Researchers in Italy have designed a water source heat pump system intended to generate cooling, heating and hot water for domestic use in social housing stock built between 1970 and 1990. The new concept integrates photovoltaic thermal energy with thermal storage and promises a seasonal coefficient of performance of 5.
A group of researchers led by the Sapienza University of Rome has developed a new water source heat pump system (WSHP) that integrates photovoltaic thermal energy (PVT) and thermal energy storage (TES) for the production of integrated heating, cooling, domestic heating water production and electricity.
The system was developed under the umbrella of the EU-funded REHeat research project, which aims to identify renewable and energy-efficient solutions for heating and cooling, as well as for hot water production in multi-apartment residential buildings. “This work focuses on the Italian version of the REHeat project,” the scientists said, noting that the proposed system uses a hot water storage tank instead of an underground heat storage unit, like the system versions developed for European countries at higher altitudes. latitudes.
The system consists of a water source heat pump combined with cooled photovoltaic panels, two storage units – one source side and the other side load – and a fan coil unit. In the proposed system configuration, the low temperature heat from the panels is used to fill the cold source of the heat pump during the heating season. During the cooling season, excess heat from PV panels, which reach higher temperatures, is transported to the sanitary hot water production system.
“PVT panels provide thermal and electrical cogeneration, where the electrical energy is used to power the WSHP, any backup heaters, auxiliary equipment and condominium areas, while the low temperature heat produced during the winter period is used as a source for the WSHP through the TES,” the research team explained. “Outside the heating period, from April to October, the heat produced by PVT is used to produce hot water, which is stored in the special storage. Finally, in the summer period the WKO is connected to a DC, which is necessary to remove the excess heat produced by the HP for space cooling.”
Using TRNSYS software and the Multi Criteria Decision Making (MCDM) method, the academics carried out 184 simulations to identify the ideal size of the system components with the aim of deploying it in a social housing building with 13 apartments built around 1980 in Palombara Sabina, near Rome, Italy.
“The reference sample is the result of the urban planning started in Italy in the 1960s to program interventions related to social buildings before the regulations on energy performance in buildings,” they explained, adding that the building , which currently relies on a centralized gas heating system, has a winter and summer heat load of 61 kW and 65 kW respectively, and a hot water consumption of 55 l/person for a total of 50 people.
In the simulations and MCDM analysis, the academics took into account key parameters such as the coefficient of performance (COP), the solar fraction, primary energy consumption, primary energy savings, system and operating costs, as well as logistics-spatial criteria. The researchers discovered that the best system configuration can be achieved with 75 PVT panels totaling 25 kW distributed over 15 strings, a buffer tank volume connected to the source side of the HP of 3 m³ and a volume of 1.5 m³ for the thermal DHW storage. .
“The identified temperature set points were 25 C for the DC, while for the HP both the evaporator and condenser operating temperatures vary depending on the external conditions,” they further explained. “On the cold side they range from 7 to 20 C and vary depending on the incident radiation and the low temperature heat production of the PVT panels, while on the warm side they vary depending on the outside temperature.”
The system was described in the study “Definition of a PVT coupled water source heat pump system through optimization of individual components,” published in Energy.
“This work aims to use the building in Palombara Sabina as a pilot project for upgrading a central heating system for mild climates, to propose it as an ideal approach to be widely applied to the entire social housing stock developed in the was built in the seventies. 1990s, with a view to energy renovation on an urban scale,” the researchers conclude. “The objectives are the efficiency of the system, with a minimum seasonal COP of 5 and a minimum coverage of 70% from renewable sources, aimed at managing the ambient temperature.”
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