Statistics Explained

Heating and cooling degree days - statistics


Data extracted in May 2022.

Planned article update: February 2023.

Highlights

In EU, the needs for heating a given building in 2021 were approximately one tenth lower than in 1979.
The need for cooling a given building in 2021 was almost three times higher compared to 1979.

The use of indicators or indexes such as Heating degree days and Cooling degree days can contribute to the correct interpretation of energy consumption for cooling and heating buildings. Heating degree days (HDD) and cooling degree days (CDD) are weather-based technical indexes designed to describe the energy requirements of buildings in terms of heating (HDD) or cooling (CDD). This article presents the variations of HDD and CDD since 1979, based on data available. The Joint Research Centre kindly provides each year the data necessary to produce this article .

Full article


Heating and cooling degree days at EU level

Heating degree days values are decreasing across time

Heating degree days (HDD) values decreased by 11 % between 1979 and 2021 in the EU, indicating that, compared with 1979, only 89 % of the heating needs were observed in 2021. The arithmetic average across 42 years of data is 3 207. The trend shows that heating degree days are decreasing across time. After 1999, with the exception of four years (2010, 2004, 2003 and 2001), heating degree days were lower than average (see Figure 1).

Figure 1: Heating degree days in EU, 1979-2021 Source: Eurostat (nrg_chddr2_a)

Cooling degree days values are increasing across time

In contrast, Cooling degree days (CDD) values in 2021 were almost three times higher between 1979 (37) and 2021 (100), indicating that the needs for cooling (air conditioning) in a given building increased over the last decades. For cooling degree days, the trend observed from our measurements shows an increase across time. The average CDD for EU value is 73. After 2001, only a few years (2002, 2004, 2005 and 2014) were below average (see Figure 2).

Figure 2: Cooling degree days in EU, 1979-2021Source: Eurostat (nrg_chddr2_a)

By Member State

Highest heating degree days values in Finland and Sweden

Heating degree days vary across EU Member States. Considering all data available over the 1979-2021 period, Finland had the highest average annual HDD value (5 665), while for Malta, the value of this index was 534. This means that for a given building, the need for heating was ten times less in Malta than in Finland between 1979 and 2021 (see Figure 3). Finland was followed by Sweden (with an average HDD of 5 325) and Estonia (4 343). The EU Member States with the lowest HDD were Malta (534), followed by Cyprus (780) and Portugal (1 239).

Figure 3: Average Heating Degree Days, 1979-2021 Source: Eurostat (nrg_chdd_a)

Considering the latest year under observation (2021), the countries with the highest HDD values were Finland (5 623), Sweden (5 201) and Estonia (4 283) (see Figure 4). This means that in 2021, a given building would have greater needs for heating in Finland, Sweden and Estonia compared with the rest of the EU, since lower temperatures (below 15°C) were more frequent. The Member States with the lowest HDD values in 2021 were Malta (466), Cyprus (610) and Portugal (1 065).

Figure 4: Heating Degree Days, 2021 Source: Eurostat (nrg_chdd_a)

The correlations between the countries annual heating degree days data are available in Table 1. They are organised in increasing arithmetic average value order. On the correlation analysis, neighbouring countries have higher heating degree days values. Countries of similar latitude have similar arithmetic average values, but if their longitude is different, the correlation varies. For example, looking at Portugal and Cyprus, even if their average values are similar, the correlation is relatively low 0.06. On the other hand, Luxembourg, Belgium and the Netherlands have high correlation.

Table 1: Heating degree days countries correlations Source: Eurostat (nrg_chdd_a)

Highest cooling degree days in Cyprus and Malta

Similar to heating, cooling degree (CDD) days vary across the EU. Figure 5 shows the annual averages across 42 years, from 1979 to 2021. Cyprus had the highest CDD (577), followed by Malta (574) and Greece (272). The lowest values for this index were calculated for Ireland (0.03), Sweden (0.37) and Denmark (0.91). This means that for a given building, the need for cooling (or air conditioning) in Ireland, Sweden and Denmark were negligible between 1979 and 2021.

Figure 5: Average Cooling Degree Days, 1979-2021 Source: Eurostat (nrg_chdd_a)

Considering the latest year under observation (2021), the countries with the highest values were Malta (793), Cyprus (732) and Greece (421) (see Figure 6). This means that in 2021, a given building would have greater needs for cooling (or air conditioning) in Cyprus, Malta and Greece compared with the rest of the EU, because higher temperatures (over 24°C) were more frequent. The lowest CDD index calculated was observed for Ireland (0.24) followed by Denmark (0.75) and Sweden (0.99) in 2021.

Figure 6: Cooling Degree Days, 2021 Source: Eurostat (nrg_chdd_a)

The correlations between the countries annual cooling degree days data are available in Table 2. On the correlation analysis, neighbouring countries have higher cooling degree days values, for example Lithuania, Latvia and Estonia. Countries of similar latitude have similar arithmetic average values but if their longitude is different, the correlation varies. Cooling degree days datasets correlation between Portugal and Greece is 0.08.

Table 2: Cooling degree days countries correlations Source: Eurostat (nrg_chdd_a)

By NUTS 1 regions

NUTS 1 regions classification based on their average HDD values

On NUTS (Nomenclature of territorial units for statistics) 1 regional level, Table 3 classifies the regions in increasing HDD values. As expected, the regions/Member States Canarias in Spain (126), Malta (466), Cyprus (610) and Nisia Aigaiou, Kriti in Greece (744) have the lowest average HDD values. It is interesting to observe that other regions/Member States, geographically distant have similar average values, such as Makroregion Poludniowo-Zachodni in Poland (3294), Slovakia (3382) and Bayern in Germany (3359). Ireland (2643) has similar average values as West-Nederland (2612) and Yugozapadna i yuzhna tsentralna Bulgaria (2653). The same applies to Lithuania (4016) and the regions Westösterreich in Austria (3976) and Östra Sverige in Sweden (3968). Values for all regions are available in the attached excel file.

Table 3: NUTS 1 regions in increasing average Heating Degree Days values Source: Eurostat (nrg_chddr2_a)

NUTS 1 regions classification based on their average CDD values

On NUTS 1 regional level, Table 4 classifies the regions in increasing CDD values. Normandie (0.04), the region Norra Sverige in Sweden (0.08), Ireland (0.24), Hauts-de-France (0.33), as well as Danmark (0.75) have the lowest average CDD values. It is interesting to observe that other regions/Member States, geographically distant have similar average values, such as Makroregion Województwo Mazowieckie in Poland (31.82), and Nouvelle-Aquitaine (33.82). The same applies to the regions Yugozapadna i yuzhna tsentralna Bulgaria (188) and Corse (189). Values for all regions are available in the attached excel file.

Table 4: NUTS 1 regions in increasing average Cooling degree days values Source: Eurostat (nrg_chddr2_a)

By NUTS 3 regions

Higher HDD values in Norrbottens län and Lappi regions

On NUTS 3 regional level, the annual averages for all available data spanning across 42 years, from 1979 to 2021 show that Norrbottens län region in Sweden had the highest HDD value (6 658), while the lowest value was observed in Fuerteventura, Spain (18). In 2021, in Lappi in Finland the highest HDD value measured was 6 592, while the lowest was observed in La Gomera in Spain with 8.

Map 1: Heating degree days in NUTS 3 regions Source: Eurostat (nrg_chddr2_a)

Higher cooling degree days values in Malta and Cyprus

On NUTS 3 regional level, the annual averages for all available data spanning across 42 years, from 1979 to 2021 showed that Gozo and Comino / Ghawdex u Kemmuna region in Malta had the highest CDD value (589). The second Member State where, for a given building, the need for cooling (or air conditioning) was significant was Cyprus (577). In 2021, the highest cooling degree days value was measured in Gozo and Comino / Ghawdex u Kemmuna (800).

Map 2: Cooling degree days in NUTS 3 regions Source: Eurostat (nrg_chddr2_a)

Source data for tables and graphs

Context

Over the last decades, the effects of global warming caused relevant impacts in many sectors. Given the previsions, this tendency is expected to persist at least until the end of this century. Identifying climate-related impacts and assessing how important these impacts are is an important element of any effective strategy for managing future climate risks. Weather-related energy consumption for heating and cooling buildings indicators such as HDD and CDD can contribute to monitor energy demand for cooling and heating buildings under climate change.

Methodology

Heating degree days (HDD) index is a weather-based technical index designed to describe the need for the heating energy requirements of buildings. Cooling degree days (CDD) index is a weather-based technical index designed to describe the need for the cooling (air-conditioning) requirements of buildings.

We derive HDD and CDD data from meteorological observations of air temperature, interpolated to regular grids at 25 km resolution for Europe. We aggregate calculated gridded HDD and CDD and we present them on NUTS-3 level.

Heating Degree Days (HDD) index: the severity of the cold in a specific time period taking into consideration outdoor temperature and average room temperature (in other words the need for heating). The calculation of HDD relies on the base temperature, defined as the lowest daily mean air temperature not leading to indoor heating. The value of the base temperature depends in principle on several factors associated with the building and the surrounding environment. By using a general climatological approach, the base temperature is set to a constant value of 18°C in the HDD calculation.

If Tm ≤ 15°C Then [HDD = ∑i(18°C - Tim)] Else [HDD = 0] where Tim is the mean air temperature of day i. Examples: If the daily mean air temperature is 12°C, for that day the value of the HDD index is 6 (18°C-12°C). If the daily mean air temperature is 16°C, for that day the HDD index is 0. Only days with a daily mean air temperature equal or below 15°C are considered for this calculation.

Cooling degree days (CDD) index: the severity of the heat in a specific time period taking into consideration outdoor temperature and average room temperature (in other words the need for cooling). The calculation of CDD relies on the base temperature, defined as the highest daily mean air temperature not leading to indoor cooling. The value of the base temperature depends in principle on several factors associated with the building and the surrounding environment. By using a general climatological approach, the base temperature is set to a constant value of 21°C in the CDD calculation.

If Tm ≥ 24°C Then [CDD = ∑iTim - 21°C)], Else [CDD = 0] where Tim is the mean air temperature of day i. Examples: If the daily mean air temperature is 26°C, for that day the value of the CDD index is 5 (26°C-21°C). If the daily mean air temperature is 22°C, for that day the CDD index is 0. Only days with a daily mean air temperature equal or above 24°C are considered for this calculation.

These calculations are executed on a daily basis, added up to a calendar month and subsequently to calendar years. Annual data are calculated as sum of monthly data by Eurostat.

Data sources

This dataset includes monthly data as published by the Joint Research Centre's AGRI4CAST Resources Portal . Note that Eurostat is not the producer of the monthly data, but is only re-publishing them.

Direct access to

Other articles
Tables
Database
Dedicated section
Publications
Methodology
Visualisations




Database

Cooling and heating degree days by country - annual data (nrg_chdd_a)

Cooling and heating degree days by country - monthly data (nrg_chdd_m) 
Cooling and heating degree days by NUTS 3 regions - annual data (nrg_chddr2_a) - data for NUTS 1, NUTS 2 and NUTS 3 are in the same dataset
Cooling and heating degree days by NUTS 3 regions - monthly data (nrg_chddr2_m) 

Dedicated section

Methodology