Question:
I have posted to my web site a document describing a novel thermal scheme for a solar heated house for a cold climate. Drawings, graphs, and calculations may be seen at the web site. Text below. See <http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> I would be grateful for comments. David Delaney, Ottawa Start of text from web document Thermosyphon solar air heater and overhead thermal crawl space for 100% solar heating keywords: solar air heater, thermosyphon, natural convection, flow organiser, flow organizer, thermal crawl space, thermal closet, heat store, passive solar, solar fraction, solar thermal energy, bed of stones, bin of stones, rock bed, damper A house in Ottawa, Ontario (45.3N, 75.6W, continental climate) can get 100% of its winter space heat from a solar air heater that operates by natural convection to charge a heat store in an overhead thermal crawl space. The house uses common materials, simple components, simple control, and simple building techniques, but needs a stronger structure than an ordinary house to support the weight of the overhead thermal mass. There are no dampers requiring daily operation. The only parts that move every day are the blades of a conventional ceiling fan. The heavily insulated thermal crawl space, lies above the living space, and extends above a thermosyphon solar air heater that forms the south facade of the house. When the sun shines, heating the air heater, air moves by natural convection from the air heater to the thermal crawl space and back. When the sun stops shining, air stops moving between the air heater and the thermal crawl space, because the air in the heater is then colder and denser than the air in the thermal crawl space above it. The flow organizer (flow organiser) allows the sheet of hot air rising from the air heater to cross through the sheet of cool air moving south along the floor of the crawl space. The sheet of cool air eventually falls through an east-west slit in the floor of the crawl space, then falls through the air heater against the glazing, keeping the rising hot air away from the cold glazing. A massive but relatively thin layer of small smooth river stones provides heat storage. The stones are from 1-1/2" to 2-1/2" (35 mm to 65 mm) in diameter. The stone layer is suspended one or two feet above the floor of the crawl space on a wire mesh. There is a one foot air space above the stone layer so that hot air from air heater can spread out above the stones. The stone layer extends above the whole of the habitable space below. The stones present an enormous surface area for heat transfer between stone and air. There is very little resistance to convective vertical flow through the stone bed because of its very large horizontal cross sectional area. To match the volume flow rate of air coming up from the air heater, air will move down through the stones at a volume rate equal to the volume rate of the air rising from the flow organiser. The rate of descent through the stones will be the volume rate divided by the effective duct area of the stones. The effective duct area of the stones will be approximately the product of the void fraction and the area of the top of the stone bed. Given that the stone bed extends over the whole of the living area, the velocity of air descending through the stones will not exceed about a twentieth of the velocity of the air rising by natural convection through the flow organiser. As a result, resistance to the flow through the stone bed should be extremely small. 100 lb of stone per square foot of ceiling area (490 kg/m2) is about right to produce the desired thermal capacity. 100 lb/ft2 corresponds to a 1 ft (0.3 m) depth of stone with a 40% void fraction. The crawl space extends 3 to 4 ft (0.9 to 1.2 m) from its floor to its ceiling. A ducted ceiling fan moves hot air from above the stone layer down into the living space. A conventional 4 ft (1.2 m) diameter ceiling fan is located in the lower end of a 4.5 (1.4 m ) diameter circular duct that runs from the ceiling of the living space up through the crawl space and the stone layer to the top of the stone layer. The ceiling fan operates at reduced speed, and consumes 50 watts or less when running. It might be powered by a small area of solar photovoltaic panel. Control of the temperature of the living space can be very simple: a thermostat that turns on the fan when the living space is colder than desired. A large solar air heater, super insulation, and thermally efficient windows that are not too large, are required to get all needed space heat from the sun in Ottawa Ontario. Ottawa has a difficult December, with 1483 F heating degree days below 64.4F, (824 C heating degree days below 18 C) (according to NASA). The average December temperature is 14F (-10C). In December, a total of 2.16 kWh per day of solar radiation falls on each square meter of a south facing vertical surface (NASA). Design calculations are currently based on the assumption that the air heater can transfer 50% of the December incident solar energy into the thermal crawl space as heat. Dimensions and suitable R values for a small bungalow in Ottawa, Ontario: Living space: 40 ft (12.2m) east-west, 30 ft (9.1 m) north-south, 1200 square feet (112 m2). Insulation: ceiling of crawl space: R 100 (RSI 17.6); walls of crawl space: R 57 (RSI 10); walls of living space R 50 (RSI 8.8); underslab: R20 (RSI 3.5). Windows: window R-value: R 4 (RSI 0.7 ); window area: 120 square feet (11.1 m2). Fresh air: 45 ft3/min (21 l/s) The air heater must have an area of 430 ft2 (40 m2), which could be achieved with an east-west glazing 40 ft (12.2 m) long and 11 ft (3.4 m) high. These air heater dimensions are based on the assumption that the air heater can transfer 50 per cent of the energy of the solar radiation that falls on the exterior of its glazing into the crawl space. The calculations to justify these specifications, and to create the graphs below, may be seen in 100% Solar heated house for Ottawa, Ontario, with overhead thermal crawl space. (PDF) AT 430 ft2 (40 m2) the air heater is sufficient for December space heat, but 30% larger than is needed for either November or January, the next most demanding months. The surplus heat available in the less demanding winter months might be used to heat domestic hot water. The air-water heat exchanger might be placed in the top of the thermal crawl space directly above the air heater, where it would be accessible for maintenance and repair. A stone layer area of 1100 ft2 (102 m2) at 100 lb (45.5 kg) of stone per square foot provides a thermal capacity of 22,000 Btu/F (11.6 kWh/C). Assume a non solar heat gain of 600 W, of which 200 W is due to two human bodies. If the temperature of the stones is 100 F (38 C) and the outdoor temperature is 14 F (-10 C) when the sun ceases to shine for several days, and the fan is controlled to maintain a desired temperature of 70 F (21 C), the temperature of the habitable space will not fall below that desired temperature until after 120 hours of darkness, and will fall to 59.8F after 168 hours of darkness, and to 39.1 F (4 C) after 20 days of darkness. This calculation is quite conservative. In Ottawa, a prolonged period of no-sun days is almost always accompanied by relatively warm weather, say around 32 F (0 C). When the temperature descends to 14F ( -10 C) , as in this calculation, or lower, there is almost always some clear sky each day. The 430 ft2 (40 m2) air heater specified above can maintain the average temperature of the heat store (the thermal crawl space) at 110 F (43 C) and the habitable space at 70 F (21 C) during an Ottawa December of infinite duration but typical temperatures and sun. (with 600 W non-solar heat gain). If the utility electricity fails in a typical December, but there is PV power to run the fan, the temperature of the habitable space will not fall below the desired temperature unless there is a long string of no-sun days. (Assuming a 200 W non-solar heat gain, just the two human bodies). As the graph to the right shows, the heat store (the thermal crawl space) even in the absence of dark days, the temperature falls to equal (a comfortable) habitable space temperature, making it impossible to maintain this temperature during multiple dark days. Backup heat might be desired to anticipate multiple dark days during a prolonged December electrical utility failure. Backup heat would not be needed for prolonged electrical failures in other months. A wood or propane cooking stove would provide sufficient backup heat. If there is a failure of the fan or of the electricity supply that drives the fan, a door, a window, or a special opening in the south wall of the house may be opened during the day, producing the flow pattern through the house and air heater shown to the right. The air heater will be less efficient in this configuration, and much of the benefit of the crawl space thermal mass will be lost, but substantial solar heat gain will still occur. The thermal mass will still keep the thermal crawl space hot, providing some heat at night by radiation to the living space below and eliminating heat loss from the living space through its ceiling. End of text from web document
Response:
>I have posted to my web site a document describing a novel thermal > scheme for a solar heated house for a cold climate. > Drawings, graphs, and calculations may be seen at the web site. Text > below. > See > <http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> > I would be grateful for comments. > David Delaney, Ottawa
100 lb of stone per square foot of ceiling area (490 kg/m2) about 100 square meters area of stones? (wild guess here) Total weight 49000kg = 49 tons. Wow, not too good for earth quake prone areas I guess. Why not use water as energy storage _under_ the house? Gunnar.
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– Hide quoted text — Show quoted text ->I have posted to my web site a document describing a novel thermal >scheme for a solar heated house for a cold climate. >Drawings, graphs, and calculations may be seen at the web site. Text >below. >See ><http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> >I would be grateful for comments. >David Delaney, Ottawa >Start of text from web document >Thermosyphon solar air heater and overhead thermal crawl space for >100% solar heating
I’m building something similar to what you describe, except that I plan to use a water tank for thermal storage. You have a big problem with your design. Connecting the living space to the crawl space by circulating air would eventually cause all the moisture in the house to end up on the glazing of the hot air collector(s). That’s if you can pay for the extra structure for the 100 psf load for the stoan bed on your ceiling. Do the structural calculations and you might be surprized at the extra cost. Also, the extra insulation (R 100? That’s about 2 feet of fiberglass!) would be another negative. Good luck!! — Eric Swanson — E-mail address: e_swanson(at)skybest.com 
Response:
> I have posted to my web site a document describing a novel thermal > scheme for a solar heated house for a cold climate. > Drawings, graphs, and calculations may be seen at the web site. Text > below. > See > <http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> > I would be grateful for comments.
What’s the "novel" part of this? I don’t see any reason why the heating chamber shouldn’t be wider, 6-8′ deep would make it useable as living space during the day, and possibly even as greehouse space during much of the year. I’d also consider extending the roof overhang farther, enough to block sunlight during the non-heating seasons. (although that may not take much overhang, in ottawa. Is the air-flow diagram really optimal? It seems like there’s an awful lot of air going in strange directions, to no real good purpose. What happens if you move the fan and add some ducting, to force air OUT of the living-space by shoving it into the greenhouse during the day, or up into the overhead at night, and suck heat down from the overhead through ports scattered around the ceiling. That would reduce the draftiness, and if you put the intake(s) down near floor level, you wouldn’t have to worry about stratification. Also, if you can reduce the depth of the overhead assembly to 24" (And I don’t imagine you really NEED more than 6" of airspace to get flow, do you?) then you can build the ceiling with standard flat trusses, and stuff your thermal mass between them. –Goedjn
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> Total weight 49000kg = 49 tons. Wow, not too good for earth quake > prone areas I guess. > Why not use water as energy storage _under_ the house?
Heat rises?
Response:
> I have posted to my web site a document describing a novel thermal > scheme for a solar heated house for a cold climate. > Drawings, graphs, and calculations may be seen at the web site. Text > below. > See > <http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> > I would be grateful for comments.
snipped Zome Works in New Mexico especially the bead window Trumbal wall (spelling?) Best of luck I have friends in Iowa that tried some thing similar to this. I helped rip it out after the first winter. Worked ok in the day time. Brought in cold air at night.
Response:
> I have posted to my web site a document describing a novel thermal > scheme for a solar heated house for a cold climate. > Drawings, graphs, and calculations may be seen at the web site. Text > below. > See > <http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> > I would be grateful for comments. > David Delaney, Ottawa
[snip] I like the out-of-the-box thinking, but I’m concerned about efficiency gains here. I’m sure you’re aware of Kachadorian’s book *The Passive Solar House* on a similar principle, but moving the air through the floor rather than the wall and ceiling. How come you don’t store the thermal mass in the floor? The expense of storing it in the ceiling [added expense of engineering] and forcing it down surely won’t pay for any efficiency gains [if any]. Three-four days of no sun and you won’t be running your PV fan anyway, and the mass in the ceiling won’t do you any good if you heat it up in some other way, because you have to still force the air down, losing the efficiency of storage. I’m designing a solar-gain straw bale house and am storing the thermal mass in the floor and some walls, and I won’t be forcing the air around anywhere. So at first blush, your idea looks impractical from a simplicity standpoint, and you always want simplicity. Good luck, D
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> Total weight 49000kg = 49 tons. Wow, not too good for earth quake > prone areas I guess. > Why not use water as energy storage _under_ the house? > Heat rises?
exactly! with no power to run fans, having some means of manually adjusting the heat transfer into the living area is a Good Thing. (IMHO). Gunnar.
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Look into "Hambro floor systems" and "Blue Max" style wall systems. Go massive with lots of concrete – it’ll make your house like a thermos bottle. What is the grade level? Why not go deeper into the earth and take advantage of the free heat? More economical for storage too.
– Hide quoted text — Show quoted text ->I have posted to my web site a document describing a novel thermal > scheme for a solar heated house for a cold climate. > Drawings, graphs, and calculations may be seen at the web site. Text > below. > See > <http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> > I would be grateful for comments. > David Delaney, Ottawa > Start of text from web document > Thermosyphon solar air heater and overhead thermal crawl space for > 100% solar heating > keywords: solar air heater, thermosyphon, natural convection, flow > organiser, flow organizer, thermal crawl space, thermal closet, heat > store, passive solar, solar fraction, solar thermal energy, bed of > stones, bin of stones, rock bed, damper > A house in Ottawa, Ontario (45.3N, 75.6W, continental climate) can get > 100% of its winter space heat from a solar air heater that operates by > natural convection to charge a heat store in an overhead thermal crawl > space. The house uses common materials, simple components, simple > control, and simple building techniques, but needs a stronger > structure than an ordinary house to support the weight of the > overhead thermal mass. There are no dampers requiring daily operation. > The only parts that move every day are the blades of a conventional > ceiling fan. > The heavily insulated thermal crawl space, lies above the living > space, and extends above a thermosyphon solar air heater that forms > the south facade of the house. When the sun shines, heating the air > heater, air moves by natural convection from the air heater to the > thermal crawl space and back. When the sun stops shining, air stops > moving between the air heater and the thermal crawl space, because the > air in the heater is then colder and denser than the air in the > thermal crawl space above it. > The flow organizer (flow organiser) allows the sheet of hot air rising > from the air heater to cross through the sheet of cool air moving > south along the floor of the crawl space. The sheet of cool air > eventually falls through an east-west slit in the floor of the crawl > space, then falls through the air heater against the glazing, > keeping the rising hot air away from the cold glazing. > A massive but relatively thin layer of small smooth river stones > provides heat storage. The stones are from 1-1/2" to 2-1/2" (35 mm > to 65 mm) in diameter. The stone layer is suspended one or two feet > above the floor of the crawl space on a wire mesh. There is a one > foot air space above the stone layer so that hot air from air heater > can spread out above the stones. The stone layer extends above the > whole of the habitable space below. The stones present an enormous > surface area for heat transfer between stone and air. There is very > little resistance to convective vertical flow through the stone bed > because of its very large horizontal cross sectional area. To match > the volume flow rate of air coming up from the air heater, air will > move down through the stones at a volume rate equal to the volume rate > of the air rising from the flow organiser. The rate of descent > through the stones will be the volume rate divided by the effective > duct area of the stones. The effective duct area of the stones will be > approximately the product of the void fraction and the area of the top > of the stone bed. Given that the stone bed extends over the whole of > the living area, the velocity of air descending through the stones > will not exceed about a twentieth of the velocity of the air rising > by natural convection through the flow organiser. As a result, > resistance to the flow through the stone bed should be extremely > small. 100 lb of stone per square foot of ceiling area (490 kg/m2) > is about right to produce the desired thermal capacity. 100 lb/ft2 > corresponds to a 1 ft (0.3 m) depth of stone with a 40% void fraction. > The crawl space extends 3 to 4 ft (0.9 to 1.2 m) from its floor to > its ceiling. > A ducted ceiling fan moves hot air from above the stone layer down > into the living space. A conventional 4 ft (1.2 m) diameter ceiling > fan is located in the lower end of a 4.5 (1.4 m ) diameter circular > duct that runs from the ceiling of the living space up through the > crawl space and the stone layer to the top of the stone layer. The > ceiling fan operates at reduced speed, and consumes 50 watts or less > when running. It might be powered by a small area of solar > photovoltaic panel. Control of the temperature of the living space > can be very simple: a thermostat that turns on the fan when the > living space is colder than desired. > A large solar air heater, super insulation, and thermally efficient > windows that are not too large, are required to get all needed space > heat from the sun in Ottawa Ontario. Ottawa has a difficult December, > with 1483 F heating degree days below 64.4F, (824 C heating degree > days below 18 C) (according to NASA). The average December temperature > is 14F (-10C). In December, a total of 2.16 kWh per day of solar > radiation falls on each square meter of a south facing vertical > surface (NASA). Design calculations are currently based on the > assumption that the air heater can transfer 50% of the December > incident solar energy into the thermal crawl space as heat. > Dimensions and suitable R values for a small bungalow in Ottawa, > Ontario: Living space: 40 ft (12.2m) east-west, 30 ft (9.1 m) > north-south, 1200 square feet (112 m2). Insulation: ceiling of crawl > space: R 100 (RSI 17.6); walls of crawl space: R 57 (RSI 10); walls of > living space R 50 (RSI 8.8); underslab: R20 (RSI 3.5). Windows: > window R-value: R 4 (RSI 0.7 ); window area: 120 square feet (11.1 > m2). Fresh air: 45 ft3/min (21 l/s) The air heater must have an area > of 430 ft2 (40 m2), which could be achieved with an east-west glazing > 40 ft (12.2 m) long and 11 ft (3.4 m) high. These air heater > dimensions are based on the assumption that the air heater can > transfer 50 per cent of the energy of the solar radiation that falls > on the exterior of its glazing into the crawl space. The > calculations to justify these specifications, and to create the graphs > below, may be seen in 100% Solar heated house for Ottawa, Ontario, > with overhead thermal crawl space. (PDF) > AT 430 ft2 (40 m2) the air heater is sufficient for December space > heat, but 30% larger than is needed for either November or January, > the next most demanding months. The surplus heat available in the > less demanding winter months might be used to heat domestic hot water. > The air-water heat exchanger might be placed in the top of the thermal > crawl space directly above the air heater, where it would be > accessible for maintenance and repair. > A stone layer area of 1100 ft2 (102 m2) at 100 lb (45.5 kg) of stone > per square foot provides a thermal capacity of 22,000 Btu/F (11.6 > kWh/C). Assume a non solar heat gain of 600 W, of which 200 W is due > to two human bodies. If the temperature of the stones is 100 F (38 C) > and the outdoor temperature is 14 F (-10 C) when the sun ceases to > shine for several days, and the fan is controlled to maintain a > desired temperature of 70 F (21 C), the temperature of the habitable > space will not fall below that desired temperature until after 120 > hours of darkness, and will fall to 59.8F after 168 hours of darkness, > and to 39.1 F (4 C) after 20 days of darkness. This calculation is > quite conservative. In Ottawa, a prolonged period of no-sun days is > almost always accompanied by relatively warm weather, say around 32 F > (0 C). When the temperature descends to 14F ( -10 C) , as in this > calculation, or lower, there is almost always some clear sky each day. > The 430 ft2 (40 m2) air heater specified above can maintain the > average temperature of the heat store (the thermal crawl space) at 110 > F (43 C) and the habitable space at 70 F (21 C) during an Ottawa > December of infinite duration but typical temperatures and sun. (with > 600 W non-solar heat gain). > If the utility electricity fails in a typical December, but there is > PV power to run the fan, the temperature of the habitable space will > not fall below the desired temperature unless there is a long string > of no-sun days. (Assuming a 200 W non-solar heat gain, just the two > human bodies). As the graph to the right shows, the heat store (the > thermal crawl space) even in the absence of dark days, the > temperature falls to equal (a comfortable) habitable space > temperature, making it impossible to maintain this temperature during > multiple dark days. Backup heat might be desired to anticipate > multiple dark days during a prolonged December electrical utility > failure. Backup heat would not be needed for prolonged electrical > failures in other months. A wood or propane cooking stove would > provide sufficient backup heat. > If there is a failure of the fan or of the electricity supply that > drives the fan, a door, a window, or a special opening in the south > wall of the house may be opened during the day, producing the flow > pattern through the house and air heater shown to the right. The air > heater will be less efficient in this configuration, and much of the > benefit of the crawl space thermal mass will be lost, but substantial > solar heat gain will still occur. The thermal mass will still keep > the thermal crawl space hot, providing some heat at night by > radiation
… read more »
Response:
- Hide quoted text — Show quoted text ->I have posted to my web site a document describing a novel thermal >scheme for a solar heated house for a cold climate. >Drawings, graphs, and calculations may be seen at the web site. Text >below. >See ><http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> >I would be grateful for comments. >David Delaney, Ottawa > [snip] > I like the out-of-the-box thinking, but I’m concerned about efficiency > gains here. > I’m sure you’re aware of Kachadorian’s book *The Passive Solar House* > on a similar principle, but moving the air through the floor rather > than the wall and ceiling. > How come you don’t store the thermal mass in the floor? The expense of > storing it in the ceiling [added expense of engineering] and forcing > it down surely won’t pay for any efficiency gains [if any]. Three-four > days of no sun and you won’t be running your PV fan anyway, and the > mass in the ceiling won’t do you any good if you heat it up in some > other way, because you have to still force the air down, losing the > efficiency of storage. > I’m designing a solar-gain straw bale house and am storing the thermal > mass in the floor and some walls, and I won’t be forcing the air > around anywhere. So at first blush, your idea looks impractical from a > simplicity standpoint, and you always want simplicity. > Good luck, > D
i had a passive system in central ohio. glass on the south heat rose a fan blew it to the crawspace filled with large gravel. it worked alright. where i lived, the solar gain was not as good as other parts of the country. the house was built with 2×6 16 on center. double sliding doors(which was great) there was a 18 inch space between the two. outer one had a small roof over it. i believe in a well insulated house and tight doors for central ohio area. there is a map somewhere that shows areas that are great for solar gain.
Response:
> I have posted to my web site a document describing a novel thermal > scheme for a solar heated house for a cold climate. > Drawings, graphs, and calculations may be seen at the web site. Text > below. > See > <http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> > I would be grateful for comments. > David Delaney, Ottawa
I don’t get it Dave. Some time or the other you will have to move air against convection. Why not just put the stone down in the crawl space, force the heat down during the day then let it rise at night. I’m in the process of building a "Normal" house. Looking at your design, I just shake my head. Don’t get me wrong, I admire the work and thought you’ve put into this project. I just don’t think you’ve done a lot of building. The further you stray from the norm, the more it’s going to cost. You’d be lucky to build this place for double the cost of a regular house, and it won’t be worth sweet tweet when your done. You build a house to live in, not to live for. Are you married? I’m shaking my head again. "Ho-ney, I’m co-old. Turn up the heat pleeeaze." Your a dead man. Lorence
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– Hide quoted text — Show quoted text ->>I have posted to my web site a document describing a novel thermal >>scheme for a solar heated house for a cold climate. >>Drawings, graphs, and calculations may be seen at the web site. Text >>below. >>See >><http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> >>I would be grateful for comments. >>David Delaney, Ottawa > [snip] > I like the out-of-the-box thinking, but I’m concerned about efficiency > gains here. > I’m sure you’re aware of Kachadorian’s book *The Passive Solar House* > on a similar principle, but moving the air through the floor rather > than the wall and ceiling. > How come you don’t store the thermal mass in the floor? The expense of > storing it in the ceiling [added expense of engineering] and forcing > it down surely won’t pay for any efficiency gains [if any]. Three-four > days of no sun and you won’t be running your PV fan anyway, and the > mass in the ceiling won’t do you any good if you heat it up in some > other way, because you have to still force the air down, losing the > efficiency of storage. > I’m designing a solar-gain straw bale house and am storing the thermal > mass in the floor and some walls, and I won’t be forcing the air > around anywhere. So at first blush, your idea looks impractical from a > simplicity standpoint, and you always want simplicity. > Good luck, > D >i had a passive system in central ohio. glass on the south heat rose a >fan blew it to the crawspace filled with large gravel. it worked >alright. where i lived, the solar gain was not as good as other parts of >the country. the house was built with 2×6 16 on center. double sliding >doors(which was great) there was a 18 inch space between the two. outer >one had a small roof over it. i believe in a well insulated house and >tight doors for central ohio area. there is a map somewhere that shows >areas that are great for solar gain.
Yes, the basic problem with simple passive systems is that they lose heat rapidly t night or on cloudy days. And, if the collector efficiency is good, they can overheat at the end of a sunny day. Straw bales are good insulators, as long as they can be kept dry. It’s hard to build with them as they tend to sag when loaded, so using them as a structural element is not a good idea. This can be a real problem around windows, as there is less straw to sag, thus there can be differential sag across the window (or door) area. — Eric Swanson — E-mail address: e_swanson(at)skybest.com
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>Go massive with lots of concrete – it’ll make your house like a thermos >bottle.
You seem to have confused the difference between thermal mass and insulation. Nick
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>I’m sure you’re aware of Kachadorian’s book *The Passive Solar House*…
Ah yes… Warm air rises. Why would it want to flow under the floor? Lots of warm air needs to touch Lots of thermal mass surface to raise the slab temp on a sunny day without overheating the house and ensure a low day/night temperature swing. During a cloudy week, such a house gets exponentially colder and colder, without woodstoves and so on. Moving most of the solar glazing to a low-thermal-mass sunspace (one that gets cool overnight and stays cool during a cloudy week) with an insulated wall between the living space and the sunspace allows the same or more solar gain when warm air flows between the sunspace and the house during the day, but reduces the nighttime and cloudy-day heat loss from the living space… Dr. Rich Komp (author of Practical Photovoltaics and president of the Maine Solar Energy Association) says warm hollow floors like his (which predates Kachadorian’s) aren’t new. Romans built hypocausts, hollow floors heated with warm air from hot water or fires. So did Chinese peasants. Warm hollow floors make good homes for dust and varmints. Rich’s friend Ernie the Ermine takes care of that problem. Living inside the heat battery, we are subject to its temperature swings, and if there are no temperature swings, there is no solar heat storage. We can’t charge the slab up to a high temperature because we have to live with it in the room. The same amount of thermal mass at a higher temperature stores more useful heat than lower temp mass, and it allows keeping a constant room temp until the mass cools to something close to that room temperature. Floor slabs don’t usually have much insulation between themselves and the room air, and they are difficult to insulate because of their shape. The same amount of insulation applied to a cube with equivalent mass lowers the rate of heatflow a lot more. And water stores about 3X more heat than masonry by volume. It can also be cheaper and more useful, even in sealed containers. K’s slab uses a fan. It might make more than a 40% heating fraction, with lots of airflow and slab channels (ie heat transfer surface) and a carpet on top of some foamboard over the slab and a low thermal mass sunspace with separate 100 F air ducts between the sunspace and the slab and lots of house insulation, eg 12" R48 SIPs. Then again, we might make the house walls hollow block with the holes lined up so air can naturally flow vertically through the walls, with lots of insulation (eg Dri-Vit) outside the block. But either way, we have lots of inaccessible nooks and crannies to attract dust and spiders and varmints. Storing heat for 5 cloudy 30 F days in a house that cools from 75 to 65 F means 65=30+(75-30)exp(-120h/RC), so RC = -120/ln((65-30)/(75-30)) = 477 h. A 48′x48′x8′ house with an 8" 25 Btu/F-ft^3 slab with C = 48×48x8/12×25 = 38.4K Btu/F needs a max thermal conductance G = 38.4K/477 = 80.5 Btu/h-F, or 57.5 for 3748 ft^2 of R65 walls and ceiling, after subtracting 4% of the floorspace as R4 windows, with no air leaks or internal heat gain. Sounds Herculean… Making the house 32×32x16′ tall with a 17K Btu/F slab and 2048 ft^2 of 5 Btu/F-ft^2 block walls makes C = 27.2K Btu/h-F, so G = 27.2K/477 = 57, or 36.5 for 2990 ft^2 of R82 walls, with no air leaks. More Herculean. K’s book has lots of whopping mistakes. For instance, he thinks a house needs 2/3 ACH for health, 27X more than the 0.025 ACH Swedish standard and 83X more than the Canadian IDEAS standard. Page 17 says "As you can see, the reduction in solar benefit increases exponentially as you rotate the home’s orientation away from true south." Page 30 says If this combination of poured concrete slab over horizontally laid blocks is ventilated by air holes along the north and south walls, air will naturally circulate through this concrete radiator when the sun is out… the south wall will be warmer than the north wall… air that is next to or alongside the south wall will rise. Warmed air will then be pulled out of the ventilated slab, and the cooler air along the north wall will drop into the holes along the north wall. This thermosiphoning effect will naturally continue to pull air through the Solar Slab. Page 49 says "Incorporate an air lock entrance" with miniscule energy savings except for a department store, or a house with a huge active family. Page 53 describes "reflective" foil smack up against plywood The interior foil face will reflect heat back into the room, even though it is sealed inside the thermo-shutter… The outside foil face of the insulation contained within the wood veneers will reflect the sun’s summer heat back out the window. Page 94 belies the natural air circulation described on page 30 The duct shown running down the middle of the bgase under the poured slab is included in all cases. It should always be used as the return-air duct: do not reverse the air flow pattrern shown on the control diagrams. By using the Solar Slab as part of the return-air duct system, the Solar Slab will constantly assist the furnace by preheating the return air. Even if the home will be heated with a woodstove and emergency electric furnace, the return duct should be included and the air mover hooked up per the appropriate control diagram… Page 101 says 2. Size of electric heating system = 9.25 kilowatt=hours, with an annual consumption of 7.616 kilowatts, Page 102 says The calculation for the electric backup option determined that we would need 9.25 kilowatts per hour for the Saltbox 38… Page 106 says "The theoretical minimum temperature to which a home with a Solar Slab will drop is the ground temperature under the solar slab…" (Yes, that will keep the pipes from freezing in most parts of the US, if a perfectly airtight house with infinite insulation Page 107 says "it also costs more to cool air than to heat air," as if K. is unaware of evaporation, night sky radiation, or the phrase "coefficient of performance." Page 137 ignores one-way passive backdraft dampers It may seem that a sunspace that is gathering enough heat to become 90 degrees Fahrenheit on a cold, 15-degree but sunny winter day would be beneficial to the home. And yes, it can be beneficial. However, the same overglazed sunspace that accumulated all that heat during the cold but sunny day will need lots of added heat when the sun goes down to prevent it from freezing, which means that the sunspace or greenhouse will tend to draw heat from the rest of the house as its flow of solar heat reverses course, back out through the glazing. but his solar slab is a good way to store overnight heat from inexpensive passive air heaters or a low-thermal mass sunspace that can add valuable floorspace to a house. One drawback is dust–it’s hard to clean the rough passages in the hollow concrete blocks. Another is fan power. A vertical thermal mass (eg a chimney with extra flues open at top and bottom) might store and release heat to a house with no fan power at all… Page 46 says Let there be no misunderstanding about where the fresh air makeup is coming from. The walls and roof of your home should be very tightly constructed… Fresh air will enter your home through controlled or deliberate openings… not through gaps in the insulation or poorly sealed windows and doors. A 3,000 ft^2 house with 2/3 ACH has 267 cfm, enough for 18 full-time occupants, using the 15 cfm/occupant ASHRAE standard. K. doesn’t mention heat recovery, although he talks about an "air exchange or ventilator system." HRVs seem useless for most US houses, since natural air leaks can easily supply most of the ventilation air. A 3,000 ft^2 house only needs 30×60/(3000×8) = 0.075 ACH for 30 cfm. We might run a ventilation fan if the house feels stuffy or the RH exceeds 60% in wintertime… We might store more heat with better room temp control by circulating 100 F air from a sunspace under the floor… If a solar house needs, say, $200 per year of electrical energy to operate, we might heat a superinsulated house at the same cost, and forget about fans and mass and glass… A 2K ft^2 2-story house with R40 6.5" Urethane SIP walls and 130 ft^2 of U0.38 south windows with 46% solar transmission (SHGC = 0.46) and a thermal conductance of 214 Btu/h-F needs 24h(65-27.4)214 = 193K Btu on an average December day in Worchester, MA. If 300 kWh/mo of electrical energy use contributes 34K of that and 0.46×130x860 = 51K comes in south windows, we only need 107.6K more. A square foot of R1 vertical south air heater or sunspace glazing with 90% solar transmission and 80 F air on the inside would gain 0.9×860 = 774 Btu of sun and lose about 6h(80-27.4)1ft^2/R1 = 316, for a net gain of 458. We might heat the house on an average day with 107.6K/458 = 235 ft^2 of extra south glazing, eg a 32′x8′ tall single layer of polycarbonate glazing on the outside of an open stud wall with SIPs on the inside, or over exposed posts and beams at the south edge of a second floor cantilevered 4′ to the south of the first floor, forming a 4′x32′ arcade with a transparent wall beneath, for a medieval look. UK planners might like this, from a distance. We need about 18h/24hx193K = 145K Btu of overnight heat. With a 10 F daily temp swing, 7K Btu/F of inherent house thermal mass and furnishings with a short (2 hour) time constant could store 70K Btu. We might store the rest in 150 10′x4" PVC water pipes among rafters in 600 ft^2 of basement ceiling. We need 5(193K-34K) = 795K Btu for 5 cloudy 27 F days, at (65-27)214 = 8132 Btu/h. With 2250 Btu/h-F of thermal conductance to room air, the pipes could warm the house with 65+8132/2250 = 69 F water. A 4×8x8′ tall EPDM-rubber- lined R40 SIP boxful cooling from 69+795K/(256+64) = 118 to 69 F would lose 24h(118-65)256ft^2/R40 … read more »
Response:
November 23, 2004 >Go massive with lots of concrete – it’ll make your house like a thermos >bottle. > You seem to have confused the difference between thermal mass and insulation.
Which is why you want to insulate the concrete, and earth shelter it. But NOOOO … humanity insists on burning all the plastic insulation. Thomas Lee Elifritz http://elifritz.members.atlantic.net
Response:
– Hide quoted text — Show quoted text ->I’m sure you’re aware of Kachadorian’s book *The Passive Solar House*… >Ah yes… >Warm air rises. Why would it want to flow under the floor? Lots of warm >air needs to touch Lots of thermal mass surface to raise the slab temp >on a sunny day without overheating the house and ensure a low day/night >temperature swing. During a cloudy week, such a house gets exponentially >colder and colder, without woodstoves and so on. >Moving most of the solar glazing to a low-thermal-mass sunspace (one >that gets cool overnight and stays cool during a cloudy week) with an >insulated wall between the living space and the sunspace allows the same >or more solar gain when warm air flows between the sunspace and the house >during the day, but reduces the nighttime and cloudy-day heat loss from >the living space… >Dr. Rich Komp (author of Practical Photovoltaics and president of the >Maine Solar Energy Association) says warm hollow floors like his >(which predates Kachadorian’s) aren’t new. Romans built hypocausts, >hollow floors heated with warm air from hot water or fires. So did >Chinese peasants. Warm hollow floors make good homes for dust and >varmints. Rich’s friend Ernie the Ermine takes care of that problem. >Living inside the heat battery, we are subject to its temperature swings, >and if there are no temperature swings, there is no solar heat storage.
Hi Nick, I see you are still at it. Did you ever build your sunspace house? I’m finishing mine up now (finally!). I hope to move in before Christmas, if I can get past the last inspection. My south wall house has a 5500 gal water tank in the middle that’s 19 feet high. There won’t be any big temperature swings, if I can get it all to work as planned. — Eric Swanson — E-mail address: e_swanson(at)skybest.com
Response:
> i had a passive system in central ohio. glass on the south heat rose a > fan blew it to the crawspace filled with large gravel. it worked > alright. where i lived, the solar gain was not as good as other parts of > the country. the house was built with 2×6 16 on center. double sliding > doors(which was great) there was a 18 inch space between the two. outer > one had a small roof over it. i believe in a well insulated house and > tight doors for central ohio area. there is a map somewhere that shows > areas that are great for solar gain.
[snip] I have the solar gain map here. I’m in Western WA, one of the worst places for solar gain, so I’m doing radiant heat as a backup, SIP roof for ~R-39 & bales on side for ~R-40 walls. I’m interested in your ideas. How long will you get heat storage with gravel? Do the air spaces affect the thermal mass? Would you fill, perhaps, with sand? What does code say about the load overhead? Best, D
Response:
>Hi Nick,
Hi Eric, >I see you are still at it. Did you ever build your sunspace house?
I’ve built several small versions, and may tweak the large retrofit version this winter, as well as building a modified sunspace-Barra structure… >I’m finishing mine up now (finally!).
Congratulations (almost . >My south wall house has a 5500 gal water tank in the middle that’s 19 feet >high. There won’t be any big temperature swings, if I can get it all to >work as planned.
A stack of 7′ diameter sewer pipes? Lots of pressure at the bottom, and possible pump power savings… Nick
Response:
says… – Hide quoted text — Show quoted text ->Hi Nick, >Hi Eric, >I see you are still at it. Did you ever build your sunspace house? >I’ve built several small versions, and may tweak the large retrofit version >this winter, as well as building a modified sunspace-Barra structure… >I’m finishing mine up now (finally!). >Congratulations (almost . >My south wall house has a 5500 gal water tank in the middle that’s 19 feet >high. There won’t be any big temperature swings, if I can get it all to >work as planned. >A stack of 7′ diameter sewer pipes? Lots of pressure at the bottom, >and possible pump power savings…
Yes, a 7 foot diameter corregated drain pipe. It’s galvanized and it’s sitting in concrete. I still haven’t figured out what to put on top. I started with the idea of using a surplus carbon steel tank from some oil company, but they were not very tall. My tank still needs to be coated inside to deal with corrosion. I may just get a PVC tank liner. Looking back, I wish I’d taken the plunge and bought stainless steel, but they are about $6k and I thought I could save some bucks. The sewer pipe cost about $1200, but there was the extra expence of welding the seams, which took me 2 weeks. BTW, the pressure at the bottom will be about 8 psi. Pumping losses are mostly from pipe friction. The electricity used to run the pump(s?) will not be wasted, as it will go into heating the water. My backup heating system will use propane. Around here, propane at $2 per gallon costs more per BTU than electricity at $0.08 per kWh. — Eric Swanson — E-mail address: e_swanson(at)skybest.com
Response:
> I have posted to my web site a document describing a novel thermal > scheme for a solar heated house for a cold climate. > Drawings, graphs, and calculations may be seen at the web site. Text > below. > See
<http://geocities.com/davidmdelaney/thermal-cs/thermal-crawl-space-1.html> > I would be grateful for comments. > snipped > Zome Works in New Mexico especially the bead window > Trumbal wall (spelling?) > Best of luck I have friends in Iowa that tried some thing similar to this. I > helped rip it out after the first winter. Worked ok in the day time. Brought > in cold air at night.
That’s a bit drastic. How about installing insulated dampers to close it off? Must be cheaper and a control system may have made it work properly.
Response:
– Hide quoted text — Show quoted text ->> Total weight 49000kg = 49 tons. Wow, not too good for earth quake >> prone areas I guess. >> Why not use water as energy storage _under_ the house? > Heat rises? > exactly! with no power to run fans, having some means of manually adjusting > the heat transfer into the living area is a Good Thing. (IMHO). > Gunnar.
The problem with a passive solar house is that you live in the heat generator, which may be uncomfortable. Storing solar gained heat and then directing that heat to the living areas is better for comfort levels. This design dose that and simply too.
Response:
– Hide quoted text — Show quoted text ->>I’m sure you’re aware of Kachadorian’s book *The Passive Solar House*… >Ah yes… >Warm air rises. Why would it want to flow under the floor? Lots of warm >air needs to touch Lots of thermal mass surface to raise the slab temp >on a sunny day without overheating the house and ensure a low day/night >temperature swing. During a cloudy week, such a house gets exponentially >colder and colder, without woodstoves and so on. >Moving most of the solar glazing to a low-thermal-mass sunspace (one >that gets cool overnight and stays cool during a cloudy week) with an >insulated wall between the living space and the sunspace allows the same >or more solar gain when warm air flows between the sunspace and the house >during the day, but reduces the nighttime and cloudy-day heat loss from >the living space… >Dr. Rich Komp (author of Practical Photovoltaics and president of the >Maine Solar Energy Association) says warm hollow floors like his >(which predates Kachadorian’s) aren’t new. Romans built hypocausts, >hollow floors heated with warm air from hot water or fires. So did >Chinese peasants. Warm hollow floors make good homes for dust and >varmints. Rich’s friend Ernie the Ermine takes care of that problem. >Living inside the heat battery, we are subject to its temperature swings, >and if there are no temperature swings, there is no solar heat storage. > Hi Nick, > I see you are still at it. Did you ever build your sunspace house? > I’m finishing mine up now (finally!). I hope to move in before Christmas, > if I can get past the last inspection. My south wall house has a 5500 gal > water tank in the middle that’s 19 feet high. There won’t be any big > temperature swings, if I can get it all to work as planned.
Do you have a web site, or a house description?
Response:
>100 lb of stone per square foot of ceiling area (490 kg/m2) >about 100 square meters area of stones? (wild guess here)
In this particular example 1100 ft2, 102 m2 >Total weight 49000kg = 49 tons. Wow, not too good for earth quake prone >areas I guess.
It "just" costs money for an appropriate structural design. >Why not use water as energy storage _under_ the house?
More fan power for charging. More complicated control required. Dampers required. I want a brutally simple system with minimal maintenance.
Response:
- Hide quoted text — Show quoted text ->i had a passive system in central ohio. glass on the south heat rose a >fan blew it to the crawspace filled with large gravel. it worked >alright. where i lived, the solar gain was not as good as other parts of >the country. the house was built with 2×6 16 on center. double sliding >doors(which was great) there was a 18 inch space between the two. outer >one had a small roof over it. i believe in a well insulated house and >tight doors for central ohio area. there is a map somewhere that shows >areas that are great for solar gain. > [snip] > I have the solar gain map here. I’m in Western WA, one of the worst > places for solar gain, so I’m doing radiant heat as a backup, SIP roof > for ~R-39 & bales on side for ~R-40 walls. > I’m interested in your ideas. How long will you get heat storage with > gravel? Do the air spaces affect the thermal mass? Would you fill, > perhaps, with sand? What does code say about the load overhead? > Best, > D
as i said i had a passive system. don’t get me wrong, but unless you live in a good solar gain area just build a well insulated home. i got divorced so now i live in a smaller 1962 ranch. i insulated the walls and ceiling. installed new windows and partial insulated basment. i will never have a sliding door unless it is doubled up like my old home. you could sleep next to it and never feel cold. remember blowing the heated air from the top of the house over gravel does cause dust. but it held for 24 hours. a vermont casting stove and 2 cords or so heated the house. one time when it was about 10 degrees out we had to open the doors because it got too hot in the house. i had plastic type sheets same size as windows and 1/2 inch thick(air space between the two plastic sides) and at night i closed them against the southern glass. there was a 3 to 4 inch space between the glass and the plastic. i wish i could remember the name of it(plastic). it came in semi clear and colored. a man named joe kawecki design and but the house along with a number other house in the division in 1980. he won several gov’t awards for his designs. he also was a fair and nice guy.
Response:
– Hide quoted text — Show quoted text ->I’m sure you’re aware of Kachadorian’s book *The Passive Solar House*… > Ah yes… > Warm air rises. Why would it want to flow under the floor? Lots of warm > air needs to touch Lots of thermal mass surface to raise the slab temp > on a sunny day without overheating the house and ensure a low day/night > temperature swing. During a cloudy week, such a house gets exponentially > colder and colder, without woodstoves and so on. > Moving most of the solar glazing to a low-thermal-mass sunspace (one > that gets cool overnight and stays cool during a cloudy week) with an > insulated wall between the living space and the sunspace allows the same > or more solar gain when warm air flows between the sunspace and the house > during the day, but reduces the nighttime and cloudy-day heat loss from > the living space… > Dr. Rich Komp (author of Practical Photovoltaics and president of the > Maine Solar Energy Association) says warm hollow floors like his > (which predates Kachadorian’s) aren’t new. Romans built hypocausts, > hollow floors heated with warm air from hot water or fires. So did > Chinese peasants. Warm hollow floors make good homes for dust and > varmints. Rich’s friend Ernie the Ermine takes care of that problem. > Living inside the heat battery, we are subject to its temperature swings, > and if there are no temperature swings, there is no solar heat storage. > We can’t charge the slab up to a high temperature because we have to > live with it in the room. The same amount of thermal mass at a higher > temperature stores more useful heat than lower temp mass, and it allows > keeping a constant room temp until the mass cools to something close to > that room temperature. > Floor slabs don’t usually have much insulation between themselves and > the room air, and they are difficult to insulate because of their shape. > The same amount of insulation applied to a cube with equivalent mass > lowers the rate of heatflow a lot more. > And water stores about 3X more heat than masonry by volume. It can also > be cheaper and more useful, even in sealed containers. > K’s slab uses a fan. It might make more than a 40% heating fraction, with > lots of airflow and slab channels (ie heat transfer surface) and a carpet > on top of some foamboard over the slab and a low thermal mass sunspace with > separate 100 F air ducts between the sunspace and the slab and lots of house > insulation, eg 12" R48 SIPs. > Then again, we might make the house walls hollow block with the holes > lined up so air can naturally flow vertically through the walls, with > lots of insulation (eg Dri-Vit) outside the block. > But either way, we have lots of inaccessible nooks and crannies to attract > dust and spiders and varmints. > Storing heat for 5 cloudy 30 F days in a house that cools from 75 to 65 F > means 65=30+(75-30)exp(-120h/RC), so RC = -120/ln((65-30)/(75-30)) = 477 h. > A 48′x48′x8′ house with an 8" 25 Btu/F-ft^3 slab with C = 48×48x8/12×25 > = 38.4K Btu/F needs a max thermal conductance G = 38.4K/477 = 80.5 Btu/h-F, > or 57.5 for 3748 ft^2 of R65 walls and ceiling, after subtracting 4% of > the floorspace as R4 windows, with no air leaks or internal heat gain. > Sounds Herculean… > Making the house 32×32x16′ tall with a 17K Btu/F slab and 2048 ft^2 of > 5 Btu/F-ft^2 block walls makes C = 27.2K Btu/h-F, so G = 27.2K/477 = 57, > or 36.5 for 2990 ft^2 of R82 walls, with no air leaks. More Herculean. > K’s book has lots of whopping mistakes. For instance, he thinks a house > needs 2/3 ACH for health, 27X more than the 0.025 ACH Swedish standard > and 83X more than the Canadian IDEAS standard. > Page 17 says "As you can see, the reduction in solar benefit increases > exponentially as you rotate the home’s orientation away from true south." > Page 30 says > If this combination of poured concrete slab over horizontally laid blocks > is ventilated by air holes along the north and south walls, air will > naturally circulate through this concrete radiator when the sun is out… > the south wall will be warmer than the north wall… air that is next to > or alongside the south wall will rise. Warmed air will then be pulled out > of the ventilated slab, and the cooler air along the north wall will drop > into the holes along the north wall. This thermosiphoning effect will > naturally continue to pull air through the Solar Slab.
Are you saying this would not promote circulation through the south wall, floor and north wall? – Hide quoted text — Show quoted text -> Page 49 says "Incorporate an air lock entrance" with miniscule energy savings > except for a department store, or a house with a huge active family. > Page 53 describes "reflective" foil smack up against plywood > The interior foil face will reflect heat back into the room, even though > it is sealed inside the thermo-shutter… The outside foil face of the > insulation contained within the wood veneers will reflect the sun’s summer > heat back out the window. > Page 94 belies the natural air circulation described on page 30 > The duct shown running down the middle of the bgase under the poured slab > is included in all cases. It should always be used as the return-air duct: > do not reverse the air flow pattrern shown on the control diagrams. By > using the Solar Slab as part of the return-air duct system, the Solar Slab > will constantly assist the furnace by preheating the return air. Even if > the home will be heated with a woodstove and emergency electric furnace, > the return duct should be included and the air mover hooked up per the > appropriate control diagram…
Using the hollow floors as a return air duct will sue purchased heat to charge up the floor. Not what you ant. Although using dampers and controls can eliminate that. – Hide quoted text — Show quoted text -> Page 101 says > 2. Size of electric heating system = 9.25 kilowatt=hours, > with an annual consumption of 7.616 kilowatts, > Page 102 says > The calculation for the electric backup option determined that > we would need 9.25 kilowatts per hour for the Saltbox 38… > Page 106 says "The theoretical minimum temperature to which a home with > a Solar Slab will drop is the ground temperature under the solar slab…" > (Yes, that will keep the pipes from freezing in most parts of the US, > if a perfectly airtight house with infinite insulation > Page 107 says "it also costs more to cool air than to heat air," as if > K. is unaware of evaporation, night sky radiation, or the phrase > "coefficient of performance." > Page 137 ignores one-way passive backdraft dampers > It may seem that a sunspace that is gathering enough heat to become > 90 degrees Fahrenheit on a cold, 15-degree but sunny winter day would > be beneficial to the home. And yes, it can be beneficial. However, > the same overglazed sunspace that accumulated all that heat during > the cold but sunny day will need lots of added heat when the sun goes > down to prevent it from freezing, which means that the sunspace or > greenhouse will tend to draw heat from the rest of the house as its > flow of solar heat reverses course, back out through the glazing. > but his solar slab is a good way to store overnight heat from inexpensive > passive air heaters or a low-thermal mass sunspace that can add valuable > floorspace to a house. One drawback is dust–it’s hard to clean the rough > passages in the hollow concrete blocks. Another is fan power. A vertical > thermal mass (eg a chimney with extra flues open at top and bottom) might > store and release heat to a house with no fan power at all… > Page 46 says > Let there be no misunderstanding about where the fresh air makeup > is coming from. The walls and roof of your home should be very > tightly constructed… Fresh air will enter your home through > controlled or deliberate openings… not through gaps in the insulation > or poorly sealed windows and doors. > A 3,000 ft^2 house with 2/3 ACH has 267 cfm, enough for 18 full-time > occupants, using the 15 cfm/occupant ASHRAE standard. > K. doesn’t mention heat recovery, although he talks about an "air exchange > or ventilator system." HRVs seem useless for most US houses, since natural > air leaks can easily supply most of the ventilation air. A 3,000 ft^2 house > only needs 30×60/(3000×8) = 0.075 ACH for 30 cfm. We might run a ventilation > fan if the house feels stuffy or the RH exceeds 60% in wintertime… > We might store more heat with better room temp control by circulating > 100 F air from a sunspace under the floor… > If a solar house needs, say, $200 per year of electrical energy to operate, > we might heat a superinsulated house at the same cost, and forget about > fans and mass and glass… > A 2K ft^2 2-story house with R40 6.5" Urethane SIP walls and 130 ft^2 of > U0.38 south windows with 46% solar transmission (SHGC = 0.46) and a thermal > conductance of 214 Btu/h-F needs 24h(65-27.4)214 = 193K Btu on an average > December day in Worchester, MA. If 300 kWh/mo of electrical energy use > contributes 34K of that and 0.46×130x860 = 51K comes in south windows, > we only need 107.6K more. > A square foot of R1 vertical south air heater or sunspace glazing with 90% > solar transmission and 80 F air on the inside would gain 0.9×860 = 774 Btu > of sun and lose about 6h(80-27.4)1ft^2/R1 = 316, for a net gain of 458. We > might heat the house on an average day with 107.6K/458 = 235 ft^2 of extra > south glazing, eg a 32′x8′ tall single layer of polycarbonate glazing on > the outside of an open stud wall with SIPs on the inside, or over exposed > posts and beams at the south edge of a second floor cantilevered 4′ to the > south of the first floor, forming a 4′x32′ arcade with a transparent wall > beneath, for a medieval look.
… read more »
Response:
Posted in Electric Furnace | 
No Comments » | 
DJ 
> We also have a UPS with a functioning 12V inverter, enough to power > the furnace using truck alternator. (1.4 kva Ferrups). > i 