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Radiant heat back up (5 Posts)
Radiant heat back upI live in central California, outside design temperature is 32 degrees, using a mod-con boiler suppling the heat for a in-floor radiant heating system (26,000btu on demand load) and a 80gal DHW indirect tank. The tank is a Boderus with two heat exchangers. One hx is for the boiler the other is for two 3x8 solar panels. I would like to supplement the radiant heating by use of stored solar water, but I am not sure what equipment and controls I would need and how cost efficient it would be. If any one has any suggestions they would be greatly appreciated.
solar back upHopefully someone more knowledgeable than I will chime in, in the meantime this is a good read and should give you a bit more of a general sense of what would be involved.
Solar thermalYou'll need a lot more panels than 2, to do any supplemental addition to your heating. 2 flat panels can do DHW, but add very little for heating. You'd need 8-12 panels to make any difference because the solar angle in the winter is very low when you need it the most.
a heat load calcis a good first step. Find a load calc form or program and determine what the actual heating load for your building. A rule of thumb is to design the solar to handle 25- 30% of the heat load.
As Paul mentioned you may need more array square footage, to cover much heating load.
Run a simulation with a solar program like T-sol, RET Screen, or F-chart. This will match the load with the solar available in your exact area. You can experiment with different size arrays in the program and look at the financial side of the system.
Remember with larger arrays you will need to consider summertime low load conditions. I like a drainback system to deal with low summer loads, when you start looking at large arry size. You need to use it or lose it with solar energy and you get the most when you need it the least, sometimes :)
The simulation programs also have a module to calculate the dollars and sense of the system you are considering. Doubling the array size doesn't always double the return.
system re-workFirst you want to understand you tank capacity and architecture. You may be able to extract solar input from the boiler coil, but valving and controls could get a bit tricky. Thermal capacity of the tank will determine how many panels it can support, but I'd worry about DHW temp dropping below safe levels.