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Researchers in Sweden have investigated how laminated photovoltaic-thermal (PVT) collectors can act as secondary heat sources in geothermal heat pumps and have found that they provide better performance than conventional PVT panels. Their techno-economic analysis also showed that laminated PVT systems can be up to 9% more expensive than conventional installations based on sheet and tube absorbers.
Researchers at KTH Royal Institute of Technology in Sweden claim to have identified the optimal techno-economic system design for coupling a geothermal heat pump (GSHP) with photovoltaic-thermal (PVT).
The scientists designed the system with sheet-bonded photovoltaic collectors with channels embedded between two sheets of laminated aluminum, which have a higher heat transfer coefficient than conventional photovoltaic panels that use sheet-and-tube absorbers.
“A drawback of the roll-joint design is a higher pressure drop, which was found to be more than double that of the reference sheet-and-tube PVT under the same operating conditions,” they explained. “A box-channel design can be used to further increase the heat transfer area between the absorber and the fluid.” However, they also noted that roller-bonded panels have higher manufacturing costs.
The research team tested the foil collectors at sub-ambient fluid temperatures in combination with a GSHP under a wide range of low-temperature operating and meteorological conditions using open-air laboratory experiments in Stockholm. In the proposed system configuration, the PVT collectors act as secondary heat sources.
“The tests of the ISO 9806:2017 standard are used as a basis for the evaluation of thermal performance, although the fact that the tests are carried out at temperatures below ambient and dew point is an exception to the standard,” they specified. the academics.
The techno-economic analysis was based on the basis that the system would be deployed in a multi-family home with a total heated area of ??2,000 m2, a heating demand of 125 kWh/m2a and a domestic hot water (DHW) demand of 38 kWh/m2a. . The system consisted of an 88 kW GSHP boiler and 144 photovoltaic collectors facing south with an inclination angle of 45 degrees.
The system included a hot water accumulator and a 10 kW air-water heat exchanger to dissipate the heat generated by the heat pump. System performance was compared to that of a reference system with conventional PVT collectors.
Tests showed that box channel propylene PVT collectors produce more heat per square meter than their conventional counterparts, while exhibiting 34.4% lower thermal output. Additionally, rolled propylene collectors were found to be 9% more expensive than reference panels.
“Of the finless designs, the sheet and tube design has a similar thermal unit cost to the finned box channel aluminum design, but produces 40% less heat per square meter annually,” highlighted the academics, who noted that the roll bond design results in better overall performance.
“This approach will allow its effects on borehole regeneration and heat pump performance to be further explored, ultimately allowing the identification of the optimal techno-economic design to integrate PVT collectors with geothermal heat pump systems taking into account the PVT, drilling and energy prices,” they noted in reference to the future direction of their work.
The system was presented in the study “ Empirical investigation of solar photovoltaic-thermal collectors for heat pump integration ,” published in Applied Thermal Engineering .
Another research group at the KTH Royal Institute of Technology recently investigated the possible coupling of a GSHP with both photovoltaic-thermal (PVT) and free cooling (FC). |
