Sorry to start yet another thread on this topic, but I've been asked to help someone build a demonstration system to use a solar water heater to provide space heating. I've read all the other threads and fully appreciate that such a system can't provide enough energy (with a reasonable sized collector) to heat a whole house, esp in cold climates. But we're talking Perth here so not too cold.
The location is a shop so there's no need to store the collected heat in a tank - we just want to collect it and pump direct to a radiator as soon as the water is hot enough. We will probably point the ET tubes north east to get early warmth and have them almost vertical - perpendicular to the sun. The area to be heated is on the opposite side of the house (SW) so using water will make transferring the heat easier.
I wanted to do some calculations to see what the feasibility looks like. The runonsun website has some great information on components, especially a 30 tube collector($1500) and suitable radiators. The site owner has even provided me with the full German test results for the collector, specifically to answer my question about the absorber area (2.3sqm), as well as heaps of other helpful suggestions (sorry if this sounds like an ad but I have no connection with him).
I have data tables that tell me that a 1sqm, vertical surface, facing east, in June in Perth will potentially collect 7MJ over the whole day. So the ET array will potentially collect 2.3 * 7 = 16 MJ.
The heat capacity of air is about 1 kJ/(kg C) and also about 1 kJ/(cum C).
Using E = Cp * M(or volume) *deltaT, we get that ....
Volume * deltaT = 16000.
ie for a small room, 4x4x3m which is about 50 cum, the deltaT would be 320C which sounds excessive. I know I haven't considered any losses here but other than that is there a mistake ? Also I appreciate that when we pump the hot air in, it will also need to heat up the contents, walls etc and the thermal capacity of those could far outweigh just the air contents.
If we were heating water with Cp of 4, then mass (or litres) * deltaT = 4000
so we could heat 100litres by 40degC or 200litres x 20C, which sounds reasonable for such a big ET array.
So is the big issue with trying to estimate room heating that the air is only a small component of the total heat load ?
