I got a question this weekend that’s often asked — and, I’m sure, wondered about — by homeowners: “Will my household AC system run more efficiently (perhaps cycle on/off fewer times, or the compressor won’t have to run as long when it cycles on) by shading the compressor?”
I’ve written about the outdoor unit of air conditioners and heat pumps a few times, but I’ve never tackled this question directly. Let’s change that now.
Why this is a natural question to ask
First, a little explanation about air conditioners. If you have a split-system air conditioner, that metal noisemaker that sits out in back or on the side of your house is called the condensing unit. The compressor is one component in that box, but the condensing coil and a few other parts are there, too. (To understand how an air conditioner works, see my article, “The Magic of Cold.”)
The condensing coil’s job is to dump the heat picked up inside the home to the outdoor air. (If you have a ground-source heat pump, that heat gets dumped into the ground rather than the air, and you won’t have an outdoor unit like the one shown above.) The hotter it is outdoors, the harder it is to dump that heat and the more you’ll spend keeping your house cool.
Hence the question: Can shading your air conditioner’s outdoor unit provide significant savings? The answer is yes and no. It depends on what type of shading we’re talking about, but for the type of shading most people are thinking about when they ask that question, the answer is no.
Why the answer is mostly no
Shading the outdoor unit with a structure as shown in Image #2 (below)…