The EPB methodology is used to determine the energy performance of new buildings and major energy renovations (IER). Currently, the EPB calculation is done on a monthly basis; this means that among others it is necessary to determine correction factors for technologies that are subject to high fluctuation.


In 2019, Agoria carried out a study into the possibilities for the integration of the energy performance calculation of a building on an hourly basis into the Belgian EPB methodology. The NBN EN ISO 52016-1 standard, that can be used to determine the energy needs of a building, was used as the basis of this exercise.

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The hourly method in practice

Traditionally, heat loss in buildings due to for example inadequate insulation or single-glazed windows have the largest impact on its thermal balance. However, this is not the case in buildings with a high energy performance; because of the limited heat loss, internal and external heat gains account for the largest share. An example of external heat gain is a room that heated up by the sun. Typical for such heat gains is the sensitivity to fluctuations due to changing weather conditions. In the determination of the energy performance of a building, this means that it becomes increasingly difficult to determine suitable correction factors to account for these variations; this is an important difference from calculations in which heat losses have the most significant impact. For heat losses it is easier to determine monthly averages as they are less sensitive to fluctuations. The ever improving energy performance of buildings has therefore raised the question whether there is a way to determine more accurate monthly correction factors; the hourly method was developed as one possible answer to this question.

How does it work?

The energy performance calculation roughly consists of the determination of the heat demand, the required amount of energy based on the energy efficiency of a heating (or cooling) appliance minus the amount of locally generated renewable energy. For both the determination of the heat demand and the required amount of energy for the appliance product specific and condition related data are used. Product specific data can be retraced to the stand-alone product. Examples are energy efficiency coefficients, which are also used within energy labelling to determine categorisation. 'Correction factors' are used as input data, which may be influenced by the building, location or the behaviour of a technology under the influence of external factors. Examples are climate related data and the ventilation flow rate. These correction factors are laid down in regulations. In case the hourly method is used, the behaviour of a technology is modelled via an algorithm instead of the correction factors. Even though aggregation is applied here as well, its impact on the determination of the energy performance is negligible. In theory, the hourly method therefore eliminates the need to lay down separate correction factors in regulations. An additional advantage is that simultaneous cooling and heating demands can be calculated more accurately.

Figure 1: Simplified schematic representation of the difference between simultaneous heating and cooling

Main considerations in the NBN EN ISO 52016-1 standard

The NBN EN ISO 52016-1 is part of a series of EPB standards designed to support the development of knowledge on the energy performance methodologies for buildings. The standards were revised around 2017 at the request of the European Commission, with the aim of making it easier for Member States to implement them. With the revision the ISO 13790 was replaced by the NBN EN ISO 52016-1. The standard describes an advanced calculation method for determining the energy demand for a building. The corresponding technical report NBN EN ISO 52016-2 describes cases that validate the methodology. With the introduction of the NBN EN ISO 52016-1 a possibility to apply a combination of the hourly and monthly method was provided (see figure 1). The standard also includes options for entering multiple zones. Each country can develop its own variants based on their need for refinement. A proposal has been included in the standard. The calculation of the zones is in principle the same for the monthly and hourly method; however, the calculation time for the software can be longer in case of the hourly method. The revision of the standard also included the creation of an Excel, in which the calculation per technology can be simulated. This Excel was published at the end of 2019. The EPB-Center is currently working on a number of additional tools on the Excel (see chapter 3 in the study report).

Figure 1: Simplified display of the combined hourly and monthly method

The hourly method and the EPB

The integration of the hourly method in combination with the monthly method is one of the options currently explored to simplify the integration of innovative building technologies. In energy performance methodologies, product specific parameters such as correction factors and energy efficiency coefficients are necessary for the calculation. For each new product placed on the market, the parameters have to be adapted to the characteristics of that product. In principle, the manufacturer or supplier has this data available via product sheets. However, using that data entails a risk for the EPB reporter; in preparing an EPB report, the reporter is responsible for using correct data. When using 'validated' parameters, i.e. input data that has been approved by the government, the data is automatically considered 'valid'. In this case, the EPB reporter runs no risk . Examples of validated parameters are correction factors laid down in regulations and default values. Adjusting these values for new technologies requires an adjustment of policy procedures that can take years. Ways are therefore being sought to speed up the integration of innovation in EPB; making correction factors superfluous by integrating the hourly method into the EPB methodology is one of the options.

Agoria Study: Exploration possibilities implementation hourly method

At the beginning of 2019, Agoria launched a study to explore the possibilities of integrating the hourly method into the Belgian EPB methodology based on the NBN EN ISO 52016-1 standard. This study was carried out by the EPB-Center, an organisation set up by the European HVAC federation REHVA and the knowledge institute for construction and installation engineering ISSO to support the implementation of the EPB standards. The study is based on case studies for heat pumps and night ventilation; these cases were selected because of the large impact of fluctuating indoor and outdoor conditions on an energy performance calculation. The report describes the calculation, the interaction with the product specific Excel (e.g. the Excel for EN 16798-4-2 for heat pumps) and the graphic results. The required parameters for the calculation are described in chapter 6.3 of the standard. In principle, application of the combined method does not require any additional parameters compared to the monthly method. The results show that a calculation based on the hourly method results in a lower energy demand in case mechanical cooling (see table 1 on page 12 in the report). In order to assess the extent to which this approaches energy performance better than the current monthly EPB methodology used in Belgium, it is necessary to still perform comparative calculations between the two methodologies for a number of technologies.

Conclusion and next steps

The study showed that the hourly method certainly has the potential to determine the energy performance of a building more accurately. However, the integration of the methodology also requires an investment cost, because the calculation methodology and software have to be adapted. Also, other approaches as dynamic calculation have to be considered. In order to see whether the integration of the hourly method is a cost-effective way to speed up the integration of innovation, it is necessary to make a comparative calculation between the standard and the current EPB. As a follow-up to the study, Agoria therefore intends to see whether a number of concrete business cases can be further elaborated. The EPB-Center has indicated that they can provide support. In addition, the EPB-Center is working on a number of initiatives to increase knowledge on the EPB standards. The hourly method is also a topic of discussion here. In collaboration with BUILD-UP, the EPB Center started a monthly series of webinars explaining the possibilities of the standards in February. These can be followed free of charge by registering on the website. The fourth webinar on 26 May 2020 will be entirely devoted to the hourly versus the monthly method.

Relevant links

The study was carried out as part of the policy preparation work on the energy performance policy framework (EPB) in the context of the monitoring of energy and climate policies with an impact on buildings (2019). In 2020, this work will continue as the project Climate Neutral Building Park.