Question:
I have been considering different building methods for a small cottage, (~20′ x 26′ interior). I have already dismissed ICFs and am thinking of using hollow core concrete blocks with solar heated air running through the cavities. This air would be separate from the regular room air. The floors would also use concrete blocks which I think would offer a very comfortable radiant envelope with built-in thermal mass. I was originally thinking of pex tube hydronic in-floor heat until I saw this link http://www.blockjoist.com/ that uses a special truss system with concrete blocks and top coat of regular concrete. If the hollow cores in the floor were in line with the cores in the walls they might make for a good thermo-syphon conduit. I could cover the exterior with foam board and siding. Although I would prefer field stone for the exterior, (lots of it laying around my place), it would require another wythe of concrete on the foundation wall down to the footing, which may be too costly. This would make for a fairly solid sandwich wall structure that would be nearly impervious to the elements and vapor movement. One of my other concerns is freezing during extended power outages, (this is in northern Wisconsin). If I avoid using hydronic heating I won’t have to worry about that system freezing and can plan my plumbing to allow for fast drain down for the time I am not there. However, it would still be nice to have it maintain an above freezing temperature to avoid having to bring home all the things that could be damaged, (canned goods comes to mind). If I could maintain about 40F with a passive system it would be easier to get comfortable after arriving late on a Friday evening when the outside temp is -20F. A friend of mine heats his place with wood, (24′ x 32′ with loft) and it takes half the weekend to get comfortable with several stokings at night. Regardless of what type of other heat source I use I want things to be comfortable in a few hours and I thought this whole hollow core thermal mass passive thermal idea might work. I would probably use the entire gable end south wall as a collector with few or no windows. The air would syphon through the attic above the second story loft, down the walls, through the floors and back through some sort of plenum in the basement floor to the bottom of the collector. I’d also like to work it out so the air flow is in opposite directions in every other core of the floor to minimize any hot/cold spots. If the south wall has 9 vertical feet of collector space and a 22 x 11 foot triangular area above that on the 12 pitch gable I should be able to build a (9′ x 22′) + (11′ x 11′) = 319 sqft collector. I don’t know enough yet to calculate any more results from this. If anyone has anything to add I would appreciate it. I also have not calculated the cost difference of building with block as opposed to conventional materials. If anyone has used the block truss floor system I would also appreciate any feedback on costs/performance of that as well. Thanks, Dennis
Response:
How do you know these construction block holes will not be full of mortar, as they should? How will you connect one tube with the next and still support the roof or are they all in parallel?
> I have been considering different building methods
for a small cottage, > (~20′ x 26′ interior). I have already dismissed ICFs and am thinking > of using hollow core concrete blocks with solar heated air running > through the cavities. This air would be separate
from the regular room > air. The floors would also use concrete blocks which I think would > offer a very comfortable radiant envelope with
built-in thermal mass. > I was originally thinking of pex tube hydronic
in-floor heat until I – Hide quoted text — Show quoted text -> saw this link http://www.blockjoist.com/ that uses a special truss > system with concrete blocks and top coat of regular concrete. If the > hollow cores in the floor were in line with the cores in the walls they > might make for a good thermo-syphon conduit. > I could cover the exterior with foam board and siding. Although I > would prefer field stone for the exterior, (lots of it laying around my > place), it would require another wythe of concrete on the foundation > wall down to the footing, which may be too costly. This would make for > a fairly solid sandwich wall structure that would be nearly impervious > to the elements and vapor movement. > One of my other concerns is freezing during extended power outages, > (this is in northern Wisconsin). If I avoid using hydronic heating I > won’t have to worry about that system freezing and
can plan my plumbing > to allow for fast drain down for the time I am not there. However, it > would still be nice to have it maintain an above
freezing temperature – Hide quoted text — Show quoted text -> to avoid having to bring home all the things that could be damaged, > (canned goods comes to mind). If I could maintain about 40F with a > passive system it would be easier to get comfortable after arriving > late on a Friday evening when the outside temp is -20F. > A friend of mine heats his place with wood, (24′ x 32′ with loft) and > it takes half the weekend to get comfortable with several stokings at > night. Regardless of what type of other heat source I use I want > things to be comfortable in a few hours and I thought this whole hollow > core thermal mass passive thermal idea might work. > I would probably use the entire gable end south wall as a collector > with few or no windows. The air would syphon through the attic above > the second story loft, down the walls, through the floors and back > through some sort of plenum in the basement floor to the bottom of the > collector. I’d also like to work it out so the air flow is in opposite > directions in every other core of the floor to
minimize any hot/cold > spots. > If the south wall has 9 vertical feet of collector space and a 22 x 11 > foot triangular area above that on the 12 pitch gable I should be able > to build a (9′ x 22′) + (11′ x 11′) = 319 sqft
collector. I don’t know > enough yet to calculate any more results from this. > If anyone has anything to add I would appreciate it. I also have not > calculated the cost difference of building with block as opposed to > conventional materials. If anyone has used the block truss floor > system I would also appreciate any feedback on
costs/performance of – Hide quoted text — Show quoted text -> that as well. > Thanks, > Dennis
Response:
>How do you know these construction block holes will not >be full of mortar, as they should?
First, I will know if they are full of mortar if I am the one laying them. Second, nothing says that they must be filled. I could fill every 3rd core, this is common practice. In fact, the empty cores are often filled with styrofoam beads. In addition to that, if I use the double wythe foam sandwich wall with field stone above grade, that I mentioned, I wouldn’t have to fill any of the cores if the exterior wythe was the structural member. If I understand everything correctly at this web sight http://www.blockjoist.com/ these blocks also are not filled with mortar. >How will you connect one tube with the next and still >support the roof or are they all in parallel?
I guess I’m not quite sure what you are asking. I haven’t worked out every tiny detail yet. However, the roof will be supported by some type of rafter system to allow for usable living space, ie. two bedrooms. It might even be possible to use the block joist system for this. A little cutting of block and/or strategic placement will allow the horizontal block cores and the vertical cores to line up. There are also three sided blocks. Maybe I could use three sided blocks at the corse that intersects with the floors. I’m really interested to know if anyone has tried the block joist system and if anyone who knows a lot more about solar collectors and thermal mass than I do thinks this may work or not and why. Dennis
Response:
>I have been considering different building methods for a small cottage, >(~20′ x 26′ interior)…
In northern Wisconsin, eg Eau Claire, where NREL says 430 Btu/ft^2 falls on the ground and 790 falls on a south wall on an average 16.8 F December day with a 25.3 F max. Not an easy solar house heating climate. >… thinking of using hollow core concrete blocks with solar heated air >running through the cavities. This air would be separate from the regular >room air.
I’ve seen that, with room air entering and leaving block walls through holes at the top and bottom. Mice and dust come to mind, and a low temp swing. Mass with a higher temp swing can store more heat. Water can be cheaper than concrete and it stores about 3X more heat by volume. >The floors would also use concrete blocks which I think would >offer a very comfortable radiant envelope with built-in thermal mass.
Warm air rises, so getting solar heat into a floor is difficult. >I could cover the exterior with foam board and siding…
How much? >One of my other concerns is freezing during extended power outages…
You might just drain the pipes. >If I could maintain about 40F with a passive system it would be easier >to get comfortable after arriving late on a Friday evening when >the outside temp is -20F.
You might maintain 40 F with electric heat, or the loss from a large heat storage tank on the ground. You can heat SIPs a lot faster than concrete. Or 9" TGI walls with poured cellulose insulation. >A friend of mine heats his place with wood, (24′ x 32′ with loft) and >it takes half the weekend to get comfortable with several stokings at >night. Regardless of what type of other heat source I use I want >things to be comfortable in a few hours and I thought this whole hollow >core thermal mass passive thermal idea might work.
I like the idea of massy ceilings for heat storage. Or a low-e ceiling surface above fin tube pipe, with a big heat storage tank on the ground. With a slow ceiling fan and a room temp thermostat and an occupancy sensor to warm a room as needed. >I would probably use the entire gable end south wall as a collector >with few or no windows. The air would syphon through the attic above >the second story loft, down the walls, through the floors and back >through some sort of plenum in the basement floor to the bottom of the >collector.
The air is unlikely to flow naturally below the base of the collector. >If the south wall has 9 vertical feet of collector space and a 22 x 11 >foot triangular area above that on the 12 pitch gable I should be able >to build a (9′ x 22′) + (11′ x 11′) = 319 sqft collector. I don’t know >enough yet to calculate any more results from this.
A square foot of R2 sunspace glazing with 80% solar transmission might collect 0.8×790 = 632 Btu and lose 6h(70-20)1ft^2/R2 = 150 on an average December day, ie 482 Btu net, so a 9′x22′ sunspace might collect 95.4K, or more, with an enclosed solar staircase roof. With 48 ft^2 of R4 windows and 694 ft^2 of Rw walls and 520ft^2/Rc of ceiling conductance and 12+694/Rw for windows and walls and 94.5K = 24h((65-16.8)(12+694/Rw+(Tc-16.8)520/Rc), 64.3/Rw+(Tc-16.8)/Rc = 6.45. With R32 walls, Tc = 16.8+4.44Rc. Rc = 40 makes Tc = 194 F, theoretically. If Tc = 120 and the ceiling can still warm the cottage at 80 and it loses 5×24h((100-16.8)520ft^2/R40+(65-16.8)(12+694ft^2/R32)) = 325K Btu over 5 cloudy days and (120-80)520P = 325K, P = 15.6 psf of ceiling water, ie a 3" depth. Or put fin-tube pipe under a low-e ceiling with 15.6×520 = 8112 pounds of water in a 130 ft^3 tank on the ground, eg a 4′x8′x4′ deep tank. Nick
Response:
>I’ve seen that, with room air entering and leaving block walls through holes >at the top and bottom. Mice and dust come to mind, and a low temp swing. >Mass with a higher temp swing can store more heat. Water can be cheaper >than concrete and it stores about 3X more heat by volume.
Yes, I’ve read a book about this concept. However, I am considering a closed loop system in which the room air does not mix with the air in the cores. If the system was sealed mice would not be able to get in and any concrete dust would stay in the cavities. I understand that water is cheaper and a better thermal mass storage system. The biggest issue I have with it, in this remote location, is that I don’t want any water that could freeze due to a system failure. I’m also curious if HDPE tubes burried several feet under the basement floor might work for thermal heat storage. I gotta dig that hole anyway, I may as well have it dug deeper while the guy is there with his back hoe. This is on a hill top 20 feet above the water table. >The floors would also use concrete blocks which I think would >offer a very comfortable radiant envelope with built-in thermal mass. >Warm air rises, so getting solar heat into a floor is difficult.
If the system is a closed loop I’m not sure this will be a problem. I’m only just learning about this stuff, so help me to understand. Also, I was not very clear in my first description of what I envision. I’ll do my best to describe it without a drawing. This cottage would have a basement floor, main floor/basement ceiling and second floor/main floor ceiling with concrete blocks lying on their sides, connected to each level via the cores in concrete block walls. In the 45 degree angle slanting wall area of the loft/second floor there would be a ceiling about 7 feet high. The area above this second floor ceiling is where the heated solar collector air would first go after leaving the south wall. If you were standing outside looking north at the solar collector and could see through the walls and could see the air moving it might look like this. As the air is heated in the collector it rises into the attic area, which is sealed and ducted through the rafters to the walls. This displaces relatively cooler air through the ducts to the walls. By blocking or partially blocking some of the cores I believe it could be directed at each intersection. The path of air flow for one core might go down an east duct to knee wall to floor. At the floor/main floor ceiling it moves west to the opposite wall, down the west wall to the main floor/basement ceiling, back through the floor to the east wall, down the east wall to the basement floor, through the basement floor into a large duct area running north to south under the center of the basement floor to the south wall, up the south wall cavities back to the lower entrance of the solar collector. Does this make sense? I guess I understood a thermo-syphon with a solar collector to function similar to a DC electrical circuit. If the air is run through ducts aren’t they like electrical conductors? As long as they return to the source to make a complete circuit does it matter if some of them are physically lower than the collector? >I could cover the exterior with foam board and siding… >How much?
I’m not sure yet. Perhaps 4", maybe more. >One of my other concerns is freezing during extended power outages… >You might just drain the pipes.
Yes, that would be easy enough to do, especially If I don’t have to get rid of 40 gallons of hot water. Maybe I should install point of use water heaters. >You might maintain 40 F with electric heat, or the loss from a large heat >storage tank on the ground. You can heat SIPs a lot faster than concrete. >Or 9" TGI walls with poured cellulose insulation.
I agree and have considered SIPs. My concerns about SIPs, (which I think are way cool), is the lack of availability in the area, the need for contractor installation with an expensive crane and crew make it a non DIY/local help project. What are TGI walls? >I like the idea of massy ceilings for heat storage. Or a low-e ceiling >surface above fin tube pipe, with a big heat storage tank on the ground. >With a slow ceiling fan and a room temp thermostat and an occupancy >sensor to warm a room as needed.
This sounds like something I might like to try, maybe in my garage, or a house that I occupy regularly. >The air is unlikely to flow naturally below the base of the collector.
See my thought on this above. I appreciate your input. You seem to be the most knowledgeable poster in this group on how to cost effectively incorporate solar heating. Like I said before, I am just learning. One of my biggest misunderstandings is in some of the calculations. I can grasp the concepts when explained, but many of the variables are foreign to me. Is there a file I can get that has this information? There are some other reasons why I am currently stuck on masonry construction, (yes, I could change my mind). I like the strength it offers, it is resistant to things like storms and fire and is low maintenance. The most likely causes of damage that I have seen are freezing pipes and burglary/vandalism. This is a place I go to relax. I don’t want to worry about it or be saddled with a lot of maintenance like with the mobile home that is there now. I would also like to make steel shutters to cover the outside of the windows that would have sliding bolts on the inside that would slide into the wall for security when I am not there. I could also make steel entrance door covers that have locking similar to some of the doors on Navy ships, which would also only be used when not there. By making it extremely difficult to break in the thiefs will most likely move on to easier targets. The weakest link then would be an angry vandal, ("how dare he try to keep me out"), who might take his frustration out on the solar collector, causing the building to freeze. So anyway, that is what I would like to accomplish a few years from now. A small, cozy, aesthetically pleasing, story book cottage. One that will last for generations. Dennis
Response:
- Hide quoted text — Show quoted text ->Warm air rises, so getting solar heat into a floor is difficult. >If the system is a closed loop I’m not sure this will be a problem… >This cottage would have a basement floor, main floor/basement ceiling >and second floor/main floor ceiling with concrete blocks lying on their >sides, connected to each level via the cores in concrete block walls. >In the 45 degree angle slanting wall area of the loft/second floor >there would be a ceiling about 7 feet high. The area above this second >floor ceiling is where the heated solar collector air would first go >after leaving the south wall. If you were standing outside looking >north at the solar collector and could see through the walls and could >see the air moving it might look like this. >As the air is heated in the collector it rises into the attic area, >which is sealed and ducted through the rafters to the walls. This >displaces relatively cooler air through the ducts to the walls.
I’m not entirely clear about your plan, but it seems to me you might end up with a stagnant pocket of hot air in the attic. Cool air can "displace" warmer air by sliding below it, but I’m not sure the opposite works. >similar to a DC electrical circuit. If the air is run through ducts >aren’t they like electrical conductors?
Sort of, but it’s hard to make warm air go downhill. >As long as they return to the source to make a complete circuit does it >matter if some of them are physically lower than the collector?
Maybe not. The basic force is bouyancy. Air at 70 F weighs about 0.075 lb/ft^3. At T (F), it weighs about 0.075(460+70)/(460+T). So in principle, you might figure out all the temperatures in a loop and find out whether air will circulate or not. But air is sneaky. >What are TGI walls?
TGIs are 2×3/plywood/2×3 trusses. They are normally used for joists vs studs, but you can use them for studs. You might make walls with 9.25" TGIs on 2′ centers. >Like I said before, I am just learning. One of my biggest >misunderstandings is in some of the calculations. I can grasp the >concepts when explained, but many of the variables are foreign to me. >Is there a file I can get that has this information?
I’ll append one. Nick Notes for a Pennsylvania Renewable Energy Festival Workshop on Solar House Heating and Natural Cooling Techniques Kempton, PA September 24, 2005 Written by Nick Pine, with Drew Gillett and Rich Komp Debatable Conclusions 1. Heat flows like electricity. 2. Solar heat can be 100 times cheaper than solar electricity. 3. Superinsulated houses have to be very small or very large. 4. Direct gain houses can be improved. 5. Indirect gain can be more efficient. 6. We might store heat in the ceiling. 7. We might have a separate cloudy-day heat store. 8. Low temp heat storage and distribution are difficult. 9. Shurcliff’s lung might be a good air-air heat exchanger. 10. Greywater heat exchangers, Big Fins and solar ponds can help. 11. We might also gather heat from PVs. 12. Smart ventilation can be helpful. 13. Swamp coolers can be improved. 0.0 Introduction The US has 5% of the world’s population and consumes 26% of the world’s energy. House heating and cooling accounts for about one third of that. In 1980, "envelope house" inventor Tom Smith said: It’s a snap to save energy in the US. As soon as more people become involved in the basic math of heat transfer and get a gut-level, as well as intellectual, grasp on how a house works, solution after solution will appear. This workshop aims at improving that grasp, which we can control better than our US cheap energy policy… If we paid related costs of healthcare and air pollution and Gulf wars at the pump, gasoline would be a lot more expensive. Drew says this writeup needs exercises for the reader. OK: Exercise 0.1: The US consumed 21 million 42 gallon $41 barrels of oil per day in 2004. What goes into the real cost per gallon? (Debatable answers appear at the end of these notes 
Most people think "electricity" when they hear "energy," even though most houses need more heating energy than electrical energy (the ratio is 1:1 in Hawaii and 5:1 in Vermont.) It’s easy to shrink the small electrical slice of the home energy pie with compact fluorescent (CF) lights and more efficient appliances. Solar heat can be very inexpensive compared to solar electricity. PV panels at $3 per peak watt cost 150X more than polycarbonate glazing at $1/50W = 0.02/Pw. And sunspaces add floorspace to a house. A square foot of "solar collector" only collects about $1/year at $1/gallon so anything (except PVs??? that costs more than $10/ft^2 (half labor) and only collects energy with no other purpose seems economically-doomed… Exercise 0.2: Should we a) replace a 60 W bulb with a 14 watt CF or b) buy 60-14 = 46 additional watts of PV power? Most of us "know" how to design passive solar houses with well-established rules of thumb, but let’s relax and take a fresh look from a standpoint of basic physics… Berlin is a nice town and there were many opportunities for a student to spend his time in an agreeable manner, for instance with the nice girls. But instead of that we had to perform big and awful calculations. Konrad Zuse, inventor of the 1936 Z1 computer Overview This is a workshop on "Ohm’s law for heatflow" with applications to solar water and house heating and natural cooling. We’ll discuss a solar pond and a simple greywater heat exchanger, some inexpensive plastic pipe coiled inside a 55-gallon drum. With hot water bursts of 13 gallons or less, it could be 97% efficient. If it is, why bother with solar hot water? We’ll provide arithmetic tools and data and strategies needed to site-build effective house heating and cooling systems using inexpensive materials and skills. Participants will need some familiarity with high school algebra. We’ll discuss power, energy, heatflow, and overnight and cloudy day heat storage at a high-school math and physics level, with insulation values and heat capacities of materials, simple equations involving time constants, evaporative and night ventilation cooling, passive and low-energy solar heating, climate data, and schemes for houses that are 100% solar-heated and naturally cooled, by design. We’ll provide a calculator (Steve Baer says "Throw away your calculator." and a CD-ROM. Promising techniques include solar closets, trickle collectors, "pancake houses," soap bubble foam insulation, and solar attics, including systems to collect heat and electricity from water-cooled standard PV panels. Rich Komp is president of the Maine Solar Energy Association and a PV author with a PChem PhD, Drew Gillett is a Professional Engineer with civil engineering and architectural degrees, and I’m an EE by training. Disclaimer Some of the techniques we describe are experimental. Some have never been tried. We do not accept responsibility for their safety or functionality. 1. Power and energy Energy is the stuff we pay for, measured in Joules or watt-hours or kilowatt-hours (kWh) or Calories or "British thermal units" (Btu), no longer used in Britain The British now use joules or kWh. A Btu is a quantity of heat, about the same as the energy in a kitchen match or a mouse-hour. One Btu can heat one pound (16 ounces) of water one degree F. One Calorie (capital C, 4.19 kilojoules) can heat one kilogram of water 1 C. Exercise 1.1: How many Btu [joules] are needed to heat 8 ounces [0.25 kg] of water from 50 to 212 F [10 to 100 C] to make a cup of tea? [the brackets describe _comparable but not identical_ metric exercises.] Power is the rate of energy flow over time. A mere number, vs the stuff we pay for. Energy is power times time. One watt-hour of energy is equivalent to 3.41 Btu. If energy were miles traveled, power would be miles per hour. If energy were a paycheck, power would be an hourly rate of pay. Exercise 1.2: How long would it take to heat the tea water with a 300 W immersion heater? We might check this with an immersion heater and a watch and a $100 Raytek IR thermometer. Or a HOBO from Onset Computer Corp (1-800-LOGGERS.) Their $119 battery-powered U12-013 HOBO is about the size of a matchbox. It can record 43,000 12-bit samples at 1 second to 18 hour intervals of its own temperature and relative humidity (RH), with jacks for 2 more temperature probes or other devices on cables, and upload them to a PC spreadsheet via a USB port. People often confuse power and energy, as in "My house uses lots of power" (vs energy) or "My furnace capacity is 50,000 Btu," (vs Btu/h.) Power is measured in watts or kilowatts (kW.) Unlike energy, it can’t be used or consumed. People confuse heat and temperature, too. A bathtub full of hot water contains a lot of useful house heat, compared to a candle, but the candle is much hotter. A lower minimum usable temperature increases useful heat. Temperature is a measure of heat intensity. A 12-volt 100 amp-hour 50 pound automobile battery stores 267 times more energy (12Vx100Ah = 1200 Wh) than a 9-volt 500 milliamp-hour (9Vx0.5Ah = 4.5 Wh) 2 ounce transistor radio battery, at a lower voltage (ie "electrical temperature.") The $40 battery can store about 200 kWh over its lifetime, at 20 cents/kWh. A $1 cubic foot of water cooling from 130 to 80 F stores (130F-80F)64Btu/F = 3200 Btu, ie about 1 kWh, with a much longer lifetime and simpler I/O. 2. Rich Komp, Ohm, and Newton Rich Komp (who is still alive) says heat moves by conduction (a hot frying pan handle), convection (including air movement), radiation (the sun brings about 1000 watts per square meter or 300 Btu per hour per square foot on a clear day at noon in the Sahara), and phase change (144 Btu melts a pound of ice and 1000 Btu evaporates a pound of water.) About 300 years ago, Isaac Newton said the amount of heat that flows through a wall is proportional to its area and the temperature … read more »
Response:
Thanks Nick, I saved a copy of your notes. I’ll have to print them out and run through the exercises. >As long as they return to the source to make a complete circuit does it >matter if some of them are physically lower than the collector? >Maybe not. The basic force is bouyancy. Air at 70 F weighs about 0.075 >lb/ft^3. At T (F), it weighs about 0.075(460+70)/(460+T). So in principle, >you might figure out all the temperatures in a loop and find out whether >air will circulate or not. But air is sneaky.
I see. I guess I would be wise to try a small scale experiment before investing large sums of money. Maybe I can try something with the old run down mobile home or the small shed out back. Too late this year, everything is already closed up for the winter. In the mean time I will continue to moniter this sight and work on improving my knowledge of things solar. Dennis
Response:
Dennis, If you want the cottage to heat up quickly when you get there, you do not want to have a lot of thermal mass in the *living space*, because you are going to have to heat up all that mass when you arrive for the weekend. However, if you want a solar collector to keep the cottage from freezing overnight, you’ll need some thermal storage somewhere to supply heat during the night. This storage should be isolated from the living space so that you do not have to heat it when you are there on the weekends. Air is a terrible heat transfer fluid. – You need to move a lot of it. If you pick up 500 BTU/ft^2/day off a 300 ft^2 collector with a 10F temperature rise, you’ll need to move 750,000 cubic feet of air a day. That’s about 3000 cfm, which is not going to happen with natural convection. – You need big ducts to move all that air, which are big enough to have internal convection. It is this internal convection that makes it so hard to get an air thermosyphon to move the heat where you want it to go. – Air doesn’t store heat, so you need to transfer the heat from the collector to the air, then from the air to the store, and then back to the air in the cottage so it can leak out at night. I know you don’t want to hear it, but water is a much better fluid for this application. Would it be possible to orient the cottage so that one eave of the roof faces south? If the cottage is 26′ east-west, you might build a 30′ wide by 18′ high trickle collector on the south slope, using corrugated aluminum painted black with double-wall polycarbonate over it. Use double wall for the strength rather than the insulation, because you want it to deal with snow loads and winds without flexing and rattling around so much that it develops stress fractures. I would avoid glass at first. I’d want to actually see the polycarb fail before I tried something so much more expensive. Note that the polycarb you’ll be using is more usually employed in greenhouses which have very high inside humidity and temperatures above 60F. That’s pretty similar to the conditions you’ll put it in. In particular, I’d shoot for a water temp rise from 70F to 90F during the day. Your collector will see maybe 800 BTU/ft^2/day insolation, transmit 600 BTU/ft^2/day when it’s dirty, and lose 160 during 4-5 hours of collection. So it’ll put 240,000 BTU/day into the heat store. Now you’re cooking with gas. If you can get the whole cottage down to an average of R-10 (x 1700 ft^2 area) the trickle collector could keep the thing at 65 degrees in February. (But that’d require a hydronic floor.) My understanding is you’ll use concrete block construction for the basement, which will be 20′ x 26′. Build a low wall 3 feet tall across the short distance, perhaps 12 feet from the side of the basement. Install 4 inches of EPS foam on the bottom and against the basement sides (2 layers of 2" boards). Don’t insulate the side facing the rest of the basement. It would probably be better for this insulation to be between the basement and the dirt, but that gets into a bunch of details I don’t want to consider. Cover the resulting space with a 30′ x 20′ EPDM sheet, "folded up like a Chinese take-out box" (this, like everything else, is taken from Nick Pine’s playbook). Fill it with water, cover with another 20′ x 10′ EPDM sheet. That’s your 4500 gallon tank — big enough to store a few of nights worth of heat. It’ll heat the house by conducting heat to the air in the basement across that top face. You might need more heat flow than that, but you can tinker with it after you move in. I tend to like oversize tanks. To keep the collector from baking the polycarb to an early death each summer, you’ll need to vent that collector to the air, top and bottom, but only when you’re not running the trickle pump, of course. Polycarb: https://www.sundancesupply.com/PolyPage.html EPDM: http://www.coloradolining.com/products/epdm_price_list.htm Specs/assumptions/sizes: – 20′ x 26′ cottage – 8mm 2-wall R-value 1.7, 81% transmission – 30′ x 18′ trickle collector – 6 gpm pump, 40′ head: 1/8 HP pump, on for 4-5 hours a day (electric cost: about $12 for a 160-day heating season) – 20′ x 12′ x 2.5′ insulated tank: 4500 gallons
Response:
>I know you don’t want to hear it, but water is a much better fluid >for this application.
I’d rather hear the facts and put something together that works, even if it isn’t my first choice. So I am keeping all suggestions so I can digest it all and make some good decisions. Thanks, Dennis
Response:
>Build a low wall 3 feet tall >across the short distance, perhaps 12 feet from the side of the >basement. Install 4 inches of EPS foam on the bottom and against the >basement sides (2 layers of 2" boards).
Is there a way I can cost effectively make this water proof without the EPDM? Also, what do you think about putting the water storage under the basement floor? I see sometimes my posts are being repeated. Does anyone have a suggestion as to what I might be doing wrong? Dennis
Response:
When you post your news provider sends back a signal that the message is received. This misses sometimes and the message sits waiting again. If you use the same browser for email then your "check for updates on a periodic basis" option is probably on and keeps sending and looking for new messages, over and over. Turn that off if you can. In short, bad receive communications.
>Build a low wall 3 feet tall >across the short distance, perhaps 12 feet from the side of the >basement. Install 4 inches of EPS foam on the
bottom and against the – Hide quoted text — Show quoted text ->basement sides (2 layers of 2" boards). > Is there a way I can cost effectively make this water proof without the > EPDM? Also, what do you think about putting the water storage under > the basement floor? > I see sometimes my posts are being repeated. Does anyone have a > suggestion as to what I might be doing wrong? > Dennis
Response:
Dennis> Is there a way I can cost effectively make this water Dennis> proof without the EPDM? Also, what do you think about Dennis> putting the water storage under the basement floor? EPDM cost is the least of your worries. Think about the roof. Budget: 15′ x 20′ EPDM sheet: 117.00 25′ x 20′ EPDM sheet: 146.25 4" EPS foam on sides and bottom: 300.00 30′ x 18′ corrugated aluminum roof: 900.00 (wild guess) 30′ x 18′ 2-wall 8mm polycarbonate: 918.00 1/8 HP circulator pump: 200.00 control: 300.00 (guess) misc: 500.00 total: $3381 Note: system will provide ~2.5 therms/day for a 200+ day heating season, or around $700/year in equivalent cost of gas heating. Payback time around 5 years, but you should assume that controller is going to fail every 5 years or so. You could scale it down, of course. Now, would I be worried about putting all that water in the basement? I’m looking at having a 10k gallon tank in the house my wife and I are building. This is in California, where having a hot tank in the basement during the summer is not a great idea. We are essentially on top of the San Andreas, and the basement is already complicated as a result. …so I backed off, and we’re specifying it as an in-ground tank about 20 feet from the house, under a deck. So am I being hypocritical suggesting you put your tank in the basement? Maybe. We have issues you don’t. Our house is probably more valuable than this cottage, and will be used more. (Extra sources:) EPS foam: http://www.waynesbuildingsupply.com/eps.html
Response:
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daestrom 