Differences between Measured and Calculated Energy Use in EPCs versus Building Permits. QUALICHeCK Report: "Status on the Ground" (New field study/2016)

Rapport, 2016

In 2006, the Energy Performance Certificates (EPC) were implemented in the Swedish national building code. At the same time, the energy use demands in the building code (BBR) were transformed to be only performance based, i.e. a demand only on the maximum energy use. The country is divided in four climate zones, with the highest allowed energy use in the north and the lowest in the south. The EPCs are based solely on the measured energy use in the building. The regulation requires that the measured energy use is corrected to normal use during a reference year. However, there is no standardised methodology to account for normal use in the EPC and this is therefore seldom done. This study is focused on investigating the cause of differences between the calculated and measured energy use in buildings, in order to detect compliance problems with measured EPCs. Based on interviews, analysis of two databases with EPCs in single-family houses and multi-family buildings, complemented with energy use calculations, potential general procedures and parameters that cause these differences are identified and investigated. Suggestions on improvements to the Swedish EPC scheme are also presented.

For new buildings, the regulation requires that the energy use is calculated and presented for the municipality in the building permit application. This calculation is most often based on early design drawings where limited knowledge is available on the technical properties of the building. Previous studies have shown that the variations on energy use caused by the occupants’ behaviour is often underestimated in energy use calculations. In single-family houses, differences in the occupants’ behaviour can account for up to 50% of the building’s energy use. In low energy houses the variation of the occupants’ behaviour has a larger relative impact on the energy use than for buildings with higher energy use.

To rule out the possibility of failures in the construction and operation of buildings, the building process needs to be followed by measurements at regular intervals of e.g. airtightness. However, these measures are not enough to guarantee an energy use in line with calculations. Not only the occupants’ behaviour, construction and operation influence the measured energy use. It is also influenced by the location and number of energy use meters for heating, domestic hot water and facility electricity. For example, a previous study showed that unexpected heat losses in culverts in the heating distribution system increased the energy use in a multi-family building by 12.6%. Similar results were also described in the interviews.

Two energy and climate advisors and two energy experts were interviewed in this study. They are involved in different stages of the design of buildings and follow-up of energy use in buildings. According to Boverket, around 90-95% of all the buildings sold in Sweden have a valid EPC. The regulation also requires that all new buildings have an EPC two years after commissioning. There are no national studies performed on this topic in Sweden to the knowledge of the authors. The municipalities cannot legally force a home owner to supply them with an EPC and there are no sanctions if the regulation is not fulfilled. The home owner is often reluctant to pay the fee for an EPC and instead waits until the house is put on sale on the market. In this study, 100 single-family houses were expected to have a valid EPC since 2 years passed after commissioning. However, the number of EPCs was 44 which means 44% compliance with the current regulation. This is problematic since the energy experts do not get the feedback needed to improve calculation procedures and input data. In larger construction projects, an energy coordinator is often appointed to follow up changes in the design and their influence on the energy use. For single-family houses this is rarely done. There is no formal certification or knowledge needed to submit an energy use calculation for a building permit application. However, there are guidelines and standardised input data available for energy use calculations. Even though the calculated energy use corresponds well with the energy use reported in the EPC, the calculation can be wrong, caused by erroneous allocation of the energy supply and energy demand, making comparisons unfeasible. Wrong data on e.g. efficiency of ventilation heat exchangers, thermal bridges and losses from circulating hot water circuits could rule out e.g. the influence by occupant’s behaviour.

Analysis of a database containing the calculated energy use for 313 single-family houses built since 2009 in the municipality of Lerum revealed that there was no tendency for calculations targeting 4 Sweden - Differences between Measured and Calculated Energy Use in EPCs versus Building Permits the maximum allowed energy use. The most common heating system was an air to air heat pump followed by ground source heat pump. For 80 houses in the database, information on the heated floor area was available. This data showed that the energy use per square meter was lower for larger buildings. The floor area also influences the difference between the calculated and measured energy use which is higher in percentage for smaller buildings. The information on energy use, floor area, household electricity and hot water use in the calculation and EPC report were compared for six of the buildings in the database. The analysis showed that there are large deviations on which data is used and how it is obtained for the different buildings. For instance, non-compliant heated floor area was reported where the garage erroneously was included in the EPC report. For one of the houses, detailed numerical analysis were performed where 54 occupant scenarios were studied. The energy use varied between 39 kWh/m2 to 73 kWh/m2 compared to 26.6 kWh/m2 in the calculation report and 39 kWh/m2 in the EPC. This illustrates the importance of a methodology for correcting the energy use to normal use.

The dispersion in energy use in buildings with different heating systems was analysed using a database of 1,753 EPCs for buildings in the metropolitan Gothenburg area. Both single-family houses and multi-family buildings were analysed. The energy use is influenced to a larger extent by the choice of heating system than by the choice of ventilation system. As discussed above, it is important to use the correct heated floor area and attribute the energy use to its correct demand and supply in the calculations. In many cases, the heated floor area was transformed from other sources than direct measurements in the building. The heated floor area was obtained by direct measurements in 63% of the multi-family buildings and in 100% of the single-family houses. The domestic hot water and facility electricity was allocated based on experience, and not measurements, for a majority of the buildings.

The main conclusions of this study are that:
- Energy use by occupant’s behaviour explain a large part of the difference between calculated and measured energy use.
- Normal use is not standardised and therefore not accounted for in the EPC.
- Few buildings have energy meters that separate energy use for heating from energy use which should not be included in the EPC, e.g. household electricity.
- Bad compliance of the number of EPCs reported for new buildings 2 years after commissioning is caused by lack of follow-up actions.

To improve the EPC scheme and quality of energy use calculation, further work is needed in the area of standardising input data, calculation procedures and reporting of EPC.