solar heating storage questions

walt1122 · 06-09-2010, 08:35 PM

Hi all, Have 4 older solar hot water heating panels. I got them second hand with most of the pumps and heat exchanger. Planning on doing a ground mount installation at our Tennessee home. What I'm thinking of doing is to put in a storage chamber consisting of a space about 12 X 20 X 5 deep filled with 3 inch rocks and piping to allow me to store the surplus heat generated from the panels operation and use the warmed air to supplement our heating system. The space will be made up of cement block and faced with 2 inches of rigid foam insulation R-12. This space will be covered with same rigid foam and then a couple inches of concrete then we will make a 3 season room on top of that. I just don't know how effective the panels are and if they will perform as I hope. Does anyone have any experience with solar panels and or know where I can get information/calculations/formulas that might help me to figure out if I am way off base and have to high an expectation regarding the system capabilities. We are building a two story deck on our three car garage that has a apartment above anyway (need egress from second floor in case of a fire. We have to go through garage to get out currently) so I just thought I could incorporate the storage chamber but it does add considerably to the over all cost. I need to determine if it is worth all the additional expense.

sorry for being so long winded but trying to give enough info.
thanks

Walt

Yoyizit · 06-09-2010, 08:44 PM

The size of your panels and the solar insolation for your area determines the average output of the panels, and the avg. heating req'mt for a house is 2 to 10 BTU per sq. ft. per heating degree day.
The heat storage capacity, i.e. the specific heat, is determined by how many sunless days you need to get through.

I've seen uninsulated stone structures in German houses built around an oven for smoothing out the day/night temp. differences. Possibly they occupied two cubic yards, but the whole of houses in Germany is designed to take advantage of heat storage.

walt1122 · 06-09-2010, 09:05 PM

Hi Yoyizit, thanks. I don't have any details on the performance of the panels and guess i can search the web for info to determine how many sunny days and or temp ranges. Just thought I could pose the question here and see if others have had similar issues or have more knowledge on the subject. I too believe in using mass to temper temperature extremes. We were told we were crazy to insulate our house in Tenn as well as we did. But I beleieve it is well worth the up front cost cause it lessens heat loss and cooling loads.

Walt

Yoyizit · 06-09-2010, 09:14 PM

I think Scuba Dave is using panels, as we speak.

Scuba_Dave · 06-09-2010, 09:48 PM

Yes, I have (2) 4x12' solar hot water panels
I am using one to heat a 450g hot tub to ~106-108
When I had both on the tub it was exceeding 114 degrees - in early May
I took the 2nd panel & I'm using it to heat a 2nd hot tub out by the pool

I found one persons results online that was heating a 3,000g tank of water in his garage & using the mass to heat his house - using coils in the water for heat exchange

I may take both 4x12 panels & see if I can use them somehow this Fall
But for now it was a quick & easy way to put them to use
And my electric bill has dropped quite a bit

walt1122 · 06-10-2010, 08:20 AM

Hi Scuba_Dave, that sounds pretty good considering your location. I was able to get a little information from a web search that seems to suggest that warm air storage using rocks may have some undesirable consequences. They say there can be problems with mold and/or bacteria. Cool moist outside air mixing with warm rocks is perfect breading ground. I want something I don't have to worry about so I'm not sure this is the way to go. I have avoided looking at a big storage tank for the same reason that there can be issues with algae growth. Knowing that water is a better heat storage medium I am now leaning more to using it. I'm trying to find out how much a septic tank costs. I wonder if it is worth buying a couple of them, place them together and make this the foundation for our deck? Instead of a concrete slab just use some pressure treated plywood and then cover with brick? Give me access just in case. Anyway, hope the new project goes well but until then...leave a place for me in the hot tub.

Walt