The Hissing of Summer Air Conditioners

My relationship with air conditioning is ambivalent.  I grew up in Minnesota, and my parents didn’t get AC put into the house until I had graduated and was “away” at college.  Consequently, I endured many hot, sticky nights with the windows thrown wide and (occasionally) a fan to blow the already-saturated air over my sweat.  My brother and I loved going to movies in the summer, because the air in the theater was cool and dry, and because (in those days) the theater wouldn’t clear the seats between shows, and we could sit in that wonderful air for large parts of a day without interruption (someone should ask me how many times I’ve seen the Trinity series).  I got used to the idea that paper became limp with humidity in summer.  Just the way it was.

When I got my own apartment (while in college, and still in Minnesota) it was on the 12th and 13th floors (yes, really) of an urban building.  In the 12th floor living room, there was a window-style AC unit that passed though one wall.  All summer that thing hummed along, making the living room a place of (loud) refuge, while the bedrooms upstairs sweltered.

Years later, my spouse and I had a first house, in upstate New York, that had a similar arrangement but with the AC on the second floor, with the bedrooms, and nothing below that.  One particularly hot and humid summer, though, we set the AC to max, put a deflector in place, and slept in the dining room, because the temperature under the roof was just too high.  When my spouse had her last pregnancy–in that house–some good friends insisted that we borrow their AC unit for the downstairs, and we did.

As we got newer and nicer houses, whether in the NorthEast or the Midwest, AC became a larger and larger part of our lives.  I still had the ’91 Honda Civic that I had bought explicitly without AC (and also without power windows or an automatic transmission) but for our later purchases, like vans, AC was a must.  Our houses, with vents for forced air cooling, were of course also air conditioned.  When we built the last house we owned prior to this one, AC and an air exchange system ran all the Wisconsin spring, summer, and if warm, fall, taking humidity out of the air.  Opening windows was, well, pretty much unnecessary.

Still, AC troubled me.  AC works this way:  you run a machine that uses power to cool the air in your house.  Cooling that air means that heat energy has to be extracted from it.  Let’s say you manage to extract A amount of energy from your air.  You then blow that air back into the house, where it is reheated, and re-cooled, and so on.  The circle of life.  Only the heat that you extracted, A?  It has to go someplace.  So we pump it out into the outdoor part of the AC unit and it floats off into the atmosphere (or rather, is blown off, with a fan).  This in turn raises the outdoor temperature by a little.  A very little, because there’s more air outdoors (much more!) than indoors.  But it happens.

But that’s not all!  The machine that cools the air?  It is less than 100% efficient,  How much less, I don’t know, but we do know that because things like electric motors (the compressor and blower parts of the system) are less than 100% efficient, they generate waste heat.  So that’s going to go into the air in the house (and outside) and will also need to get pumped away.  We’ll call this B.

Finally, though, remember that all of this runs on electricity.  And electricity comes from–that’s right–hydropower, or burning fossil fuels, or nuclear power.  Some from direct solar, but that’s rare–as is hydro in much of the US.  Most US electricity is fossil-based.

(image stolen from here)

OK.  Now we also know that power generation and transmission are not 100% efficient.  There are heat losses there, too.  So let’s call that C.

This means, finally, that when you cool your house by removing an amount of heat A that you are warming the atmosphere by amount A+B+C.  The same principle applies in your car.  In other words, when we try to make ourselves more comfortable, we are making our planet an inherently less comfortable place to live.  Oh, and let’s not forget that energy transfer works best when there is a large difference between the temperature of two objects a and a’, where a could be the outside AC unit and a’ could be the air.  So the hotter it is outside, the less efficient air conditioning becomes.  And so on.

This is not good for any known value of the word “good.”

So I was very happy when I managed to persuade my spouse that maybe, with all the trees around, we might be able to get by in our new house with running the AC a little less often.  Other factors contribute to this:  using LED light bulbs, which are around 30-40% efficient, instead of incandescents, which are more like 5% efficient.  that sort of thing.

This morning, we woke up in a house that was a little sticky (it rained heavily, off and on, all night) but with the windows open.  And we heard–from outside–a few AC units running, but mostly, we heard the birds in the trees around our house and those of our neighbors.

I have this idea that in communities where people leave their windows open, they might even behave a little better, because they know they are not isolated, but members of the community.  We’ll see.  We’re new here.  And when it gets ugly in August, we likely will dive for the cooling switch on the thermostat.

But I do know I prefer the songs of birds to the hissing of summer air conditioning.

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