Eli5: How is the square footage that a portable air conditioner is rated for calculated?
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It’s been a while since trade school but from what I remember. Cooling is calculated by tonnage. The guy that started carrier calculate that it takes 12000 btus of cooling to keep one ton of ice from melting per hour.
The rule of thumb is one ton of cooling per 600 squat feet. But there’s heat load calculations that are done with special software now. Basically you determine the heat load of a building based on construction materials to determine how much cooling is required for said space.
AC units basically can move a given amount of heat energy from one side to another. That’s determined by the components inside (compressor, hear exchangers, etc). This is expressed in cooling power in kW (or in tons/btu* per hour).
Then there’s basically some “standard” for how much floorspace you can cool per kW of capacity which is applied to. Plus a discount factor for the inefficiencies in portable units.
It’s only an estimate. More insulation would stretch that cooling power further, and it wouldn’t work as well if you had big sunny windows or hot appliances in the room (as they’d release a lot of heat energy into the room).
*BTU British thermal units are a measure of energy (thus quoted per hour to give the power of an AC unit), as our tons (based off how much a ton of ice could cool).
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