A research team led by scientists from Sweden’s KTH Royal Institute of Technology has investigated the use of air-based photovoltaic thermal (Air-PVT) technology in Nordic climates.
“At a first stage, we are exploring Air-PVT, which is an unconventional solar technology to begin with. We wanted to show how upgrading from standard PV to Air-PVT in renovations can help reduce energy costs, improve the energy class of buildings, and add to the property value while adhering to eventual solar mandates in the future,” corresponding author Giorgos Aspetakis told pv magazine. “On a scientific level, this study goes beyond theoretical modeling in the lab. It is grounded in real-world data from an operational Air-PVT prototype and a multi-family building in Stockholm, Sweden.”
The Air-PVT prototype was tested in an apartment building in Stockholm, where it was used for both heat recovery ventilation (HRV) and domestic hot water (DHW).
Image: KTH Royal Institute of Technology, Applied Thermal Engineering, CC BY 4.0
The prototype was manufactured by attaching a backplate to a solar PV panel and drawing ambient air through a 14 mm channel using negative pressure. The experimental system included air ducts, an air blower, and measurement instruments. Continuous measurements were taken over 42 days during the summer, and simulation results for the same period were compared with the experimental data. Based on their validation results, the team was able to determine “that the models adequately validated the real-life operation of the collector.”
After validating the system, the group simulated its operations in a building with 56 apartments. Collaborating property owners provided schematics and equipment datasheets, along with sensor measurements, including temperature, pressure, and volume flows, which were monitored for multiple years. The analysis focused on two main activities: preheating the cold-water supply for DHW production in summer and preheating fresh incoming ventilation air for the rest of the year. Two additional locations were selected to illustrate the effects of climatic conditions, namely Lund in southern Sweden and Umeå in the north.
“It was surprising to discover that heating domestic hot water using warm air, which sounds counterintuitive, is actually feasible from a district heating peak shaving perspective,” Aspetakis noted. “Another unexpected fact was that on some sunny winter days, the Air-PVT was capable of increasing the incoming fresh ventilation air from 0 to 20 C.”
Furthermore, the system can reduce annual district heating demand by 16% for ventilation and 7% for domestic hot water. The system also significantly reduces peak district heating demand for hot water, with an average reduction of 11% over the season and more than 50% on some days. Ventilation savings were similar across climates, but frost reduction was less effective in northern Sweden. Panel inclination had little impact, and vertical installation provided only minor additional heating benefits.
“The relative energy savings for ventilation induced by Air-PVT remained steady for varying levels of heat exchanger efficiency,” the team concluded. “Units with efficiency under 85% benefited most in absolute terms. On the contrary, frost formation in the HRV system was mitigated, particularly for high efficiency units, with a difference of up to 200 h.”
Having primarily worked with heating systems in cold climates, Aspetakis said, his team plans now to “expand the scope to warmer regions and evaluate the potential of Air-PVT for solar cooling. We also plan to take a deep dive into the economics of the technology, to demonstrate viable business cases.”
The system was described in “Exploring Air-PVT for buildings in cold climates: Experimentally validated energy system modeling,” published in Applied Thermal Engineering. Researchers from Sweden’s KTH Royal Institute of Technology, installation and technical services company Bravida Holding, and building solutions supplier Uponor have contributed to the study.
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