Heating and cooling degree days - statistics


Data extracted in February 2021.

Planned article update: March 2022.

Highlights
In EU-27, the needs for heating a given building in 2020 were approximately one fifth lower than in 1979.
The need for cooling a given building in 2020 was more than two times higher compared to 1979.
Ireland has similar Heating degree days arithmetic average values as the regions Grand Est in France and Alföld és Észak in Hungary.
The regions Noroeste on Spain, Hessen in Germany and Région de Bruxelles-Capitale/Brussels Hoofdstedelijk Gewest in Belgium all have similar Heating degree days arithmetic average values.

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 aims to present the variations of HDD and CDD since 1979, that we have data availability. The Joint Research Centre kindly provides each year the data necessary to produce this article .

Full article


Heating and cooling degree days at EU-27 level

Heating degree day values are decreasing across time

Heating degree days (HDD) value decreased by 21 % between 1979 and 2020 in the EU-27, indicating that, compared with 1979 only 79 % of the heating needs were observed in 2020. The arithmetic average across 41 years of data is 3 209. From the measurements we have, the trend shows that heating degree days are decreasing across time. With the exception of a four years (2010, 2005, 2004 and 2001) heating degree days were lower than the average after 1999 (see Figure 1).

Figure 1: Heating degree days in EU-27, 1979-2020 Source: Eurostat (nrg_chddr2_a)

Cooling degree day values are increasing across time

In contrast, Cooling degree days (CDD) values in 2020 was more than two times higher between 1979 (37) and 2020 (99), indicating that the needs for cooling (air conditioning) in a given building increased over the last decades. For cooling degree days, the trend we observe from our measurements shows an increase across time. The average CDD for EU-27 value is 72. After 2001, only a few years (2002, 2004, 2005 and 2014) were below the average (see Figure 2).

Figure 2: Cooling degree days in EU-27, 1979-2020Source: Eurostat (nrg_chddr2_a)

By Member State

Highest heating degree day values in Sweden and Finland

Heating degree days varies across European Member States. Considering all data available over the 1979-2020 period, Finland had the highest average annual HDD value (5 665), while for Malta, the value of this index was 536. This means that for a given building, the need for heating was ten times less significant in Malta than in Finland between 1979 and 2020 (see Figure 3). Finland was followed by Sweden (with an average HDD of 5 328) and Estonia (4 344). The European Member States with the lowest HDD were Malta (536), followed by Cyprus (784) and Portugal (1 243).

Figure 3: Average Heating Degree Days, 1979-2020 Source: Eurostat (nrg_chdd_a)

Considering the latest year under observation (2020), the countries with the highest HDD values were Finland (4 871), Sweden (4 593) and Estonia (3 553) (see Figure 4). This means that in 2020, a given building would have greater needs for heating in Finland, Sweden and Estonia compared to the rest of the EU, since lower temperatures (below 15°C) were more frequent. The Member States with the lowest HDD values in 2020 were Malta (402), Cyprus (630) and Portugal (1 008).

Figure 4: Heating Degree Days, 2020 Source: Eurostat (nrg_chdd_a)

The correlations between the countries annual heating degree day 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. We see for example, Portugal and Cyprus. Even if their average values are near, 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 2020. Cyprus had the highest CDD (573), followed by Malta (569) and Greece (268). The lowest values for this index were calculated for Ireland (0.02), Sweden (0.36) 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 2020.

Figure 5: Average Cooling Degree Days, 1979-2020 Source: Eurostat (nrg_chdd_a)

Considering the latest year under observation (2020), the countries with the highest values were Cyprus (803), Malta (672) and Greece (345) (see Figure 6). This means that in 2020, a given building would have greater needs for cooling (or air conditioning) in Cyprus, Malta and Greece compared to the rest of the EU, because higher temperatures (over 24°C) were more frequent. The lowest CDD index calculated were observed for Ireland (0.00), Sweden (0.08) and in Finland (0.42) in 2020.

Figure 6: Cooling Degree Days, 2020 Source: Eurostat (nrg_chdd_a)

The correlations between the countries annual cooling degree day data are available in Table 2. They are organised in increasing arithmetic average value order. 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 0.12.

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 (174), Região Autónoma da Madeira in Portugal (314), Malta (536), Cyprus (784) and Nisia Aigaiou, Kriti in Greece (927) 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 (3349), Slovakia (3360) and Bayern in Germany (3367). Ireland (2844) has similar average values as Grand Est in France (2819) and Alföld és Észak in Hungary (2848). The same applies to Lithuania (3986) and the regions Westösterreich in Austria (3998) and Östra Sverige in Sweden (4130). Values for all regions are available at 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. Ireland (0.02), the regions Norra Sverige in Sweden (0.09), Åland in Finland (0.55), Södra Sverige in Sweden (0.78) as well as Danmark (0.91) 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 (15.70), the Czech Republic (15.76) and Zuid-Nederland in the Netherlands (15.98). The same applies to the regions Noroeste in Spain (16.17), Hessen in Germany (16.47) and Région de Bruxelles-Capitale/Brussels Hoofdstedelijk Gewest in Belgium (16.88) as well as to the regions Közép-Magyarország in Hungary (85.90), Provence-Alpes-Côte d'Azur in France (88.33) and Yugozapadna i yuzhna tsentralna Bulgaria (91.95). Values for all regions are available at 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 41 years, from 1979 to 2020 show that Norrbottens län region in Sweden had the highest HDD value (6 660), while the lowest value was observed in Fuerteventura, Spain (18). In 2020, in Lappi in Finland the highest HDD value measured was 5 965, while the lowest was observed in Fuerteventura in Spain with 0.57.

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 2020 showed that Gozo and Comino / Ghawdex u Kemmuna region in Malta had the highest CDD value (583). The second Member State where, for a given building, the need for cooling (or air conditioning) was significant was Cyprus (573). In 2020, the highest cooling degree days value was measured in Cyprus (803).

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 day (HDD) index is a weather-based technical index designed to describe the need for the heating energy requirements of buildings. Cooling degree day (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 15°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.

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 24°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.

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.

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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) 

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