Question:
>>I have a 50 gal electric hot water heater in My Attick . I was thinking of >running about 120 feet of 1.5 " pvc pipe back and forth in the attick to >bost the hot water supply…
I wonder if you can somehow put the pipe under the water heater… Build a shallow glazed box on the south wall of your house, with some pipe running along the top edge, inside the box? Or put the pipe in a sunspace, or put it near the peak of the attic, and use a small circulating pump… >the attack maintains a temp of around 95-110 ( monitored useing a min-max >thermotere. at night it cools to around 75-90 depending on the outside >temp ( have an ovesized attack fan on a thermostat up there). My question is: >A) how long will it take for the water in the pipe to reach temp?
120′ of 1.5" pipe has an area of about 47 ft^2, and the thin pipe wall has a large thermal conductance (10?) compared to the still air film around it, which has a thermal conductance of about 1.5 Btu/hr-F-ft^2. If the pipe contains 10 gallons of water, by Gene’s calculation, it will have an RC time constant of 10gx8lb/g/1.5/47 = 1.13 hours. So if the water starts out at say, 60 F, and it sits in a 100 F attic for t hours, its temp T(t) will follow T(t) = 100 – (100-60)exp(-t/1.14)). After 1 hour, it should have a temperature of T(t) = 100 – 40exp(-1/1.14) = 83.4 F. After 2, 93 F, after 3 hours, 97 F, etc. >B) has any one had any experience with this idea before is there any >thing i need to watch out for?
Watch out for freezing… But if your water heater plumbing hasn’t ever frozen in your attic, chances are the PVC pipe won’t either. If you don’t use any hot water at all in your house, how long will it take this pipe to freeze solid and burst and flood your house, when your attic is -1 F, the record min temp in Columbia, SC? Delta T would be 33 F, with U about 1.5 Btu/hr-F, and the pipe has 47 ft^2 and there is 80 lb of water inside, and it takes 144 Btu to freeze a pound of water. So… 144×80 = tx33×1.5×47, ie t = 5 hours. But the pipe might not freeze evenly. A little heat tape with a thermostat might not be a bad idea. Another thing to watch out for is hydraulic short circuits. You don’t want the incoming cold water to somehow end up coming out of the shower instead of the hot water that is inside the water heater. >The PVC pipe must go on the cold water side of the heater…
Seems like it might help a lot, if it’s in a loop below the water heater, so it can heat the water in the heater over and over, vs just heating the incoming cold water in one pass. >…now if only those pipes were painted black and put on the outside…
Good idea. Near the top of a shallow glazed box on the south wall? Say the box were 12′wide x 16′ tall x 3 1/2" thick, over an edgewise 2×4 frame with no insulation around the edges, and the glazing were 4 $50 4′ x 12′ sheets of Dynaglas corrugated polycarbonate plastic greenhouse roofing material, with your 47 ft^2 of dark painted pipes in a 10′ x 20" rectangle near the top edge, and you had a $50 motorized damper behind them to allow some warm air to flow into the house when you had enough hot water, but needed some house heat (two thermostats), on an average January day in Columbia, with 1140 Btu/ft^2/day of sun falling on the south wall, at an outdoor temp of 55 F. If you kept the box at 130 F inside, you might collect 50K Btu/day of hot water that way on a 6 hour day, while 6(130-55)192ft^2/R1 = 86K of heat passed back out through the glazing, and you could put the rest of the sun’s heat, ie 0.9×1140x192 – 86K = 111K Btu/day into the house, saving the heat equivalent of about a gallon of oil a day in the winter. Now why not make that shallow box on the wall a bit bigger, say a lean-to sunspace, 8′ wide at the base, with a pebble floor and a railroad tie foundation, and a picnic table, and use a bit more PVC pipe and keep the sunspace temp at 80 F in January, to add some interesting daytime living space and collect more heat for the house? Nick
Response:
– Hide quoted text — Show quoted text ->>I have a 50 gal electric hot water heater in My Attick . I was thinking of >>running about 120 feet of 1.5 " pvc pipe back and forth in the attick to >>bost the hot water supply… > I wonder if you can somehow put the pipe under the water heater… Build a > shallow glazed box on the south wall of your house, with some pipe running > along the top edge, inside the box? Or put the pipe in a sunspace, or put > it near the peak of the attic, and use a small circulating pump… >…now if only those pipes were painted black and put on the outside… > Good idea. Near the top of a shallow glazed box on the south wall? Say the > box were 12′wide x 16′ tall x 3 1/2" thick, over an edgewise 2×4 frame with > no insulation around the edges, and the glazing were 4 $50 4′ x 12′ sheets > of Dynaglas corrugated polycarbonate plastic greenhouse roofing material, > with your 47 ft^2 of dark painted pipes in a 10′ x 20" rectangle near the > top edge, and you had a $50 motorized damper behind them to allow some > warm air to flow into the house when you had enough hot water, but needed > some house heat (two thermostats), on an average January day in Columbia, > with 1140 Btu/ft^2/day of sun falling on the south wall, at an outdoor temp > of 55 F. If you kept the box at 130 F inside, you might collect 50K Btu/day > of hot water that way on a 6 hour day, while 6(130-55)192ft^2/R1 = 86K of > heat passed back out through the glazing, and you could put the rest of the > sun’s heat, ie 0.9×1140x192 – 86K = 111K Btu/day into the house, saving > the heat equivalent of about a gallon of oil a day in the winter.
Instead of running the pipe along the top of the box, how about running it through a few of the water filled barrels? If you used flexible plastic tubing you could probably loop a couple hundred feet inside barrels. Run the tubing in an opening, coil it around the sides and run it back out again. You could hook up several of these in series and have a heat exchanger that should heat the incoming cold water much faster than pipes exposed to the air in the box. > Now why not make that shallow box on the wall a bit bigger, say a lean-to > sunspace, 8′ wide at the base, with a pebble floor and a railroad tie > foundation, and a picnic table, and use a bit more PVC pipe and keep the > sunspace temp at 80 F in January, to add some interesting daytime living > space and collect more heat for the house?
This sounds nice, but I can’t picture how this would work. I’d like to have a collector that doubles as a sun space, but I don’t want to sit in a 130 F room, even in January, and 80 F won’t get the water hot enough. Do you mean the sunspace would be in addition to the shallow box? So the collector for the solar closet would be located at the back of the sun space? Dan Settles – Hide quoted text — Show quoted text -> Nick
Response:
- Hide quoted text — Show quoted text -> >>I have a 50 gal electric hot water heater in My Attick . I was thinking of > >>running about 120 feet of 1.5 " pvc pipe back and forth in the attick to > >>bost the hot water supply… > I wonder if you can somehow put the pipe under the water heater… Build a > shallow glazed box on the south wall of your house, with some pipe running > along the top edge, inside the box? Or put the pipe in a sunspace, or put > it near the peak of the attic, and use a small circulating pump… > >…now if only those pipes were painted black and put on the outside… > Good idea. Near the top of a shallow glazed box on the south wall? Say the > box were 12′wide x 16′ tall x 3 1/2" thick, over an edgewise 2×4 frame with > no insulation around the edges, and the glazing were 4 $50 4′ x 12′ sheets > of Dynaglas corrugated polycarbonate plastic greenhouse roofing material, > with your 47 ft^2 of dark painted pipes in a 10′ x 20" rectangle near the > top edge, and you had a $50 motorized damper behind them to allow some > warm air to flow into the house when you had enough hot water, but needed > some house heat (two thermostats), on an average January day in Columbia, > with 1140 Btu/ft^2/day of sun falling on the south wall, at an outdoor temp > of 55 F. If you kept the box at 130 F inside, you might collect 50K Btu/day > of hot water that way on a 6 hour day, while 6(130-55)192ft^2/R1 = 86K of > heat passed back out through the glazing, and you could put the rest of the > sun’s heat, ie 0.9×1140x192 – 86K = 111K Btu/day into the house, saving > the heat equivalent of about a gallon of oil a day in the winter. > Instead of running the pipe along the top of the box, how about running it > through a few of the water filled barrels? If you used flexible plastic > tubing you could probably loop a couple hundred feet inside barrels. Run > the tubing in an opening, coil it around the sides and run it back out > again. You could hook up several of these in series and have a heat > exchanger that should heat the incoming cold water much faster than pipes > exposed to the air in the box.
This barrel/coiling method sounds to be a great solution. I would think that it would increase the rate of heat transfer to the water with less space. > Now why not make that shallow box on the wall a bit bigger, say a lean-to > sunspace, 8′ wide at the base, with a pebble floor and a railroad tie > foundation, and a picnic table, and use a bit more PVC pipe and keep the > sunspace temp at 80 F in January, to add some interesting daytime living > space and collect more heat for the house? > This sounds nice, but I can’t picture how this would work. I’d like to > have a collector that doubles as a sun space, but I don’t want to sit in a > 130 F room, even in January, and 80 F won’t get the water hot enough. Do > you mean the sunspace would be in addition to the shallow box? So the > collector for the solar closet would be located at the back of the sun > space?
Just make it a tall thin space. The bottom portion would be where you would reside with your greenhouse plants. Towards the top would be where the works would reside with all the "hot air". To prevent overheating, vent excess hot air to adjoining internal spaces. Or incorporate some shading measures designed only to shade during the hottest times of the day/year (i.e. a small treless(sp) with folage(sp) for summer, that is then bare in the winter. The barrel concept could be used here. Where the barrels were sort of suspended in the air, or on a cat walk. with some dangling plants along the base of it and lights for night time use. Sort of soften the solar ambience a bit. ‘Just $.02 worth of info.’ > Dan Settles > Nick
– Chad Berreau
Response:
- Hide quoted text — Show quoted text -> I wonder if you can somehow put the pipe under the water heater… Build a > shallow glazed box on the south wall of your house, with some pipe running > along the top edge, inside the box? Or put the pipe in a sunspace, or put > it near the peak of the attic, and use a small circulating pump… > >…now if only those pipes were painted black and put on the outside… > Good idea. Near the top of a shallow glazed box on the south wall? Say the > box were 12′wide x 16′ tall x 3 1/2" thick, over an edgewise 2×4 frame with > no insulation around the edges, and the glazing were 4 $50 4′ x 12′ sheets > of Dynaglas corrugated polycarbonate plastic greenhouse roofing material, > with your 47 ft^2 of dark-painted pipes in a 10′ x 20" rectangle near the > top edge, and you had a $50 motorized damper behind them to allow some > warm air to flow into the house when you had enough hot water, but needed > some house heat (two thermostats), on an average January day in Columbia, > with 1140 Btu/ft^2/day of sun falling on the south wall, at an outdoor temp > of 55 F. If you kept the box at 130 F inside, you might collect 50K Btu/day > of hot water that way on a 6 hour day, while 6(130-55)192ft^2/R1 = 86K of > heat passed back out through the glazing, and you could put the rest of the > sun’s heat, ie 0.9×1140x192 – 86K = 111K Btu/day into the house, saving > the heat equivalent of about a gallon of oil a day in the winter.
Oops, too many Btus… 197K Btu of sun gets into the sunspace, and 86K leaks back out of the glazing (2 layers would help here), and 59K allegedly goes into the hot water, leaving —- 61K for the house. >Instead of running the pipe along the top of the box, how about running it >through a few of the water filled barrels?
Water filled barrels? Where are the barrels? There’s no solar closet here, altho there could be… This is just a sunspace with a bare water type solar collector inside, that circulates its hot water through a conventional water heater on the floor above by thermosyphoning, natural warm water convection… If all goes well, the water heater heating element seldom turns on. >If you used flexible plastic tubing you could probably loop a couple >hundred feet inside barrels. Run the tubing in an opening, coil it around >the sides and run it back out again. You could hook up several of these >in series and have a heat exchanger that should heat the incoming cold water >much faster than pipes exposed to the air in the box.
True, but if we had a solar closet, it seems simpler to just put 10-20′ of fin-tube pipe near the ceiling, an air-water heat exchanger that works 24 hours a day, to heat water in a water heater upstairs by thermosyphoning again. Seems to me it would be difficult to make water flow through all that plastic tubing without a pump, and you might have evaporation at the points where the tubing enters and leaves the drums. If the tubing is in series with the water heater, which is inside the solar closet, the water supply pressure could move the water through the plastic pipe, once, but it’s more efficient to have the water continuously circulate through the heat exchanger, to make a heat exchanger with a given surface area do more of a full-time job, rather than have the water only pass through it once. > Now why not make that shallow box on the wall a bit bigger, say a lean-to > sunspace, 8′ wide at the base, with a pebble floor and a railroad tie > foundation, and a picnic table, and use a bit more PVC pipe and keep the > sunspace temp at 80 F in January, to add some interesting daytime living > space and collect more heat for the house? >This sounds nice, but I can’t picture how this would work.
The usual way is some sort of bare solar collectors inside a sunspace, eg Zomeworks Big Fins, which are flat aluminum extrusions, about 4′ long and 8" wide, painted black on one side, that clip on to and are supported by standard copper pipes running along the back side… Then there’s the standard water heater upstairs and a thermosyphoning water loop from the Big Fins to heat it, when the Big Fins are warmer than the water in the water heater. So in this usual case, the fins and pipes are, say 130 F, with the sun shining on them, but the sunspace is only 80 F. >I’d like to have a collector that doubles as a sun space, but I don’t want >to sit in a 130 F room, even in January, and 80 F won’t get the water hot >enough.
I see what you mean… If you put Big Fins or a bare solar panel in your sunspace, IT would be 130 F with the sun shining on it, but your sunspace could be 80 F, with some solar heat going out the glazing and some warm air flowing into the house. The losses from the 130 F collector would be heating your house, vs the outside world, which is a good thing… And you don’t need a big heavy expensive weatherproof insulated collector on the roof, where you may break your neck trying to fix it, which is a good thing. However, in this case we have 47 ft^2 of surface area, but only half faces the sun, or a little more if we spread the pipes out to 24 or 36" vs 20" so they shade each other less when the sun is not striking them head on… and we want to collect a typical hot water heating load of 50K Btu/day… How can we do that? The PVC pipes themselves, painted a dark color, might absorb 20-30K Btu/day. How can we collect another 20-30K? Perhaps we can also use them as an air-water heat exhanger… 47 ft^2 of pipe with 80 F water inside can collect about (130F-80F)47×1.5 = 3750 Btu/hr of heat ie 22K Btu per day, if the air around it is 130 F, even with no sun shining on the pipe. >Do you mean the sunspace would be in addition to the shallow box?
I had in mind that the black pipe manifold would be up near the top of the lean-to sunspace. Since warm air rises, we can trap heat up there, stratified hot air, much warmer than the rest of the sunspace. It would be a good idea to put an extra layer of glazing across the top 4′ of the 16′ high x 12′ wide sunspace, on the inside, in front of the black pipes, here – . | . . sun . . . 16′ . . . . 8′ >So the collector for the solar closet would be located at the back of >the sun space?
Yes, if there were one, but then we wouldn’t need the black pipes, just a little fin-tube pipe near the top of the closet, working 24 hours a day… Nick
Response:
>The barrel concept could be used here. Where the barrels were sort of >suspended in the air, or on a cat walk…
Might make for an interesting tension in the humans beneath, since 55 gallon drums weigh about 500 pounds each 
Is there a swimming pool like that in Barcelona, with something huge suspended over the pool…? How would we keep all the heat in the drums at night? Seems like they need insulation around them at night. I’d put ‘em on the ground, so they don’t fall on people’s heads, inside a box with insulation all round, with one side facing the sun, inside the sunspace, and the other sides inside the house, perhaps. A solar closet, that stores heat for the house for several days, and makes hot water with a fin-tube pipe. So… the sun shines in through the sunspace glazing, then thru the 80 F sunspace, then it shines on thru the solar closet glazing, then on thru an air gap containing 130 F air (_not_ the same air as the 80 F sunspace air), where it finally hits the outside of the dark-colored insulation of the south wall of the solar closet, which warms the insulation, which heats the 130 F air, which air passes thru a one-way damper to heat the drums inside the box, and the air returns about 5 F cooler from a hole at the bottom of the box to this air heater, and runs around again. At night, the air damper closes, the fan, if any, stops, the air stops circulating in and out of the box, and the drums are insulated all round. Nick
Response:
> >Instead of running the pipe along the top of the box, how about running it >through a few of the water filled barrels? > Water filled barrels? Where are the barrels? There’s no solar closet here, > altho there could be… This is just a sunspace with a bare water type solar > collector inside, that circulates its hot water through a conventional water > heater on the floor above by thermosyphoning, natural warm water convection… > If all goes well, the water heater heating element seldom turns on.
My mistake. I was thinking of the solar closet idea. – Hide quoted text — Show quoted text ->If you used flexible plastic tubing you could probably loop a couple >hundred feet inside barrels. Run the tubing in an opening, coil it around >the sides and run it back out again. You could hook up several of these >in series and have a heat exchanger that should heat the incoming cold water >much faster than pipes exposed to the air in the box. > True, but if we had a solar closet, it seems simpler to just put 10-20′ of > fin-tube pipe near the ceiling, an air-water heat exchanger that works 24 > hours a day, to heat water in a water heater upstairs by thermosyphoning > again. Seems to me it would be difficult to make water flow through all > that plastic tubing without a pump, and you might have evaporation at the > points where the tubing enters and leaves the drums. If the tubing is in > series with the water heater, which is inside the solar closet, the water > supply pressure could move the water through the plastic pipe, once, but > it’s more efficient to have the water continuously circulate through the > heat exchanger, to make a heat exchanger with a given surface area do more > of a full-time job, rather than have the water only pass through it once.
Okay, why not put the water heater inside the solar closet instead of upstairs? The heater is now in the 130 F room, so you don’t need to circulate water through it in order to keep it warm. The tubing would be connected to the cold water input, so the water pressure provides all the pumping energy. 100 feet of 3/4 inch inner diameter polybutylene hot water pipe from Home Depot costs $60 and would have a surface area of (
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