Comparison In a secondary refrigeration system with a heat transfer fluid (HTF) as the energy transfer medium, three main components can be identified. Namely heat exchangers/evaporator, cooling battery/fan air coolers and the pumps.
The calculations are made for a fictitious cold and freezing warehouse located in Gothenburg, on Sweden's west coast, but also discussions about what they would mean if the plant was located on the southern coast of Spain in Malaga.
• The size of the cold storage is typically 6,000 m2 and should maintain + 2°C. Temper-15 and MPG 30 %, respectively, are chosen as the cold carrier in comparison, both with a freezing point of -15°C. Inlet temperature for fan air cooler is -4/-5 °C. Required cooling power is 235 kW.
• The size of the freeze storage is typically 3,000 m2 and should maintain -22 °C.
• As HTF's in comparison, Temper-40 and MPG 50 %, Temper-40 with a freezing point of -40°C and MPG 55 % with a freezing point of -35 °C are selected. Temper-40 was chosen as “Temper -35” is
not a standard product. Inlet temperature for fan air cooler is -29/-30°C.
• Required cooling power is 168 kW.
The optimization calculations are done for minimizing size of components, i.e. heat exchangers, pipes dimensions and pumps. For the surface-optimal case, these properties of the fluids are mainly considered. For the energy optimal case, COP and total pressure drop are calculated. For this scenario, the brine temperature for Temper and the evaporation temperature could also be increased making the COP higher.
Conclusion
By choosing a suitable heat transfer fluid, a lot of energy or materials/components can be saved through optimization. The optimal-surface case show reduction of area in both cooling and freezing and similar when optimizing energy consumption. For the cooling case a reduced pump energy of 43 % could be determined. Due to higher temperature in the evaporator and better COP, 4 % reduced energy consumption for the refrigeration unit could be determined. For the freezing case a reduced pump energy of 61 % could be determined. Due to higher temperature in the evaporator and better COP, 3 % reduced energy consumption for the refrigeration unit could be determined. Health and environmental hazards, fire hazards, energy efficiency - thermophysical properties, corrosivity, corrosion protection, installation - restrictions in material, lifespan, costs, or rather life cycle costs are important features. Temper fulfils all these requirements.
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