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What’s a “good” kwh/cooling degree day ratio?

kjmass1 | Posted in General Questions on

I’m trying to see how good/efficient my Fujitsu multi’s are when cooling (Boston, 2400sf conditioned space). I have 4 heads on 2x multi’s, most run in dry mode to knock down humidity and 1 runs in cool auto fan at the top of the stairs to handle most of the home load. No setbacks and run all the time unless we are on vacation. Humidity was low 50% on hot days, creeps towards 63% on milder and rainy days. Taking out my monthly base usage of 445 kWhs, here are the last 2 summers of cooling only data:

’18 June/July/August: 1798 kWh, 902 CDDs, 1.99 kWh/CDD
’19 June/July/August: 1768 kWh, 843 CDDs, 2.09 kWh/CDD

We had some in-wall insulation down prior to his years data, but also ran more heads for comfort so it seems like a wash. Where do these numbers rank against a number I should try to achieve with a retrofit 1940s home?


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  1. Expert Member
    Dana Dorsett | | #1

    Cooling loads are all over the place- those could be really great numbers or really terrible numbers depending on your solar gain and 1% load.

    >"Humidity was low 50% on hot days, creeps towards 63% on milder and rainy days."

    Without the temperatures to which those number are relative, they are meaningless numbers. The outdoor dew point (a measure of absolute humidity) would be more relevant.

    1. kjmass1 | | #2

      Good point- house was consistently 70/71 F all summer. Humidity numbers were just to show it was somewhat under control most of the summer. No idea on outdoor dew points over the course of 3 months.

      We've had 3 massive oak trees come down so I completely understand solar gain now- we went from a completely shaded lot to now baking in 6-8 hours of sun hitting our house. That might show the minimal gains with insulation this summer.

      No real way to put a scale on costs or usage?

  2. Jon_R | | #3

    There are no perfect metrics, but kWh/person/year is an easy one that better relates to being green.

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