Ramblings on thermal mass, AC and window fans
This is isn’t really a specific question so feel free to offer random thoughts
I live in a century old home (700 sq ft) with plenty of thermal mass (vinyl siding, wood siding, true 2×4, 1.5-2in thick barnboard, plaster, lath, more plaster), traditional attic, little insulation (no basement, loose fill cellulose and single batts in attic rafters), the windows are double pane ~7 year old vinyl but i could not find out if they have a low SHGC coating or R value (e-mailing the company was not helpful, they could not tell me) and the house has lots of air infiltration (~15ACH50, much from half basement/half crawlspace). I’m upgrading as funds and ability allow.
I try not to use the central air because its a decade old 1.4-5(?) ton 10SEER unit, but being near Toronto Ontario we have had a heat wave the last few weeks. So what i try to do is cool down at night, since our electricity is near 20c/kWh even off peak. What i have noticed is that it takes about an 1-1.25 hr to reduce the temp by 1C (2F) which also reduces humidity 5-10%. It never seems to go below 50% humidity even after 4 hours of A/C. So I’m assuming that 1C has 20,000 btu or about 6kWh (rough calculation). Agree?
The A/C unit uses about 1.8kW while running according to the whole house energy meter, of which 0.4kW is the ECM furnace fan (running on full, when heating its 0.1kW on low fire, 0.2kW on high fire and 0.4kW AC)
If starting at 25C on the hottest day of about 35C outside the temp will go up to about 30C by the end of the day. With 32C which we have had multiple days 24-25C going to 29C
If 6kWh/ºC is correct that suggests the house is gaining about 30kWh of heat on very hot days
I have found window fans work poorly, but they also seem to be low CFM. At a 5C differential 2-3 hours gets me 1C of reduction. They don’t have a rated CFM, I would hope my ~10 000cf house would be coolable with a powerful enough fan, but to match the 1C and hour how much air flow would i need?
If someday i got an HRV could it somehow work at reducing summer temps, because at night i would want lots of cfm coming in to cool the house with no heat exchange