Spanish researchers have proposed a new approach to combine photovoltaic thermal panels with a reversible air-to-water heat pump in industrial buildings. The system is intended for space heating, cooling, hot water and electricity production.
The system is intended to supply heating, cooling, hot water (HW) and electricity to industrial buildings.
“In the space heating/cooling distribution circuit, fan coils are used as terminal units, which enables an inlet temperature of at least 35 C in winter and 7 C in summer,” they describe the way the system works. “In order to increase the use of low heat, LKV is delivered at 50 C instead of 60 C and periodic heat treatments are performed at 60 C to avoid legionellosis in accordance with sanitary regulations.”
The scientists tested the proposed system design for 5 months in a real system deployed at an industrial facility in Zaragoza owned by Spanish PVT specialist Endef. The hybrid pilot plant consists of eight PVT modules with a combined capacity of 2.6 kW and covering an area of 13.6 meters2two water tanks with a volume of 350 l for HVAC and 263 l for space heating and cooling, and a Yutaki S6 reversible air-to-water heat pump from the Japanese manufacturer Hitachi.
The nominal power of the heat pump is 16 kW in heating mode and 10.5 kW in cooling mode. Its nominal coefficient of performance (COP) in heating mode is 4.57 and in cooling mode 3.31. The DHW water heater has two internal heat exchangers, one for the solar circuit and the other for the heat pump. The system can produce 20 C to 60 C in heating mode, 30 C to 60 C in LKV production and 5 C to 22 C in cooling mode.
The research team used temperature sensors and flowmeters to monitor the thermal performance of the system and a DC/AC inverter to analyze the performance of the solar power generation unit. “The actual weather data observed in the test facility is integrated into the model. The transient model is run at a time step of 5 minutes and the results shown in this work are averaged every hour to smooth the results, as otherwise the fluctuations obscure the graphical interpretation and comparison of the results,” it further explained. “Weekly energy results are also calculated by integrating weekly performance indicators for comparison.”
Through this analysis, the researchers found that the system is potentially “generally self-sufficient” in meeting the building’s energy needs. They also stated that the deviation of the pilot plant from the simulated setting is negligible. “The results show that the heat pump COP estimated in the transient model is similar to that obtained in the pilot plant with an average error of -10%,” they further explained.
The proposed system is presented in the document “Experimental validation of a solar system based on photovoltaic-thermal hybrid collectors and a reversible heat pump for energy production in non-residential buildings, published Estimates of renewable and sustainable energy.