HVAC & Refrigeration

Intermediate

Heating Degree Days

Cumulative measure of how much and how long outdoor temperature sits below a base.

Formula

HDD = \sum (T_{base} - T_{avg})

Variables

HDDHeating degree days

T_{base}Base temp (°C)

T_{avg}Daily average temp

Example

Base 18°C, avg 10°C for 30 days: HDD = 240

Did You Know?

Utilities use degree days to predict seasonal heating fuel demand with surprising accuracy.

hvac degree day energy

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