Summers in Massachusetts are easy in comparison to winters. Some people (myself included — a bit) saw air conditioning as the devil or something.
I’m not sure why. When it’s 98°F outside, and 78°F inside (a typical setting) — especially if you live in a house with three times as much insulation as a typical new house — it takes hardly any energy to cool the place. The temperature differential between inside and outside is only 20 F°. And the house is well sealed, so there is not much chance for the basement to get damp. I don’t need a dehumidifier running 24/7 as in a typical New England house!
In winter, the delta-T is bigger
And compare this 20 F° temperature difference (in/out) to the difference on a very cold winter day or night. Let’s say it’s 0°F outside and 70°F inside. That’s a 70 F° difference, so obviously there is going to be a lot more energy needed to maintain that inside temperature.
Our house has a Mitsubishi ductless minisplit system. We have one outdoor compressor serving four indoor heads, with one head per floor (basement, 1st, 2nd, and 3rd floors). We had the AC on a bit yesterday (when the outdoor temperature was around 90°F) and that cost 24 cents. We only used 1.6 kWh. That’s less than having the heat on for an hour when it’s 0°F!
We should feel a lot more guilty about all the energy we all use to heat our house; AC is nothing in comparison!
Our HRV keeps the indoor air fresh
During the summer, we open our windows at night, as long as it cools off and we’re not suffering from 100% humidity. And then in the morning, we close up the house and dry things off.
I find that our house is more comfortable (IAQ-wise) than other air-conditioned houses I have lived in because the heat-recovery ventilator (HRV) provides fresh air into the house, 24/7, no matter the weather. This happens even on days when there is no temperature difference to promote the stack effect, or any wind to drive air exchange.
Whereas with other houses, sometimes when they are closed up for a day with AC on, they feel stuffy.
PV arrays prefer cold weather
On another topic: I’ve noticed that our photovoltaic (solar electric) panels are much less efficient in the hot weather than in cold.
On cool but sunny spring days, our system (comprised of 30 panels, each rated at 200 watts) peaks at 6 kW (power, instantaneous). In the hot summer months, on the other hand, we peak at something like 5 kW. But during the summer, there are more days of sun and more daylight (especially around June 22), so we still generate more in the summer months because of that.
Our system would occasionally go just barely over 6 kW — except that we have M190 Enphase microinverters which top out at 199 watts, so the very most we can make is 5,970 watts. And then the curve goes flat for a few minutes around solar noon before it goes down again.
Erik Haugsjaa is a software engineer living in Massachusetts. He likes to blog about superinsulation, solar panels, and democratic schools.
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