Achieved energy performance indicators at the ZEB laboratory in Trondheim, Norway

The aim of this article is to present monitoring possibilities, and measurement parameters available in the ZEB laboratory in Trondheim, Norway, and to highlight some of the positive lessons learned observed so far. The examples included in this article may offer valuable insights for similar buildings, illustrating the potential to reach ambitious energy performance targets through the application of existing technologies. The indicators investigated, presented, and discussed are the indoor air quality, heating energy use, heat pump performance, and specific fan power and total energy use.

Keywords: zero emission buildings, energy performance, monitoring system, PV

This article presents summarized results on the achieved energy performance in the ZEB laboratory (ZEB Lab) in Trondheim, Norway. ZEB Lab is an experimental facility located in Trondheim, operated by the Norwegian University of Science and Technology (NTNU) and SINTEF. The building purpose is office, laboratory, and education. The building is equipped with different energy service systems and monitoring equipment. As a part of the e-Infrastructure project, Smart Building Hub (SBHub) [1] monitoring results from this building will be collected as an example of a high-performance building.

Description of the ZEB laboratory

ZEB Lab, shown in Figure 1 is a zero-emission building that is as a pilot project for energy-efficient building strategies. It is located in the south of Trondheim and is used by NTNU and SINTEF and was completed in 2020. The ZEB Lab is categorized as a ZEB-COM building, which means that it should be able to produce enough energy to be able to compensate for related emissions for operation, equipment, materials, and construction phases.

Figure 1. ZEB Laboratory. (Photo: m.c.herzog / visualis-images)

The ZEB Lab has an area of 1 800 m² over four floors and it was designed by LINK Arkitektur with Veidekke as the main contractor [2] and consists of both offices and meeting rooms. The construction mainly consists of wood and is insulated with fiberglass wool. The southern facade on the first floor is built in such a way that both facade and window elements can easily be replaced. This makes it possible to test the properties of different products, materials, and technologies [3]. The building uses several different thermal solutions for heat supply and is equipped with PV system to enable electricity production [3]. In addition, the ZEB Lab is equipped with automatic sun shading to ensure satisfactory temperature in summer and that the sunlight should not be of a disturbance for the occupants [4].

The thermal system consists of a heat pump, phase change material (PCM) heat storage, water storage tank, connection to district heating, and electric boiler on the heating side, and cooling coils, fan coil, and an accumulator tank on the cooling side.

The building integrated PV installation ensures the production of electricity both for own use and export [5]. The PV produces direct current (DC) that is delivered to inverters/converters that convert the DC into alternating current (AC) which can be supplied back to the electrical grid via the inverter room. The PV plant consists of six areas, and the entire plant is a combination of several solutions from different suppliers. It has a total installed output of 181.5 kWp. For measuring produced electricity, the panel surfaces are grouped together into three different zones.

The ZEB Lab has been designed in such a way that it should be possible to test and use several different ventilation strategies. Therefore, the building has the option of using both natural, mechanical, and hybrid ventilation for supply air. While the exhaust in the building is done by warm air rising to the fourth floor, via the stairwells, and taken into the ventilation units via intake hatches up on the roof. There are some exceptions such as toilet rooms and technical rooms. The mechanical ventilation has two ventilation units that provide air supply. The units have rotating heat exchangers for heat recovery. Different distribution systems have been installed on each floor to be able to compare the various methods of distributing air supply. For the natural ventilation, the windows that are controlled have an automatic control that can be opened manually. The windows are placed strategically so that there is cross ventilation when they are opened. The stairwell in the building works as an exhaust for both natural and mechanical exhaust ventilation.

ZEB Lab has installed sensors for both the electrical and thermal systems that log different measurements. These measurements are then sent to a central building energy monitoring system (BEMS). This BEMS aggregates and organizes the measurement information before it is distributed to different platforms, such as InFluxDB, Grafana, and Energinet. Grafana is an open platform where the information that is published is public, and there is no requirement for a user access and password to access the data. Grafana retrieves data from the InfluxDB database and presents these data on its own platform. Grafana can be reached via the following link [6]. Energinet is an energy monitoring platform for energy management of many buildings. This platform is used by NTNU Campus Service and retrieves energy use and energy generation data directly from the BEMS.

Achieved indoor air quality

The parameters of the indoor air quality such as room temperature, relative humidity, and CO₂ level have been logged for all the rooms and analyzed. Here only the frequency analysis of the hourly indoor temperature values logged in 2023 are given in Figure 2. The numbers in the legend in Figure 2 show the room numbers, meaning that 2.07 is an office room on the second floor, while 3.21 is the office on the third floor.

Figure 2. Frequence analysis of the indoor temperature in the offices.

In general, the results in Figure 2 show that the most rooms maintained indoor temperatures within the 22–26°C range, indicating generally acceptable conditions. Please note Figure 2 includes the data for the entire year, covering very warm and cold days, and fails in operation. A few rooms experienced occasional overheating above 26°C, particularly room 3.12, while temperatures below 19°C were rare across all spaces. This suggests effective overall temperature control, with some potential for improvement in warmer zones.

Heating energy use

The energy signature curve describes the relationship between the outdoor temperature and the total heating use. The energy signature curve is shown in Figure 3.

Figure 3. Energy signature curve for ZEB Lab.

The results in Figure 3 show that the maximum heating use was between 15 and 20 W/m² for the lowest outdoor temperature, which is comparable with the passive house requirements for the heating use. Figure 3 shows a clear relationship between the outdoor temperature and heat rate (heating energy use), with higher heating use observed during colder conditions. Heating is most requested during working hours, while significantly lower during nights and non-working periods. The energy signature curve in Figure 3 can be used for comparison or validation for the other buildings with similar properties.

Heat pump performance

The ZEB Lab is equipped with an R-290 (propane) heat pump. By analyzing the heat pump measurements, relevant performance data can be extracted. Figure 4 shows the heat pump performance in the form of compressor power vs. condenser heat graph. Due to a good measurement system, it is possible to extract the relevant data and document performance of the heat pump.

Figure 4. Compressor rate vs. condenser heat of the heat pump.

For the data shown in Figure 4, COP of the heat pump is about 2.7 over the wide range of delivered condenser heat. This means that for every kW of compressor input, around 2.7 kW of heat is delivered, reflecting an efficient heat pump performance. Further optimization operation will give better performance.

Specific fan performance

The specific fan power (SFP) for one of the AHUs is given in Figure 5. Due to the ductless exhaust system in ZEB Lab, the achieved SFP is very low. Such low SFP is three times lower than the national building code requirement [7]. The results shown in Figure 5 can be used for validation and comparison with similar ventilation systems in energy efficient buildings.

Figure 5. SFP for AHU1.

Total energy use

Finally, the total energy use, electricity and district heating, and PV generation for 2024 is shown in Figure 6. The values for the analysis in Figure 6 are obtained from the Energinet monitoring system. The results for 2024 showed that the total specific energy use of ZEB Lab was 30.63 kWh/m² of electricity and 6 kWh/m² of district heating. The district heating use decreased significantly after February 2024, because the heat pump was changed to one that can operate better than the one installed initially. Furthermore, the results showed that the total electricity export to the local university electricity grid was 97.33 MWh or 54 kWh/m². The fact that the building could export more electricity than purchased showed that the building would be able to achieve ZEB-COM building requirements.

Figure 6. Total energy use and PV production at ZEB Lab.

Conclusions

This article presented some of the indicators of the achieved energy performance at ZEB Lab in Trondheim. The building is well equipped for monitoring and testing of building service systems. The results achieved could be used for validation and calibration purposes when modeling similar buildings. Results also show energy performance targets that may be achieved with the use of available technologies, such as high COP for the heat pump and low SFP in ventilation. Finally, through utilization of the advanced monitoring sytem at the ZEB Lab, different analyses and optimization methods for the improvement of building performance could be identified. In the future, we will be glad to share more of our results and to participate in different collaboration projects.

Acknowledgements

The work presented in this article was developed under the Smart Building Hub project that is funded by the Research Council of Norway's INFRA programme under Grant number 322573.

References

[1]     E-infrastructure for energy-flexible and healthy buildings, in https://smartbuildinghub.no/

[2]     Veikdekke, ZEB Flexible Lab, Trondheim, in https://www.veidekke.no/prosjekter/zeb-flexible-lab/.

[3]     B. Time, A. Nocente, H.M. Mathisen, A. Førland-Larsen, A.R. Myhr, T. Jacobsen, A. Gustavsen, Research possibilities in the Norwegian ZEB Laboratory, in: REHVA European HVAC Journal, 2019.

[4]     O. Lædre, A. Engebø, E. Andenæs, S. Hajizadeh, T. Kvande, O.J. Klakegg, Erfaringer fra ZEB-laboratoriet: byggeprosessen, bygningsteknologien og bruken, in, Institutt for bygg- og miljøteknikk, NTNU, 2023, pp. 48.

[5]     A. Nocente, B. Time, T. Kvande, H.M. Mathisen, A. Gustavsen, BIPV in Nordic climate: the ZEB Laboratory, REHVA European HVAC Journal, 2022.

[6]     ZEB Laboratory, Current energy flow, in https://zeblab.sintef.no/grafana/d/RjBGPzuVk/landing-page?orgId=1&refresh=5s.

[7]     Building Technical Regulations with guidance, Directorate of Construction Quality, https://www.dibk.no/regelverk/byggteknisk-forskrift-tek17/14/14-2, 2025.