Researchers in Italy have designed a new carbon dioxide heat pump that can work with photovoltaic thermal energy, a fin heat exchanger and a heat exchanger of the U-tube borehole. Their experiment has shown that the simultaneous use of at least two energy sources always results in improved system performance, even with limited heat transfer areas.
A team of scientists, led by the Italian University of Padova, has simulated a new heat pump Numerically, which is said to combine three renewable energy sources with high efficiency.
The system uses photovoltaic-thermal (PVT) collectors such as the sun source, a U-tube borehole heat dresser (bra) for the ground source and a Forsed Coil Heat Exchanger (FCHE) for the air source.
“Two configurations of the Multisource heat pump are being investigated: Solar-Air mode (SA mode) with Finned Coil and PV-T collectors that are performed at the same time and the Grond-Air mode (GA-Mode) with Fold Coil and BHE that are active at the same time,” the team explained. “The Multisource system works as a Dual Source Heat Pump (DSHP) in every mode. It is important to note that this configuration differs from all existing parallel and series setups in the literature.”
The numerical simulation was constructed using MatLab software. Apart from the PVT units, braes and the FCE, the system also included a compressor, a gas cooler (GC), an internal heat exchanger (IHE), an electronic expansion valve (EEV) and a low pressure receiver (REC). The Finned Coil -Verdamper is fed with dry expansion, while the solar and soil evaporators work in the flooded mode. It works with CO2 as a coolant.
“The overheated coolant is compressed and sent to the GC to be cooled. It then goes through the IHE, where the further lower cooling is undergoes. After expansion in the EEV, the coolant enters the two -fitting area and evaporates in the Fche,” the group explained. “With an elevated vapor quality, the CO2 enters the REC, whereby the two-phase liquid separates itself into vapor and liquid as a result of density differences. Liquidco2 is taken from the bottom of the REC and led either to the BHE in GA mode or to the PV-T-collectors in Sa-Modus.
The system was simulated to work in the North -Italian city of Padova, with its average monthly solar radiation of 300 W/m², an annual average soil temperature of 13 ° C and an average air temperature of 7 C. It was tested with different quantities of BHE, each with a depth of 30 m and a changing number of PVT units. Which were placed with a capacity of 270 W at a tilt angle of 45 °.
The simulation showed that, for both systems, the solar or soil evaporators work at the same time with the air deflection and 1 K Air temperature rise results in an increase in the performance of 4.8% (COP) in SA mode and a 4.3% COP rise in GA mode. Furthermore, it showed that the SA mode is influenced by solar radiation, whereby any global tilted irradiation (GTI) of 100 W/m² improves the COP by 2.8%, while GA mode is influenced by soil temperature and 1 K of soil temperature rise produces a rise of 0.9%.
In addition, the academics discovered that adding one to three braes results in an increase of 8% -21% in the soil temperature range of 7 C to 13 C. Nevertheless, adding 1 to 4 PVT units added a COP -increase of 4% -22% within a 300 W/M² range.
“What is even more important is that the agent of the multisource heat pump is always higher than that of the heat pump of the air source,” the researchers emphasized and noted that they now intend to vary the number of PV-T modules and borehire heat exchangers on heat pump performance.
The system was described in “iNestigation on a direct expansion Multisource carbon dioxide heat pump to maximize the use of renewable energy sources“Published in Applied thermal engineering. The group also included scientists from the Delft University of Technology in the Netherlands.
Another research group at the University of Padova has recently designed a 5 kW direct expansion on solar energy-assisted heat pump that uses two different evaporator technologies alternatively. The cooling of the PV module unit by CO2 evaporation increases the power production by 8%.
This content is protected by copyright and may not be reused. If you want to work with us and reuse part of our content, please contact: editors@pv-magazine.com.
