Cooling thought experiment
My house works like this, century old balloon framed poorly insulated home. I have calculated that each degree uses about 5kWh of energy, 5kW to heat the house by 1 degree Celsius with the natural gas furnace and 5Kw of energy removed per degree with central air. I have done these experiments as best i can to control for time lag in heating and cooling of the mass of the building and have taken efficiencies and outputs into account. So for this thought experiment lets assume its correct. If its not the magnitude will change but not the concept.
Also i have found that a heatwave of 35ºC outdoor temperature will add about 5-6ºC a day to the indoor temp or about 25-30kWh of heat. This scales roughly linearly, less temp will add less per day and even on days its the same temp outside as inside will add some heat because of solar gains through the windows and walls and ceiling. Obviously i can reduce the heat gain with better insulation, another question will be about my attic insulating problems so i don’t want to address the house’s shortcomings here.
As an aside what i currently do is run exhaust fans at night when its below the indoor temp cool the house down to a goal of 22ºC, let the house temp rise during the day to 25-27ºC and the next night repeat, but use the central air on nights when its not cool enough outside to cool the house appreciably. I reduce my central air use maybe 50-75% this way.
Lets say the goal is a comfortable 23ºC but some oscillation is acceptable, say 2ºC so 21-25C is acceptable.
Central air will keep the house cool during the day at high energy cost. Then at night the temp often falls below the indoor temp.
At night the outdoor temperature often runs to 15-20C. Not always of course.
Would it work to have a thermal mass that can absorb say 30kWh of heat and then discard it outdoors at night? Say a concrete block in the basement that has water or air tubes running through it so during the day the internal gain is dumped into the thermal mass and at night cold outdoor air “recharges” it with coldness?
On nights where it does not go below the indoor temp no recharge will be possible and the central air would have to cool the house and wait until a night when its cool enough to recharge and the earth could also provide some nice cooling to the mass. Probably best to thermally separate this mass from the house as well because in winter it will suck heat out of the home. Say R20 of foam on sides that face indoors.
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