Thanks Guys. I did leave out a few points.
I'm in Melbourne. I tried working out what I needed by adding up the U's and R's and areas, assuming a worst case of a 20 degree temperature difference and end up with heat loss way less than any house sized heater/cooler.
Perimeter of house is 76m, 3m high ceilings gives 228 sqm for the walls, take of 49 for the windows. Leaves 179 sqm of walls. Assume 180 and R of 6 for simplicity, give Uw x A of 30 for walls. Round Uw of the windows to 2, and area to 50. To get Uw x A of windows of 100. Round roof to 250, round insulation down to 10, to get Uw x A of 25, for a house total of 155. Assume 20 degree difference gives a max of 3100W.
Problem is I don't know how to model the heat loss/gain via by convection. Rendered panels have very low air infiltration. The windows are all casement, so well sealed. So left with the front door, which will be sealed also, so Pessimistically I can't see myself losing more than 50% of the 3100W lost by conduction.
As for radiant loss, I'm not too bothered about cooling in summer, more than cold winter nights, when all curtains/blinds are shut, so can't see a lot of radiant loss then. So really can't see why I couldn't get away with 5KW for the entire house. But that seems pretty low for a 4BR house. I'm in an old poorly sealed double brick 2BR house, and the 14KW gas heater can't keep up on really cold nights. Find it hard to believe plastic walls and extra glass can more than halve that in a house double the size.
Enough rambling!
Looking at the efficiency side, the best 2KW split systems have COPs of 5.5. The bigger whole house units hit around 4. So looking at the alone, I'd be best with an independant split system in every room. Being less convenient would also make us turn it on less often as well. Aesthetically they're butt ugly though, compared to some non-descript vents in the ceiling. I'm leaning towards 6 split system units, but the wife wants ducted.
Anyway, I do ramble. Appreciate the responses.
Posted Sunday 17 Jun 2012 @ 9:40:59 pm from IP
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