Question:
solar power water heater information Look up the average outdoor temperature in January, where you live. The National Renewable Energy Laboratory’s free solar power water heater information _Solar Radiation Data Manual for Buildings_ has this information for 239 US locations. NREL’s phone number is (303) 275-4099. Where I live, near Philadelphia, the average January temperature is about 30 F or -1 C, and NREL’s manual says that 1,000 Btu/day or 3.3 kWh/m^2 of sun falls on a south wall here on an average January day, with a ground reflectance of about 0.2. A reflective surface in front of the wall like ice or snow or white paint might add 30% to the solar power that falls on the wall. solar power water heater information Step 2. Estimate how much energy your house needs to stay warm on an average Jan day. For example, a very-well-insulated 30′ x 30′ (10mx10m) 2-story house with about 2,000 square feet (200 m^2) of average US R20 (metric R3.5) walls and 1,000 ft^2 of R40 ceiling (100 m^2 of metric R7 ceiling) needs approximately 2,000ft^2/R20 + 1000ft^2/R40 = 125 Btu per hour per degree F or 37 watts to stay 68 F inside when it’s 67 F outside. The energy needed to keep a house warm is 24 (hours) times the product of (1) the difference between the average indoor and outdoor temperatures and (2) the thermal conductance of the house, ie the sum of each exterior surface area divided by its R-value. The number of kWh/day needed to keep a house warm is 3400 times less than the number of Btu, using the same formula with different units. This example house needs 24 hr x (68 F – 30 F) x 125 Btu/hr-F = 114,000 Btu or 33 kWh to stay warm on an average January day, the approximate heat equivalent of a gallon of oil. Step 3. Calculate how large a sunspace the house needs to stay warm, ie how much vertical south glass or plastic film glazing area a low-thermal-mass sunspace needs to gather enough solar heat to keep the house warm on an average Jan day with an average amount of sun. If the low-thermal-mass sunspace has an insulated low-thermal-mass wall between it and the house, solar power water heater information ie a non-masonry floor and a non-masonry wall, with no rocks nor bricks nor water containers nor collections of scrap iron inside the sunspace, with a window fan to move most of the warm air into the house during the day, the sunspace will be about 68 F (20 C) during the day. If we let the sunspace get icy cold at night, the heat lost from the glazing over an average 6 hour Jan day will be about 6x(68F-30F)1 ft^2/USR1 = 228 Btu/ft^2 or 6x(20C-(-1C))1m^2/R0.176 = 716 wh/day, so the sunspace glazing can provide about 1000-228 = 772 Btu/ft^2 or 3.3-0.716 = 2.6 kWh to the house on an average Jan day, in this example. The example house needs about 114,000,000/772 = 150 sq. feet or 33/2.6 = 12.7 m^2 of sunspace glazing to keep it warm on an average day. Say, a 16′ high x 16′ wide x 12′ deep (5m x 5m x 4m) lean-to plastic film greenhouse, made from standard commercial greenhouse hardware, including 5 long curved galvanized pipes costing $35 each, with a lightweight gravel floor over plastic film on the ground. Step 4. Estimate how many cloudy days in a row there are in January, where you live, and what the outdoor temperature is during those days. In some places, cloudy days and nights are warmer than days and nights in sunny weather, because the clouds act as insulation. (US residents can be more precise about this by buying a $130 CD ROM from NREL/NOAA which includes 30 year’s worth of _hourly_ solar weather data for their locations, and looking over the data for long sunless periods with low air temperatures, ie “cloudy degree day” periods, or running a very simple computer simulation of a particular solar house to estimate the interior temperature every hour for 20 years and predict daily temperature swings.) Suppose this example house is in a climate in which we expect at most 5 cloudy Jan days in a row with 99% confidence, with an average outdoor temperature during those days of 30 F (-1 C), ie we expect colder and cloudier periods to occur only every 100 years. Step 5. Calculate how many sealed 55 gallon or 200 liter plastic drums full of water (or 5 gallon pails or 2 liter soda bottles or canned goods on shelves) are needed inside the closet to keep the house warm for that cloudy period. The example house needs 5×114K = 570K Btu or 167 kWh to stay warm for 5 cloudy days. If the water in the drums is, say 130 F (54 C), and the drums can keep the house warm until the water cools to, say, 80 F (27 C), then each drum stores about 25K Btu or 6 kWh of useful heat, and the house needs 570K/25K = 23 55 gallon or 167/6 = 28 200 liter drums. We might keep the drums at 54 C by building an “solar closet,” ie a box that is completely surrounded by insulation, behind the sunspace, ideally inside the house, with an air heater as part of the insulated wall between the sunspace and the house, using some transparent “solar siding,” eg Home Depot’s “Paltough” corrugated polycarbonate plastic, costing about $1/ft^2, or Replex’s ((800) 726-5151) clear flat polycarbonate plastic, which costs about $1.25 per square foot ($13/m^2) and comes in long rolls, 49 inches wide. The transparent siding might have some black aluminum window screen or greenhouse shadecloth to the north and behind it, with an air gap on each side of the shadecloth, to reduce reradiation and increase the solar collection efficiency of the closet. 80% carbon-filled polypropylene shadecloth costs about 15 cents per square foot or $2/m^2 and should last many years out of the weather. Shadecloth comes in various colors. We might have a 1″ (3 cm) air gap between the siding and the shadecloth, and another 1″ gap between the shadecloth and 3 1/2″ (10 cm) of fiberglass insulation in a 6″ (15 cm) wall, with some small vents (about 1% of the closet glazing area, eg 1 square foot or 0.1 m^2 in the example house) at the top and bottom of this air heater, to allow cooler air from the solar closet to flow into the outside air gap through the vent hole at the bottom of the air heater, which would then flow horizontally through the shadecloth from south to north, becoming warmer, and rise up and flow back through the upper vent hole and back into the closet. solar power water heater information The vent holes might have plastic-film backdraft dampers to keep air from flowing when the sun is not shining. These require checking every week or so, since they can stick open, and if they are large enough to pass air well, they lose significant heat through the US R1 plastic film. They might be made from chicken wire and the plastic film used for dry cleaner bags. Using a small fan can reduce thermal losses and raise solar collection efficiency. The inside walls of the closet could simply be fiberglass insulation, covered with plastic film. The floor might be earth, covered with more plastic film. The spaces between the sealed containers of water allow air to circulate around them, heating or cooling them.solar power water heater information We need a room-temperature-sensitive vent (eg a $12 automatic foundation vent with its bimetallic spring reversed to open some louver as temperature drops) or a fan that turns on between the closet and house on cool cloudy days, and a return air path from the house to the closet near the floor. The example house might have 24 2′ diameter x 3′ high drums stacked 2 high in 2 rows of 6 drums making the solar closet about 8′ high x 12′ long x 4′ deep. ie about 3m high x 4m long x 1m deep. We might make it 6′ (2m) longer, and use the empty space for a sauna, or a place to dry clothes. The closet might have 3 1/2″ (10 cm) of fiberglass insulation in its ceiling, ie the second floor of the house, as well as in the other walls inside the house. Most of the “waste heat” from this closet ends up in the house, and it provides very little heat for the house on an average winter day, with some sun. On such a day, the house is almost entirely heated by the warm air from the sunspace. If the closet were 2 stories tall, 1 or 2 plastic drums with threaded bungs at the top might be plumbed in series to make a low-pressure gravity-fed hot water system using a float valve or rainwater from the roof to keep the drums full. A 1-story solar closet might have a fan-coil unit or about 20′ (6m) of baseboard radiator pipe with fins near the ceiling to make an air-water heat exchanger connected to a warm-water thermosyphoning loop with some insulated pipe through an ordinary water heater on the second floor with a heating element that rarely turns on. In either case, the sunspace and closet need about 64 ft^2 (6m^2) more solar glazing. The sauna area in the closet might have a small woodstove, for burning newspapers, junk mail, old paper towels, college committee recommendations, letters from congressmen, and press releases announcing amazing new price breakthroughs in photovoltaic technology. solar power water heater information. Air infiltration robs houses of heat, and electrical power use adds heat to houses, as do south windows. These things tend to cancel out, conservatively-speaking, so they aren’t mentioned above. Other helpful factors not mentioned above are that daytime temperatures inside and outside the house are higher than nighttime temperatures, and that the solar power water heater information part of the south wall of the house that is covered by the sunspace needs no heat on an average day. 2. Sunspace airflow volume increases with the square root of the height. A quote from the Energy Crafted Homes spec: “For optimal heat flow into the house from the sunspace, install sliding or French doors between the two. Natural air flow through an open door can be as high as 1000 cfm… most effective if a complete loop through the house is possible- two-story sunspaces can be tremendously effective at heating a house for this reason.” A two-story sunspace probably needs no fan. It might operate automatically with a 2 watt $50 Honeywell 6161B1000 damper motor in series with two thermostats,
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Response:
The National Renewable Energy Laboratory’s free _Solar Radiation Data Manual for Buildings_ has this information for 239 US locations. NREL’s phone number is (303) 275-4099.
The NREL web site has much of this information also. http://rredc.nrel.gov/ Or see: http://rredc.nrel.gov/solar/ sdb
Response:
- Hide quoted text — Show quoted text – Step 1. Look up the average outdoor temperature in January, where you live. The National Renewable Energy Laboratory’s free _Solar Radiation Data Manual for Buildings_ has this information for 239 US locations. NREL’s phone number is (303) 275-4099. Where I live, near Philadelphia, the average January temperature is about 30 F or -1 C, and NREL’s manual says that 1,000 Btu/day or 3.3 kWh/m^2 of sun falls on a south wall here on an average January day, with a ground reflectance of about 0.2. A reflective surface in front of the wall like ice or snow or white paint might add 30% to the solar power that falls on the wall. Step 2. Estimate how much energy your house needs to stay warm on an average Jan day. For example, a very-well-insulated 30′ x 30′ (10mx10m) 2-story house with about 2,000 square feet (200 m^2) of average US R20 (metric R3.5) walls and 1,000 ft^2 of R40 ceiling (100 m^2 of metric R7 ceiling) needs approximately 2,000ft^2/R20 + 1000ft^2/R40 = 125 Btu per hour per degree F or 37 watts to stay 68 F inside when it’s 67 F outside. The energy needed to keep a house warm is 24 (hours) times the product of (1) the difference between the average indoor and outdoor temperatures and (2) the thermal conductance of the house, ie the sum of each exterior surface area divided by its R-value. The number of kWh/day needed to keep a house warm is 3400 times less than the number of Btu, using the same formula with different units. This example house needs 24 hr x (68 F – 30 F) x 125 Btu/hr-F = 114,000 Btu or 33 kWh to stay warm on an average January day, the approximate heat equivalent of a gallon of oil. Step 3. Calculate how large a sunspace the house needs to stay warm, ie how much vertical south glass or plastic film glazing area a low-thermal-mass sunspace needs to gather enough solar heat to keep the house warm on an average Jan day with an average amount of sun. If the low-thermal-mass sunspace has an insulated low-thermal-mass wall between it and the house, ie a non-masonry floor and a non-masonry wall, with no rocks nor bricks nor water containers nor collections of scrap iron inside the sunspace, with a window fan to move most of the warm air into the house during the day, the sunspace will be about 68 F (20 C) during the day. If we let the sunspace get icy cold at night, the heat lost from the glazing over an average 6 hour Jan day will be about 6x(68F-30F)1 ft^2/USR1 = 228 Btu/ft^2 or 6x(20C-(-1C))1m^2/R0.176 = 716 wh/day, so the sunspace glazing can provide about 1000-228 = 772 Btu/ft^2 or 3.3-0.716 = 2.6 kWh to the house on an average Jan day, in this example. The example house needs about 114,000,000/772 = 150 sq. feet or 33/2.6 = 12.7 m^2 of sunspace glazing to keep it warm on an average day. Say, a 16′ high x 16′ wide x 12′ deep (5m x 5m x 4m) lean-to plastic film greenhouse, made from standard commercial greenhouse hardware, including 5 long curved galvanized pipes costing $35 each, with a lightweight gravel floor over plastic film on the ground. Step 4. Estimate how many cloudy days in a row there are in January, where you live, and what the outdoor temperature is during those days. In some places, cloudy days and nights are warmer than days and nights in sunny weather, because the clouds act as insulation. (US residents can be more precise about this by buying a $130 CD ROM from NREL/NOAA which includes 30 year’s worth of _hourly_ solar weather data for their locations, and looking over the data for long sunless periods with low air temperatures, ie “cloudy degree day” periods, or running a very simple computer simulation of a particular solar house to estimate the interior temperature every hour for 20 years and predict daily temperature swings.) Suppose this example house is in a climate in which we expect at most 5 cloudy Jan days in a row with 99% confidence, with an average outdoor temperature during those days of 30 F (-1 C), ie we expect colder and cloudier periods to occur only every 100 years. Step 5. Calculate how many sealed 55 gallon or 200 liter plastic drums full of water (or 5 gallon pails or 2 liter soda bottles or canned goods on shelves) are needed inside the closet to keep the house warm for that cloudy period. The example house needs 5×114K = 570K Btu or 167 kWh to stay warm for 5 cloudy days. If the water in the drums is, say 130 F (54 C), and the drums can keep the house warm until the water cools to, say, 80 F (27 C), then each drum stores about 25K Btu or 6 kWh of useful heat, and the house needs 570K/25K = 23 55 gallon or 167/6 = 28 200 liter drums. We might keep the drums at 54 C by building an “solar closet,” ie a box that is completely surrounded by insulation, behind the sunspace, ideally inside the house, with an air heater as part of the insulated wall between the sunspace and the house, using some transparent “solar siding,” eg Home Depot’s “Paltough” corrugated polycarbonate plastic, costing about $1/ft^2, or Replex’s ((800) 726-5151) clear flat polycarbonate plastic, which costs about $1.25 per square foot ($13/m^2) and comes in long rolls, 49 inches wide. The transparent siding might have some black aluminum window screen or greenhouse shadecloth to the north and behind it, with an air gap on each side of the shadecloth, to reduce reradiation and increase the solar collection efficiency of the closet. 80% carbon-filled polypropylene shadecloth costs about 15 cents per square foot or $2/m^2 and should last many years out of the weather. Shadecloth comes in various colors. We might have a 1″ (3 cm) air gap between the siding and the shadecloth, and another 1″ gap between the shadecloth and 3 1/2″ (10 cm) of fiberglass insulation in a 6″ (15 cm) wall, with some small vents (about 1% of the closet glazing area, eg 1 square foot or 0.1 m^2 in the example house) at the top and bottom of this air heater, to allow cooler air from the solar closet to flow into the outside air gap through the vent hole at the bottom of the air heater, which would then flow horizontally through the shadecloth from south to north, becoming warmer, and rise up and flow back through the upper vent hole and back into the closet. The vent holes might have plastic-film backdraft dampers to keep air from flowing when the sun is not shining. These require checking every week or so, since they can stick open, and if they are large enough to pass air well, they lose significant heat through the US R1 plastic film. They might be made from chicken wire and the plastic film used for dry cleaner bags. Using a small fan can reduce thermal losses and raise solar collection efficiency. The inside walls of the closet could simply be fiberglass insulation, covered with plastic film. The floor might be earth, covered with more plastic film. The spaces between the sealed containers of water allow air to circulate around them, heating or cooling them. We need a room-temperature-sensitive vent (eg a $12 automatic foundation vent with its bimetallic spring reversed to open some louver as temperature drops) or a fan that turns on between the closet and house on cool cloudy days, and a return air path from the house to the closet near the floor. The example house might have 24 2′ diameter x 3′ high drums stacked 2 high in 2 rows of 6 drums making the solar closet about 8′ high x 12′ long x 4′ deep. ie about 3m high x 4m long x 1m deep. We might make it 6′ (2m) longer, and use the empty space for a sauna, or a place to dry clothes. The closet might have 3 1/2″ (10 cm) of fiberglass insulation in its ceiling, ie the second floor of the house, as well as in the other walls inside the house. Most of the “waste heat” from this closet ends up in the house, and it provides very little heat for the house on an average winter day, with some sun. On such a day, the house is almost entirely heated by the warm air from the sunspace. If the closet were 2 stories tall, 1 or 2 plastic drums with threaded bungs at the top might be plumbed in series to make a low-pressure gravity-fed hot water system using a float valve or rainwater from the roof to keep the drums full. A 1-story solar closet might have a fan-coil unit or about 20′ (6m) of baseboard radiator pipe with fins near the ceiling to make an air-water heat exchanger connected to a warm-water thermosyphoning loop with some insulated pipe through an ordinary water heater on the second floor with a heating element that rarely turns on. In either case, the sunspace and closet need about 64 ft^2 (6m^2) more solar glazing. The sauna area in the closet might have a small woodstove, for burning newspapers, junk mail, old paper towels, college committee recommendations, letters from congressmen, and press releases announcing amazing new price breakthroughs in photovoltaic technology. Nick Notes: 1. Air infiltration robs houses of heat, and electrical power use adds heat to houses, as do south windows. These things tend to cancel out, conservatively-speaking, so they aren’t mentioned above. Other helpful factors not mentioned above are that daytime temperatures inside and outside the house are higher than nighttime temperatures, and that the part of the south wall of the house that is covered by the sunspace needs no heat on an average day. 2. Sunspace airflow volume increases with the square root of the height. A quote from the Energy Crafted Homes spec: “For optimal heat flow into the house from the sunspace, install sliding or French doors between the two. Natural air flow through an open door
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Response:
no_decaf, you are missing the point. No amount of king’s horses and king’s men can make urban living an efficient use of resources. Large cities are political creations, designed to assemble voters into bantustans where they become dependent upon the entitlement-program “favors” of politicians. A large city is an un-natural act. Ask anyone who’s ever worked in a congressman’s office. Only a tiny fraction of incoming correspondence is of the “my opinion on issue XX is…” flavor. Rather, there is a huge flood of letters that complain about social security checks being late, or of denial of benefits under transfer-payments programs.
Response:
I’m sorry, but I would have to disagree with your first paragraph entirely. Large cities are *not* unnatural acts/designs. Have you ever seen a termite nest? The very idea behind congregations of this magnitude is to help increase in the efficiency of distributing materials. In terms of *efficiency*, a city can produce a large amount of goods, in a very small amount of time. In fact, politics (as defined as the creation of rules to help us live together) often interferes in *efficiency*, by requiring child labor, and other such things, to be abolished (at least in the US). Why? Simple – we want more to life than just efficiency…we also want quality. I guess what I’m getting at is your choice of words…I am not a particularly rabid environmentalist, nor do I routinely read “alt.pave.the.earth”. I think I am like most people in this respect. In truth, I want to be able to maximize my opportunities, while minimizing potential difficulties. Living in a large community, such as a city, allows for the use of large amounts of material in a very small area, thus allowing for more complex projects to be undertaken in a city than near an isolated house in the middle of the “country”. For example: how many libraries do you see in cities? Now, think about how many you see near the previously mentioned country house. Unless fantastic new technologies are developed, then individuals in cities will always have more potential for “development” (in the intellectual sense), just because they are much closer to said learning institutions, and can go to museums, concerts, and plays with a substantially smaller investment of time than an equivalent person living in our country house. Now, I do realize that it would probably have been better to start a new thread with this response, but I didn’t want to bother everybody who reads the newsgroup with my diatribe…if people find it interesting/outrageous, I’m sure it will get around. Having read through this and several other newsgroups, I have seen that many people in these newsgroups want everybody to switch over to fuels other than the fossil-based variety, so that we may collectively have a better future. While I agree that there are fuels out there that are substantially cleaner, fossil fuels produce a larger amount of energy per unit volume than most of them. As a result, many people have gotten used to slightly “dirty” skies, and are willing to live with them in exchange for the many conveniences of modern-day life. Is exchanging a “clean” planet for modern society a so-called “pact with the Devil”? Perhaps it is, perhaps it isn’t, perhaps it doesn’t matter. Very few people are swayed by impassioned pleas…they prefer obvious, definite benefits for changing something they currently do / believe in. Thus, I present this as a question…how do you (as groups or as individuals) intend to persuade the world at large that alternative fuels are the way to go? I am well aware of the calculations that say our world oil supplies will probably be used up in between fifty and one hundred years, based on our current and projected rate of consumption. Despite these calculations, most people have not been willing to forsake their current style of living, so I am curious as how you intend to convince “average Joe” to switch to alternative fuels. I look forward to your responses. Sincerely, Scott Ferguson – Hide quoted text — Show quoted text – no_decaf, you are missing the point. No amount of king’s horses and king’s men can make urban living an efficient use of resources. Large cities are political creations, designed to assemble voters into bantustans where they become dependent upon the entitlement-program “favors” of politicians. A large city is an un-natural act. Ask anyone who’s ever worked in a congressman’s office. Only a tiny fraction of incoming correspondence is of the “my opinion on issue XX is…” flavor. Rather, there is a huge flood of letters that complain about social security checks being late, or of denial of benefits under transfer-payments programs.
Response:
I had my hat on backwards when I said “North”, meant to say “South”. Hey, I’m old…. – Hide quoted text — Show quoted text – Relative to the passive solar house – I’ve always wondered why someone doesn’t put up louvers instead of solid roof overhang on the North side of a house. If you angled them to match the angle of the Winter sun, heat would enter the house when you wanted, but not in the Summer…. Has been done see http://www.emilis.sa.on.net/emil_60.htm only this is on the bottom half of the planet Emilis
Response:
Nick, I hope you just clipped that post from a document you already had. Poor keyboard :-) Dan
Relative to the passive solar house – I’ve always wondered why someone doesn’t put up louvers instead of solid roof overhang on the North side of a house. If you angled them to match the angle of the Winter sun, heat would enter the house when you wanted, but not in the Summer….
Response:
I’m sorry, but I would have to disagree with your first paragraph entirely. Large cities are *not* unnatural acts/designs. Have you ever seen a termite nest? The very idea behind congregations of this magnitude is to help increase in the efficiency of distributing materials. In terms of *efficiency*, a city can produce a large amount of goods, in a very small amount of time. In fact, politics (as defined as the creation of rules to help us live together) often interferes in *efficiency*, by requiring child labor, and other such things, to be abolished (at least in the US). Why? Simple – we want more to life than just efficiency…we also want quality. I guess what I’m getting at is your choice of words…I am not a particularly rabid environmentalist, nor do I routinely read “alt.pave.the.earth”. I think I am like most people in this respect. In truth, I want to be able to maximize my opportunities, while minimizing potential difficulties. Living in a large community, such as a city, allows for the use of large amounts of material in a very small area, thus allowing for more complex projects to be undertaken in a city than near an isolated house in the middle of the “country”. For example: how many libraries do you see in cities? Now, think about how many you see near the previously mentioned country house. Unless fantastic new technologies are developed, then individuals in cities will always have more potential for “development” (in the intellectual sense), just because they are much closer to said learning institutions, and can go to museums, concerts, and plays with a substantially smaller investment of time than an equivalent person living in our country house. Now, I do realize that it would probably have been better to start a new thread with this response, but I didn’t want to bother everybody who reads the newsgroup with my diatribe…if people find it interesting/outrageous, I’m sure it will get around. Having read through this and several other newsgroups, I have seen that many people in these newsgroups want everybody to switch over to fuels other than the fossil-based variety, so that we may collectively have a better future. While I agree that there are fuels out there that are substantially cleaner, fossil fuels produce a larger amount of energy per unit volume than most of them. As a result, many people have gotten used to slightly “dirty” skies, and are willing to live with them in exchange for the many conveniences of modern-day life. Is exchanging a “clean” planet for modern society a so-called “pact with the Devil”? Perhaps it is, perhaps it isn’t, perhaps it doesn’t matter. Very few people are swayed by impassioned pleas…they prefer obvious, definite benefits for changing something they currently do / believe in. Thus, I present this as a question…how do you (as groups or as individuals) intend to persuade the world at large that alternative fuels are the way to go? I am well aware of the calculations that say our world oil supplies will probably be used up in between fifty and one hundred years, based on our current and projected rate of consumption. Despite these calculations, most people have not been willing to forsake their current style of living, so I am curious as how you intend to convince “average Joe” to switch to alternative fuels. I look forward to your responses. Sincerely, Scott Ferguson – Hide quoted text — Show quoted text – no_decaf, you are missing the point. No amount of king’s horses and king’s men can make urban living an efficient use of resources. Large cities are political creations, designed to assemble voters into bantustans where they become dependent upon the entitlement-program “favors” of politicians. A large city is an un-natural act. Ask anyone who’s ever worked in a congressman’s office. Only a tiny fraction of incoming correspondence is of the “my opinion on issue XX is…” flavor. Rather, there is a huge flood of letters that complain about social security checks being late, or of denial of benefits under transfer-payments programs.
Response:
Let me know what you think of this idea. I am building a passive green house on the southern face of my house. Inside I plan on having a water heating system consisting of piping shrouded by fins to heat my water. The semi heated water will go into a holding tank and when needed into the main tank. Would solar water heating panels work or should I stick with the fin idea (that is from a dealer in solar products locally)? I already have the water heating panels and would like to just use those. But the dealer said that wouldn’t work. I originally planned on placing them no more then 4 inches from the glazing to take advantage of the trtransmittedeat.
Response:
Nick, I hope you just clipped that post from a document you already had. Poor keyboard :-) Dan
Response:
no_decaf, you are missing the point. No amount of king’s horses and king’s men can make urban living an efficient use of resources. Large cities are political creations, designed to assemble voters into bantustans where they become dependent upon the entitlement-program “favors” of politicians. A large city is an un-natural act. Ask anyone who’s ever worked in a congressman’s office. Only a tiny fraction of incoming correspondence is of the “my opinion on issue XX is…” flavor. Rather, there is a huge flood of letters that complain about social security checks being late, or of denial of benefits under transfer-payments programs.
Response:
- Hide quoted text — Show quoted text – Step 1. Look up the average outdoor temperature in January, where you live. The National Renewable Energy Laboratory’s free _Solar Radiation Data Manual for Buildings_ has this information for 239 US locations. NREL’s phone number is (303) 275-4099. Where I live, near Philadelphia, the average January temperature is about 30 F or -1 C, and NREL’s manual says that 1,000 Btu/day or 3.3 kWh/m^2 of sun falls on a south wall here on an average January day, with a ground reflectance of about 0.2. A reflective surface in front of the wall like ice or snow or white paint might add 30% to the solar power that falls on the wall. Step 2. Estimate how much energy your house needs to stay warm on an average Jan day. For example, a very-well-insulated 30′ x 30′ (10mx10m) 2-story house with about 2,000 square feet (200 m^2) of average US R20 (metric R3.5) walls and 1,000 ft^2 of R40 ceiling (100 m^2 of metric R7 ceiling) needs approximately 2,000ft^2/R20 + 1000ft^2/R40 = 125 Btu per hour per degree F or 37 watts to stay 68 F inside when it’s 67 F outside. The energy needed to keep a house warm is 24 (hours) times the product of (1) the difference between the average indoor and outdoor temperatures and (2) the thermal conductance of the house, ie the sum of each exterior surface area divided by its R-value. The number of kWh/day needed to keep a house warm is 3400 times less than the number of Btu, using the same formula with different units. This example house needs 24 hr x (68 F – 30 F) x 125 Btu/hr-F = 114,000 Btu or 33 kWh to stay warm on an average January day, the approximate heat equivalent of a gallon of oil. Step 3. Calculate how large a sunspace the house needs to stay warm, ie how much vertical south glass or plastic film glazing area a low-thermal-mass sunspace needs to gather enough solar heat to keep the house warm on an average Jan day with an average amount of sun. If the low-thermal-mass sunspace has an insulated low-thermal-mass wall between it and the house, ie a non-masonry floor and a non-masonry wall, with no rocks nor bricks nor water containers nor collections of scrap iron inside the sunspace, with a window fan to move most of the warm air into the house during the day, the sunspace will be about 68 F (20 C) during the day. If we let the sunspace get icy cold at night, the heat lost from the glazing over an average 6 hour Jan day will be about 6x(68F-30F)1 ft^2/USR1 = 228 Btu/ft^2 or 6x(20C-(-1C))1m^2/R0.176 = 716 wh/day, so the sunspace glazing can provide about 1000-228 = 772 Btu/ft^2 or 3.3-0.716 = 2.6 kWh to the house on an average Jan day, in this example. The example house needs about 114,000,000/772 = 150 sq. feet or 33/2.6 = 12.7 m^2 of sunspace glazing to keep it warm on an average day. Say, a 16′ high x 16′ wide x 12′ deep (5m x 5m x 4m) lean-to plastic film greenhouse, made from standard commercial greenhouse hardware, including 5 long curved galvanized pipes costing $35 each, with a lightweight gravel floor over plastic film on the ground. Step 4. Estimate how many cloudy days in a row there are in January, where you live, and what the outdoor temperature is during those days. In some places, cloudy days and nights are warmer than days and nights in sunny weather, because the clouds act as insulation. (US residents can be more precise about this by buying a $130 CD ROM from NREL/NOAA which includes 30 year’s worth of _hourly_ solar weather data for their locations, and looking over the data for long sunless periods with low air temperatures, ie “cloudy degree day” periods, or running a very simple computer simulation of a particular solar house to estimate the interior temperature every hour for 20 years and predict daily temperature swings.) Suppose this example house is in a climate in which we expect at most 5 cloudy Jan days in a row with 99% confidence, with an average outdoor temperature during those days of 30 F (-1 C), ie we expect colder and cloudier periods to occur only every 100 years. Step 5. Calculate how many sealed 55 gallon or 200 liter plastic drums full of water (or 5 gallon pails or 2 liter soda bottles or canned goods on shelves) are needed inside the closet to keep the house warm for that cloudy period. The example house needs 5×114K = 570K Btu or 167 kWh to stay warm for 5 cloudy days. If the water in the drums is, say 130 F (54 C), and the drums can keep the house warm until the water cools to, say, 80 F (27 C), then each drum stores about 25K Btu or 6 kWh of useful heat, and the house needs 570K/25K = 23 55 gallon or 167/6 = 28 200 liter drums. We might keep the drums at 54 C by building an “solar closet,” ie a box that is completely surrounded by insulation, behind the sunspace, ideally inside the house, with an air heater as part of the insulated wall between the sunspace and the house, using some transparent “solar siding,” eg Home Depot’s “Paltough” corrugated polycarbonate plastic, costing about $1/ft^2, or Replex’s ((800) 726-5151) clear flat polycarbonate plastic, which costs about $1.25 per square foot ($13/m^2) and comes in long rolls, 49 inches wide. The transparent siding might have some black aluminum window screen or greenhouse shadecloth to the north and behind it, with an air gap on each side of the shadecloth, to reduce reradiation and increase the solar collection efficiency of the closet. 80% carbon-filled polypropylene shadecloth costs about 15 cents per square foot or $2/m^2 and should last many years out of the weather. Shadecloth comes in various colors. We might have a 1″ (3 cm) air gap between the siding and the shadecloth, and another 1″ gap between the shadecloth and 3 1/2″ (10 cm) of fiberglass insulation in a 6″ (15 cm) wall, with some small vents (about 1% of the closet glazing area, eg 1 square foot or 0.1 m^2 in the example house) at the top and bottom of this air heater, to allow cooler air from the solar closet to flow into the outside air gap through the vent hole at the bottom of the air heater, which would then flow horizontally through the shadecloth from south to north, becoming warmer, and rise up and flow back through the upper vent hole and back into the closet. The vent holes might have plastic-film backdraft dampers to keep air from flowing when the sun is not shining. These require checking every week or so, since they can stick open, and if they are large enough to pass air well, they lose significant heat through the US R1 plastic film. They might be made from chicken wire and the plastic film used for dry cleaner bags. Using a small fan can reduce thermal losses and raise solar collection efficiency. The inside walls of the closet could simply be fiberglass insulation, covered with plastic film. The floor might be earth, covered with more plastic film. The spaces between the sealed containers of water allow air to circulate around them, heating or cooling them. We need a room-temperature-sensitive vent (eg a $12 automatic foundation vent with its bimetallic spring reversed to open some louver as temperature drops) or a fan that turns on between the closet and house on cool cloudy days, and a return air path from the house to the closet near the floor. The example house might have 24 2′ diameter x 3′ high drums stacked 2 high in 2 rows of 6 drums making the solar closet about 8′ high x 12′ long x 4′ deep. ie about 3m high x 4m long x 1m deep. We might make it 6′ (2m) longer, and use the empty space for a sauna, or a place to dry clothes. The closet might have 3 1/2″ (10 cm) of fiberglass insulation in its ceiling, ie the second floor of the house, as well as in the other walls inside the house. Most of the “waste heat” from this closet ends up in the house, and it provides very little heat for the house on an average winter day, with some sun. On such a day, the house is almost entirely heated by the warm air from the sunspace. If the closet were 2 stories tall, 1 or 2 plastic drums with threaded bungs at the top might be plumbed in series to make a low-pressure gravity-fed hot water system using a float valve or rainwater from the roof to keep the drums full. A 1-story solar closet might have a fan-coil unit or about 20′ (6m) of baseboard radiator pipe with fins near the ceiling to make an air-water heat exchanger connected to a warm-water thermosyphoning loop with some insulated pipe through an ordinary water heater on the second floor with a heating element that rarely turns on. In either case, the sunspace and closet need about 64 ft^2 (6m^2) more solar glazing. The sauna area in the closet might have a small woodstove, for burning newspapers, junk mail, old paper towels, college committee recommendations, letters from congressmen, and press releases announcing amazing new price breakthroughs in photovoltaic technology. Nick Notes: 1. Air infiltration robs houses of heat, and electrical power use adds heat to houses, as do south windows. These things tend to cancel out, conservatively-speaking, so they aren’t mentioned above. Other helpful factors not mentioned above are that daytime temperatures inside and outside the house are higher than nighttime temperatures, and that the part of the south wall of the house that is covered by the sunspace needs no heat on an average day. 2. Sunspace airflow volume increases with the square root of the height. A quote from the Energy Crafted Homes spec: “For optimal heat flow into the house from the sunspace, install sliding or French doors between the two. Natural air flow through an open door
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Response:
Step 1. Gather some weather data. The most-difficult month for solar house heating is the one with the lowest ratio of average solar energy to indoor-outdoor temperature difference, ie the lowest amount of “sun per degree day.” The long-term average outdoor temperatures near Philadelphia, PA are 35.8 and 30.4 F (TB, in the calculation below) in December and January, with 900 and 1,000 Btu/ft^2 of sun (SS, below) falling on a south wall on an average day. This makes January the worst-case month for house heating, with 1,000/(68-30.4) = 26.6 Btu/F, vs 900/(68-35.8) = 28 in December. The National Renewable Energy Laboratory’s free “Solar Radiation Data Manual for Buildings” (http://rredc.nrel.gov) has solar weather data for 239 US locations. NREL’s phone number is (303) 275-4099. The average daily maximum temperature in January is 37.9 F in Phila. NREL’s manual says an average of 620 Btu/ft^2 of sun per day falls on a horizontal surface, east and west walls receive about 420, and a north wall gets 190. How many cloudy days in a row, and what is the temperature then? In some places, cloudy days and nights are warmer than days and nights in sunny weather, because clouds act as insulation. NREL’s TMY2 weather data or one of their 3 CD-ROMs might help answer this question. Their _hourly_ solar weather data for 239 US locations. We might look for long low-temperatue “cloudy degree-day” periods, or or do a simple computer simulation of a particular solar house design to estimate the interior temperature every hour for 30 years, or the total amount of backup heat required. Then again, some people define a “solar house” as “one with no other form of heat.” The issue then becomes comfort, vs “solar fraction.” Suppose our house is in a climate in which we expect at most 5 cloudy days in a row with 99% confidence, with an average outdoor temperature during those days of 30 F (-1 C)… Step 2. Gather some house data The thermal conductance of a house is the sum of each exterior surface area divided by its R-value, plus an effective conductance for air leaks. For example, a fairly airtight and well-insulated 32′x32′ (10mx10m) 2-story house with 2,048 square feet (190 m^2) of US R30 (metric R5.3) walls and 80 ft^2 of R4 windows (7.4 m^2 at 0.7 m^2C/W) and 1,024 ft^2 of R40 ceiling (95 m^2 at metric R7) and a natural air leakage rate of 0.3 house volume Air Changes per Hour has a thermal conductance of about 1,968ft^2/R30 + 80ft^2/R4 + 1024ft^2/R40 + 30×30x16×0.3/55 = 164 Btu per hour per degree F difference between indoor and outdoor temperatures (HC, below.) It needs about 164 Btu or 48 watts to stay 68 F indoors when it’s 67 F outdoors. The daily house heating energy needed is 24 (h) times the product of the thermal conductance of the house and the difference between the average indoor and outdoor temperatures. Our example house needs about 24h(68F-30F)x164Btu/h-F = 150K Btu (EDAY, below) or 44 kWh to stay warm on an average January day, roughly equivalent to a gallon of oil. (The yearly energy needed to keep a house warm is 24 times the conductance times the number of heating degree days per year, 5,500 (F) for Phila.) Some of this energy comes from the occupants and their electrical usage. Each person makes about 100 watts of heat power, and a kilowatt-hour is equivalent to 3,412 Btu of heat energy. If our house has an average of 1 person inside and uses 500 kWh per month (an average of 694 watts) of electrical energy, it gains about 0.794×24 = 19 kWh or 65K Btu/day (INTHEAT, below) of heat from internal sources. Sun also shines into house windows. If our house has equal window areas facing 4 compass directions, and they have 70% solar transmittance, it gains another 20ft^2×0.7x(1000+420+420+190) = 28K Btu of solar heat (WINHEAT) on an average January day. So we need 150K Btu/day of heat, of which 65K comes from internal sources and 28K from windows, leaving an additional solar heating requirement of 150K-65K-28K = 57K Btu (SDAY) on an average January day. The inherent thermal mass of a house can store solar heat on an average day, if it is allowed to cool at night. If our house has 4×32x16 = 2,048 square feet of external walls and another 2,048 ft^2 of internal walls and 3×1,024 ft^2 of ceiling and floors, ie 7,168 ft^2 of surface, all covered with 1/2″ drywall or something with equivalent heat capacity (1/2 Btu/F-ft^2), the total capacity of the house is 7,168×0.5 = 3,584 Btu/F, ie the house can store 3,584 Btu for each degree F of day/night temperature swing. With a 10 F swing (eg 70 F during the day and 60 F at night, our house could store 35,840 Btu (SWINGHEAT, below.) (1) After a house is 100% solar heated, the next largest energy need is often hot water. Suppose our house needs enough hot water for 4 10-minute showers per day, heating 3 gallons of water per minute from 60 F to 110 F. Heating a pound of water 1 F takes 1 Btu, so we need 4×10mx3gpmx8lb/gal(110F-60F) = 48K Btu/day (WATHEAT) for hot water. Step 3. Solar closet sizing. We need 57K Btu of additional solar heat on an average January day. A sunspace keeping our house warm for 6 hours can supplies 6/24(57K) = 14K Btu, which leaves 43K, of which the house itself can store and supply 35.8K, leaving 7K. Adding another 48K Btu for heating water makes a total of 55K Btu/day (ESCUSE.) Suppose that comes from a “solar closet” inside the sunspace, ie a box full of sealed containers of water completely surrounded by insulation, with a solar air heater over its insulated south wall. The water is heated by solar warmed-air from the air heater. The sun doesn’t shine on the water containers. Solar closets live inside sunspaces, but they have their own glazings and air circulation. Sunspace air never mixes with closet air. Solar closets need to be fairly airtight. Air leaks between the sunspace and the outdoors are less important. The closet air heater glazing might be Replex’s (800) 726-5151 clear flat polycarbonate plastic, which has a 10 year guarantee and costs about $1.25/ft^2 ($13/m^2) and comes in long rolls 49 inches wide by 0.02 inches thick. Rimol Greenhouse Systems at (603) 425-6563 (NH) sells it for $250/roll + $10 UPS. It can be cut with scissors. Suppose we design the closet so the water inside is 130 F after a long string of average days, in which each square foot of its glazing gains 0.9×0.9×1000 Btu of sun and loses about 6h(130F-100F)1ft^2/R1 to a 100 F sunspace during the day plus something like 18h(130F-30F)1ft^2/R20 at night, for a net gain of 540 Btu/day. Then storing 55K Btu/day of sun takes about 55K/540 = 100 ft^2 of closet glazing (AGC.) A 1 cfm airstream with a 1 F temperature difference carries about 1 Btu/h (1 m^3/s with a 1 C difference carries about 1 kW), so “charging” the closet with air that enters 10 F warmer than air that leaves (to keep the air heater cool and efficient) requires an airflow of about 55KBtu/6h/10F = 900 cfm. “Discharging” the closet at night or on cloudy days takes about (148K-65K)Btu/24h/10 F = 350 cfm (SCDCFM.) Our house needs 5x(150K-65K) = 425K Btu (ECL) or 125 kWh to stay warm for 5 cloudy days in a row. If the closet water starts out at 130 F (54 C), and it keeps the house warm until it cools to, say, 80 F (27 C), then the closet needs 425KBtu/(130F-80F) = 8.3K Btu/F of thermal capacity (CC), eg about 8,300 pounds of water. The closet thermal mass also needs sufficient area to allow heat to flow efficiently between the air and the water through the container surfaces. Having 10X or more thermal mass surface than glazing surface allows heat to flow from air into water with a low air-water delta-T: if each square foot of glazing collects 540 Btu over 6 hours, ie 90 Btu/h, which flows into 10 ft^2 of container surface with a slowly-moving air film thermal conductance of 1.5 Btu/h-F, DT = 6 F. We could increase thermal mass surface by using more drums, or putting hollow concrete blocks under the drums (each 8×8x16″ block adds 6 ft^2 and 5 Btu/F.) In that case, we might well draw air through the blocks with fans, since moving air at V mph past a rough surface raises the thermal conductance to 2 + V/2 Btu/h-F, which lowers the needed surface. A 10′x4″ PVC pipe threaded through block holes adds 10 ft^2 and 50 Btu/F, at a cost of about $6, including 2 end caps and a #3 rubber stopper. We can increase container surface by using smaller containers. Plastic soda bottles might lose 10% of their contents each year by moisture vapor transmission. Milk jugs are easier to support and hold more water per cubic foot, and their cross-linked polyethylene walls have about half the vapor transmission of PET soda bottles. Recycled 5 gallon plastic pails (about 1′tall x 1′diam.) with tight-fitting lids are easy to ship, since they nest… A 2′ high x 3′ diameter 55 gallon drum has about 25 ft^2 of surface. A 1 gallon plastic milk jug (about 15 cents each, new, with a screw top, or 50 cents, already filled with water) is about 6″ square x 10″ tall, with about 2 ft^2 of surface. We might use D drums and J jugs on shelves. With 100 ft^2 of glazing, the total surface requirement is 1,000 ft^2 < 25D + 2J, and we need 8,300 < 55×8D + 8J for thermal mass. Combining these constraints, 8,300 – 4000 < 55×8D – 100D, so we might use 12 drums and 344 jugs on shelves made from 1×3s on 4″ centers screwed to 2 4′ 2×4s on 4′ centers, which in turn rest on concrete blocks. Supporting the shelves with 2×4 posts instead leaves more room for 36 jugs on each 4′x4′ shelf made from 12 4′ 1×3s. With 8×8x12″ = 0.44 ft^3/jug, we need 153 ft^3 for 344 jugs and another 12×2x2×3′= 144 ft^3 for 12 drums. We might use 2 8×8′ single pane sliding glass doors to make a 16′ wide x 8′ tall x 4′ deep 512 ft^3 closet with a 4′x6′ area for 12 drums stacked 2-high over a 2′ high x 10′ long shelf made with 3 layers of 15 hollow blocks on 1′ centers threaded with 18 10′x 4″ … read more »
Response:
Step 1. Look up the average outdoor temperature in January, where you live. The National Renewable Energy Laboratory’s free _Solar Radiation Data Manual for Buildings_ has this information for 239 US locations. NREL’s phone number is (303) 275-4099. Where I live, near Philadelphia, the average January temperature is about 30 F or -1 C, and NREL’s manual says that 1,000 Btu/day or 3.3 kWh/m^2 of sun falls on a south wall here on an average January day, with a ground reflectance of about 0.2. A reflective surface in front of the wall like ice or snow or white paint might add 30% to the solar power that falls on the wall. Step 2. Estimate how much energy your house needs to stay warm on an average Jan day. For example, a very-well-insulated 30′ x 30′ (10mx10m) 2-story house with about 2,000 square feet (200 m^2) of average US R20 (metric R3.5) walls and 1,000 ft^2 of R40 ceiling (100 m^2 of metric R7 ceiling) needs approximately 2,000ft^2/R20 + 1000ft^2/R40 = 125 Btu per hour per degree F or 37 watts to stay 68 F inside when it’s 67 F outside. The energy needed to keep a house warm is 24 (hours) times the product of (1) the difference between the average indoor and outdoor temperatures and (2) the thermal conductance of the house, ie the sum of each exterior surface area divided by its R-value. The number of kWh/day needed to keep a house warm is 3400 times less than the number of Btu, using the same formula with different units. This example house needs 24 hr x (68 F – 30 F) x 125 Btu/hr-F = 114,000 Btu or 33 kWh to stay warm on an average January day, the approximate heat equivalent of a gallon of oil. Step 3. Calculate how large a sunspace the house needs to stay warm, ie how much vertical south glass or plastic film glazing area a low-thermal-mass sunspace needs to gather enough solar heat to keep the house warm on an average Jan day with an average amount of sun. If the low-thermal-mass sunspace has an insulated low-thermal-mass wall between it and the house, ie a non-masonry floor and a non-masonry wall, with no rocks nor bricks nor water containers nor collections of scrap iron inside the sunspace, with a window fan to move most of the warm air into the house during the day, the sunspace will be about 68 F (20 C) during the day. If we let the sunspace get icy cold at night, the heat lost from the glazing over an average 6 hour Jan day will be about 6x(68F-30F)1 ft^2/USR1 = 228 Btu/ft^2 or 6x(20C-(-1C))1m^2/R0.176 = 716 wh/day, so the sunspace glazing can provide about 1000-228 = 772 Btu/ft^2 or 3.3-0.716 = 2.6 kWh to the house on an average Jan day, in this example. The example house needs about 114,000,000/772 = 150 sq. feet or 33/2.6 = 12.7 m^2 of sunspace glazing to keep it warm on an average day. Say, a 16′ high x 16′ wide x 12′ deep (5m x 5m x 4m) lean-to plastic film greenhouse, made from standard commercial greenhouse hardware, including 5 long curved galvanized pipes costing $35 each, with a lightweight gravel floor over plastic film on the ground. Step 4. Estimate how many cloudy days in a row there are in January, where you live, and what the outdoor temperature is during those days. In some places, cloudy days and nights are warmer than days and nights in sunny weather, because the clouds act as insulation. (US residents can be more precise about this by buying a $130 CD ROM from NREL/NOAA which includes 30 year’s worth of _hourly_ solar weather data for their locations, and looking over the data for long sunless periods with low air temperatures, ie “cloudy degree day” periods, or running a very simple computer simulation of a particular solar house to estimate the interior temperature every hour for 20 years and predict daily temperature swings.) Suppose this example house is in a climate in which we expect at most 5 cloudy Jan days in a row with 99% confidence, with an average outdoor temperature during those days of 30 F (-1 C), ie we expect colder and cloudier periods to occur only every 100 years. Step 5. Calculate how many sealed 55 gallon or 200 liter plastic drums full of water (or 5 gallon pails or 2 liter soda bottles or canned goods on shelves) are needed inside the closet to keep the house warm for that cloudy period. The example house needs 5×114K = 570K Btu or 167 kWh to stay warm for 5 cloudy days. If the water in the drums is, say 130 F (54 C), and the drums can keep the house warm until the water cools to, say, 80 F (27 C), then each drum stores about 25K Btu or 6 kWh of useful heat, and the house needs 570K/25K = 23 55 gallon or 167/6 = 28 200 liter drums. We might keep the drums at 54 C by building an “solar closet,” ie a box that is completely surrounded by insulation, behind the sunspace, ideally inside the house, with an air heater as part of the insulated wall between the sunspace and the house, using some transparent “solar siding,” eg Home Depot’s “Paltough” corrugated polycarbonate plastic, costing about $1/ft^2, or Replex’s ((800) 726-5151) clear flat polycarbonate plastic, which costs about $1.25 per square foot ($13/m^2) and comes in long rolls, 49 inches wide. The transparent siding might have some black aluminum window screen or greenhouse shadecloth to the north and behind it, with an air gap on each side of the shadecloth, to reduce reradiation and increase the solar collection efficiency of the closet. 80% carbon-filled polypropylene shadecloth costs about 15 cents per square foot or $2/m^2 and should last many years out of the weather. Shadecloth comes in various colors. We might have a 1″ (3 cm) air gap between the siding and the shadecloth, and another 1″ gap between the shadecloth and 3 1/2″ (10 cm) of fiberglass insulation in a 6″ (15 cm) wall, with some small vents (about 1% of the closet glazing area, eg 1 square foot or 0.1 m^2 in the example house) at the top and bottom of this air heater, to allow cooler air from the solar closet to flow into the outside air gap through the vent hole at the bottom of the air heater, which would then flow horizontally through the shadecloth from south to north, becoming warmer, and rise up and flow back through the upper vent hole and back into the closet. The vent holes might have plastic-film backdraft dampers to keep air from flowing when the sun is not shining. These require checking every week or so, since they can stick open, and if they are large enough to pass air well, they lose significant heat through the US R1 plastic film. They might be made from chicken wire and the plastic film used for dry cleaner bags. Using a small fan can reduce thermal losses and raise solar collection efficiency. The inside walls of the closet could simply be fiberglass insulation, covered with plastic film. The floor might be earth, covered with more plastic film. The spaces between the sealed containers of water allow air to circulate around them, heating or cooling them. We need a room-temperature-sensitive vent (eg a $12 automatic foundation vent with its bimetallic spring reversed to open some louver as temperature drops) or a fan that turns on between the closet and house on cool cloudy days, and a return air path from the house to the closet near the floor. The example house might have 24 2′ diameter x 3′ high drums stacked 2 high in 2 rows of 6 drums making the solar closet about 8′ high x 12′ long x 4′ deep. ie about 3m high x 4m long x 1m deep. We might make it 6′ (2m) longer, and use the empty space for a sauna, or a place to dry clothes. The closet might have 3 1/2″ (10 cm) of fiberglass insulation in its ceiling, ie the second floor of the house, as well as in the other walls inside the house. Most of the “waste heat” from this closet ends up in the house, and it provides very little heat for the house on an average winter day, with some sun. On such a day, the house is almost entirely heated by the warm air from the sunspace. If the closet were 2 stories tall, 1 or 2 plastic drums with threaded bungs at the top might be plumbed in series to make a low-pressure gravity-fed hot water system using a float valve or rainwater from the roof to keep the drums full. A 1-story solar closet might have a fan-coil unit or about 20′ (6m) of baseboard radiator pipe with fins near the ceiling to make an air-water heat exchanger connected to a warm-water thermosyphoning loop with some insulated pipe through an ordinary water heater on the second floor with a heating element that rarely turns on. In either case, the sunspace and closet need about 64 ft^2 (6m^2) more solar glazing. The sauna area in the closet might have a small woodstove, for burning newspapers, junk mail, old paper towels, college committee recommendations, letters from congressmen, and press releases announcing amazing new price breakthroughs in photovoltaic technology. Nick Notes: 1. Air infiltration robs houses of heat, and electrical power use adds heat to houses, as do south windows. These things tend to cancel out, conservatively-speaking, so they aren’t mentioned above. Other helpful factors not mentioned above are that daytime temperatures inside and outside the house are higher than nighttime temperatures, and that the part of the south wall of the house that is covered by the sunspace needs no heat on an average day. 2. Sunspace airflow volume increases with the square root of the height. A quote from the Energy Crafted Homes spec: “For optimal heat flow into the house from the sunspace, install sliding or French doors between the two. Natural air flow through an open door can be as high as 1000 cfm… most effective if a complete loop through the house is possible- two-story sunspaces can be tremendously effective at heating a house for this reason.” A two-story sunspace probably needs no fan. It might operate automatically with a 2 watt $50 Honeywell 6161B1000 damper motor in series with two thermostats,
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Response:
The National Renewable Energy Laboratory’s free _Solar Radiation Data Manual for Buildings_ has this information for 239 US locations. NREL’s phone number is (303) 275-4099.
The NREL web site has much of this information also. http://rredc.nrel.gov/ Or see: http://rredc.nrel.gov/solar/ sdb
Response:
Relative to the passive solar house – I’ve always wondered why someone doesn’t put up louvers instead of solid roof overhang on the North side of a house. If you angled them to match the angle of the Winter sun, heat would enter the house when you wanted, but not in the Summer….
Has been done see http://www.emilis.sa.on.net/emil_60.htm only this is on the bottom half of the planet Emilis
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: Nick, I hope you just clipped that post from a document you already had. Nope. Nice fresh prose. Typed every character. :Relative to the passive solar house – I’ve always wondered why someone :doesn’t put up louvers instead of solid roof overhang on the North side 
f a house. In the southern hemisphere… :If you angled them to match the angle of the Winter sun, heat would :enter the house when you wanted, but not in the Summer…. I’ve seen them on solar houses, and also on the back windows of sports cars. “Bris-soleil,” ie “sun-breaker” in French. Norman Saunders, PE, has a patent on a “solar staircase” with horizontal reflectors and vertical glazing. Surely a better idea would be to plant deciduous trees – leaves in the summer and no leaves in the winter! Also they look better that louvres!
It’s hard to shade a house from high summer sun with trees, and not have big branches that can fall on the roof. Runner beans, maybe, or clematis, trumpet vines, honeysuckle, grapes, and so on. Or some gaily decorated greenhouse shadecloth. Nick In my country, progress in love follows progress in architecture. First we had jalousies, then we had louvers. Bertle Lucas, Harbormaster, Port au Spain, Trinidad.
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: : :
: : Nick, I hope you just clipped that post from a document you already had. : Poor keyboard :-) : : Dan : :Relative to the passive solar house – I’ve always wondered why someone :doesn’t put up louvers instead of solid roof overhang on the North side of a :house. If you angled them to match the angle of the Winter sun, heat would :enter the house when you wanted, but not in the Summer…. : Surely a better idea would be to plant deciduous trees – leaves in the summer and no leaves in the winter! Also they look better that louvres! // John Fulton, Ngaio, Wellington NEW ZEALAND // Phone +64 4 4792043 FAX +64 4 4792043
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[I've corrected sunspace sizing and house thermal mass errors, and added some information about the effects of different sunspace temperatures.] Step 1. Gather some weather data. The most-difficult month for solar house heating is the one with the lowest ratio of average solar energy to indoor-outdoor temperature difference, ie the lowest amount of “sun per degree day.” The long-term average outdoor temperatures near Philadelphia, PA are 35.8 and 30.4 F (TB, in the calculation below) in December and January, with 900 and 1,000 Btu/ft^2 of sun (SS, below) falling on a south wall on an average day. This makes January the worst-case month for house heating, with 1,000/(68-30.4) = 26.6 Btu/F, vs 900/(68-35.8) = 28 in December. The National Renewable Energy Laboratory’s free “Solar Radiation Data Manual for Buildings” (http://rredc.nrel.gov) has solar weather data for 239 US locations. NREL’s phone number is (303) 275-4099. The average daily maximum temperature in January is 37.9 F in Phila. NREL’s manual says an average of 620 Btu/ft^2 of sun per day falls on a horizontal surface, east and west walls receive about 420, and a north wall gets 190. How many cloudy days in a row, and what is the temperature then? In some places, cloudy days and nights are warmer than days and nights in sunny weather, because clouds act as insulation. NREL’s TMY2 weather data or one of their 3 CD-ROMs might help answer this question. Their _hourly_ solar weather data for 239 US locations. We might look for long low-temperature “cloudy degree-day” periods, or or do a simple computer simulation of a particular solar house design to estimate the interior temperature every hour for 30 years, or the total amount of backup heat required. Then again, some people define a “solar house” as “one with no other form of heat.” The issue then becomes comfort, vs “solar fraction.” Suppose our house is in a climate in which we expect at most 5 cloudy days in a row with 99% confidence, with an average outdoor temperature during those days of 30 F (-1 C)… Step 2. Gather some house data The thermal conductance of a house is the sum of each exterior surface area divided by its R-value, plus an effective conductance for air leaks. For example, a fairly airtight and very well-insulated 32′x32′ (10mx10m) 2-story house with 2,048 square feet (190 m^2) of US R30 (metric R5.3) walls and 80 ft^2 of R4 windows (7.4 m^2 at 0.7 m^2C/W) and 1,024 ft^2 of R40 ceiling (95 m^2 at metric R7) and a natural air leakage rate of 0.3 house volume Air Changes per Hour has a thermal conductance of about 1,968ft^2/R30 + 80ft^2/R4 + 1024ft^2/R40 + 30×30x16×0.3/55 = 164 Btu per hour per degree F difference between indoor and outdoor temperatures (HC, below.) It needs about 164 Btu or 48 watts to stay 68 F indoors when it’s 67 F outdoors. The daily house heating energy needed is 24 (h) times the product of the thermal conductance of the house and the difference between the average indoor and outdoor temperatures. Our example house needs about 24h(65F-30F)x164Btu/h-F = 136K Btu (EDAY, below) or 40 kWh to stay warm on an average January day, roughly equivalent to a gallon of oil. (The yearly energy needed to keep a house warm is 24 times the conductance times the number of heating degree days per year, 5,500 (F) for Phila.) Some of this energy comes from the occupants and their electrical usage. Each person makes about 100 watts of heat power, and a kilowatt-hour is equivalent to 3,412 Btu of heat energy. If our house has an average of 1 person inside and uses 500 kWh per month (an average of 694 watts) of electrical energy, it gains about 0.794×24 = 19 kWh or 65K Btu/day (INTHEAT, below) of heat from internal sources. Sun also shines into house windows. If our house has equal window areas facing 4 compass directions, and they have 70% solar transmittance, it gains another 20ft^2×0.7x(1000+420+420+190) = 28K Btu of solar heat (WINHEAT) on an average January day. So we need 136K Btu/day of heat, of which 65K comes from internal sources and 28K from windows, leaving an additional solar heating requirement of 136K-65K-28K = 43K Btu (SDAY) on an average January day. The inherent thermal mass of a house can store solar heat on an average day, if it is allowed to cool at night. If our house has 4×32x16 = 2,048 square feet of external walls and another 1,024 ft^2 of internal walls and 3×1,024 ft^2 of ceiling and floors, ie 6,144 ft^2 of surface, all covered with 1/2″ drywall or something with equivalent heat capacity (1/2 Btu/F-ft^2), the total capacity of the house is 6,144×0.5 = 3,072 Btu/F, ie it can store 3,072 Btu per degree F. With a 10 F day/night temperature swing (eg 70 F during the day and 60 F at night, it can store 30,724 Btu (SWINGHEAT, below.) With a few more internal walls, this house wouldn’t need any extra overnight heat on an average January day. (1) After a house is 100% solar heated, the next largest energy need is often hot water. Suppose our house needs enough hot water for 4 10-minute showers per day, heating 3 gallons of water per minute from 60 F to 110 F. Heating a pound of water 1 F takes 1 Btu, so we need 4×10mx3gpmx8lb/gal(110F-60F) = 48K Btu/day (WATHEAT) for hot water. Step 3. Solar closet sizing. We need 43K Btu of additional solar heat on an average January day. A sunspace keeping our house warm for 6 hours can supply 6/24(43K) = 11K Btu, which leaves 32K, of which the house itself can store and supply 30.7K, leaving about 2K. Adding another 48K Btu for heating water makes a total of 50K Btu/day (ESCUSE.) Suppose that comes from a “solar closet” inside the sunspace, ie a box full of sealed containers of water completely surrounded by insulation, with a solar air heater over its insulated south wall. The water is heated by solar warmed-air from the air heater. The sun doesn’t shine on the water containers. Solar closets live inside sunspaces, but they have their own glazings and air circulation. Sunspace air never mixes with closet air. Solar closets need to be fairly airtight. Air leaks between the sunspace and the outdoors are less important. The closet air heater glazing might be Replex’s (800) 726-5151 clear flat polycarbonate plastic, which has a 10 year guarantee and costs about $1.25/ft^2 ($13/m^2) and comes in long rolls 49 inches wide by 0.02 inches thick. Rimol Greenhouse Systems at (603) 425-6563 (NH) sells it for $250/roll + $10 UPS. It can be cut with scissors. Suppose we design the closet so the water inside is 130 F after a long string of average days. Each square foot of its glazing gains 810 Btu of sun per day, if it’s not shaded much by the sunspace. With R20 south wall insulation behind the glazing, it loses about 6h(130F-100F)1ft^2/R1 to a 100 F sunspace during the day plus 18h(130F-30F)1ft^2/R21 at night, for a net gain of about 540 Btu/day (SCNET.) Storing 50K Btu/day of sun takes about 50K/540 = 90 ft^2 of closet glazing (AGC.) A 1 cfm airstream with a 1 F temperature difference carries about 1 Btu/h (1 m^3/s with a 1 C difference carries about 1 kW), so “charging” the closet heat battery with air that enters 10 F warmer than air that leaves (to keep the air heater cool and efficient) requires an airflow of about 50KBtu/6h/10F = 830 cfm. “Discharging” the closet at night or on cloudy days takes about (136K-65K)Btu/24h/10 F = 300 cfm (SCDCFM.) Our house needs 5(136K-65K) = 356K Btu (ECL) or 104 kWh to stay warm for 5 cloudy days in a row. If the closet water starts out at 130 F (54 C), and it keeps the house warm until it cools to, say, 80 F (27 C), then the closet needs 356KBtu/(130F-80F) = 7.1K Btu/F of thermal capacity (CC), eg about 7,100 pounds of water. The closet thermal mass also needs sufficient area to allow heat to flow efficiently between the air and the water through the container surface. Having 10X thermal mass surface than glazing surface allows heatflow with a low air-water delta-T: if each square foot of glazing collects 540 Btu over 6 hours, ie 90 Btu/h, which flows into 10 ft^2 of container surface with a slowly-moving air film thermal conductance of 1.5 Btu/h-F, DT = 90/(10×1.5) = 6 F, by “Ohm’s law for heatflow.” We could increase thermal mass surface by using more drums, or putting hollow concrete blocks under the drums (each 8×8x16″ block adds 6 ft^2 and 5 Btu/F.) In that case, we might well draw air through the blocks with fans, since moving air at V mph past a rough surface raises the thermal conductance to 2 + V/2 Btu/h-F, which lowers the needed surface. A 10′x4″ PVC pipe threaded through block holes adds 10 ft^2 and 50 Btu/F, at a cost of about $6, including 2 end caps and a #3 rubber stopper. We can increase container surface by using smaller containers. Plastic soda bottles might lose 10% of their contents each year by moisture vapor transmission. Milk jugs are easier to support and hold more water per cubic foot, and their cross-linked polyethylene walls have about half the vapor transmission of PET soda bottles. Recycled 5 gallon plastic pails (about 1′tall x 1′diam.) with tight-fitting lids are easy to ship, since they nest… A 2′ high x 3′ diameter 55 gallon drum has about 25 ft^2 of surface. A 1 gallon plastic milk jug (about 15 cents each, new, with a screw top, or 50 cents, already filled with water) is about 6″ square x 10″ tall, with about 2 ft^2 of surface. We might use D drums and J jugs on shelves. With 90 ft^2 of glazing, the surface requirement is 900 ft^2 < 25D + 2J, and we need 7,100 < 55×8D + 8J for thermal mass. Combining constraints, 7,100 – 4000 < 55×8D – 100D, so we might use 10 drums and 330 jugs on 4×4’shelves made from 12 4′ 1×3s on 4″ centers screwed to 2 4′ 2×4s on 4′ centers, which in turn rest on concrete blocks. Supporting the shelves with 2×4 posts instead leaves more room for 36 jugs on each 4′x4′ shelf. With 8×8x12″ = 0.44 ft^3/jug, we need 147 ft^3 for 330 jugs and … read more »
Response:
Simulations are capable of infinite elaboration, but one needn’t consider these electromagnetic and dielectric properties of a house unless one is into the evils of metal bedsprings. Differential and integral analysis would be required.
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