Home a/c systems – Why is it more efficient for it to run continuously a couple of hours rather than cycling on/off so often?

Question

For the sake of argument and discussion, let’s use a perfectly matched, balanced, and calibrated R-410a home a/c system as an example.

Why do folks say it’s more efficient for said home a/c system to run continuously for 2 hours and then off for 5 minutes instead of cycling on/off much more often to achieve the same interior cooling setting on the thermostat? (I understand how home a/c system work, but I’d like to know why some say longer run times = greater efficiency.)

I’ve heard this claim time and again, but I’d like to know the science behind it. I live in Texas where a/c units run for hours during the day from June through September.

In: Engineering

Answer 1

Part of it is size, a more powerful unit that could cool faster would cost more money to build. Also, a larger unit would have larger coils and more refrigerant that’d have to cool before starting to cool the house. The first little bit after your AC starts, it’s just cooling the AC system down enough to really start working. Then you have to run the fan after the AC cuts off to extract all the cold from the already chilled AC system. Another part of it is humidity control. Longer cycle times tend to remove more humidity, making it feel cooler.