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Community and Q&A

How much energy does the evaporator coil waste?

jonathanforddalton | Posted in Mechanicals on

While working through Manual D calculations I was surprised at how much of the total static pressure from a blower motor is dropped through the air conditioning evaporator coil. In my case I had a drop of .3 iwc at the coil for a total external static pressure of .7 iwc at 990 cfm. That’s almost half of the blower load being used to push air through a coil that in my climate (zone 5) is just in the way most of the year.

I’ve never seen any posts here about how much energy is wasted blowing air through A-coils. I get that they’re a necessary evil in much of the US but in cooler climates where you only need A/C for a month or two I’d think it would be a factor in whether or not to use central air and also the benefits of upgrading to a higher SEER system with a larger coil and hence less pressure drop.

I did a quick calculation using the formula for work done by a fluid – W = P x dV and came up with 35 watts for my system. Accounting for a motor efficiency of 70% the system would use 50 watts of power to force air through the A-coil. That does not seem onerous but there are other areas where we split hairs over less than 50 watts of energy use. Is there any real world data on this?

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