Cooling degree days (CDD)
A measure of how much and for how long outdoor temperature exceeds a base temperature, used to estimate air-conditioning demand.
Cooling degree days sum the daily excess of outdoor temperature above a base temperature, typically 18 °C, 21 °C (Eurostat uses a 24 °C threshold with 21 °C base) or 65 °F in the US. They are the mirror image of heating degree days.
Annual CDD = Σ daily CDD
Cooling electricity (kWh) ≈ cooling load (kWh_th) / SEER
Indicative annual CDD at 18 °C base: Chennai and Singapore above 3,000–3,500; Dubai about 3,500–4,000; Houston about 1,600 (roughly 2,900–3,000 °F-days at the US 65 °F base); Madrid about 500–700; London below 100. Pure temperature-based CDD understates cooling demand in humid climates, so some analyses use enthalpy- or humidity-adjusted degree days to account for latent (dehumidification) loads.
CDD growth matters for electricity systems: the IEA's Future of Cooling report (2018) estimated space cooling used about 2,000 TWh, roughly 10% of global electricity, with demand expected to roughly triple by 2050 as incomes and temperatures rise in India, Southeast Asia and Africa. Cooling peaks on hot afternoons coincide well with solar output, softening the impact on peak load. Efficient equipment (high SEER) and building shading reduce the load.
Related terms
All terms →- Heating degree days (HDD)
A measure of how much and for how long outdoor temperature falls below a base temperature, used to estimate and normalise building heating demand.
- SEER
Seasonal Energy Efficiency Ratio: total cooling output over a cooling season divided by electricity used, in BTU/Wh (US) or W/W (EU).
- Peak load
The highest electricity demand recorded on a grid during a given period, which sets the capacity the system must be able to supply.
- Heat pump
A device that uses a refrigeration cycle to move heat from a cooler source (air, ground, water) to a warmer sink, delivering 2–5 units of heat per unit of electricity.
- U-value
The thermal transmittance of a building element: heat flow in watts per square metre per kelvin of temperature difference (W/m²K). Lower is better.