a/c heat gain vs. winter heat loss

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Old 06-16-18, 05:14 PM
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a/c heat gain vs. winter heat loss

My calculated heat loss at -10 deg is 89,000 Btu/hr. This checks with clocking my gas meter.

My a/c is 3-tons, 36,000 Btu/hr. It barely keeps up today, at 95 deg,

We need to adjust for the differential temps, winter vs. summer. Assuming 72 deg inside temp, (95 - 72) /( -10 + 72) = 23/82 = 28%.

89,000 Btu/hr (heating) x 28% = 25,000 Btu/hr (cooling), Based on this, it would seem that my a/c should be keeping up a bit better? But, I think there may be more losses in my a/c ductwork than in my hot-water radiator system.

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Old 06-17-18, 04:20 PM
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The major difference between heat loads summer and winter is radiant sun energy on walls and roofs.
Attic summer can be 120F or more when outside is 95F.

Measure attic temps. Make sure it is well ventilated with adaquate make up air. Seal all the openings between interior and attic.

Calculations have their place but I like real world data.

My home is well insulated and the attic well ventilated. The boiler and AC both run 7.5 hours a day at design temps. Given all the variables in systems that may not mean anything but I think there is a connection.
 
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Old 06-18-18, 03:00 PM
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An AC should run all the time when the outside temperature is at it's hottest for your area. If 95° is as hot as it gets, you sound ok. If it gets hotter than that, then you may need a bigger system.
 
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Old 06-18-18, 04:24 PM
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The homeowner's goal should be to have the place comfortable at reasonable costs. If it does not run 100% of the time then there is added capacity or cushion. Generally it is better not operate equipment a max capacity.

Yes, at design the idea is to meet max load. But operationally it is a different story.

Around here max temperatures are upper 90's but it has gone over 100F. Having extra capacity was nice and the AC did not over load or cut out.

Mike Speed 30 issue may be solved by finding easy ways to cut heat load. Before buying a new AC system it is something to consider and be a lot cheaper.
 

Last edited by doughess; 06-18-18 at 04:40 PM.
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