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Chinese scientists have analyzed the performance of cold storage warehouses powered by photovoltaics and found that they can ensure stable operation thanks to a refrigeration performance coefficient of up to 2.66.
A group of researchers in China have analyzed the performance of ice storage modes in a photovoltaic-powered cold store and found that this combination can offer significant advantages.
Ice storage involves the production of ice in insulated containers for later use, for example, during times of lower solar irradiation. In the research, academics considered both serial ice storage (SM) and parallel ice storage (PM).
In SM ice storage, the storage tank is connected in series to an air chiller. “In this way, the system allows to simultaneously supply cold through the air cooler and store cold energy in the ice storage tank when solar energy is available. In addition, the ice storage tank provides cooling at night or when irradiance is insufficient,” they explained.
In PM ice storage, the air cooler and ice storage tank are connected in parallel. “In this way, the system stores cold energy in the ice storage tank before supplying cooling when solar energy is available, thus allowing the ice storage tank to supply cooling continuously,” they added.
The research was carried out in a cold storage warehouse with a volume of 24,472 m3 that could operate on both photovoltaic energy and grid energy. It consisted of 5.4 kW of solar panels and an inverter, which operated the vapor compression refrigeration (RCPV) system. “The VCR subsystem mainly consisted of an AC compressor with a frequency converter, a condenser, a throttle valve, an air cooler and an ice storage tank, all connected in sequence and using R22 as the refrigerant,” they further explained. the scientists.
The research group also noted that the system was built so that it could switch between SM and PM modes. To operate in the first mode, a valve between the throttle valve and the air cooler was opened, while a valve between the throttle valve and the ice storage tank was closed, as well as a valve between the pump and the ice storage tank. ice storage tank. For the second mode, the opposite connection was used.
The system worked in different conditions: powered by the grid or by photovoltaics; empty and fully loaded; and with SM or PM.
With FV-SM operation, the cooling coefficient of performance (COP) was 2.47 at no load and 2.66 at full load. Under the same conditions, the COP of the entire system was 0.26 and 0.28, respectively. The PV-PM system, however, showed worse results, with a cooling COP of 2.26 at no load and 2.56 at full load. The COP of the PV-PM system was 0.25 and 0.27, respectively.
“The cost of SM mode is lower than that of PM mode. Compared with PM mode, the total cost of annual equal payment of SM with PV drive decreased from $6,494.69 to $5,906.16, which is 9.96% less than PM mode,” they also stated. “Compared with the grid-powered system, PV is more energy efficient, and the economic cost of SM mode is lower than that of PM mode.”
Since the PV-SM proved to be superior, the academics proceeded to store 1,500 kg of green grapes in it for fresh preservation for two weeks. After this period, its net weight with fresh preservation was reduced from 1,475.10 to 1,460.25 kg. Moisture was reduced from 86.51% to 85.135%, and sugar content was reduced from 16.18% to 15.78%. For reference, without fresh preservation, the humidity dropped from 86.154% to 79.593%, and the sugar content from 16.28% to 12.28%.
"The results indicate that maintaining the storage temperature of the system at 5 ºC prevented a decrease in the quality of the grapes, which translated into a decrease of 5.186% in the water content and 3.61% in the sugar content. sugar”, they concluded. “The mass reduction allowed us to deduce that if the grapes had been preserved at room temperature, their overall mass loss would have been considerably high. "The fresh preservation method prevented the mass reduction of the green grapes due to the minimization of water evaporation."
The system was presented in “ Research on the characteristics of photovoltaic-driven refrigerated warehouse system under different ice storage modes,” published in Results . in Engineering . The group consisted of scientists from Yunnan Normal University and the Yunnan Key Refrigeration Laboratory. |
