NZEB Requirements vs European Benchmarks in Residential Buildings

The European Commission (EC) has set benchmarks for buildings’ primary energy by categorizing countries into four climate zones. Focusing on residential NZEBs in Oceanic and Nordic climate zone countries - Denmark, Estonia, and Finland – we compare the requirements and highlight the relative strictness of these benchmarks.

The EC has set recommended benchmarks for energy performance of NZEB for four EU climatic zones [1]: Mediterranean, Oceanic, Continental and Nordic. Aside from different primary energy (PE) requirements, each country has implemented its own methodology for PE calculation, which vary in terms of usage profiles, energy systems and include different aspects of building energy use as well as primary energy factors. Table 1 presents these PE factors used in EC recommendations and national energy performance calculations in Estonia, Denmark, and Finland. The energy flows included in the national calculations and the allowed maximum PE values to comply with NZEB requirements are given in Table 2.

Table 1. PE factors used in European Commission recommendations (EC) [1], Estonia (EE) [2], Denmark (DK) [3] and Finland (FI) [4].

Table 2. National and EC NZEB requirements and energy flows included in the PE calculations [1-4].

The energy performance requirements are defined through the maximum allowed PE consumption, set in the national regulations [2, 3, 5] and is presented as Energy Performance Indicator (EPI) value in kWh/(m²·y). The EPI value incorporates so called EPBD uses, but in Estonia and Finland also lighting and appliances. Additionally, the Danish calculation includes specific “sanctions” for overheating, in which case a penalty is included as a fictive energy need, equal to the energy need (including PE factor of electricity) by an imaginary mechanical cooling system. The EPI value calculation follows in all countries the system boundaries of REHVA’s definition [6], but only on-site produced energy which is used by the building systems is taken into the account and is subtracted from the delivered energy [7]. The Danish methodology allows to account max 25 kWh/(m²·y) of PE from local electricity production. Exported energy is not accounted in any country when calculating the EPI value:

where Q1 is the annual delivered energy use for electricity, fuel, district heating, district cooling etc, [kWh/y], fi is the PE factor for the corresponding energy carrier, [dimensionless] and Anet is the net heated building area (gross area in Denmark), [m²]. The Estonian building regulation gives an additional requirement: maximum allowed PE use without accounting (subtracting) the on-site produced and used renewable energy from the building’s total energy use.

The analysis of the energy performance requirements was divided into following parts:

·         Comparing national requirements by the key numbers, energy performance calculation specifics and methodological differences.

·         Simulating building performance as required by the national regulations of each country.

·         Simulating building performance using national TRY weather and input data for standard use from EN 16798-1:2019 [8] to fulfil the EC PE recommendation for NZEB [1].

·         Comparing and analysing the results to quantify the strictness of the NZEB requirements.

Reference buildings

Two residential buildings were selected for the analysis: a single storey detached house and a multi storey apartment building. Both buildings were initially designed as NZEB according to its nation of origins: the single-family house in Denmark and the apartment building in Estonia. The buildings are representative examples of new NZEBs with modern designs and technical solutions (Figure 1). The main parameters of the buildings are described in Table 3.

Table 3. Building parameters.

National NZEB levels comparison

Single-family house

Following the Danish requirements, installation of 12 m² of PV (Figure 2, case 1) sets the building on the BR 2018 voluntary “low-energy” line [PE ≤ 27 kWh/(m² y)] that is more strict than mandatory NZEB. The NZEB requirement, PE ≤ 36.1 kWh/(m² y), is achieved with 5 m² of PV panels (case 2). The initial design installation of the house with 24 m² of PV produces a surplus of 73% PV energy compared with the amount required for NZEB. However, when calculating the building with 5 m² of PV using the EU standardized input data while leaving technical systems, envelope, and other building parameters initial (case 3), the building does not achieve the recommended energy performance level (Oceanic zone) of PE ≤ 30 kWh/(m²∙y), but is requiring additional 16 m² of PV panels (case 5). This means that even the amount of PV required for Danish low energy level is not sufficient to achieve EC level (case 4). In this case also the EC recommendation of PE without renewable energy production (Oceanic zone) is not fulfilled.

Figure 2. Annual PE consumption of the reference single-family house. PV energy production is added or removed to meet NZEB requirements. Code example: DK [TRY=DK; DK_LowE_PVreq=12 m²] – Danish methodology [Simulated with Danish TRY, meets Danish Low energy threshold with 12 m² of installed PV].

The PE recommendation for Nordic zone, PE ≤ 65 kWh/(m²∙y), is met with 18.5 m² of PV (case 6). This amount however is not sufficient to achieve the Estonian NZEB performance level (case 7). Even the initial installation of 24 m² PV panels (case 8) is not sufficient to meet the threshold of PE ≤ 120 kWh/(m²∙y). It would require 39 m² of PV panels in total (case 9) for the building to qualify in Estonia as NZEB (energy performance class A). The higher need for PV electricity production in the Estonian cases at one hand is because only the fraction of produced energy that is used in the building is accounted in energy calculation.

Even with the added PV production, the building does not meet all Estonian requirements - it would need to comply with energy performance class B without accounting the on-site renewable energy production; that is PE ≤ 140 kWh/(m²∙y). This requirement however is not fulfilled, meaning that, for example, the thermal or technical systems performance of the building envelope should be improved. This is also expected when moving the initial Oceanic design to a colder climate. In contrast, the Finnish NZEB requirements were met even without local renewable energy production (case 12). It must be emphasised that besides methodological and climatic differences, the PE performance results are largely influenced by the national PE factors. As the reference building utilises heat pump system for space, ventilation air, and DHW heating, the PE consist of only electricity consumption, highlighting the impact of the nationally different electricity PE factors.

Apartment building

The reference apartment building (designed for Nordic climate and including RE production to meet Estonian NZEB requirement) calculated according to the Danish building regulations met the NZEB requirement of PE ≤ 30.2 kWh/(m²∙y) quite easily with total PE of 9.9 kWh/(m²∙y) (Figure 3, case 1), which is also expected due to climatic differences. Even without PV production the building performance surpasses the required PE threshold by only 0.7 kWh/(m²∙y) (case 2).

The reference apartment building without PV production (case 3) is far to meet the EC Oceanic NZEB and exceeds the EC PE limit without on-site renewable energy production PE ≤ 65 kWh/(m²∙y). The reference building with PV does also not meet EC NZEB maximum value (case 4, calculated with EU standardised input data). This illustrates the relatively high performance level for EC Oceanic zone, considering the building is initially designed for Nordic climate. Basically, the results show that EC Oceanic NZEB is not achievable with district heating with EU default primary energy factor because the roof of the reference building is fully covered with PV and it is practically impossible to further improve the energy performance.

Calculation results using the EU standardised input data for Nordic climate position the building exactly to the EC recommended level for PE without accounting RE production, that is PE ≤ 90 kWh/(m²∙y) (case 5). Also, the EC PE recommendation with RES is fulfilled (case 6). As the building is designed as NZEB in Estonia, it is also designed to meet the national NZEB requirements with initial PV production (case 8) and the required low energy (energy class B) requirements (case 7).

Figure 3. Annual PE consumption of the reference apartment building. PV energy production is added to meet NZEB requirements. Code example: DK [DK_LowE; TRY=DK; PV=24 m²] – Danish methodology [Danish Low energy threshold; Danish TRY and 24 m² of installed PV].

As was the case with Finnish requirements for detached houses, the apartment building fulfils the requirements also without on-site renewable energy production as well (cases 9 and 10). The results indicate that the Estonian requirements match the EC recommendations if the building utilises district heating energy. It can also be stated that buildings designed to comply with Finnish building regulations, would not meet the EC PE recommended levels.

Conclusions

In case of the Oceanic zone, the EC recommendations for residential NZEB PE appear to require relatively higher energy performance compared to the Nordic zone recommendations. This is illustrated with the case of Denmark, located in colder part of the Oceanic zone. A highly insulated reference apartment building with district heating and PV fulfilling EC Nordic NZEB recommendation exceeded EC Oceanic NZEB recommendation(!). At the same time, a reference detached house with ground source heat pump and extensive PV installation was capable to meet EC Oceanic NZEB recommendation. However, this performance level clearly exceeded Danish NZEB and Low Energy.

In the Nordic climate zone, Estonian NZEB requirements complied very closely to EC Nordic NZEB recommendation. Finnish NZEB requirements were less strict and did not fulfilled EC Nordic NZEB recommendation.

The study illustrates the need of having two sets of requirements: with and without renewable energy production, as is the case for Denmark and Estonia and also for EC benchmarks. Denmark has solved the issue by setting the maximum amount of RE allowed to account in the PE calculation, requiring the building to achieve a sufficient level of energy efficiency by means of thermal insulation and HVAC systems. In Estonia there are PE requirements for the building without accounting on-site RE production as well as for the building including RES. Finland with less strict requirements, however, has not followed the separation of requirements.

Acknowledgement

This research was supported by the Nordic Energy Research, The joint Baltic-Nordic Energy Research programme (Project No.: 96752), by the Estonian Centre of Excellence in Zero Energy and Resource Efficient Smart Buildings and Districts, ZEBE, grant 2014-2020.4.01.15-0016 funded by the European Regional Development Fund and by the European Commission through the H2020 project Finest Twins (grant No. 856602).

References

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[8]    CEN. EN 16798-1:2019. Energy performance of buildings. Ventilation for buildings. Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics. Module M1-6, CEN, 2019. [Online]. Available: https://standards.cen.eu/dyn/www/f?p=204:110:0.