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Old 06-08-16, 09:38 AM   #8
JRMichler
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Join Date: Apr 2012
Location: Phillips, WI
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CarbonKevin raises a valid point, so I pulled out an ASHRAE #1 pschrometric chart and did a pair of example calculations.

1) 40 deg F in, 60 deg F out, 0 RH, 100 CFM in. From the chart, 12.6 ft^3 per lb in, 9.6 BTU/lb in, and 14.6 BTU/lb out. The calculation: (14.6 - 9.6) X 100 CFM / 12.6 ft^3/lb X 60 min/hr = 2380 BTUH.

2) 85 deg F in, 105 deg F out, 100% RH in, 100 CFM in. From the chart, 14.3 ft^3/lb in, 49.4 BTU/lb in, and 54.1 BTU/lb out. The calculation: (54.1 - 49.4) X 100 CFM / 14.3 ft^3/lb X 60 min/hr = 1970 BTUH.

The simplified approximation is 0.018 BTU/ft^3/deg F X 20 deg F X 100 CFM X 60 min/hr = 2160 BTUH. That's 10% low at the lower temperature, and 10% high at the higher temperature, and very close at normal room temperature. The error from the simplified approximation is less than the typical error from measuring temperature and CFM.
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