To what extent may the Belgian rules for calculating the heat load of buildings differ from the rules prescribed by Europe? This was the central discussion during the E228 working group that started in January. The Belgian proposal for an additional simplified calculation method is now ready for public consultation. You can read about the most important developments in the article.


In the article of January 16thwe announced the start of two new E228 working groups to develop Belgian Annexes to the standards on the calculation of the heat load for spaces (EN 12831-1) and domestic hot water (EN 12831-3). The proposal for the Belgian Annex to EN 12831-1 is now ready for the next phase of the public enquiry. Below a summary of the main developments so far.

Heat load conditions for spaces in practice

Heat loads represent the needs for heating and cooling in (parts of) a building. The loads can be the result of people present, but also for example of appliances or the weather. The calculation of the heat load serves to determine the maximum heat release per hour that is required of a heat generator to reach or maintain the internal design temperature in case of a set external temperature. Based on the calculation of the heat load an installer is able to determine the dimensioning of a boiler, radiator and other parts of a central heating installation. The concept of heat loads is often intermingled with heat losses. These losses are part of the heat load, but considered alone not sufficient for the dimensioning of a heating system. The two concepts are, however, used interchangeably, because prior to the use of EN 12831-1 the dimensioning of a heating system was based on a determination of the heat losses via the standard  NBN B 62-003.  However, next to heating, the importance of cooling is increasing. Also internal heat gains need to be taken into account more and more. The arrival of the standard EN 12831-1 has made it possible to take transmission, ventilation and heat-up power into account in addition to heat losses.

Heat load conditions and the Belgian energy performance regulation (EPB)

Within the Belgian EPB the heat load standard for spaces can be used to demonstrate that a designed heat emission system is capable to reach a certain comfort level. For this purpose a 'dimensioning note' (dimensioneringsnota) needs to be drafted; within EPB there are requirements specified for the design water flow temperature to and water return temperature from the emission system. The water flow temperature refers in this case to the temperature of the water that flows into the heating elements; the water return temperature is the temperature of the water that returns from the system. The standard EN 12831-1 constitutes the basis for the standard spreadsheet that is provided by the WTCB-CSTC to determine the water flow and return temperature of a heating (or cooling) system. The spreadsheet counts as validated evidence for the dimensioning note in Flanders. Alternatives for a dimensioning note are the use of default values or other documentation (e.g. from the manufacturer), but these are not always sufficient to meet the energy performance requirements.

Important considerations in the Belgian Annex

The European standard EN 12831-1 includes an elaborate and a simplified European calculation method and a number of European parameters. Belgium has the possibility to make additions to these through an Belgian Annex with the aim to make the method fit into the local context. The standard offers the possibility to include both parameters and an adapted calculation method in the Annex. The proposal that is currently on the table makes use of both possibilities. The main topic within the discussion on the Annex is the risk of overdimensioning upon application of the standard. Overdimensioning can be caused by the application of parameters that are 'too safe'. Minimum temperatures that are for example set too low can lead to a calculation of the capacity of a heating or cooling installation that is too high. A closer look into the climate data is therefore of importance. Also the values for airtightness, which are expected to further improve through innovations in buildings technologies in the coming years, deserve to be a point of attention. Within the calculation methodology heat-up power can be a factor in overdimensioning. The standard provides for it to be included optionally. A remaining point of discussion is the way that ventilation can best be included. This will need to be further investigated to come to a concrete proposal.

Public enquiry as the next step

Around the end of October consensus was reached within the working group to allow for the proposal for the Belgian Annex to EN 12831-1 to enter the next phase of the public enquiry. This phase offers the possibility to all stakeholders to provide feedback on the proposal. As secretary Agoria currently works on the translation of the text proposal for the Annex. Upon approval of the Belgian Mirror Committee it will be sent to the Bureau for Standardisation (NBN), after which it will be submitted for public consultation. Concretely this means that the documents will be placed on the 'NBN public enquiry portal'  in the beginning of 2019. The proposal will then be open to remarks from any type of stakeholder. The remarks of the public enquiry will be processed in both the French and Dutch translation of the Annex. In case of technical remarks, the draft will be presented to the Belgian Mirror Committee for approval a second time. In case of only editorial comments the additional approval is not necessary. The Annex will be finalised with the official publication in the Belgian Official Gazette.

EN 12831-1: Role of the working group within the standardisation landscape 

The standard EN 12831-1 is part of the portfolio of standards that is managed by the European standardisation committee CEN/TC228. This commission is focused on the development and maintenance of standards for heating systems and water based cooling systems. Currently the committee manages around 30 (EPBD) standards, of which the majority was approved in 2017. The Belgian Mirror Committee E228 is the Belgian representation of the CEN committee. Sirris-Agoria is its sector operator. The activities of the Mirror Committee consist of voting, commenting and revising the proposals for (European) standards. In addition the Mirror Committee has the possibility to develop a Belgian standard or Annex to for example define local parameters. The two working groups that are currently active within the Belgian Mirror Committee are aimed at the development of Annexes for the European '12831' standards. The standards describe the calculation methodology to determine the heat load of buildings for spaces (EN 12831-1) and domestic hot water (EN 12831-3). 

Would you like more information about the standards or annexes? Members of Agoria can become members of the Mirror Committee E228. Contact Ludo.Vanroy@agoria.be