Table of contents

3.5.1. Heating and cooling degree days

Space heating and cooling is responsible for a large fraction of European energy use. Heating degree days (HDD) and cooling degree days (CDD) are proxies for the energy demand needed to heat or cool, respectively, a home or a business. Both variables are derived from measurements of outside air temperature. The heating and cooling requirements for a given structure at a specific location are considered, to some degree, proportional to the number of HDDs and CDDs at that location. However, they also depend on a large number of other factors, in particular building design, energy prices, income levels and behavioural aspects.

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HDDs and CDDs are defined relative to a base temperature — the outside temperature — below which a building is assumed to need heating or cooling. They can be computed in different ways, depending, among other things, on the specific target application and the availability of sub-daily temperature data. The EEA indicator on heating and cooling degree days applies an approach developed by the UK Met Office. This approach is based on sub-daily temperature data and uses baseline temperatures for HDDs and CDDs of 15.5 °C and 22 °C, respectively (Spinoni et al., 2015; EEA, 2016b).

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The number of population-weighted HDDs decreased on average by 6.5 HDDs per year during the period 1981– 2017; this corresponds to 0.29 % per year, relative to the average over this period. The largest absolute decrease occurred in northern and north-western Europe, where the heating demand is highest (Figure 3‑3, left panel). Over the same period, the number of population-weighted CDDs increased 0.9 CDDs per year, which corresponds to 1.0 % per year. The largest absolute increase occurred in southern Europe (latitudes below 45 °N), where the energy demand for cooling in summer is highest (Figure 3‑3, right panel). In absolute terms, the decrease in HDDs is faster than the increase in CDDs. In relative terms, however, the relative increase in CDDs is much higher than the decrease in HDDs, because of lower absolute values.

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Figure 3‑3 Trend in heating and cooling degree days, 1981-2017

Source: Adapted from (EEA, 2017b, section 5.4.2; Spinoni et al., 2018).

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Past trends in HDDs and CDDs are projected to continue in the future. Figure 3‑4 shows projections for two different global emissions scenarios. The projected decrease in HDDs is still larger than the increase in CDDs. However, heating and cooling systems are often based on different technologies, with different primary energy needs and economic costs.

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Figure 3‑4 Projected change in heating and cooling degree days

Note: The maps show projected changes in heating degree days (left column) and cooling degree days (right column) by mid-century (2041–2070 period, compared to 1981–2010 period) for two emission scenarios: RCP 4.5 (medium emissions, top row) and RCP8.5 (high emissions, bottom row).
[The signs of the changes in HDD and CDD are stated incorrectly in the map legends. HDDs are decreasing and CDDs are increasing.
Furthermore, the top right map erroneously states RCP8.5 rather than RCP4.5.]

Source: (Spinoni et al., 2018)

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