# solar hot water ????s



## ericjeeper (Feb 25, 2006)

My home is heated with hydronic radiant in slab heat.. I am trying to cut back on my fuel oil consumption.
Here are my thoughts. solar panels.. I found four used 3.5x14foot panels used. for 150 each. and for a storage tank, I am thinking a 1,000 gallon concrete cistern insulated with 4 inche of polystyrene, and burind in the yard. closed loop glycol filled using a 60 foot 1 inch coil of type L copper and it will be teed and on zone valves..
so when the sun is producing heat the differential switch will turn on the pump to circulate only into the tank. If the house calls for heat the zone valve will open and send the glycol on to the house and then return back to the panels.
If the house calls for heat when the sun is not out, only the tank loop will circulate into the house.
if the temps in the tank drop below 90 degrees the loop will not circulate and my oil fired heater will provide the heat.
Ok I am open for all opinions. If in event the solar option does not pull its weight I can always toss another closed loop into the tank and fire a wood fired water heating device/.
Thanks in advance for all who reply


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## WisJim (Jan 14, 2004)

Should work. The possible problem area that I see is burying the storage tank. Any soil moisture working it's way past the insulation will suck heat out of the tank. Otherwise it is a good idea. I would probably use smaller diameter copper tubing for the heat exchanger coil. My son has worked on homes in Minnesota and norther Wisconsin using solar heated hot water for radiant floor slab heat. Usually install a back up boiler or water heater, but the systems work well.


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## Ross (May 9, 2002)

What type of oil fired boiler do you have? Domestic water heater or boiler? DWH are not very efficient space heaters, boilers can need some serious cleaning but are tops for heating when set up correctly. Just a thought that getting the water heater serviced and cleaned is your best first step to gettign the most heat from your oil. (should take 2-4 hours so if it's not taking that long maybe you're not getting good service) If you're using a DWH for heat you can't T in a glycol system easily as it's likely supplying your potable water too. Adding in a solar collector as you describe sounds great, but check you local building code for the gycol containment it's a reportable environmental hazzard if it leaks. They can get nasty about underground containment in some parts. And it's your well you'll poison first so you want the best design and seal system for that tank anyhow! Where approximately are you located? It'd help the solar experts is all.


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## Jim-mi (May 15, 2002)

Here is a link to a book I would highly recomend to any and all who want to do solar hot water;
........[email protected].......
Tom Lane has been doing SHW since 1977? and has gotten the hot water guru kind of reputation. The book is pricy but its got all the info you will need for a water system.

eric, go for it, put those pieces together and then tell all the people you can......."See..it does work"


ps I shure wish that I had gotten the color edition rather than the black and white. The diagrams would be easier to follow if they were in color.


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## ericjeeper (Feb 25, 2006)

answrs. yes it is a Bock water heater. 
No well on the place.
30 miles south of Indianapolis Indiana
The water table is fairly low.. as in no where near the surface.
Tank guy suggested I set in on a number 11 bed of stone in case any water would get in the hole that it should settle into the one foot of gravel.
Thanks for the replies.. I have to head out the door for work.


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## Ross (May 9, 2002)

OK so there's a problem, your domestic water heater, is likely supplying the potable water system as well so you can't circulate glycol in the same loop. You could disconect the DWH and run the radient floor heat on the glycol tank and then route a coil from the DWH to the tank to suppliment the solar. Or as you said ad a wood heat source instead. I guess you could add a seperate coil for that too but the cost is starting to add up. If you were using an oil fired boiler rather than a DWH you'd see substantial savings there alone! DWH and radient in slab heating is about the least efficient method of turning oil into useable heat. Oil fired DWH generally only run 75% eff for large volumes of domestic water heating (which is still terrific compared to gas or electric) but using it as a combo heating system drops 7-10% off that. Start with a boiler running close to 90% efficiency and you're 15% better off to start and in all honesty it ends up alot higher than that because of a higher deltaT and even faster recovery rate. Just a thought the is your current DWH and radient loop using tempered water or is it metered through a manifold directly from the heater?


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## SolarGary (Sep 8, 2005)

Hi,

Thats a great price on the solar panels if they are in OK shape. About $3 per sqft compared to about $25 per sqft for new commercial ones!

Radiant floor heating and solar go well togehter, because the radiant floor heating can make use of low temperature water (like 90F), and solar collectors are much more efficient operating at these lower temps.

The RadaintTec site has quite a bit of info on radiant heating installations, including some solar ones: http://www.radiantcompany.com

My site also has some info on solar/radiant systems here:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm
Just look down the page for the radiant stuff.

The 1000 gallons may be more storage than you need. The storage size depends on how much collector you have, how sunny it is where you are, what the heat loss on your house is (ie how long it takes your house to use up the heat from a sunny day), and what temperature range you run the storage through.

I am working on a similar system, and I am ended up making the tank about 500 gallons. For me this works out to being able to store about one full sunny days worth of sun in the tank. I have 240 sqft of collector.

If you have around 3.5*14*4 = 196 sqft (maybe 180 sqft net?), then on a sunny day you might collect:

Heat collected = (180 sqft)(1500 BTU/sqft-day)(0.5 efic) = 135000 BTU/day

This would heat up a 1000 gal tank by:
Temp rise = (135000 BTU)(1 BTU/lb-F) / (8200 lb) = 16F

or, a 500 gallon tank by 32F

For my house, the heat loss is large enough that I will use the heat in the tank over the night after the sunny day and a part of a next cloudy day, so (for me) I can't see putting in a tank that is much larger than 500 gallons. 

You might want to try and do a heat loss calc on your house, and see (for a typical winter outside temperature) how it compares to the 135K BTU you would collect on a sunny day. If it turns out that your daily heat loss is around 135K a day, then it probably does not make a lot of sense to have a tank that will store more than this one sunny days worth, but if your daily heat loss is lower, then a larger tank could store enough heat to carry you over more days. 

I am going to make my tank by 1) excavating a hole in the ground about 3 ft deep with angled sides, 2) putting a wood "curb" around the top, 3) lining the whole thing with 4 inchs of rigid foam, 4) installing a liner made from EPDM rubber sheeting ($0.5/sqft), and 5) closing over the top with a cover that is made like a SIP. I think this will work, but have not tried it except on a much smaller version. 
http://www.builditsolar.com/Experimental/InWorkshop/SolarShed/solarshed.htm

Gary


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## ericjeeper (Feb 25, 2006)

Ok my heatloss on the house is 27k Basically it is very tight, and very well insulated for 3200 feet/. walls are R27-28 ceiling is R-58-60
as for the water heater trying to heat the solar loop, that is an issue yes.. will just have to figure out how to put in some brass bypassing valving.. Once I find out if the solar works then I can take the water heater out of the loop. I do not expect the solar to get hot enough to get the stored water up to 140 degrees. maybe I am selling solar short.
as for the 1,000 gallon tank it is the smallest this outfit offers..I am not sure if they would custom build me a 500 or not.. I just figured I did not have to fill it full 500 gallons will be more than enough to keep it from floating out of the ground,
as for a high delta T on my radiant the way I am pumped and valved I am right at a 12-15 degree delta tee.. Of course if all loops in the house were to open at once.. which to my knowledge has never occured The delta T might be quite a bit higher.
Question about the use of smaller copper for the Loop? what will that gain me? Other than save me 50 bucks on copper? I am pretty sure he said the panels were piped with 1 inch ins and outs.
Thanks for all the replies


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## Ross (May 9, 2002)

Wow 27,000 BTU heat loss?? No wonder they hooked up a water heater! Excellent insulation but I'm thinking you're south of me in Ontario, correct? Once you use the loops for glycol you can't use your water heater again, so either hook it up to the solar and disconnect the DWH or don't. I was wondering if the loop got tempered 120 degree water or heater 140 degree water. Could be a minor plumbing issue adding cost. Doesn't really change anything with adding solar, you still have the glycol contamination problem. You could keep the DWH in the system by adding a heat exchanger to the glycol solar tank as you're planning to do with the wood heat. I'm glad Gary mentioned the tank size, I assumed it needed to be that big for the solar collection. Could half of the 1000 gallons be filled with something that works with the glycol to store heat? A particular stone or ?????? Glycol isn't cheap!


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## ericjeeper (Feb 25, 2006)

sorry for the delay , Had to attend a choir recital. Ok my current heating system is already glycol Using a double wall heat exchanger . I have a bronze taco 007 pump recirculating water from the water heater through the heat exchanger.And I have an 013 bronze that circulates the glycol through the floor via the heat exchanger.
So basically the glycol in the panel will be the same glycol that flows through the floor loops too.. The way I am thinking is.. The glycol will pass through the heat exchanger using the 013, but unless it is not above the temp of my hot water, the 007 will not come on.. so the glycol will basically just heat the heat exchanger as if it were a regular piece of pipe.
The tank will be full of regular water. no antifreeze, 
If the tank temp does ever surpass the water heater low limit I can use a differential switch to turn on the 007 and heat the water heater tank. Thanks.. I am learning from everyones input here..


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## Ross (May 9, 2002)

I was thinking the solar panels might need the glycol, if they don't then its sounding better all the time! I still can't get over your heat loss, my house is around 2300 sq feet (that's heated with oil) and the heat loss is 5 times yours! I'd heard DWH combo systems were used lot more in the USA.


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## Jim-mi (May 15, 2002)

Have you considered a drain back system so that you don't need glycol ... ?
My system will be drain back ---


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## ericjeeper (Feb 25, 2006)

What is it against glycol? The potable water system is protected by a double wall heat exchanger . I can see no reason to ever take a chance on the panels with water.Plus the loop will be pressurized, tied into my expansion tank and also will incorporate a air vent at the highest point on the panels.


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## Ross (May 9, 2002)

While propylene glycol isn't especially toxic, glycol is an environmental hazard if it leaks (could raise your home owners insurance substantially) its very expensive, even by the barrel, and it's harder to keep entrapped air out for your circ pumps (you get more cavitation even using microbubblers). Its really a cost thing with me but it's still a good choice.


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## Jim-mi (May 15, 2002)

Yes glycol is pricy. Nothing against it.

After reading from those who have been there done that I decided to go drain back---which doesn't need glycol.

Although ...I might put a small amount in the collector loop...........just for kicks.


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## SolarGary (Sep 8, 2005)

Hi again,

I am wondering what the 27K is?
Heat loss in BTU per day, or heat loss in BTU per hour at some temperature difference?
Can you say a bit more about what it represents?

It does seem very low. The heat loss on my house is about 400 BTU/hr-F, meaning it losses 400 BTU each hour for each degree F of temperature difference between inside and outside. So, on a day with an average outside temp of 30F, the day loss is about (400 BTU/hr-F)(24 hrs)(70F-30F) = 384K BTU per day. While my house has a lot of window area, it is well insulated and about the same size as yours, so it seems like a big difference??

How hot the storage gets on a sunny day depends on the collector area and storage size. If you put in a small storage tank, it will get very hot -- maybe 180F or more, but this is not a good thing, as the solar collector will be very inefficient at this high temperature. Its good to have enough storage so that the storage temp gets hot enough to be useful, but not so hot that it reduces the collector efficiency.


Gary
www.BuildItSolar.com


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## JAK (Oct 15, 2005)

Mine works out to the equivalent of R10, and is 1400sqft, no basement, with 4000sqft of surface area. This works out to 400 BTU/hr-F also, but is probably a smaller house. So I'm working on some ideas to save energy.


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## ericjeeper (Feb 25, 2006)

actually I just went back into my documents the heatloss is 21,158 BTU/hr at 10 degrees outside temp


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## SolarGary (Sep 8, 2005)

ericjeeper said:


> actually I just went back into my documents the heatloss is 21,158 BTU/hr at 10 degrees outside temp


Hi, 
So thats about 380 BTU/hr-F -- a bit less than mine.

With your 200 sqft of collector, the 1000 gallons may be somewhat more than you need, but, as you say, you don't need to use the full volume of the tank if you find it just does not run hot enough to be useful. Probably better to have too much than too little -- especially if you arn't really paying any extra for it.

Gary
www.BuildItSolar.com


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## ericjeeper (Feb 25, 2006)

I am not concerned about getting enough heat for domestic hot water if I do in the summer that will be fine.. But for the winter months it is the heat that I am aiming to help out. So if I can get the tank to 90-100 degrees I am basically heating for the few amps it takes to run the pump.. 
I honestly feel that the power from the sun is the only fuel source that the price is not going to jump up on. Thanks to all that have replied with opinions..
I will be sure to keep everyone informed on the energy performance.


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## Jim-mi (May 15, 2002)

[. 
I honestly feel that the power from the sun is the only fuel source that the price is not going to jump up on. 

Boy oh boy ain't that the truth.

Now we gotta get many million others to wake up to that fact.


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## mightybooboo (Feb 10, 2004)

Jim-mi said:


> [.
> I honestly feel that the power from the sun is the only fuel source that the price is not going to jump up on.
> 
> Boy oh boy ain't that the truth.
> ...


Ditto.

BooBoo


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## raymilosh (Jan 12, 2005)

I have a few thoughts about your idea...
Everyone seems to think it sounds valid. I think so, too. Keeping moisture away from the tank is key. Tank companies also sell smaller tanks on the order of 500 gallons as pump tanks. It should be easy to find the size you want.
Regarding using coolant in the tank and the collectors, I'd recommend it. I built a water based one for a neighbor. They wanted it simple, non toxic and thermosiphoning. They had to drain it every freezing night. Turns out that the thing can freeze at ABOVe 32 degrees F. It cracked after a a few freezes. I'll be upgrading it with a glycol heat exchanger before next winter.

I wonder if a copper coil is adequate for picking up enough heat out of the tank. I collected "radiators" from airconditioners to use to immerse in the tanks of glycol. (I haven't yet built this system). Lots of surface area, free, capable of holding pressure(if you have a pressurized system of potable water) and connectable using epoxy and copper tubing. 
I have read that thermosiphoning is forceful enough that the tanks can be at or even slightly below the collectors. With my limited experience with thermosiphoning wood heated water, I would bet you a cup of coffee that it would work. I'd recommend you at least set up an experiment to try it. You may save yourself lots of time, piping, plumbing, pumps, etc. Try placing the collectors on the ground near the tank hook them up , angle them properly and see if they will thermosiphon. If not, nothing lost.


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## ericjeeper (Feb 25, 2006)

the panels will be tied directly into my heating system.. The glycol that flows through them will be the same glycol that will eventually flow though my floor. 
I have it figured that when the sun is shining(panels are producing) and my floor calls for heatthe glycol will be pumped from the panels through the loop in the tank and then into the house.
When the panels are cold( no sun) and the house calls for heat a zone valve will block off the panel loop and let the glycol bypass the panels.. and will pull only heated water from the tank.
If the water in the tank drops below 85-90 degrees that zone will entirely drop off and the fuel oil fired water heater will take over.
so basically the antisiphon feature will not be to any avail

The tank will have only plain water.. the glycol will stay inside the tubing.
as for enough area.. an old radiator of some sort might give me some more surface area..and save me some dollars on copper too..Thanks for the input
BTW the septic tank/cistern company did not offer a 500 gallon tank.. I might call them and see if they could specially produce one for me..


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