commercial applications would have a much higher heat load due to constant use, a storage system would become very large, commercial sites typically want a 1-2 year payback instead of the 10-15 year payback the system might be able to provide – not to mention their concern over the aesthetics of the project. ie: no market to sell a solar system. I’m trying to deal with the realities of the marketplace here, not wish upon a star that “something” could be done. Chacun a son chauffage.

A meme tout vous! Nick It’s a snap to save energy in this country. As soon as more people become involved in the basic math of heat transfer and get a gut-level, as well as intellectual, grasp on how a house works, solution after solution will appear.

Tom Smith “As soon as it hurts peoples’ pocketbooks, they’ll come seeking answers.” Andrew McKegney 1996

Response:

Question:

I want to run a solar water heater recirculation pump with a PV cell. passive solar water heater plans rhodale Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt passive solar water heater plans rhodale

Response:

Just use a small bilge pump that they use in sailboats. They run on 12V and are cheap.passive solar water heater plans rhodale You will have tomodify the pump so you can connect an inlet pipe.

Response:

I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for passive solar water heater plans rhodale a 12VDC recurculation pump that will run powered by a single 50watt PV?

that 50 watts is enough.  It may be that if you do not have too much head (verticle lift + losses from the piping) you can get by with a cheap centrifugal pump than would draw 1-2amps at 12v.  Single outlet (like a faucet) pumps for RV’s cost about $20.00,passive solar water heater plans rhodale and aquarium or boat type bilge pumps may work.  You don’t need a high flow rate, but low volume and pressure over about 5PSI is real hard to come by.  Aquarium pumps are about the right size if you can live with the pressure, but 12v ones are hard to find.  They do make them tho..passive solar water heater plans rhodale..  We had to go with a RV  3GPM pump in order to get the 10 PSI we needed for the system in our cabin.  The solar H2O panels haven’t been added yet, but the stove does a nice job of heating the water.  The flow rate, pressure, and power usage are all too high. It’s pretty much ideal for supplying system water pressure for the entire building (2 sinks and a shower).  We are adding a thermostat so that the circulation pump will run intermittantly.  Also planned is passive solar water heat valved so that it can be used as a preheater when using the stove, or help maintain hot water otherwise.   Russ

Response:

I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? — Dean Gangstee

Use care in selecting the pump as it will be pumping hot water and most low cost pumps are designed for cold water.  There are a few 12 VDC pumps designed for this application.  Bilge pumps are usually not designed for continuous running.

Response:

Just use a small bilge pump that they use in sailboats. They run on 12V and are cheap. You will have tomodify the pump so you can connect an inlet pipe. Bernard

Will it be able to handle voltage fluctuations (I assume the original poster meant not batteries, just the 50W panel)?

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”? I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation…. Dean Gangstee

passive solar water heater plans rhodale-x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:      Model Volts Watts Amps Max Pressure max Temp Weight MC-201DC-B 12 3.1 0.26 150 PSI 230F 2.1 lba Housing Connection Codes:              BS 1/2″ – Brass inline housing with 1/2″sweat fittings              BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

Just use a small bilge pump that they use in sailboats. They run on 12V and are cheap. You will have tomodify the pump so you can connect an inlet pipe .

Depending on the type of bilge pump (centrifugal) it may not be able to prime itself, so if this is going to be a problem you could try and put an s bend in the inlet pipe. Also depending on the temperatures the water may get contaminated with oils, from the pump ( I am not to sure about this one.) hope this helps.

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location.

Won’t the water flow all the time if it’s using house pressure? (without a special pump)? Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”?

It will only seek it’s own level i.e. like a water level.passive solar water heater plans rhodale-I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation…. Dean Gangstee x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:      Model Volts Watts Amps Max Pressure max Temp Weight MC-201DC-B 12 3.1 0.26 150 PSI 230F 2.1 lba Housing Connection Codes:              BS 1/2″ – Brass inline housing with 1/2″sweat fittings              BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”? passive solar water heater plans rhodale

exactly sure how to figure the head in this situation.  On mine, which is real similar to your, I just added up the verticle lift and figured about 3ft. of head for the 40ft. of 1/2 copper pipe it has to pump thru, giving me about 12 ft. of head. (I simply ignored the parts where the water was flowing downhill. The simple circulation pump that came with the solar water heater wouldn’t work, so it was obviously more than 3ft. of head. But with the pump you are talking about (150 PSI!), it shouldn’t matter.  Just be aware that just the same and find out what the maximum head it will pump against is.  In fact, if these numbers are right (.25 amp ?), I may want to use one of these myself.  Do note that 3gpm is too high a pumping rate.  The water will heat up faster if it remains in the collector longer.  Since it’s a closed system, it won’t make a whole lot of difference, but you are wasting power, and adding to any losses along the way when you are circulating the water 10 times when once would do.  Which is why I want to use a thermostat.  Let me know if you find one somewhere.  Somebody makes in-line thermostats, I just haven’t been able to find one.  Of course, I can adapt an auto thermostat (160deg.) for this. passive solar water heater plans rhodale I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation…. Dean Gangstee x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:      Model Volts Watts Amps Max Pressure max Temp Weight MC-201DC-B 12 3.1 0.26 150 PSI 230F 2.1 lba Housing Connection Codes:              BS 1/2″ – Brass inline housing with 1/2″sweat fittings              BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

passive solar water heater plans rhodale This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Won’t the water flow all the time if it’s using house pressure? (without a special pump)?

No. What you have is a closed loop in a pressurized system. Since system pressure is a constant, you can treat the loop as if it were an independent circuit. If you’ve ever wondered why the hot water comes on so fast in an upper floor of a high-rise building, since the hot water heater must be on the roof or in the cellar or something, here’s why. Large buildings have a well-insulated Recirculating Hot Water Loop. A small pump keeps the water in the loop constantly in slow motion through the heater, meaning that there is hot water just a short distance from every hot water tap in the building. Similarly, large buildings will have a Recirculating Chill Water Loop, where cold water is in constant circulation from the chiller (air conditioner) to heat exchangers in the ducts near the offices. Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”? It will only seek it’s own level i.e. like a water level.

Because the head of pressure on the inlet side is equal to the head of pressure on the outlet side, the pump need only have a small differential pressure to keep the water in motion.

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater.

magazine had two issues early this year that dealt with passive solar water heaters.  It sounds like your system might easily be adapted for that.  Check their web site – I don’t know if you can download those articles but you can find them in the index and order the two back issues. URL is http://www.homepower.com  To figure head (in PSI)I just divide the verticle rise in feet by 2 (it’s actually 33 ft. of water = 1 atmosphere = 14.7 lb. at STP), and add for friction loss in the pipe.  You have to use a formula based on fluid velocity to get the actual losses for a given size of pipe.  For ballpark numbers at 3GPM, 1/2 in. pipe could be 10 foot ( water) of head for each 100ft. of pipe. That’s not really close, just ballpark for rough estimates.  You should also add for each bend.  All in all though, at a low flow rate around 3GPM, you might as well figure it’s less than 10ft. of head in anything under 100ft., as long as you don’t have a lot of bends.  So for 10ft. verticle lift, and up to 100ft. horizontal, you need at least 10PSI pump pressure to start water flowing.  A lower pressure pump might work if you position it up higher and reduce the verticle lift.  The point is that most centrifugal pumps won’t produce enough pressure to lift water to your roof.

Response:

I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation….

You might be able to use a resistance in series with a capacitor (hooked parallels to the pump) as a timer to make the system pause before startup when the sun is shining (giving it some time to actually heat the water).  It would waste some power, but seems simpler that a thermostat and a battery.

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Won’t the water flow all the time if it’s using house pressure? (without a special pump)?

Since the water goes from the bottom tank and back to the bottom tank, the pressure of water entering should have no effect.

Response:

The only problem is that you may need a regulator, as a solar panel may give a voltage up to 15 or 16 volts, which will reduce the life of the pump. Pete – Hide quoted text — Show quoted text – x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump         http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:       Model     Volts   Watts   Amps    Max Pressure    max Temp Weight MC-201DC-B      12      3.1     0.26    150 PSI         230F 2.1 lba Housing Connection Codes:               BS 1/2″ – Brass inline housing with 1/2″sweat fittings               BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV?

We install direct PV powered to DC pump solar hot water systems here in the UK for customers who do not wish to use grid utility electricity. We import the pumps from the USA  and typically use an 12 volt 18 Watt March May magnetic drive pump and a 20 Watt Solarex PV. This would cost around 400 US dollars combined. We hope to change to an even smaller wattage pump soon called the El CID which may keep costs nearer 200 US dollars. Are main priority was reliability and the pump had to meet solar temperatures in excess of 120 Celsius (sealed system with glycol antifreeze) with continuos pumping. If you are in the States, you will find these pumps at the some of the larger solar suppliers on the web by using your search engine but Real Goods comes to mind. — Chris Laughton   The Solar Design Company  England. www.solar-design.demon.co.uk

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Won’t the water flow all the time if it’s using house pressure? (without a special pump)?

Since the water goes from the bottom tank and back to the bottom tank, the pressure of water entering should have no effect.

Response:

I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation….

You might be able to use a resistance in series with a capacitor (hooked parallels to the pump) as a timer to make the system pause before startup when the sun is shining (giving it some time to actually heat the water).  It would waste some power, but seems simpler that a thermostat and a battery.

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”? I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation…. Dean Gangstee

- Hide quoted text — Show quoted text -x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:      Model Volts Watts Amps Max Pressure max Temp Weight MC-201DC-B 12 3.1 0.26 150 PSI 230F 2.1 lba Housing Connection Codes:              BS 1/2″ – Brass inline housing with 1/2″sweat fittings              BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater.

magazine had two issues early this year that dealt with passive solar water heaters.  It sounds like your system might easily be adapted for that.  Check their web site – I don’t know if you can download those articles but you can find them in the index and order the two back issues. URL is http://www.homepower.com  To figure head (in PSI)I just divide the verticle rise in feet by 2 (it’s actually 33 ft. of water = 1 atmosphere = 14.7 lb. at STP), and add for friction loss in the pipe.  You have to use a formula based on fluid velocity to get the actual losses for a given size of pipe.  For ballpark numbers at 3GPM, 1/2 in. pipe could be 10 foot ( water) of head for each 100ft. of pipe. That’s not really close, just ballpark for rough estimates.  You should also add for each bend.  All in all though, at a low flow rate around 3GPM, you might as well figure it’s less than 10ft. of head in anything under 100ft., as long as you don’t have a lot of bends.  So for 10ft. verticle lift, and up to 100ft. horizontal, you need at least 10PSI pump pressure to start water flowing.  A lower pressure pump might work if you position it up higher and reduce the verticle lift.  The point is that most centrifugal pumps won’t produce enough pressure to lift water to your roof.   Russ

Response:

Just use a small bilge pump that they use in sailboats. They run on 12V and are cheap. You will have tomodify the pump so you can connect an inlet pipe. Bernard

Response:

I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? — Dean Gangstee

Response:

Just use a small bilge pump that they use in sailboats. They run on 12V and are cheap. You will have tomodify the pump so you can connect an inlet pipe. Bernard

Depending on the type of bilge pump (centrifugal) it may not be able to prime itself, so if this is going to be a problem you could try and put an s bend in the inlet pipe. Also depending on the temperatures the water may get contaminated with oils, from the pump ( I am not to sure about this one.) hope this helps.

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location.

Won’t the water flow all the time if it’s using house pressure? (without a special pump)? Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”?

It will only seek it’s own level i.e. like a water level. – Hide quoted text — Show quoted text -I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation…. Dean Gangstee x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:      Model Volts Watts Amps Max Pressure max Temp Weight MC-201DC-B 12 3.1 0.26 150 PSI 230F 2.1 lba Housing Connection Codes:              BS 1/2″ – Brass inline housing with 1/2″sweat fittings              BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

The only problem is that you may need a regulator, as a solar panel may give a voltage up to 15 or 16 volts, which will reduce the life of the pump. Pete – Hide quoted text — Show quoted text – x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump         http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:       Model     Volts   Watts   Amps    Max Pressure    max Temp Weight MC-201DC-B      12      3.1     0.26    150 PSI         230F 2.1 lba Housing Connection Codes:               BS 1/2″ – Brass inline housing with 1/2″sweat fittings               BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

- Hide quoted text — Show quoted text – This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Won’t the water flow all the time if it’s using house pressure? (without a special pump)?

No. What you have is a closed loop in a pressurized system. Since system pressure is a constant, you can treat the loop as if it were an independent circuit. If you’ve ever wondered why the hot water comes on so fast in an upper floor of a high-rise building, since the hot water heater must be on the roof or in the cellar or something, here’s why. Large buildings have a well-insulated Recirculating Hot Water Loop. A small pump keeps the water in the loop constantly in slow motion through the heater, meaning that there is hot water just a short distance from every hot water tap in the building. Similarly, large buildings will have a Recirculating Chill Water Loop, where cold water is in constant circulation from the chiller (air conditioner) to heat exchangers in the ducts near the offices. Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”? It will only seek it’s own level i.e. like a water level.

Because the head of pressure on the inlet side is equal to the head of pressure on the outlet side, the pump need only have a small differential pressure to keep the water in motion. —     *                Daly City California:                *     *       where San Francisco meets The Peninsula       *     ******* and the San Andreas Fault meets the Sea *******

Response:

I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? — Dean Gangstee

Use care in selecting the pump as it will be pumping hot water and most low cost pumps are designed for cold water.  There are a few 12 VDC pumps designed for this application.  Bilge pumps are usually not designed for continuous running.

Response:

This one sounds perfect if I understand “head” in my application. I have a tank water heater that I want to tap into at the drain bib and run the water up to the roof (about 10 feet up + 10 feet horazontal run) mounted solar water heater and back to the tank water heater. Since water will be returning to the lower tank does “head” apply when pumping up to the upper tank since the system is a closed loop and under the house pressure entering the tank at it’s normal location. Does the water moving back down to the lower tank assist the water being pumped up and negate the “head”?

exactly sure how to figure the head in this situation.  On mine, which is real similar to your, I just added up the verticle lift and figured about 3ft. of head for the 40ft. of 1/2 copper pipe it has to pump thru, giving me about 12 ft. of head. (I simply ignored the parts where the water was flowing downhill. The simple circulation pump that came with the solar water heater wouldn’t work, so it was obviously more than 3ft. of head. But with the pump you are talking about (150 PSI!), it shouldn’t matter.  Just be aware that just the same and find out what the maximum head it will pump against is.  In fact, if these numbers are right (.25 amp ?), I may want to use one of these myself.  Do note that 3gpm is too high a pumping rate.  The water will heat up faster if it remains in the collector longer.  Since it’s a closed system, it won’t make a whole lot of difference, but you are wasting power, and adding to any losses along the way when you are circulating the water 10 times when once would do.  Which is why I want to use a thermostat.  Let me know if you find one somewhere.  Somebody makes in-line thermostats, I just haven’t been able to find one.  Of course, I can adapt an auto thermostat (160deg.) for this.   Russ – Hide quoted text — Show quoted text – I got this idea from a solar water system I read about awhile back, but can’t remember the name, that used the PV cell (without battery) to power the pump. The theory was that if the sun is shining the solar water heater must be getting warm and so the pump should run. At nite the pump should stop since there is no sun. On the other hand perhaps I should use a battery and some temprature controls for more control over the circulation…. Dean Gangstee x-no-archive: yes I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? Try the Laing  dc circulating  pump http://www.lainginc.com/ They charge $85. It runs on 12 volt dc. This is a great little pump. They solved the leaking shaft seal problem by avoiding the shaft. The motive force is communnicated to the impeller via a magnetic coupling. Some specs:      Model Volts Watts Amps Max Pressure max Temp Weight MC-201DC-B 12 3.1 0.26 150 PSI 230F 2.1 lba Housing Connection Codes:              BS 1/2″ – Brass inline housing with 1/2″sweat fittings              BT 1/2″ – Brass inline housing with 1/2″ NPT female thread fittings — Vs lbh pna ernq guvf lbh ernyyl bhtug gb trg bhg zber

Response:

I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV?

We install direct PV powered to DC pump solar hot water systems here in the UK for customers who do not wish to use grid utility electricity. We import the pumps from the USA  and typically use an 12 volt 18 Watt March May magnetic drive pump and a 20 Watt Solarex PV. This would cost around 400 US dollars combined. We hope to change to an even smaller wattage pump soon called the El CID which may keep costs nearer 200 US dollars. Are main priority was reliability and the pump had to meet solar temperatures in excess of 120 Celsius (sealed system with glycol antifreeze) with continuos pumping. If you are in the States, you will find these pumps at the some of the larger solar suppliers on the web by using your search engine but Real Goods comes to mind. — Chris Laughton   The Solar Design Company  England. www.solar-design.demon.co.uk

Response:

I want to run a solar water heater recirculation pump with a PV cell. Anyone know a good (inexpensive) source for a 12VDC recurculation pump that will run powered by a single 50watt PV? — Dean Gangstee

that 50 watts is enough.  It may be that if you do not have too much head (verticle lift + losses from the piping) you can get by with a cheap centrifugal pump than would draw 1-2amps at 12v.  Single outlet (like a faucet) pumps for RV’s cost about $20.00, and aquarium or boat type bilge pumps may work.  You don’t need a high flow rate, but low volume and pressure over about 5PSI is real hard to come by.  Aquarium pumps are about the right size if you can live with the pressure, but 12v ones are hard to find.  They do make them tho….  We had to go with a RV  3GPM pump in order to get the 10 PSI we needed for the system in our cabin.  The solar H2O panels haven’t been added yet, but the stove does a nice job of heating the water.  The flow rate, pressure, and power usage are all too high. It’s pretty much ideal for supplying system water pressure for the entire building (2 sinks and a shower).  We are adding a thermostat so that the circulation pump will run intermittantly.  Also planned is passive solar water heat valved so that it can be used as a preheater when using the stove, or help maintain hot water otherwise.   Russ

Response:

Just use a small bilge pump that they use in sailboats. They run on 12V and are cheap. You will have tomodify the pump so you can connect an inlet pipe. Bernard

Will it be able to handle voltage fluctuations (I assume the original poster meant not batteries, just the 50W panel)?

Response:

Question:

Is there snything on the market that operates with solar power/other that might help keep the pond open for a few more weeks in the winter?passive solar water heater riviews  All ideas appreciated.

Response:

If you have a southern downhill exposure from your pond, you can set up a passive solar water heater BELOW the pond, and plumb it through a heat exchanger in the pond. Water will be heated by the collector, flow up to the pond, be cooled, and flow back down to the collector.passive solar water heater riviews  Be advised — you can heat a hot tub with a modestly sized collector, so you won’t need much and you will need to regulate the heat flow.

Response:

Tom, I am experimenting a little with a “solar” heater to keep my water temp above 50 to keep the fish from breeding.  I have a Plastic trash can, I put 100 feet of copper tubing in it with connections at the top and bottom of the barrel.  I then run tubing from one fitting to the pump and then tubing from the other end to the pond.  The sun should heat barrel enough to heat the water and keep it from freezing.  It is light and I can use those nifty quick-disconnect hose fittings to hook it up. The can also has wheels to make it easier to move around.  We’ll see… passive solar water heater riviews

Response:

To most effectively transfer heat from your collector — and I’m guessing this is the plastic barrel — to the pond, you need to take the heated water from the end of the tubing that is at the top of the barrel.passive solar water heater riviews   Not a surprise — hot water rises. If the tap point from the top of the barrel is below the level of your pond, you may be able to establish a thermal siphon that does not require a pump. A barrel of water is effective for thermal storage, but is lacking in effectiveness as a solar collector.  You might try removing the copper coils from the barrel and lying them on a black plastic sheet — you might be amazed at how much hotter they get.passive solar water heater riviews Might amaze the scales right off your fish, too! Most of us Texans don’t have to worry too much about heating our ponds….

Response:

passive solar water heater riviews Tom, I am experimenting a little with a “solar” heater to keep my water temp above 50 to keep the fish from breeding.  I have a Plastic trash can, I put 100 feet of copper tubing in it with connections at the top and bottom of the barrel.  I then run tubing from one fitting to the pump and then tubing from the other end to the pond.  The sun should heat barrel enough to heat the water and keep it from freezing.  It is light and I can use those nifty quick-disconnect hose fittings to hook it up. The can also has wheels to make it easier to move around.  We’ll see…passive solar water heater riviews

Not too sure , but I’ve been told that excessive leaching of copper ions into the pond water would be detrimental to your fish.    I am using an all brass pump however with no ill effects noted. Just something to think about.. passive solar water heater riviews

Response:

Is there snything on the market that operates with solar power/other that might help keep the pond open for a few more weeks in the winter?passive solar water heater riviews

Response:

If you have a southern downhill exposure from your pond, you can set up a passive solar water heater BELOW the pond, and plumb it through a heat exchanger in the pond. Water will be heated by the collector, flow up to the pond, be cooled, and flow back down to the collector.  Be advised — you can heat a hot tub with a modestly sized collector, so you won’t need much and you will need to regulate the heat flow.

Response:

Tom, I am experimenting a little with a “solar” heater to keep my water temp above 50 to keep the fish from breeding.  I have a Plastic trash can, I put 100 feet of copper tubing in it with connections at the top and bottom of the barrel.  I then run tubing from one fitting to the pump and then tubing from the other end to the pond.  The sun should heat barrel enough to heat the water and keep it from freezing.  It is light and I can use those nifty quick-disconnect hose fittings to hook it up. The can also has wheels to make it easier to move around.  We’ll see…passive solar water heater riviews

Response:

To most effectively transfer heat from your collector — and I’m guessing this is the plastic barrel — to the pond, you need to take the heated water from the end of the tubing that is at the top of the barrel.  Not a surprise — hot water rises. If the tap point from the top of the barrel is below the level of your pond, you may be able to establish a thermal siphon that does not require a pump. A barrel of water is effective for thermal storage, but is lacking in effectiveness as a solar collector.  You might try removing the copper coils from the barrel and lying them on a black plastic sheet — you might be amazed at how much hotter they get. Might amaze the scales right off your fish, too! passive solar water heater riviews  Most of us Texans don’t have to worry too much about heating our ponds….

Response:

passive solar water heater riviews I am experimenting a little with a “solar” heater to keep my water temp above 50 to keep the fish from breeding.  I have a Plastic trash can, I put 100 feet of copper tubing in it with connections at the top and bottom of the barrel.  I then run tubing from one fitting to the pump and then tubing from the other end to the pond.  The sun should heat barrel enough to heat the water and keep it from freezing.  It is light and I can use those nifty quick-disconnect hose fittings to hook it up. The can also has wheels to make it easier to move around.  We’ll see…passive solar water heater riviews

Not too sure , but I’ve been told that excessive leaching of copper ions into the pond water would be detrimental to your fish.    I am using an all brass pump however with no ill effects noted. Just something to think about.. passive solar water heater riviews

Response:

Question:

pv solar panels…I mentioned that a bit can be saved on heating costs with proper humidification.

I denied that. Humidification raises fuel bills, even with a lower thermostat setting, unless you live in an extremely airtight house. Nick

Response:

pv solar panels…a bit can be saved on heating costs with proper humidification.

ASHRAE 55 says a 48×48x8′ house with R20 walls and ceiling would be equally comfy at 69.4 F and 20% RH or 68 F and 50% RH. If it’s very tight, with 0pv solar panels.5 air changes per hour, would “proper” humidification to 50% save energy? G = 48′x48′/R20 + 48×4x8/R20 = 192 Btu/h-F, so dropping the room temp from 69.4 to 68 F saves 1.4×192 = 269 Btu/h. At 69.4 F and 20% RH, Pd = 0.2e^(17.863-9621/(460+69.4)) = 0.1466, approximately, with wd = 0.62198/(29.921/0.1466-1) = 0.003063.pv solar panels Air at 68 F and 50% RH has wh = 0.007347. With 0.5×48x48×8/60 = 154 cfm of air leakage, humidifying from wd to wh requires evaporating 154×60x0.075(wh-wd) = 2.96 pounds of water per hour, which requires about 1000×2.96 = 2960 Btu/h of energy, so the net “savings” is 2960-269 = -2691 Btu/h, or minus 64.6K Btu/day, costing about $1/day more with oil heat or $2 per day with electric heat. I’ve done these calcs several times now. HVAC people tend to forget that evaporating water takes heat energy, even if a humidifier belt uses little energy by itself, and that heat energy has to come from somewhere. And we often get into discussions about health and furniture, vs energy and forget that caulking a house (vs humidification) can raise the indoor RH while SAVING on fuel bills.

Response:

…a bit can be saved on heating costs with proper humidification. ASHRAE 55 says a 48×48x8′ house with R20 walls and ceiling would be equally comfy at 69.4 F and 20% RH or 68 F and 50% RH. If it’s very tight, with 0.5 air changes per hour, would “proper” humidification to 50% save energy?

But, too dry of indoor air causes all types of health problems such as mucosal membrane irritation, nose bleeds, increased viral infections, and more.  Further, improper indoor humidification dries out wood furniture and the house itself causing wall cracks and worse.  So there has to be a proper balance of humidity. — Think beyond your assumptions.

Response:

…a bit can be saved on heating costs with proper humidification. ASHRAE 55 says a 48×48x8′ house with R20 walls and ceiling would be equally comfy at 69.4 F and 20% RH or 68 F and 50% RH. If it’s very tight, with 0.5 air changes per hour, would “proper” humidification to 50% save energy? But, too dry of indoor air causes all types of health problems such as mucosal membrane irritation, nose bleeds, increased viral infections, and more.  Further, improper indoor humidification dries out wood furniture and the house itself causing wall cracks and worse.  So there has to be a proper balance of humidity.

And we often get into discussions about health and furniture, vs energy, and forget that caulking a house (vs humidification) can raise the indoor RH while SAVING on fuel bills. Nick

Response:

okee-dokee. Thanks for the background. pv solar panelsIt’s good to know more about the players and history in these discussions   as I get more involved in the field. Cheers. – Hide quoted text — Show quoted text – Its been quite a while back… I advised someone to add a humidifier to their home to keep the furniture from drying out and for health concerns.. Also I mentioned that a bit can be saved on   heating costs with proper humidification. Due to the fact a few points lower on the thermostat will feel that same as a dry house with a higher setting. Nick denied that. And I told the fool to screw himself. He Likes to flaunt his education to our lesser educated people and to pooh pooh their experience knowledge. I have a degree myself..But I do   respect experience greatly. I spent some time in research in   environmental systems.. I KNOW the high cost and complexity of active   systems. And the maintenance problems with inactive systems.. Even Eros had one fancy field of solar panels and heat storage system..The   cost of maintenance and labor got too high.. They are now back on high efficiency standard systems. But back to Nick…Every couple of Months he picks a stupid debate over systems that some of these lads have worked on for years. According to Nick a full pyschrometric profile and and a Heat load are not up to his standards of no Humidity! pv solar panelsI understand he runs around his own home in heavy cloths all winter long.

Response:

Its been quite a while back… pv solar panelsI advised someone to add a humidifier to their home to keep the furniture from drying out and for health concerns.. Also I mentioned that a bit can be saved on heating costs with proper humidification. Due to the fact a few points lower on the thermostat will feel that same as a dry house with a higher setting. Nick denied that. And I told the fool to screw himself. He Likes to flaunt his education to our lesser educated people and to pooh pooh their experience knowledge. I have a degree myself..But I do respect experience greatly. I spent some time in research in environmental systems.. I KNOW the high cost and complexity of active systems. And the maintenance problems with inactive systems.. Even Eros had one fancy field of solar panels and heat storage system..The cost of maintenance and labor got too high.. They are now back on high efficiency standard systems. But back to Nick…Every couple of Months he picks a stupid debate over systems that some of these lads have worked on for years. According to Nick a full pyschrometric profile and and a Heat load are not up to his standards of no Humidity! I understand he runs around his own home in heavy cloths all winter long. – Hide quoted text — Show quoted text – Sorry Don, I must be totally daft – what are you talking about? All I said is that Nick’s argument that temperatures in the low 60’s with  high humidity would feel cold is right. Any psychometrics table supports  this. As for what you’re saying below -pv solar panels of course humidity is tightly controlled  in many environments! I must have missed the threads where he’s arguing  that it isn’t. Can you point to some specifics? I searched already but  only found the raging debates with Turtle regarding the comfort levels at  various RH’s. What am I missing here? Sorry…But your wrong.. Humidity is very tightly controlled for certain  equipment..Computers…Missile silos etc.. Space capsules are extremmely  contolled for Astronaut comfort and health. A real heat load takes that into consideration. The transfer of the environment is enhance by just  the right amount of humidity. Instead of making an easy $100.. I will  merely refer you to MIT Physics department, NASA, And CERN. Nick truly believes that humidity is witchcraft and thinks about that a lot while cleaning the latrines at that law college. I recommend true Physics research and ignore Nicks over the top Bull. Mother Earth magazine had a much better concept of the inhome pyschrometrics bakc in the   1960’s then Nick can even dream of. The old “Whole Earth Catalog” had some very affordable hardware that would do the job quite well. Researcxh that.. Some of those companies are still in business and possibly that catalog has been updated to 2004.. I have another name   also..But that catalog is under tons of stuff in my office. One day I will clean it out and find it or a fire will take it.. I am praying   for Fire..

Response:

Sorry Don, I must be totally daft – what are you talking about? All I said is that Nick’s argument that temperatures in the low 60’s with   high humidity would feel cold is right. Any psychometrics table supports   this. As for what you’re saying below – of course humidity is tightly controlled   in many environments!pv solar panels I must have missed the threads where he’s arguing   that it isn’t. Can you point to some specifics? I searched already but   only found the raging debates with Turtle regarding the comfort levels at   various RH’s. What am I missing here? – Hide quoted text — Show quoted text – Sorry…But your wrong.. Humidity is very tightly controlled for certain   equipment..Computers…Missile silos etc.. Space capsules are extremmely   contolled for Astronaut comfort and health. A real heat load takes that into consideration. The transfer of the environment is enhance by just   the right amount of humidity. Instead of making an easy $100.. I will   merely refer you to MIT Physics department, NASA, And CERN. Nick truly believes that humidity is witchcraft and thinks about that a lot while cleaning the latrines at that law college. I recommend true Physics research and ignore Nicks over the top Bull. Mother Earth magazine had a much better concept of the inhome pyschrometrics bakc in the   1960’s then Nick can even dream of. The old “Whole Earth Catalog” had some very affordable hardware that would do the job quite well. Researcxh that.. Some of those companies are still in business and possibly that catalog has been updated to 2004.. I have another name   also..But that catalog is under tons of stuff in my office. One day I will clean it out and find it or a fire will take it.. I am praying   for Fire..

Response:

- Hide quoted text — Show quoted text – Out of curiousity, I went back and read several hundred messages in   threads posted to by Nick. He certainly shows a lack of respect for HVAC  professionals and I’m not going to touch that one…pv solar panels However, as for his psychometrics, the discussions come down in his favor  (IMHO). He’s simply been quoting from the bible of psychometrics. The  controversy seemed to be centered around his statement that 60F at high RH  would be perceived as “cold” whereas TURTLE says that common sense shows  that this would be felt as uncomfortably warm. The argument, which raged on for some time, is easily answered. Go into   your bathroom this fall/winter, turn off the heat and turn on the shower  and fill the air with humidity. Stand there for a while. Do you feel hot  or cold? I spent many summers on Cape Cod, where the fog would roll in every night  as the temperatures dropped from the mid 70’s during the day down to low  60’s at night with ~100% RH and I got to tell you, I froze my ass off when  I didn’t wear heavy clothes. Likewise, when I sit in my observatory at  night, the RH is often near 100% as the temperatures drop to the low 60’s  and again, I would never describe what I feel as “uncomfortably warm”. Anyway, I’m not here to defend Nick himself, but more to defend the   validity of this particular one of his assertions. While you guys may nail  him to the wall for a variety of reasons, I’d bet any of you $100 that  he’s right on this one!

Sorry…But your wrong.. Humidity is very tightly controlled for certain equipment..Computers…Missile silos etc.. Space capsules are extremmely contolled for Astronaut comfort and health. A real heat load takes that into consideration. The transfer of the environment is enhance by just the right amount of humidity. Instead of making an easy $100.. I will merely refer you to MIT Physics department, NASA, And CERN. Nick truly believes that humidity is witchcraft and thinks about that a lot while cleaning the latrines at that law college. I recommend true Physics research and ignore Nicks over the top Bull. Mother Earth magazine had a much better concept of the inhome pyschrometrics bakc in the 1960’s then Nick can even dream of. The old “Whole Earth Catalog” had some very affordable hardware that would do the job quite well. Researcxh that.. Some of those companies are still in business and possibly that catalog has been updated to 2004.. I have another name also..But that catalog is under tons of stuff in my office. One day I will clean it out and find it or a fire will take it.. I am praying for Fire.. – Hide quoted text — Show quoted text – Hey, I’m here to learn. And while Nick’s posting reads like a textbook,pv solar panels  I  learned something from it. Plus, I got a good pointer to evacuated  tube  solar panels. Sure, it might not be really appropriate to the initial poster’s   questions, but there’s no need to take Nick to task for his   interesting  posting. Then you will truly love Nicks concept of Humidity and Psychrometrics   etc. Of course he is the only one with that concept.. But the whole   world is completely wrong and Nick is right. We sent Professor Turtle to reeducate him..But that was a dismal failure!   He really hates Real engineers and HVAC professionals.. So Sad…  By the way he is attached in some way or the other to a college that educates Lawyers.. Definitely not a Science college.

Response:

…Maybe you can explain how you’re going to keep the spa at 105 on a cold night, when your using it, without heat storage…pv solar panels I suggested a separate 170 F heat store.

Which might keep the tub 105 F for 6.577264 cloudy 30 F days in a row 10 TA=30′outdoor temp (F) 20 WA=.0025′humidity ratio 30 TT=105′tub temp (F) 40 ST=6*4*4′tub surface (ft^2) 50 RT=8*7.2′tub surface R-value (ft^2-h-F/Btu) 60 GT=ST/RT’tub conductance to outdoors (Btu/h-F) 70 ETC=(TT-TA)*GT’tub conductive loss (Btu/h) 80 PA=29.921/(1+.62198/WA)’ambient vapor pressure (“Hg) 90 PT=EXP(17.863-9621/(TT+460))’tub vapor pressure (“Hg) 100 SW=4*4′water surface (ft^2) 110 ETE=100*SW*(PT-PA)’tub evaporative loss (Btu/h) 120 ETD=23*ETC+ETE’daily tub loss (Btu) 130 TS=170′average-day heat store temp (F) 140 TI=8′insulation thickness (inches) 150 RS=TI*7.2’store surface R-value (ft^2-h-F/Btu) 160 GS=ST/RS’store conductance to outdoors (Btu/h-F) 170 VW=(4-2*TI/12)^3′water volume (ft^3) 180 CW=62*VW’store thermal capacitance (Btu/F) 190 D=TA*GS-ETD/24 200 TC=-CW/GS/24*LOG((110-D/GS)/(TS-D/GS)) 210 PRINT TC 6.577264

Response:

…Maybe you can explain how you’re going to keep the spa at 105 on a cold night, when your using itpv solar panels, without heat storage…

I suggested a separate 170 F heat store. …What’s the cost of a 4′ cube with lots of insulation and an EPDM rubber liner? EPDM costs about 30 cents/ft^2. Fold up a single 12′x12′ piece… 1″ polyiso board and 6″ fiberglass also cost about 30 cents/ft^2. Yes and conveniently avoiding all the time and other major issues in trying this DIY project.  Like where to place things like the collectors and the 4ft cube insulated tank.  Do they go on the deck with the barbecue and spa?

I’d put them on the ground, since the tank will be heavy. How about the electric controls and pump to make it work, where do they go?

Nearby. And how about the maintenance/repair all this will require…

Minimal. or the landscaping costs to try to hide all this crap somewhere?

Paint it red. BTW, it’s easy to say just build a 4 ft cube for a tank, insulate it and toss in a liner.  Now, how do you seal it up, establish plumbing connections, keep it off the ground so it doesn’t rot, etc?

Plumb through the top. Polyisocyanurate does not rot. And you never addressed the issues of plumbing, valves, pv solar panelselectric controls to make all this work.

Piece of cake. Try going to your local spa store and asking them what they think of this idea, particularly the warranty after a homeowner has made modifications.

No thanks. You might call a typical spa store employee “unscientific.” You might also want to check with your health department on the advisability of avoiding disinfectants in a spa and relying on slowly changing the spa water.

Ever swim in a stream? Ever hear of hot tub foliculitis?

Tell us more… Plus many people have to pay for water…

Pity. Nick

Response:

Out of curiousity, I went back and read several hundred messages in  threads posted to by Nick. He certainly shows a lack of respect for HVAC professionals and I’m not going to touch that one… :pv solar panels However, as for his psychometrics, the discussions come down in his favor (IMHO). He’s simply been quoting from the bible of psychometrics. The controversy seemed to be centered around his statement that 60F at high RH would be perceived as “cold” whereas TURTLE says that common sense shows  that this would be felt as uncomfortably warm. The argument, which raged on for some time, is easily answered.

Nope. Go into your bathroom this fall/winter, turn off the heat and turn on the shower  and fill the air with humidity. Stand there for a while. Do you feel hot  or cold?

Thats a lousy test for that if you spend much time say sitting around at the PC screen. The test isnt long enough to give you any real idea about how you would feel in that other situationpv solar panels. I spent many summers on Cape Cod, where the fog would roll in every night as the temperatures dropped from the mid 70’s during the day down to low 60’s at night with ~100% RH and I got to tell you, I froze my ass off when I didn’t wear heavy clothes.

Yeah, 60F is too cold for comfort for me. In fact I’m sitting in it right now 75% RH. Not bad just after getting up but a bit too cold for just sitting around. Likewise, when I sit in my observatory at night, the RH is often near 100% as the temperatures drop to the low 60’s  and again, I would never describe what I feel as “uncomfortably warm”.

Yeah, thats mad. And its a tad of a clammy cold too that I dont like. – Hide quoted text — Show quoted text – Anyway, I’m not here to defend Nick himself, but more to defend the validity of this particular one of his assertions. While you guys may nail him to the wall for a variety of reasons, I’d bet any of you $100 that he’s right on this one! Hey, I’m here to learn. And while Nick’s posting reads like a textbook,  I learned something from it. Plus, I got a good pointer to evacuated  tube solar panels. Sure, it might not be really appropriate to the initial poster’s questions, but there’s no need to take Nick to task for his  interesting posting. Then you will truly love Nicks concept of Humidity and Psychrometrics  etc. Of course he is the only one with that concept.. But the whole  world is completely wrong and Nick is right. We sent Professor Turtle to reeducate him..But that was a dismal failure!   He really hates Real engineers and HVAC professionals.. So Sad…  By the way he is attached in some way or the other to a college that educates Lawyers.. Definitely not a Science college.

Response:

- Hide quoted text — Show quoted text – Evacuated tubes work well,pv solar panels even in cloudy climates. Seriously.  You can’t get an effective heat rise over ambient without high-temp storage, defeating the cost savings of solar entirely.  On a good day you’ll manage a 10-degree rise without storage, meaning a 90+ day would be okay for your spa but a 60′ish evening wouldn’t. Would you have any evidence for these articles of faith? 1. “You can’t get an effective heat rise over ambient…” If you mean “temperature rise,” recall that evacuated tubes can collect 170 F water at 50% efficiency on a 30 F day. 2. “without high-temp storage…” This temperature rise has nothing to do with high-temp storage. Heating 400 gallons of water more than 10 F in a day would take a large collector, but there’s no need to do that, if the water is well-insulated. With RC = 400×8.33Btu/F/(1.7 Btu/h-F) = 1960 hours, the water would cool from 105 to 30+(105-30)e^(-24/1960) = 104.1 F after 24 hours in 30 F air, with the cover closed. 3. “defeating the cost savings of solar entirely.” You might spend $2K on a home-built heater and save $500/year, for a simple 4-year payback. Or spend $5K for a larger solar domestic water heater that also heats the spa more simply, with a similar payback. And no chemicals. Where I live, slowly changing the water once a week via a heat exchanger seems to make sense, with a 99% thermal efficiency. On a good day you’ll manage a 10-degree rise without storage, meaning a 90+ day would be okay for your spa but a 60′ish evening wouldn’t.

We’re looking at 2. pv solar panels Maybe you can explain how you’re going to keep the spa at 105 on a cold night, when your using it, without heat storage.  Or are you suggesting getting in with the cover on? A spa can’t store much heat, if 104 F is too cool and 106 is too warm for people. Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. Bringing the cost to way more than gas or electric, even factored over ten years if the old spa lasts that long. I disagree. What’s the cost of a 4′ cube with lots of insulation and an EPDM rubber liner? EPDM costs about 30 cents/ft^2. Fold up a single 12′x12′ piece… 1″ polyiso board and 6″ fiberglass also cost about 30 cents/ft^2…

Yes and conveniently avoiding all the time and other major issues in trying this DIY project.  Like where to place things like the collectors and the 4ft cube insulated tank.  Do they go on the deck with the barbecue and spa?  How about the electric controls and pump to make it work, where do they go?   And how about the maintenance/ repair all this will require, or the landscaping costs to try to hide all this crap somewhere?  BTW, it’s easy to say just build a 4 ft cube for a tank, insulate it and toss in a liner.  Now, how do you seal it up, establish plumbing connections, keep it off the ground so it doesn’t rot, etc?  You really need to get some real world experience before you start recommending half assed solutions. And you never addressed the issues of plumbing, valves, electric controls to make all this work.  Try going to your local spa store and asking them what they think of this idea, particularly the warranty after a homeowner has made modifications. You might also want to check with your health department on the advisability of avoiding disinfectants in a spa and relying on slowly changing the spa water.  Ever hear of hot tub foliculitis?  Plus many people have to pay for water, so it may very well not be free either. Do you have any practical experience with spas or home repairs at all? – Hide quoted text — Show quoted text -Drew Gillett and I have a solar water heater article in the Nov/Dec issue of Solar Today, available soon at Borders bookstores… Solar is intriguing, but rarely is it truly practical in economic terms, especially for a spa. Heating water for showers as well helps the economics. Heck, even solar hot water has serious issues in many areas… Sure. and solar pool heating, likely the best economical use of solar beyond passive solar heating, is still inadequate for many consumers. Primarily those with inadequate pool covers

Response:

Out of curiousity, I went back and read several hundred messages in   threads posted to by Nick. He certainly shows a lack of respect for HVAC   professionals and I’m not going to touch that one…pv solar panels However, as for his psychometrics, the discussions come down in his favor   (IMHO). He’s simply been quoting from the bible of psychometrics. The   controversy seemed to be centered around his statement that 60F at high RH   would be perceived as “cold” whereas TURTLE says that common sense shows   that this would be felt as uncomfortably warm. The argument, which raged on for some time, is easily answered. Go into   your bathroom this fall/winter, turn off the heat and turn on the shower   and fill the air with humidity. Stand there for a while. Do you feel hot   or cold? I spent many summers on Cape Cod, where the fog would roll in every night   as the temperatures dropped from the mid 70’s during the day down to low   60’s at night with ~100% RH and I got to tell you, I froze my ass off when   I didn’t wear heavy clothes. Likewise, when I sit in my observatory at   night, the RH is often near 100% as the temperatures drop to the low 60’s   and again, I would never describe what I feel as “uncomfortably warm”. Anyway, I’m not here to defend Nick himself, but more to defend the   validity of this particular one of his assertions. While you guys may nail   him to the wall for a variety of reasons, I’d bet any of you $100 that   he’s right on this one! – Hide quoted text — Show quoted text – Hey, I’m here to learn. And while Nick’s posting reads like a textbook,   I  learned something from it. Plus, I got a good pointer to evacuated   tube  solar panels. Sure, it might not be really appropriate to the initial poster’s   questions, but there’s no need to take Nick to task for his   interesting  posting. Then you will truly love Nicks concept of Humidity and Psychrometrics   etc. Of course he is the only one with that concept.. But the whole   world is completely wrong and Nick is right. We sent Professor Turtle to reeducate him..But that was a dismal failure!   He really hates Real engineers and HVAC professionals.. So Sad…  By the way he is attached in some way or the other to a college that educates Lawyers.. Definitely not a Science college.

Response:

Evacuated tubes work well, even in cloudy climates. Seriously.  You can’t get an effective heat rise over ambient without high-temp storage, defeating the cost savings of solar entirely.  On a good day you’ll manage a 10-degree rise without storage, meaning a 90+ day would be okay for your spa but a 60′ish evening wouldn’t.

Would you have any evidence for these articles of faith? 1. “You can’t get an effective heat rise over ambient…” If you mean “temperature rise,pv solar panels” recall that evacuated tubes can collect 170 F water at 50% efficiency on a 30 F day. 2. “without high-temp storage…” This temperature rise has nothing to do with high-temp storage. Heating 400 gallons of water more than 10 F in a day would take a large collector, but there’s no need to do that, if the water is well-insulated. With RC = 400×8.33Btu/F/(1.7 Btu/h-F) = 1960 hours, the water would cool from 105 to 30+(105-30)e^(-24/1960) = 104.1 F after 24 hours in 30 F air, with the cover closed. 3. “defeating the cost savings of solar entirely.” You might spend $2K on a home-built heater and save $500/year, for a simple 4-year payback. Or spend $5K for a larger solar domestic water heater that also heats the spa more simply, with a similar payback. And no chemicals. Where I live, slowly changing the water once a week via a heat exchanger seems to make sense, with a 99% thermal efficiency. On a good day you’ll manage a 10-degree rise without storage, meaning a 90+ day would be okay for your spa but a 60′ish evening wouldn’t.

See 2. A spa can’t store much heat, if 104 F is too cool and 106 is too warm for people. Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. Bringing the cost to way more than gas or electric, even factored over ten years if the old spa lasts that long.

I disagree. What’s the cost of a 4′ cube with lots of insulation and an EPDM rubber liner? EPDM costs about 30 cents/ft^2. Fold up a single 12′x12′ piece… 1″ polyiso board and 6″ fiberglass also cost about 30 cents/ft^2… Drew Gillett and I have a solar water heater article in the Nov/Dec issue of Solar Today, available soon at Borders bookstores… Solar is intriguing, but rarely is it truly practical in economic terms, especially for a spa.

Heating water for showers as well helps the economics. Heck, even solar hot water has serious issues in many areas…

Sure. and solar pool heating, likely the best economical use of solar beyond passive solar heating, is still inadequate for many consumers.

Primarily those with inadequate pool covers

Response:

Hey, I’m here to learn. And while Nick’s posting reads like a textbook,pv solar panels I  learned something from it. Plus, I got a good pointer to evacuated tube  solar panels. Sure, it might not be really appropriate to the initial poster’s   questions, but there’s no need to take Nick to task for his interesting   posting.

Then you will truly love Nicks concept of Humidity and Psychrometrics etc. Of course he is the only one with that concept.. But the whole world is completely wrong and Nick is right. We sent Professor Turtle to reeducate him..But that was a dismal failure!   He really hates Real engineers and HVAC professionals.. So Sad…  By the way he is attached in some way or the other to a college that educates Lawyers.. Definitely not a Science college.

Response:

Congratulations Chet.. You have passed the intelligence test of this group. Nick has been Bullshitting folks for years with concepts that don’t work or are so complex or expensive as to be unfeasable. – Hide quoted text — Show quoted text – Solar is a waste for a spa.  Can’t provide enough heat rise… Au contraire. Heating water to 105 F is easy… Evacuated tubes work well, even in cloudy climates. Focus has this equation for tube efficiency: E = 0.717-1.52X-0.0085GX^2, where X = (Tm-Ta)/G. Tm (C) is the mean water temp, Ta (C) is the air temp, and G is the insolation (W/m^2.) Tm = 77 C (170 F) and Ta = -1 (30 F) and full sun (G = 800 W/m^2) make X = 0.975 and E = 0.5, ie a 50% solar collection efficiency. ..pv solar panels.Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. …with solar… you still will need some other additional heat source to get it to 105, particularly during winter. I disagree. Then Nick, without an additional heat source, how are you going to get the spa up to 105 in a typical outdoor location in the US in winter at 9PM when you want to use it? Let’s even assume it was already at 105, before the sun went down.  As soon as you take the cover off and hop in, it’s all down hill from there.  With no other heat source, the solar answer is an insulated storage tank to store hot water. Good idea. Where does that tank go, on the deck outside with the spa? I’d say on the ground. It might be heavy. And how big does it have to be for the climate? Which one? How about Phila in January, when 620 Btu/ft^2 of sun falls on the ground and 1000 falls on a south wall on an average 30 F day with humidity ratio w = 0.0025 pounds of water per pound of dry air. Say your tub is a 4′ cube with 8″ of polyisocyanurate insulation and an 8″ cover, with a thermal conductance of 96ft^2/R57.6 = 1.7 Btu/h-F when closed. When open, Pw = e^17.863-9621/(460+105) = 2.3 “Hg and Pa = 29.921/(1+0.62198/w) = 0.012 “Hg, so it loses 4′x4′x100(2.3-0.012) = 3488 Btu/h with the air pump disconnected, or less, if the surface is covered with partly inflated baggies or ping pong balls. If we use it 1 hour per day, it needs about 3488+23h(105-30)1.7 = 6362 Btu/day. With 50% efficiency, an optimal-slope flat plate solar collector would gather 0.5(sqrt(1000^2+620^2)) = 588 Btu/ft^2 on an average January day, so we need about 6362/588 = 10.8 ft^2 of collectors, or less, in tubes, or a bit more, to account for the heat store loss. If the heat store is very well insulated and it’s 170 F on an average day and it can keep the tub 105 until it reaches 110, we need about 5×6362/(170-110) = 530 pounds or 64 gallons or 8 ft^3 of water for 5 cloudy 30 F days in a row. We might use another 4′ cube with more insulation inside and a folded EPDM rubber liner, to bring about a pleasing aesthetic symmetry. Here’s a excerpt from an application note from a supplier of evacuated solar tubes: http://www.prime-nrg.com/water.asp Domestic hot water; 30 tubes for family of up to 4… Spa/Hot-tub; 60 tubes for up to 1500 liters (Indoor.) Heating a spa is twice as hard as heating water for a family of 4? Where do we put the 60 evacuated tubes? …60 seems like too many. On the roof with pipes running around or through the house?  Or do we put them on the deck with the spa and barbecue? How about below the deck, on the south side of the tank? …But wait, according to the supplier, the 60 tubes are for a 1500L indoor spa, which really isn’t all that big, so we need even more tubes for the outside spa in winter. Even more tubes would make the supplier happy. Then we have to fool around with all the plumbing issues of trying to insert all the solar stuff into the spa circulation system, which doesn’t have pipe fittings sticking out that say “hook up solar collector here.” Awww… And then perhaps another pump to move the water through the solar system… Sure. A little one. Maybe 3488/5/8.33/60 = 1.4 gpm, and another small pump for the glycol tube loop, unless that thermosyphons. Then we need to fool around with the power pack on the spa to integrate this all in somehow to the std temp control system, which is microprocessor controlled, so when you dial in 100 or 105, it somehow maintains that temp. You might disconnect the wires that run to the heater and attach them to the new spa pump. Who’s going to take liability for doing that right? Henry Kissinger? At the very least, you can kiss your spa warranty goodbye. Maybe not. And personally, I wouldn’t want to sit in a spa with added pumps and god knows what else that somebody made up as they went along. Chacun a son bain-Californie. And finally, how much is all this going to cost in material and labor? You’d probably say “too much.” The OP was worried about spending money for a 240V electric run, which is straightforward and simple compared to all this. Maybe so. I’d further complicate things with ozone and a copper sponge in the filter and a salinity gauge that turns on another small pump to slowly replace spa water with fresh cold water via a heat exchanger when the water conductance exceeds some threshold. Don’t get me wrong.  Solar heat can be a cost effective and workable solution for the right climate and the right application.  But doing this to save the few hundred dollars a year it costs to heat a home spa is not one of them. I disagree. Nick I can tell you one thing.  Anyone who reads this and listens to you for practical advice on anything, including solar heat, would have to be crazy, as you’ve plainly lost sight of what’s practical or cost effective.  The OP was asking for an alternative to try to avoid the cost and trouble of a 240V line to a spa.   Your solution is to buy 60+ solar evacuated tubes, an insulated tank that’s how big?, find places to put all that, plumb it in, build a control system and re-engineer the spa.  Oh, and BTW, he still needs at least a 120V line to the spa anyway to run the pump and controls. Guys like you become so enamored with some favorite campaign of theirs that they lose all sight of what’s practical or cost effective.  You remind me of a woman I know that spends time rummaging through trash cans at other peoples parties in full view of guests, retrieving plastic knives and forks to recycle them, because it’s just what she must do.

Response:

Hey, I’m here to learn. And while Nick’s posting reads like a textbook, I   learned something from it. Plus, I got a good pointer to evacuated tube   solar panels. Sure, it might not be really appropriate to the initial poster’s   questions, but there’s no need to take Nick to task for his interesting   posting.

You may find them interesting, but I found them impractical and thought the OP might like to know why, before he goes out and spends a lot of money. – Hide quoted text — Show quoted text – Solar is a waste for a spa.  Can’t provide enough heat rise… Au contraire. Heating water to 105 F is easy…pv solar panels Evacuated tubes work well, even in cloudy climates. Focus has this equation for tube efficiency: E = 0.717-1.52X-0.0085GX^2, where X = (Tm-Ta)/G. Tm (C) is the mean   water temp, Ta (C) is the air temp, and G is the insolation (W/m^2.) Tm = 77 C (170 F) and Ta = -1 (30 F) and full sun (G = 800 W/m^2) make X = 0.975   and E = 0.5, ie a 50% solar collection efficiency. …Better to have a separate, well-insulated higher temp (170 F)    heat store and meter it in as needed. …with solar… you still will need some other additional heat    source to get it to 105, particularly during winter. I disagree. Then Nick, without an additional heat source, how are you going to get the spa up to 105 in a typical outdoor location in the US in winter at 9PM when you want to use it? Let’s even assume it was already at 105, before the sun went down.  As soon as you take the cover off and hop    in, it’s all down hill from there.  With no other heat source, the solar answer is an insulated storage tank to store hot water. Good idea. Where does that tank go, on the deck outside with the spa? I’d say on the ground. It might be heavy. And how big does it have to be for the climate? Which one? How about Phila in January, when 620 Btu/ft^2 of sun falls on the ground and 1000 falls on a south wall on an average 30 F day with humidity ratio w = 0.0025 pounds of water per pound of dry air. Say your tub is a 4′ cube with 8″ of polyisocyanurate insulation and an 8″ cover, with a thermal conductance of 96ft^2/R57.6 = 1.7 Btu/h-F when closed. When open, Pw = e^17.863-9621/(460+105) = 2.3 “Hg and Pa = 29.921/(1+0.62198/w) = 0.012 “Hg, so it loses 4′x4′x100(2.3-0.012) = 3488 Btu/h with the air pump disconnected, or less, if the surface is covered with partly inflated baggies or ping pong balls. If we use it 1 hour per day, it needs about 3488+23h(105-30)1.7 = 6362 Btu/day. With 50% efficiency, an optimal-slope flat plate solar collector would gather 0.5(sqrt(1000^2+620^2)) = 588 Btu/ft^2 on an average January day, so we need about 6362/588 = 10.8 ft^2 of collectors, or less, in tubes, or a bit more, to account for the heat store loss. If the heat store is very well insulated and it’s 170 F on an average day and it can keep the tub 105 until it reaches 110, we need about 5×6362/(170-110) = 530 pounds or 64 gallons or 8 ft^3 of water for 5 cloudy 30 F days in a row. We might use another 4′ cube with more insulation inside and a folded EPDM rubber liner, to bring about a pleasing aesthetic symmetry. Here’s a excerpt from an application note from a supplier of evacuated solar tubes Domestic hot water; 30 tubes for family of up to 4… Spa/Hot-tub; 60 tubes for up to 1500 liters (Indoor.) Heating a spa is twice as hard as heating water for a family of 4? Where do we put the 60 evacuated tubes? …60 seems like too many. On the roof with pipes running around or through the house?  Or do we    put them on the deck with the spa and barbecue? How about below the deck, on the south side of the tank? …But wait, according to the supplier, the 60 tubes are for a 1500L indoor spa, which really isn’t all that big, so we need even more tubes for the outside spa in winter. Even more tubes would make the supplier happy. Then we have to fool around with all the plumbing issues of trying to insert all the solar stuff into the spa circulation system, which    doesn’t have pipe fittings sticking out that say “hook up solar collector   here.” Awww… And then perhaps another pump to move the water through the solar   system… Sure. A little one. Maybe 3488/5/8.33/60 = 1.4 gpm, and another small   pump for the glycol tube loop, unless that thermosyphons. Then we need to fool around with the power pack on the spa to integrate this all in somehow to the std temp control system, which is microprocessor controlled, so when you dial in 100 or 105, it somehow maintains that temp. You might disconnect the wires that run to the heater and attach them to the new spa pump. Who’s going to take liability for doing that right? Henry Kissinger? At the very least, you can kiss your spa warranty goodbye. Maybe not. And personally, I wouldn’t want to sit in a spa with added pumps and god knows what else that somebody made up as they went along. Chacun a son bain-Californie. And finally, how much is all this going to cost in material and labor? You’d probably say “too much.” The OP was worried about spending money for a 240V electric run, which is straightforward and simple compared to all this. Maybe so. I’d further complicate things with ozone and a copper sponge in the filter and a salinity gauge that turns on another small pump to slowly replace spa water with fresh cold water via a heat exchanger when the water conductance exceeds some threshold. Don’t get me wrong.  Solar heat can be a cost effective and workable solution for the right climate and the right application.  But doing this to save the few hundred dollars a year it costs to heat a home spa is not one of them. I disagree. Nick I can tell you one thing.  Anyone who reads this and listens to you for practical advice on anything, including solar heat, would have to be crazy, as you’ve plainly lost sight of what’s practical or cost effective.  The OP was asking for an alternative to try to avoid the cost and trouble of a 240V line to a spa.   Your solution is to buy 60+ solar evacuated tubes, an insulated tank that’s how big?, find places to put all that, plumb it in, build a control system and re-engineer the spa.  Oh, and BTW, he still needs at least a 120V line to the spa anyway to run the pump and controls. Guys like you become so enamored with some favorite campaign of theirs that they lose all sight of what’s practical or cost effective.  You remind me of a woman I know that spends time rummaging through trash cans at other peoples parties in full view of guests, retrieving plastic knives and forks to recycle them, because it’s just what she must do.

Response:

Solar is a waste for a spa.  Can’t provide enough heat rise… Evacuated tubes work well, even in cloudy climates.

Seriously.  You can’t get an effective heat rise over ambient without high-temp storage, defeating the cost savings of solar entirely.  On a good day you’ll manage a 10-degree rise without storage, meaning a 90+ day would be okay for your spa but a 60′ish evening wouldn’t. and pretty much sucks ofr a midnight soak. A spa can’t store much heat, if 104 F is too cool and 106 is too warm for people. Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed.

Bringing the cost to way more than gas or electric, even factored over ten years if the old spa lasts that long. Drew Gillett and I have a solar water heater article in the Nov/Dec issue of Solar Today, available soon at Borders bookstores…

Solar is intriguing, but rarely is it truly practical in economic terms, especially for a spa.  Heck, even solar hot water has serious issues in many areas, and solar pool heating, likely the best economical use of solar beyond passive solar heating, is still inadequate for many consumers. Jeff

Response:

Hey, I’m here to learn. And while Nick’s posting reads like a textbook, I   learned something from it. Plus, I got a good pointer to evacuated tube   solar panels. Sure, it might not be really appropriate to the initial poster’s   questions, but there’s no need to take Nick to task for his interesting   posting. – Hide quoted text — Show quoted text – Solar is a waste for a spa.  Can’t provide enough heat rise… Au contraire. Heating water to 105 F is easy… Evacuated tubes work well, even in cloudy climates. Focus has this equation for tube efficiency: E = 0.717-1.52X-0.0085GX^2, where X = (Tm-Ta)/G. Tm (C) is the mean   water temp, Ta (C) is the air temp, and G is the insolation (W/m^2.) Tm = 77 C (170 F) and Ta = -1 (30 F) and full sun (G = 800 W/m^2) make X = 0.975   and E = 0.5, ie a 50% solar collection efficiency. …Better to have a separate, well-insulated higher temp (170 F)   heat store and meter it in as needed. …with solar… you still will need some other additional heat   source to get it to 105, particularly during winter. I disagree. Then Nick, without an additional heat source, how are you going to get the spa up to 105 in a typical outdoor location in the US in winter at 9PM when you want to use it? Let’s even assume it was already at 105, before the sun went down.  As soon as you take the cover off and hop   in, it’s all down hill from there.  With no other heat source, the solar answer is an insulated storage tank to store hot water. Good idea. Where does that tank go, on the deck outside with the spa? I’d say on the ground. It might be heavy. And how big does it have to be for the climate? Which one? How about Phila in January, when 620 Btu/ft^2 of sun falls on the ground and 1000 falls on a south wall on an average 30 F day with humidity ratio w = 0.0025 pounds of water per pound of dry air. Say your tub is a 4′ cube with 8″ of polyisocyanurate insulation and an 8″ cover, with a thermal conductance of 96ft^2/R57.6 = 1.7 Btu/h-F when closed. When open, Pw = e^17.863-9621/(460+105) = 2.3 “Hg and Pa = 29.921/(1+0.62198/w) = 0.012 “Hg, so it loses 4′x4′x100(2.3-0.012) = 3488 Btu/h with the air pump disconnected, or less, if the surface is covered with partly inflated baggies or ping pong balls. If we use it 1 hour per day, it needs about 3488+23h(105-30)1.7 = 6362 Btu/day. With 50% efficiency, an optimal-slope flat plate solar collector would gather 0.5(sqrt(1000^2+620^2)) = 588 Btu/ft^2 on an average January day, so we need about 6362/588 = 10.8 ft^2 of collectors, or less, in tubes, or a bit more, to account for the heat store loss. If the heat store is very well insulated and it’s 170 F on an average day and it can keep the tub 105 until it reaches 110, we need about 5×6362/(170-110) = 530 pounds or 64 gallons or 8 ft^3 of water for 5 cloudy 30 F days in a row. We might use another 4′ cube with more insulation inside and a folded EPDM rubber liner, to bring about a pleasing aesthetic symmetry. Here’s a excerpt from an application note from a supplier of evacuated solar tubes Domestic hot water; 30 tubes for family of up to 4… Spa/Hot-tub; 60 tubes for up to 1500 liters (Indoor.) Heating a spa is twice as hard as heating water for a family of 4? Where do we put the 60 evacuated tubes? …60 seems like too many. On the roof with pipes running around or through the house?  Or do we   put them on the deck with the spa and barbecue? How about below the deck, on the south side of the tank? …But wait, according to the supplier, the 60 tubes are for a 1500L indoor spa, which really isn’t all that big, so we need even more tubes for the outside spa in winter. Even more tubes would make the supplier happy. Then we have to fool around with all the plumbing issues of trying to insert all the solar stuff into the spa circulation system, which   doesn’t have pipe fittings sticking out that say “hook up solar collector   here.” Awww… And then perhaps another pump to move the water through the solar   system… Sure. A little one. Maybe 3488/5/8.33/60 = 1.4 gpm, and another small   pump for the glycol tube loop, unless that thermosyphons. Then we need to fool around with the power pack on the spa to integrate this all in somehow to the std temp control system, which is microprocessor controlled, so when you dial in 100 or 105, it somehow maintains that temp. You might disconnect the wires that run to the heater and attach them to the new spa pump. Who’s going to take liability for doing that right? Henry Kissinger? At the very least, you can kiss your spa warranty goodbye. Maybe not. And personally, I wouldn’t want to sit in a spa with added pumps and god knows what else that somebody made up as they went along. Chacun a son bain-Californie. And finally, how much is all this going to cost in material and labor? You’d probably say “too much.” The OP was worried about spending money for a 240V electric run, which is straightforward and simple compared to all this. Maybe so. I’d further complicate things with ozone and a copper sponge in the filter and a salinity gauge that turns on another small pump to slowly replace spa water with fresh cold water via a heat exchanger when the water conductance exceeds some threshold. Don’t get me wrong.  Solar heat can be a cost effective and workable solution for the right climate and the right application.  But doing this to save the few hundred dollars a year it costs to heat a home spa is not one of them. I disagree. Nick I can tell you one thing.  Anyone who reads this and listens to you for practical advice on anything, including solar heat, would have to be crazy, as you’ve plainly lost sight of what’s practical or cost effective.  The OP was asking for an alternative to try to avoid the cost and trouble of a 240V line to a spa.   Your solution is to buy 60+ solar evacuated tubes, an insulated tank that’s how big?, find places to put all that, plumb it in, build a control system and re-engineer the spa.  Oh, and BTW, he still needs at least a 120V line to the spa anyway to run the pump and controls. Guys like you become so enamored with some favorite campaign of theirs that they lose all sight of what’s practical or cost effective.  You remind me of a woman I know that spends time rummaging through trash cans at other peoples parties in full view of guests, retrieving plastic knives and forks to recycle them, because it’s just what she must do.

– Using Opera’s revolutionary e-mail client

Response:

- Hide quoted text — Show quoted text – Solar is a waste for a spa. pv solar panels Can’t provide enough heat rise… Au contraire. Heating water to 105 F is easy… Evacuated tubes work well, even in cloudy climates. Focus has this equation for tube efficiency: E = 0.717-1.52X-0.0085GX^2, where X = (Tm-Ta)/G. Tm (C) is the mean water temp, Ta (C) is the air temp, and G is the insolation (W/m^2.) Tm = 77 C (170 F) and Ta = -1 (30 F) and full sun (G = 800 W/m^2) make X = 0.975 and E = 0.5, ie a 50% solar collection efficiency. …Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. …with solar… you still will need some other additional heat source to get it to 105, particularly during winter. I disagree. Then Nick, without an additional heat source, how are you going to get the spa up to 105 in a typical outdoor location in the US in winter at 9PM when you want to use it? Let’s even assume it was already at 105, before the sun went down.  As soon as you take the cover off and hop in, it’s all down hill from there.  With no other heat source, the solar answer is an insulated storage tank to store hot water. Good idea. Where does that tank go, on the deck outside with the spa? I’d say on the ground. It might be heavy. And how big does it have to be for the climate? Which one? How about Phila in January, when 620 Btu/ft^2 of sun falls on the ground and 1000 falls on a south wall on an average 30 F day with humidity ratio w = 0.0025 pounds of water per pound of dry air. Say your tub is a 4′ cube with 8″ of polyisocyanurate insulation and an 8″ cover, with a thermal conductance of 96ft^2/R57.6 = 1.7 Btu/h-F when closed. When open, Pw = e^17.863-9621/(460+105) = 2.3 “Hg and Pa = 29.921/(1+0.62198/w) = 0.012 “Hg, so it loses 4′x4′x100(2.3-0.012) = 3488 Btu/h with the air pump disconnected, or less, if the surface is covered with partly inflated baggies or ping pong balls. If we use it 1 hour per day, it needs about 3488+23h(105-30)1.7 = 6362 Btu/day. With 50% efficiency, an optimal-slope flat plate solar collector would gather 0.5(sqrt(1000^2+620^2)) = 588 Btu/ft^2 on an average January day, so we need about 6362/588 = 10.8 ft^2 of collectors, or less, in tubes, or a bit more, to account for the heat store loss. If the heat store is very well insulated and it’s 170 F on an average day and it can keep the tub 105 until it reaches 110, we need about 5×6362/(170-110) = 530 pounds or 64 gallons or 8 ft^3 of water for 5 cloudy 30 F days in a row. We might use another 4′ cube with more insulation inside and a folded EPDM rubber liner, to bring about a pleasing aesthetic symmetry. Here’s a excerpt from an application note from a supplier of evacuated solar tubes: Domestic hot water; 30 tubes for family of up to 4… Spa/Hot-tub; 60 tubes for up to 1500 liters (Indoor.) Heating a spa is twice as hard as heating water for a family of 4? Where do we put the 60 evacuated tubes? …60 seems like too many. On the roof with pipes running around or through the house?  Or do we put them on the deck with the spa and barbecue? How about below the deck, on the south side of the tank? …But wait, according to the supplier, the 60 tubes are for a 1500L indoor spa, which really isn’t all that big, so we need even more tubes for the outside spa in winter. Even more tubes would make the supplier happy. Then we have to fool around with all the plumbing issues of trying to insert all the solar stuff into the spa circulation system, which doesn’t have pipe fittings sticking out that say “hook up solar collector here.” Awww… And then perhaps another pump to move the water through the solar system… Sure. A little one. Maybe 3488/5/8.33/60 = 1.4 gpm, and another small pump for the glycol tube loop, unless that thermosyphons. Then we need to fool around with the power pack on the spa to integrate this all in somehow to the std temp control system, which is microprocessor controlled, so when you dial in 100 or 105, it somehow maintains that temp. You might disconnect the wires that run to the heater and attach them to the new spa pump. Who’s going to take liability for doing that right? Henry Kissinger? At the very least, you can kiss your spa warranty goodbye. Maybe not. And personally, I wouldn’t want to sit in a spa with added pumps and god knows what else that somebody made up as they went along. Chacun a son bain-Californie. And finally, how much is all this going to cost in material and labor? You’d probably say “too much.” The OP was worried about spending money for a 240V electric run, which is straightforward and simple compared to all this. Maybe so. I’d further complicate things with ozone and a copper sponge in the filter and a salinity gauge that turns on another small pump to slowly replace spa water with fresh cold water via a heat exchanger when the water conductance exceeds some threshold. Don’t get me wrong.  Solar heat can be a cost effective and workable solution for the right climate and the right application.  But doing this to save the few hundred dollars a year it costs to heat a home spa is not one of them. I disagree. Nick

I can tell you one thing.  Anyone who reads this and listens to you for practical advice on anything, including solar heat, would have to be crazy, as you’ve plainly lost sight of what’s practical or cost effective.  The OP was asking for an alternative to try to avoid the cost and trouble of a 240V line to a spa.   Your solution is to buy 60+ solar evacuated tubes, an insulated tank that’s how big?, find places to put all that, plumb it in, build a control system and re-engineer the spa.  Oh, and BTW, he still needs at least a 120V line to the spa anyway to run the pump and controls. Guys like you become so enamored with some favorite campaign of theirs that they lose all sight of what’s practical or cost effective.  You remind me of a woman I know that spends time rummaging through trash cans at other peoples parties in full view of guests, retrieving plastic knives and forks to recycle them, because it’s just what she must do.

Response:

Solar is a waste for a spa.pv solar panels  Can’t provide enough heat rise…

Au contraire. Heating water to 105 F is easy… Evacuated tubes work well, even in cloudy climates.

Focus has this equation for tube efficiency: E = 0.717-1.52X-0.0085GX^2, where X = (Tm-Ta)/G. Tm (C) is the mean water temp, Ta (C) is the air temp, and G is the insolation (W/m^2.) Tm = 77 C (170 F) and Ta = -1 (30 F) and full sun (G = 800 W/m^2) make X = 0.975 and E = 0.5, ie a 50% solar collection efficiency. …Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. …with solar… you still will need some other additional heat source to get it to 105, particularly during winter. I disagree. Then Nick, without an additional heat source, how are you going to get the spa up to 105 in a typical outdoor location in the US in winter at 9PM when you want to use it? Let’s even assume it was already at 105, before the sun went down.  As soon as you take the cover off and hop in, it’s all down hill from there.  With no other heat source, the solar answer is an insulated storage tank to store hot water.

Good idea. Where does that tank go, on the deck outside with the spa?

I’d say on the ground. It might be heavy. And how big does it have to be for the climate?

Which one? How about Phila in January, when 620 Btu/ft^2 of sun falls on the ground and 1000 falls on a south wall on an average 30 F day with humidity ratio w = 0.0025 pounds of water per pound of dry air. Say your tub is a 4′ cube with 8″ of polyisocyanurate insulation and an 8″ cover, with a thermal conductance of 96ft^2/R57.6 = 1.7 Btu/h-F when closed. When open, Pw = e^17.863-9621/(460+105) = 2.3 “Hg and Pa = 29.921/(1+0.62198/w) = 0.012 “Hg, so it loses 4′x4′x100(2.3-0.012) = 3488 Btu/h with the air pump disconnected, or less, if the surface is covered with partly inflated baggies or ping pong balls. If we use it 1 hour per day, it needs about 3488+23h(105-30)1.7 = 6362 Btu/day. With 50% efficiency, an optimal-slope flat plate solar collector would gather 0.5(sqrt(1000^2+620^2)) = 588 Btu/ft^2 on an average January day, so we need about 6362/588 = 10.8 ft^2 of collectors, or less, in tubes, or a bit more, to account for the heat store loss. If the heat store is very well insulated and it’s 170 F on an average day and it can keep the tub 105 until it reaches 110, we need about 5×6362/(170-110) = 530 pounds or 64 gallons or 8 ft^3 of water for 5 cloudy 30 F days in a row. We might use another 4′ cube with more insulation inside and a folded EPDM rubber liner, to bring about a pleasing aesthetic symmetry. Here’s a excerpt from an application note from a supplier of evacuated solar tubes:

Domestic hot water; 30 tubes for family of up to 4… Spa/Hot-tub; 60 tubes for up to 1500 liters

Heating a spa is twice as hard as heating water for a family of 4?  Where do we put the 60 evacuated tubes?

…60 seems like too many. On the roof with pipes running around or through the house?  Or do we put them on the deck with the spa and barbecue?

How about below the deck, on the south side of the tank? …But wait, according to the supplier, the 60 tubes are for a 1500L indoor spa, which really isn’t all that big, so we need even more tubes for the outside spa in winter.

Even more tubes would make the supplier happypv solar panels. Then we have to fool around with all the plumbing issues of trying to insert all the solar stuff into the spa circulation system, which doesn’t have pipe fittings sticking out that say “hook up solar collector here.”

Awww… And then perhaps another pump to move the water through the solar system…

Sure. A little one. Maybe 3488/5/8.33/60 = 1.4 gpm, and another small pump for the glycol tube loop, unless that thermosyphons. Then we need to fool around with the power pack on the spa to integrate this all in somehow to the std temp control system, which is microprocessor controlled, so when you dial in 100 or 105, it somehow maintains that temp.

You might disconnect the wires that run to the heater and attach them to the new spa pump. Who’s going to take liability for doing that right?

Henry Kissinger? At the very least, you can kiss your spa warranty goodbye.

Maybe not. And personally, I wouldn’t want to sit in a spa with added pumps and god knows what else that somebody made up as they went along.

Chacun a son bain-Californie. And finally, how much is all this going to cost in material and labor?

You’d probably say “too much.” The OP was worried about spending money for a 240V electric run, which is straightforward and simple compared to all this.

Maybe so. I’d further complicate things with ozone and a copper sponge in the filter and a salinity gauge that turns on another small pump to slowly replace spa water with fresh cold water via a heat exchanger when the water conductance exceeds some threshold. Don’t get me wrong.  Solar heat can be a cost effective and workable solution for the right climate and the right application.  But doing this to save the few hundred dollars a year it costs to heat a home spa is not one of them.

I disagree. Nick

Response:

Solar is a waste for a spa.  Can’t provide enough heat rise… Evacuated tubes work well, even in cloudy climates. and pretty much sucks ofr a midnight soak. …Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed.

Or empty the tub into a well-insulated tank between uses. I think you’ll find from a practical standpoint, it’s not worth converting it to solar or gas.  If it were practical, these would be offered as options on these types of spas and they aren’t.

Not a good argument, IMO. Why don’t we more small cars vs SUVs? And with solar, where you wouldn’t pay for any fuel, you still will need some other additional heat source to get it to 105, particularly during winter.

I disagree. Nick

Response:

- Hide quoted text — Show quoted text – Solar is a waste for a spa.pv solar panels  Can’t provide enough heat rise… Evacuated tubes work well, even in cloudy climates. and pretty much sucks ofr a midnight soak. …Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. Or empty the tub into a well-insulated tank between uses. I think you’ll find from a practical standpoint, it’s not worth converting it to solar or gas.  If it were practical, these would be offered as options on these types of spas and they aren’t. Not a good argument, IMO. Why don’t we more small cars vs SUVs?

For the same reason, which is that the small cars aren’t practical for the needs of the consumer who’s buying an SUV.  Are you suggesting a small compact car has the same functionality as an SUV?  Ever try to go snowboarding with 4 people and gear in a GEO Metro? And with solar, where you wouldn’t pay for any fuel, you still will need some other additional heat source to get it to 105, particularly during winter. I disagree. Nick

Then Nick, without an additional heat source, how are you going to get the spa up to 105 in a typical outdoor location in the US in winter at 9PM when you want to use it?  Let’s even assume it was already at 105, before the sun went down.  As soon as you take the cover off and hop in, it’s all down hill from there.  With no other heat source, the solar answer is an insulated storage tank to store hot water.  Where does that tank go, on the deck outside with the spa?  In the basement with a nice long pipe run to wherever the spa is?  And how big does it have to be for the climate? Here’s a excerpt from an application note from a supplier of evacuated solar tubes:  Domestic hot water; 30 tubes for family of up to 4. Central heating; 1-3 tubes per m2 heating area (Central heating is recommended with combination application in summer such as pool heating of spa.) Swimming pool heating; approximately 3 tubes per m2 of surface of indoor or covered outdoor pool. Spa/Hot-tub; 60 tubes for up to 1500 liters (Indoor.) Where do we put the 60 evacuated tubes?  On the roof with pipes running around or through the house?  Or do we put them on the deck with the spa and barbecue? Or build another structure in the back yard for them?   Dooh!  But wait, according to the supplier, the 60 tubes are for a 1500L indoor spa, which really isn’t all that big, so we need even more tubes for the outside spa in winter.   Then we have to fool around with all the plumbing issues of trying to insert all the solar stuff into the spa circulation system, which doesn’t have pipe fittings sticking out that say “hook up solar collector here.”  And then perhaps another pump to move the water through the solar system, together with automatic valves/sensors to make it go where it needs to go, ie from the tubes or into or out of the storage tank. Then we need to fool around with the power pack on the spa to integrate this all in somehow to the std temp control system, which is microprocessor controlled, so when you dial in 100 or 105, it somehow maintains that temp.   Who’s going to take liability for doing that right?  At the very least, you can kiss your spa warranty goodbye. And personally, I wouldn’t want to sit in a spa with added pumps and god knows what else that somebody made up as they went along.    And finally, how much is all this going to cost in material and labor? The OP was worried about spending money for a 240V electric run, which is straightforward and simple compared to all this. Don’t get me wrong.  Solar heat can be a cost effective and workable solution for the right climate and the right application.  But doing this to save the few hundred dollars a year it costs to heat a home spa is not one of them.

Response:

- Hide quoted text — Show quoted text – Solar is a waste for a spa.  Can’t provide enough heat rise… Evacuated tubes work well, even in cloudy climates. and pretty much sucks ofr a midnight soak. A spa can’t store much heat, if 104 F is too cool and 106 is too warm for people. Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. Drew Gillett and I have a solar water heater article in the Nov/Dec issue of Solar Today, available soon at Borders bookstores… Nick

I think you’ll find from a practical standpoint, it’s not worth converting it to solar or gas.  If it were practical, these would be offered as options on these types of spas and they aren’t.  And with solar, where you wouldn’t pay for any fuel, you still will need some other additional heat source to get it to 105, particularly during winter.  Regardless, you have to get an electric line out to it to run the pump, blower, etc., so you still have a lot of the cost of the electric work, even if you could avoid 240V. One question on the $380 est for energy usage.  Is that with the spa constantly at 100+?  Most spas can be programmed to come up to temp during the times/days you will be likely to use it.  Or, even without that, you can just raise it an hour or two before you want to use it and keep it at a lower temp, like 80 to save energy.  That’s what I do, as I only use mine a couple times a week.

Response:

pv solar panelsSolar is a waste for a spa.  Can’t provide enough heat rise…

Evacuated tubes work well, even in cloudy climates. and pretty much sucks ofr a midnight soak.

A spa can’t store much heat, if 104 F is too cool and 106 is too warm for people. Better to have a separate, well-insulated higher temp (170 F) heat store and meter it in as needed. Drew Gillett and I have a solar water heater article in the Nov/Dec issue of Solar Today, available soon at Borders bookstores…