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why is CDD50 used in ashrae90

asked 2022-04-08 23:26:08 -0500

yongqingzhao's avatar

updated 2023-03-17 09:03:27 -0500

Hi, everyone

A question was confused me for a long time, so have to the email to ask you, which is why CDD50 is used in Ashrae 90, CDD50 is defined as following:

cooling degree-day base 50°F (CDD50): for any one day,when the mean temperature is more than 50°F, there are as many degree-days as degrees Fahrenheit temperature difference between the mean temperature for the day and 50°F. Annual cooling degree-days (CDDs) are the sum of the degree-days over a calendar year.

However, I am very confused why 50°F is used as the threshlod between cooling and heating? That means when the outdoor air temperature is more then 50F, the cooling starts to work?In chinese standard, 26℃ is as the base of CDD.

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answered 2022-04-09 06:34:08 -0500

rgleason's avatar

I think it is because a good approximation for the balance point of buildings is often taken as 50 degreesF although a given building based on its design is likely different.

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Asked: 2022-04-08 23:26:08 -0500

Seen: 339 times

Last updated: Apr 09 '22