Unfortunately, I picked the snowiest winter in the last half-century to prove out a solar heating system, so the run time has been less than anticipated! However, when we have sun, the system is producing around 250kBTU per day, which is typically enough energy to heat the guest house this time of year. With multiple sunny days in a row, the high mass of the floor absorbs the heat and slowly releases it back to the living space- so far I have not seen more than a 8 degree change in indoor temperature during sunny periods, and we were able to make it through a cold -30F night without the need for supplemental heat one day last week. Very promising indeed. More later....
Sunday, February 20, 2011
Running on the sun.
The mega solar array has been active for over a month now and I am pleased to report that the everything has been working very well. I designed the barn foundation as a high mass sand bed storage system, capable of receiving the heat from the solar collectors during the day, storing it in the concrete slab/underslab sand bed, and slowly releasing the built-up heat to the living space. The benefit is higher efficiency from the solar collectors (since they are operating at much lower temperatures than a conventional system with tank storage) and it eliminates the cost and space required for the large water storage tank. The downside, however, is not being able to store the solar heat for more than a day or two. I was only able to find a few resources on this method (like here and here), but it seemed well suited for extreme climate areas like ours here at the north pole, where we pretty much need 100% of the heat capacity during the winter months and thus there is no reason to try to store it in a water tank.Here are a few pics of the high mass foundation system during construction, showing the underslab insulation, high mass sand bed, hydronic tubing and finally the concrete floor:Normally, hydronic tubing would be buried in the sand bed as well as the concrete, but here we only have the upper, slab run of tubing...in hindsight, I should've installed it in both areas. The poured slab. The concrete was polished and stained to be used as the finish flooring.