Degree day number
Degree days (also Gradtag s number , GTZ, G t ) and heating degree (HGT, G) are used to calculate the heat demand of a building during the heating period used. They represent the relationship between the room temperature and the outside air temperature for the heating days of a measurement period and are therefore an aid to determining the heating costs and fuel consumption .
Degree days and heating degree days are specified with the unit Kelvin (K or ° C ) , i.e. they have the same dimension as the temperature (or as a heat sum in Kd or ° Cd, degree days ). But they are also related to a heating period or a calendar month and are then meaningful for the seasonal fluctuations. There is a value for the long-term climatic mean and a value for the current weather (meteorological measurement).
Reference values for room temperature and heating limit
The reference values are the room temperature and the heating limit . There are different usages for the reference values:
- According to the German VDI guideline 2067 / DIN 4108 T6, the internal temperature is assumed to be 20 ° C and the heating limit to be 15 ° C; GTZ 20/15 is stated. The values determined by the DWD or MeteoAM are used as a basis for the outside temperature ;
- in Austria, Switzerland and Liechtenstein, an indoor temperature of 20 ° C and a heating limit of 12 ° C are used; HGT 20/12 is given . The temperature values from ZAMG (Austria) and MeteoSwiss (Switzerland and Liechtenstein) are the reference values here.
Degree days according to VDI 2067 / heating degree days according to ÖNORM B 8135 and SN 565381-3
The number of degree days G t is only calculated over those days of a period when the outside temperature is below the heating limit temperature. The degree day number is the sum of the differences between an assumed room temperature of 20 ° C and the daily mean value of the outside temperature. The number of degree days is a location-dependent parameter that reflects the local climatic conditions. It is a GTZ norm for the long-term average, and a GTZ specific differentiated for the current measurement. The latter is used, for example, for the climatic adjustment of measured consumption values.
According to VDI 2067 room heating: Calculation of the costs of heat supply systems :
- : Number of degree days with 20 ° C and a heating limit of 15 ° C
- : Number of meteorological heating days
- : mean assumed room temperature (internal temperature), here 20 ° C
- : mean outside temperature of the respective heating day
- The degree day number of a day (heating degree day value) is the difference between the indoor air temperature and the daily mean value of the outdoor temperature.
- The number of degree days for the heating time is the sum of the differences between the mean room temperature of 20 ° C and the daily mean air temperature over all heating days in the local heating season (September 1st and May 31st).
- When calculating the number of degree days for the heating season , only those heating days that lie within the heating season are taken into account.
- The degree day number of a month is the sum of the temperature differences over the month.
The procedure, as specified in VDI 3807, with a distinction between degree day GTZ and heating degree day G, is used in the Austrian ÖNORM B 8135 Simplified calculation of the time-related heat loss (heating load) of buildings or the Swiss SIA 381-3; SN 565381-3: 1982 heating degree days in Switzerland are not listed in this way, there is also the designation heating degree day HGT for degree days according to VDI.
- HGT 20/12 : heating degree days for 20 ° C room temperature and heating limit of 12 ° C
- z : number of meteorological heating days
- t em : mean outside temperature of the respective heating day
- Specification according to the standard in Kd
Heating days and heating degree days are recorded in the Austrian energy certificate in addition to the climatic region , altitude above sea level and the standard outside temperature (this is the local average minimum temperature, i.e. the parameter of full load) .
Since, in addition to the air temperature, wind , humidity and solar radiation also affect the energy required for heating, the degree day number / HGT is only suitable for rough estimation. By correcting the standardized room temperature with regard to the actually measured indoor temperature, the heating target and situation-specific situations can be taken into account.
Heating degree days according to VDI 3807
The heating degree days (G) according to VDI 3807 Part 1, energy consumption parameters for buildings are determined very similarly . Instead of the room temperature, however, the actual building-specific heating limit temperature is used.
It reflects the heating load of a specific building and takes into account the thermal insulation of the building as well as heat inflows from sources other than heating. Because the desired interior temperature is also included in the individualized heating limit, the living situation is also taken into account. In addition, one also differentiates between a mean value G HGm and a value of the current heating period G HG , thus taking into account the course of the outside temperature in the observation period, which can deviate from the long-term mean.
- : Heating degree days of the heating season
- : Number of measured heating days of the heating period, based on the individual heating limit
- : Heating limit, here 15 ° C
- : mean outside temperature of the respective heating day
The heating degree days according to VDI 3807 are slightly below the number of degree days VDI 2067 / simple heating degree days HGT with a good energy standard.
Comparison of degree days and heating degree days
Both VDI values can be converted into one another, e.g. B. corresponds to GTZ 15/15 G 15 . The following table shows some (daily) example values:
|t a in ° C||GTZ 20/15||HGT 15|
Degree day number for a month
It is assumed that the heating limit temperature is 15 degrees and the interior temperature should be 20 degrees. The heating limit temperature and the internal temperature can be varied. No degree day number needs to be calculated for individual days (e.g. April 29th), as the day was on average warmer than the heating limit temperature of 15 degrees.
|date||Daily mean temperature in ° C||Degree day number|
|April 1, 2000||5.5||14.5|
|April 2, 2000||8.0||12.0|
|April 3, 2000||10.7||9.3|
|April 4, 2000||8.2||11.8|
|April 5, 2000||4.6||15.4|
|April 6, 2000||5.0||15.0|
|April 7, 2000||5.1||14.9|
|April 8, 2000||4.7||15.3|
|April 9, 2000||5.4||14.6|
|April 10, 2000||5.8||14.2|
|April 11, 2000||6.9||13.1|
|April 12, 2000||6.2||13.8|
|April 13, 2000||7.5||12.5|
|April 14, 2000||7.4||12.6|
|April 15, 2000||10.7||9.3|
|April 16, 2000||9.8||10.2|
|April 17, 2000||14.0||6.0|
|April 18, 2000||14.2||5.8|
|April 19, 2000||13.7||6.3|
|April 20, 2000||14.2||5.8|
|April 21, 2000||16.9||0.0|
|April 22, 2000||19.6||0.0|
|April 23, 2000||21.4||0.0|
|April 24, 2000||16.5||0.0|
|April 25, 2000||11.0||9.0|
|April 26, 2000||15.4||0.0|
|April 27, 2000||19.2||0.0|
|April 28, 2000||20.2||0.0|
|April 29, 2000||21.2||0.0|
|April 30, 2000||19.6||0.0|
The average temperature per day at a location is therefore required to calculate the degree temperature.
Degree day numbers are always used in the heating requirement calculation and heating cost billing if no measured values are available or the period to be billed deviates from the measured time. However, the absolute values are not used here, but rather thousandths ( per mille ) based on a year. According to VDI 2067 and DIN 4713 , these are on average:
|in the month||‰ per day||‰ per month|
The degree day number is used to estimate the heating energy demand of a building at a certain location and is also used for normalizing ( weather adjustment ) of heating energy consumption.
If you divide the heating degree days of the heating season by the number of heating days or the annual value by 365 (average daily heating degrees), you get an estimate of the dimensioning of the heating system, you calculate the number of degrees for the minimum temperature, a characteristic value of the necessary full load.
- The heating degree days G 12 for Basel (favored Atlantic , Köppen Cfb ) are 3000 (mean 1991–2000), mean heating degrees 8.2; the mean minimum temperature is around −2 ° C, so the necessary mean full load is around 10 heating degrees, 25 heating degrees (temperatures below −13 ° C) are exceptional events;
- the heating degree days G 12 for Neusiedl in Burgenland ( Pannonian , Köppen Dfb ) are 3102 (mean 1971–2000), the mean heating degrees 8.5; the mean January low temperature is -3.0 ° C, the mean maximum daytime heating degrees thus 15, the standard outside temperature (tabulated mean minimum temperature) at −12 ° C (24 heating degrees), the measured minimum temperature was in the three decades −20.5 ° C, the hypothetical maximum heating degrees thus 32.5;
- the heating degree days G 12 for Tamsweg in Salzburg's Lungau ( inner-alpine basin , Köppen Dwc , one of Austria's cold spots ) are 4657, mean heating degrees 12.75, mean maximum heating degrees 22.3 (mean January cold −10.3 ° C), standard Outside temperature −22 ° C (34 heating degrees), and maximum heating degrees 40.3 (-28.3 ° C).
The heating energy requirement results (according to ÖNORM B 8135) as follows:
- in kWh
- p 0 : specific heating load
- A : Energy reference area
- f Ben : usage factor
- : Annual efficiency
Using the following formula, a certain heating energy consumption ( ) can be specified as:
where the indicates the long-term average for the period under consideration.
In this way, you can see whether changing consumption has climatic causes (severe winter) or whether it comes from the changed heating behavior of the user.
Calculation of heating power
In order to design the heating of a building, the Hottinger formula was established in the middle of the 20th century , which uses the heating degree days in the calculation.
For example, if the heating costs amount to 625 euros in a calendar year, 200 euros of this amount to the first two months of the year. (625 euros × (170 + 150) / 1000 = 200 euros)
If it is a leap year , the daily value in February is no longer 150/28 = 5.357, but rather 150/29 = 5.172. However, this only matters if the period to be calculated starts or ends in February, as the monthly values are not adjusted for leap years.
The heating degree calculation is also increasingly used in climatology because it makes more precise statements about climate change than mean temperatures, for example. In Basel (which has one of the longest time series in Europe; has a favorable climate on the Rhine), the number of degree days (20/12) in the half-century 1961 to 2011 fell steadily from around 3400 to a little over 2800, which is a decrease of around 15 percent (3400 is roughly the current mean value of Bern and Zurich in the Central Plateau). The annual extreme events were even reduced by almost half (maximum year in the interval 1963: over 3800, minimum year 2007: below 2300 - the first corresponds to the current value of St. Gallen on the edge of the Alps, the second around Lugano on the southern side of the Alps).
The data can also be used for an - anthropocentric - “living” - climate classification , for example, as part of the EU project Keep Cool II, an EU climate zone was created in which the heating degree days were divided by the cooling degree days.
- Cooling degree hour , the analogue of air conditioning technology
- Growing degree day for plants
- Annual mean temperature
- Climatic factors
- Degree days in Germany , Institut für Wohnen, Darmstadt (xls table, also includes the average values per weather station and is constantly updated)
- Degree day numbers (HGT12 / 20) in Switzerland for selected locations and years (from MeteoSwiss, provided by the home owners association)
- Climate data from Austria 1971–2000 , ZAMG (selected stations: heating days, heating degree days and other climate data)
- Climate table for Austria , Heidi Krischan / Institute for Electrical Systems (IFEA), Graz University of Technology (tabulated values above sea level, heating degree days, standard outside temperatures and wind position for selected Austrian communities)
- the zero point of the scale drops out when a temperature difference is formed
- the designation only specifies whether the specification is formally in K or ° C, or in K · d or ° C · d, the numerical value is the same
- ÖNORM B 8135 , Baudatenbank.at
- SIA-381-3-SN-565381-3-1982 , beuth.de
- Heating degree days , Homeowners Association Switzerland
- Heating degree days ( Memento of the original from March 27, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , ZAMG , data and statistics
- Heating degree days (HGT, HGT 20/12 ) , energiesparhaus.at
- statement Weblink MeteoSwiss / HEV Switzerland, accessed 14 Sept. 2012
- Climate diagram in flight.idealo.de , accessed September 14, 2012 - but for Basel Airport, the degree day is Basel-Binningen
- indication Weblink ZAMG accessed 14 Sept. 2012
- Weblink Krischan / IFEA, accessed September 14, 2012
- wave 1985 , significantly lower for the cold wave 2012
- Information in: Sustainable Oriented and Long-lasting Unique Team for energy self sufficient Communities (SOLUTION): Analysis Report on Simulation and Evaluation Results of New Eco-Buildings. High-level energy efficiency in new eco buildings. TREN / 06 / FP7EN / 239285 / ”SOLUTION”, Deliverable D2Ha.2.1, WP No .: 2Ha.2, Concerto, 30-04-11, Section 3 Approach to achieve the deliverable , 3.1 Building Characterization , p. 5, solution -concerto.org ( Memento of the original from November 25, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) (English).
- M.Duerig (2019): Hottinger formula, In: Hans Dürig AG - Blog: Collection of formulas, heat theory , link .
- Basler Klimarreihe ( Memento of the original from August 26, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Umweltberichtbeiderbasel.ch
- cf. Fig. 4 Representative climate zones in Europe, calculated on the basis of the heating degree days as a function of [meaning: on the days] the degree days for cooling for 30 European cities. In: Keep Cool II - EU project shows ways to sustainable summer comfort for office refurbishments ( Memento of the original from December 10, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Verlag Strobel, online portal ikz.de
- Cooling degree hours ( Memento of the original from April 25, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , ZAMG