Heating or cooling degree days reflect the demand for heating or air conditioning in a region based on the local weather conditions. This correlates with the energy usage required to achieve the desired interior temperatures.
The reference temperature used in the US is 65°F.
average temperature for day in °F =
= ((maximum temperature for day in °F) + (minimum temperature for day in °F)) / 2
Average Temperature
Appropriate Term
Value
< 65°F
heating degree days
65 - (average temperature)
65°
NA
0
> 65°F
cooling degree days
(average temperature) - 65
where:
• The reference temperature may differ between countries based on local conditions and habits. In England the reference temperature is 60°F rather than 65°F.
The cumulative heating or cooling degree days for a period (week, month, season) is the sum of heating or cooling degree days for that period.
cumulative heating degree days =
= SUM(individual heating degree days)
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