Energy Solutions
The ZEB Laboratory is equipped with building-integrated photovoltaic (BIPV) panels and heat pumps that can make use of different heat sources (i.e. heat recovery from service and outside air). This makes it possible to investigate possible combinations between available local renewable energy production and the centralised electricity grid that matches the zero-emission building requirements. A phase changing material (PCM) heat storage battery is installed in the building, which can recover thermal energy from the BIPV roof and acts as a thermal energy buffer to ensure more efficient use of the heat pumps. The PCM heat storage infrastructure is made flexible so that research and development of such systems can take place in the future. Grid integration makes it possible to implement experiments on the interface between zero-emission buildings and grids, especially smart power grids but also district heating and cooling grids. This enables for example the study of the performance of optimal predictive control strategies, load shifting and energy storage.
Photovoltaic / Solar Panels
| Number of panels | 701 |
|---|---|
| Total covered area | 963.4 m² |
| Installed PV power | 181 kWp |
| Manufacturers | SunPower, SolarLab, SoliTek |
The whole renewable energy production of the ZEB Laboratory is achieved by harvesting solar power with building-integrated photovoltaic (BIPV) panels. These solar panels were installed very early in the building process, allowing the electricity generated to be used in the construction of the rest of the ZEB Laboratory. The solar panels are waterproof and can replace building materials on the surface they are installed on (except for a small layer of asphalt beneath the solar panels), thus the name "building-integrated" photovoltaics.
The entire roof is covered by BIPV panels, as well as most of the South, East and West façades and the upper part of the North façade. The whole surface of the pergola that screens the largely glazed part of the façade of the ground floor is built with BIPV elements. In this case, the system needs to have a certain transparency to allow the natural lighting of the ground floor. The solution is based on a chessboard distribution of opaque and semi-transparent PV panels. The latter are double-sided, thus being able to extract power from the reflected and diffuse radiation present in the space below the pergola. The thought behind the pergola covered with PV panels is that it is easy to test new kinds of PV panels when they are developed. The West and North façade are only partially covered with BIPV panels. This choice was taken by cost-benefit consideration related to the ZEB goal. The BIPV panels on the North wall are particularly high-efficiency photovoltaics, well suited for the limited sun conditions here. The roof of the ZEB laboratory is angled and positioned to ensure ideal harvesting of solar power, with a slant of 30° and facing south. During the winter, the roof is often covered with snow, and mostly the façades are producing electricity. The ZEB Laboratory is oriented such that the angled roof is directly south (azimuth 180° from north).
The total number of panels installed is 701, covering 456 m² out of the 560 m² available roof area, in addition to 507 m² covering the façades of the building and the pergola, corresponding to a total area of 963.4 m². All the panels are based on mono-Si cells, but different types from different manufacturers are installed to optimise the size and distribution, and especially to be able to accommodate custom made PV-panels (triangular or trapezoidal) installed to cover most of the available surface on the East and West façades. All the panels are covered with an anti-reflex paint, contributing to the uniformity of colour. The total installed PV power is 181 kWp, where kWp (kilowatt-peak) indicates the power capacity at standard test conditions. The highest peak observed so far is around 120 kW. The solar panels are organised in strings optimised to maximise power conversion. Three multi-string inverters (DC to AC) are installed with a rated power of 110 kW, 50 kW and 10 kW, respectively. The AC power is transferred to the power grid at 400 V. Through solar power simulations run on this configuration, it was calculated a net electric work contribution of 156 MWh per year. A replacement of the panels is planned after 30 years, half of the expected lifetime of the building. The solar power production in the construction period was 54 000 kWh, while the amount used during the construction period (18 months) was 288 000 kWh. The cumulated solar power production since installation has already exceeded this.
An overview of the solar panels installed and the manufacturer of each on the different surfaces of the ZEB Laboratory is illustrated below:
| Placement | Type of BIPV | Fastening element | Installed power (kWp) | Area (m²) | Number of BIPVs |
|---|---|---|---|---|---|
| Roof (30°) | SunPower 350 | IRFTS | 98 | 456.3 | 280 |
| Northern façade | SunPower 375 | Baywa | 11.25 | 53 | 30 |
| Eastern façade | SolarLab | Nvelope | 24.47 | 156.2 | 144 |
| Southern façade | SolarLab | Nvelope | 22.36 | 144.2 | 132 |
| Western façade | SolarLab | Nvelope | 12.365 | 79.6 | 73 |
| Pergola | Half and half SunPower 375 and SoliTek | Baywa | 7.875 + 4.83 | 37.1 + 37 | 21 + 21 |
The calculated solar power flow per year is summarized in the following table:
| kWh / year average | |
|---|---|
| Production | 156 000 |
| Export | 94 000 |
| Consumption | 62 000 |
After completion of the building, the top 3 solar power production days per 10.05.23 were:
- 06.06.2022 1139 kWh
- 17.05.2022 1127 kWh
- 05.05.2023 1091 kWh
Grafana dashboard of interest: Solar panel efficiency.
Heating Systems
The ZEB Laboratory's centralized heating system relies on a heat pump system and several heat sources and heat sinks along the hot water heating circuit. The selected heat pump system is designed to provide a temperature lift on the hot side from 35 °C to 40 °C. Besides the heat pump, heat from the local district heating is used as a heat source for the building, providing hot water at 47°C. Throughout the heating circuit, preheating of domestic hot water, room radiators and heat exchangers providing heated air for ventilation are used as heat sinks to heat the building. The heating and the Domestic Hot Water (DHW) systems are based on two air-to-water heat pumps. The machines make use of natural coolant R-290 and absorb a peak power of 16 kW from a 3-phase 400V AC line. The facility is also equipped with another heat pump, only used as a refrigeration machine for technical systems when needed. The technology of this machine is the same, but it has a smaller size with a peak power absorption of 14 kW.
The low-temperature heating system in the ZEB Laboratory is centred around the heat pump providing hot water for space heating and integrating an LHS unit. The heat pump is meant to cover the maximum heat demand of the building, calculated to ca. 26 kW, necessary to maintain all rooms in the building at a comfortable temperature on the coldest days of the year in Trondheim (Norway). Using the LHS unit to support peak heating demands, the size and nominal effect of the heat pump can be significantly reduced so that it operates more effectively. A constant heat output of 14 kW from the heat pump combined with a charged LHS unit of about 200 kWh would allow for a total heating output of 26 kW for up to 16 hours. The integration of the LHS unit as an active component of the central heating system thus enables thermal buffering to support the heat pump.
The building is not equipped with an electrical cooling system, both for research purposes and to save energy. An ambition of the ZEB Laboratory project is to evaluate to what extent the building can be cooled only using passive means and ventilation strategies, representing an interesting research area. All cooling, except for within the Twin Rooms, is done through natural ventilation.
Since heat is a form of low-quality energy, it is important to reuse it, to be able to reach the goal of ZEB-COM. The building generates heat in several forms, for instance from the servers. There is a system for heat recycling in the building, to save energy and be as efficient as possible. The heat recycling site is located in the middle of the building on the first floor, so that as little as possible of the heat is released unintentionally. The PCM tank and the water storage tank located in and next to the laboratory respectively also have heat recycling properties, as well as the solar panels' DC/AC inverters having heat recovery properties.
Grafana dashboards of interest: Energy flow and Energy use vs calc.
PCM Bio-Wax Heat Storage
| Design | Custom pillow-plate heat exchanger |
| Dimensions (height * width * length) [m] | 1.5 * 1.4 * 2.25 |
| Measured PCM melting temperature range [°C] | 35 – 39 (heat flow peak at 36.5) |
| Measured PCM solidification temperature range [°C] | 32.5 – 35.5 (heat flow peak at 34.5) |
| Measured PCM latent heat of fusion [kJ/kg] | 198.6 |
| Measured PCM latent heat of crystallisation [kJ/kg] | 196.4 |
| PCM density [kg/m³] | 957 (at 32°C), 819 (at 75°C) |
| PCM thermal conductivity [W/m.K] | 0.24 |
| PCM specific heat capacity [kJ/kg.K]] | 2.3 (solid), 1.4 (liquid) |
| PCM degradation temperature [°C] | > 50 |
| Total theoretical thermal storage capacity (from 30 to 40°C) [kWh] | 194 |
| Ratio of latent heat to total heat storage capacity | 87% |
The centralized heating system in the ZEB Laboratory is equipped with an innovative, first-of-a-kind, large latent heat storage (LHS) tank based on a Phase Changing Material (PCM) and developed as a prototype for this laboratory. The LHS unit has been integrated with the central water-based heating system and stores excess heat from the main heat pump and the district heating network. The storage is coupled to the heat pump to have a peak shaving effect for the heating requests, by evening out the temperature extremes, allowing the machines to work at their best efficiency. The PCM is also able to store excess heat from various heat sources connected to the heating system, like the local excess PV electricity, when they are not required for space heating. During hours of low heat demand, the LHS unit will be able to store excess heat, charging from the heat pump or district heating. During high demand, the stored heat will be released either to provide heat directly to the heating circuit or to support the heat pump by compensating for a drop in return temperature below the optimal intake temperature.
The LHS system consists of a 5 m³ (2.4m x 1.4m x 1.5m) insulated tank with a bank of metal pillow plates immersed in a 3-ton phase-changing material. The latter is CrodaTherm 37; a water-insoluble organic PCM, derived from plant-based feedstocks. The PCM appears as a crystalline organic wax (bio-wax) in its solid state and oily liquid above its melting point, measured at around 37°C (35-39°C temperature range, 36.5°C peak). The density of the material is 957 kg/m³ in its solid state (32°C) and 819 kg/m³ in its liquid state (75°C), and the measured latent heat is 198 kJ/kg. The design of the LHS unit makes the system 4 times more compact when compared to traditional hot water storage, making it more suitable for indoor installation and use. In terms of energy, the heat storage capacity is calculated to be around 200 kWh, corresponding to the heat needed on top of the heat pump to cover for 2-3 consecutive days in the coldest days of the year, with a maximum combined heat output of 26 kW. The bio-wax was chosen because it is much greener than petroleum-based wax, as it is expected to be readily biodegradable and has a high renewable carbon content. This PCM also has a low degree of supercooling, affordable cost, and low flammability. The implementation of the LHS unit was made possible with the financial support of 1.3 MNOK granted by ENOVA.
The PCM tank operates based on five operational modes, opening and closing valves for water to flow in the desired directions, currently following a time schedule with the possibility of integrating further parameters to increase energy efficiency. The ZEB Laboratory is heated when the PCM is 40°C, and when the wax has cooled down to 25°C, heat returns to the heat storage battery. Integrating the LHS unit downstream from the heat pump, with the option to circulate the return water through it or not, provides the opportunity to both charge and discharge the LHS unit while smoothing the output demand from the heat pump. Charging occurs when the heating demand is low, using 40°C as inlet temperature, as it is generated by the heat pump. Return water with temperatures below the PCM's melting point can circulate through the charged LHS unit and be heated up before entering the heat pump. Additionally, the LHS unit can be directly charged using the district heating loop providing hot water at 47°C.
| Mode | Description |
|---|---|
| Normal mode |
|
| Charging PCM from heat pumps |
|
| Charging PCM from district heating |
|
| Discharge to plant |
|
| PCM supports heat pumps |
|
When the LHS unit is charged and the heating demand is relatively low, it is possible to use the PCM as a direct heat source in the building heating loop. The heat pump can be bypassed, significantly reducing energy consumption during these low-demand periods. This operational mode is especially interesting if energy price is integrated with the control system of the overall heating system. Control strategies through a large number of control valves and two regulated water pumps is a topic of research, including a temperature-controlled strategy for charging and discharging using only the heat pump as a heat source and heat sink, and a price-controlled strategy where the energy price is taken into account to decide (1) when to harvest heat from the district heating network or from excess production of the solar panels and (2) when to use the LHS unit as a direct heat source for the building heating circuit. The control system of the LHS system is fully integrated with the building control system, which includes a "Research Mode" to allow customizing and testing of various control strategies.
A well-known challenge with using PCM for thermal energy storage is the poor thermal conductivity for available PCMs, limiting heat transfer rates<ref name="Shukla 2008">Shukla, A. & Buddhi, D. & Sawhney, R.L.. (2008). Thermal cycling test of few selected inorganic and organic phase change materials. Renewable Energy. 33(12): 2606-2614. ISSN 0960-1481. doi:10.1016/j.renene.2008.02.026.</ref><ref name="Sevault 2017">Sevault, Alexis & Kauko, Hanne & Bugge, Mette & Banasiak, Krzysztof & Haugen, Nils & Skreiberg, Øyvind. (2017). Phase change materials for thermal energy storage in low- and high-temperature applications: a state-of-the-art. SINTEF Energy Research Report. TR A7638 - ISBN 978-82-594-3684-9. URI:http://hdl.handle.net/11250/2487493.</ref>. Comprehensive work has been done to increase the heat transfer rates within LHS systems by utilizing heat transfer enhancement techniques in numerical investigations and experimental setups. Previous studies have concluded, by utilizing a TRNSYS numerical model, that an LHS system integrated into heat pump systems can completely offset peak heat demand periods within 2 to 6 hours, reducing peaks in the power grid<ref name="Hirmiz 2019">Hirmiz, R. & Teamah, Heba & Lightstone, Marilyn & Cotton, J.S.. (2019). Performance of heat pump integrated phase change material thermal storage for electric load shifting in building demand side management. Energy and Buildings. 190: 103-118. doi:10.1016/j.enbuild.2019.02.026.</ref>. By using a PCM, it has also been found that the heat pump heating system COP increases<ref name="Bonamente 2016">Bonamente, Emanuele & Aquino, Andrea & Cotana, F.. (2016). A PCM Thermal Storage for Ground-source Heat Pumps: Simulating the System Performance via CFD Approach. Energy Procedia. 101: 1079-1086. doi:10.1016/j.egypro.2016.11.147.</ref>. The designed LHS unit in the ZEB Laboratory can store up to 194 kWh of heat and simultaneously achieve sufficiently high heat transfer rates during discharge to successfully back up the heat pump during the coldest winter days or be used as a heat source in the central heating system.
A small circular window of glass is placed on the PCM tank, allowing onlookers to observe what phase the material is currently in and supporting the communication of the ongoing processes in the building. Heat loss through the PCM glass has been calculated, resulting in a heat loss of circa 5,84 W when the insulating cover is off. The cover for the window has an insulating effect, measured to insulate about 90% of the heat loss. When the cover is on, the resulting heat loss is then only around 0,62 W.
Grafana dashboard of interest: PCM.
Water Systems
As a climate-adaptable ZEB-COM building, the ZEB Laboratory and its close surroundings must tackle climate change and enhanced precipitation. The areas on and near the building that require drainage capacity are divided into different zones, those being (1) the parking space, (2) permeable surfaces and rain beds and (3) the roof. The zones are separate and the water from each is led into a new innovative water storage tank (Alma Smart Tank) designed to store and detain water, newly developed by Skjæveland. As the roof of the ZEB Laboratory is covered in building-integrated solar panels (BIPVs), the BIPV system needs to be as water-proof as possible to avoid moisture damage. The roof's incline of 30° and the smooth surface cause heavy downpours to result in a large amount of water pouring at a high velocity down the roof. An external gutter sufficiently large enough to catch the run-off water would cover the solar panels on the upper parts of the south façade, thereby reducing energy production. With an outlet of too narrow dimensions, the water will not be able to be collected in the box gutter. Experiments have been carried out at the Rain and Wind (RAWI) Box at SINTEF Laboratory to design and dimension the ideal internal gutter, integrated with the roof surface, considering run-off at peak flow and backsplash.
The ZEB Laboratory has a combination of many stormwater handling solutions, where the run-off of the various solutions is collected in the large Alma Smart Tank that controls joined discharge to the pipe network. A permeable cover, two rain beds and other green areas provide stormwater management with its own run-off characteristics. The water from each of these solutions and the collected roof water are led in separate pipelines into the reservoir/tank. Measuring instruments that allow measurement of the runoff flow from each of these solutions are installed. This will consent to the study and the comparison of the solutions and it will favour valuable information on future different combinations with different run-off profiles adapted to local conditions and requirements. The reservoir/tank is split into two parts, making water from one part suitable to be reused for irrigation and other uses, so-called "water for utilization". The tank can also be equipped with a heat exchanger. This way, the heat contained or the whole water mass can be used as additional heat storage.
-
Drainage areas and their locations -
Alma Smart Tank - Skjæveland
References
<references />
Further reading
- Sevault, Alexis & Bøhmer, Fabian & Næss, Erling & Wang, Liang. (2019). Latent heat storage for centralized heating system in a ZEB living laboratory: integration and design. IOP Conference Series: Earth and Environmental Science. 352. 012042. doi:10.1088/1755-1315/352/1/012042.
- Sevault, Alexis & Næss, Erling. (2020). Active latent heat storage using biowax in a central heating system of a ZEB living lab. International Institute of Refrigeration (IIR). Proceedings of the 14th IIR-Gustav Lorentzen Conference on Natural Refrigerants. doi:10.18462/iir.gl.2020.1146.
- Bøhmer, Fabian. (2019). Design of a PCM-based heat storage unit for the ZEB Flexible Laboratory. Master Thesis, NTNU, Trondheim. URI:http://hdl.handle.net/11250/2623189.
- Nocente, Alessandro & Time, Berit & Mathisen, H.M. & Kvande, Tore & Gustavsen, A.. (2021). The ZEB Laboratory: the development of a research tool for future climate adapted zero emission buildings. Journal of Physics: Conference Series. 2069. 012109. doi:10.1088/1742-6596/2069/1/012109.
- Time, Berit & Nocente, Alessandro & Mathisen, Hans & Førland-Larsen, Arne & Myhr, Anders & Jacobsen, Terje & Gustavsen, Arild. (2019). ZEB Laboratory - Research Possibilities. SINTEF Academic Press. SINTEF Notes 33. URI:http://hdl.handle.net/11250/2611934.
- Johansen, Katalin Sandor & Stagrum, Anna Eknes. (2019). Takrenne for BIPV-tak. Byggeindustrien, no. 10, p. 32.
- Sivertsen, Edvard & Muthanna, Tone Merete & Møller-Pedersen, Per. (2021). Utvikling av nye overvannsløsninger. Byggeindustrien, no. 18, p. 24.