Simon Says wrote on Jul 4, 2024, 17:41:
And when you're not home, it's useless to...cool a house, shut it off and turn it back on when you arrive.

This is terrible advice. Do not do this if you live in a high heat and/or high humidity environment. This is a fast way to kill components before their rated lifespan and a great way to ensure that you develop a mold problem.

Let me explain.

At the very best efficiency and running at full rated capacity, your AC unit can drop the temperature 10 degrees in the first hour (all measurements are in Freedom Fahrenheit, not Commie Celsius). After that, you can expect a 2-4 degree drop and that is with the AC running at full blast with a clean air filter, perfectly sealed ducts, clean coils, and an unobstructed and well ventilated condenser. However, most people don't have an AC unit running at peak efficiency. Average is about 74% efficiency. So your central AC unit is going to be working harder for longer. If you add humidity in to the mix, your efficiency drops like a rock because not only does your AC unit have to cool the air, it also has to run the evap cycle at full tilt, too. Dense, humid air is incredibly difficult to dry and cool so it sucks up a lot of electricity and slows the temperature change cycle.

Other factors like insulation, which almost universally sucks in most homes, are also going to slow down the cooling process.

Keeping your AC pegged during the day to a consistent temperature actually uses less electricity and causes less wear and tear on your HVAC system because the HVAC system only needs to maintain a pre-existing environment. Your AC well kick on less, run for a shorter duration, and run at a lower duty cycle by just maintaining what is already conditioned. In addition, you are also keeping the humidity level in your home to a consistently dry level which goes a long way to thwarting the growth of mold.

To see this in action, we'll use my most current electricity bill. It's been pretty humid, hot, and generally gross here throughout June so the AC was on 24/7 throughout the entire month of June. I keep it at 77 during the time I am awake and 73 for the 4-6 hour window I am asleep. My total electricity bill for the month with the "added" AC usage? $158 bucks. An $18 dollar increase over the previous month. So 60 cents extra per day. I keep it on when I am out running errands, actually go in to work for a half-day, and so forth.

In addition, the condenser for my AC unit is literally right below my office window. It kicks on 2-3 times per day. I notice it because I am both hypervigilant and have hyperacusis (both stem from the same source) so I really notice when it kicks on.

Just leave your AC on at a reasonable temperature even when you are not home. You'll avoid costly HVAC repair bills, extend the life of your unit, ensure your own health, and actually save yourself money in the long run.