Johnnojack - I have been very impressed with northern US and Canadian houses which build whole house on a couple of metres of super insulated compacted (not compressed!)rock. They have hydronic heating pipes in the bottom and they use solar heated water to store heat in the hundreds of tonnes of mass during the summer. The heat gradually rises and it keeps their slab warm all year.
I didn't want to do anything that elaborate and in any case our subsoil temperature is about 14 and theirs is about 7 so we don't need it as much.
Anyway, I used 30mm XPS foam on base then laid 150mm manifold each end and ran 8 lengths of 90mm aluminium irrigation pipes between the manifolds. Then I filled it all up with a weak concrete made from road base and cement so there is very little entrapped air. At this stage I just have the inlet and outlet 150mm pvc coming out of the slab where built in cupboards are planned.
Eventually there will be a solar air heater (about 20 sq m) on an adjacent garage and air will be ducted all along southern wall for distribution to rooms and/or the under slab heater. Air won't be recovered for entry back into the solar heater as it's not cost effective and having a little positive air pressure inside will reduce cold air ingress plus give more distribution options. On winter days of good solar gain, direct sunshine through northern windows should mean that a lot of surplus heat can be directed under slab to be enjoyed after dark.
The under slab mass could also be heated in autumn to help through the cooler nights that are common near Canberra. It is easy to get 40 degree air out of a solar air heater so the slab could get up to 25 degrees with a bit of luck. If so, we have the option of using some water filled seats to harvest and store even more heat in that area.
It might not be very effective but it's pretty cheap fun!
Cheers
Posted Wednesday 29 Apr 2015 @ 7:16:18 am from IP
#