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Calculation of Heating Degree-Days (HDD) and Cooling Degree-Days (CDD) according to the US ASHREA for a day defined with a daily mean (Tmean) surface air temperature.
| Condition on temperature | HDD US calculation (Tbase = 18.3 °C) | Interpretation |
|---|---|---|
| CDD US calculation (Tbase = 18.3 °C) | ||
| Tmean ≤ Tbase | HDD = Tbase − Tmean | Cold day |
| CDD = 0 | Cold day | |
| Tmean ≥ Tbase | HDD = 0 | Warm day |
| CDD = Tmean − Tbase | Warm day |
HDD and CDD are calculated with a base temperature (Tbase) of 18.3 °C.
