Are these calculations wrong?
Hi all; we’re building a 2300 sqft ranch with a basement for a total of 4600 sqft of conditioned space in climate zone 4-A. The slab is 4″ concrete with R15 under it. The foundation walls are 8″ concrete with R15 against them. The rest of the walls are aerated concrete with insulation for a minimum of R21.5 – 11.5 for the block and another 10 for the foam. The windows have a low .20s U-factor and a SHGC of .26. Most of the windows face East with a few facing West and North. There is only one small South facing window. We will be using an ERV for ventilation. We are doing our best to make the construction very air tight and I think we’ll do pretty well in that regard though not spectacular.
We paid a company to produce load calculations for us (at a lot higher price than I’d expect) and this is what they delivered:
Total Heating Load: 57,564
Total Cooling (Sensible) Load: 54,838
Total Cooling (Latent) Load: 17,108
Total Cooling Load: 71,945
The problem is that pretty much everyone involved in efficient construction from the the county plans inspector to a GC specializing in AAC thinks this seems too high for our house. This works out to effectively a 6 ton system – it’s not huge but it’s pretty good sized system for sure.
Ideally, I’d be able to use a single outdoor condenser and four interior units – two horizontal 15k heads in the basement and two 15k ceiling cassettes upstairs. That would let me use something like Mitsubishi’s MXZ-8C60NA (60k BTW 2-8 zone unit). If I need to be all the way to 72k BTU then I’ll probably need two exterior units and the heads get trickier.
Anyways, that’s my question – do the numbers feel reasonable to you experts or do they seem high to you as well? Thanks in advance!
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