Originally Posted by
airbare
thanks, tipsrfine.
we had plaster walls and a large interior chimney for thermal mass. Those are now gone, so we are trying really hard to eliminate direct solar gain to compensate. I think diret sunlight is the main thermal load here.
thanks to classic,
I ask because I have two very different quotes. One, which represents good ol boy standard practice, would put a 3 ton unit on our 1300 swft first floor, and a 2 ton unit on the 750 sqft 2nd floor, for a total of 5 tons. All contractors but one have proposed this approach, with some refusing to bid the job if I insisted on smaller AC units because they don't want complaints later.
The other quote, which hews closer to HVAC orthodoxy, would install a single 2 ton unit for the whole house and operate as a single zone. A 300 W fan would operate almost continuously to maintain uniform temperatures and comfort. The problem is that a 300 W fan runnin yr round uses 2,600 kWh/yr - which is about 75% of our current annual usage, and that is for circulation only. Actual AC would increase that substantially.
My conclusion, and I'm here to get opinions from people who actually know something, is that:
1. HVAC design orthodoxy makes perfect sense for humid regions, where the AC should run many hours a day to remove moisture and have lower diurnal temperature differences.
2. doesn't make as much sense in arid regions with large diurnal temp swings where a whole house fan or equivalent can provide much of the cooling
I'd be interested to hear from pros in the west to see if they agree.