Abstract
The paper presents the investigation of a prototype cold accumulator using water–ice latent heat for the cold storage process. The concept of the cold accumulator was based on a 200-L-capacity cylindrical storage tank in which spherical capsules filled with water were placed. Beds of polypropylene capsules with diameters of 80 mm, 70 mm, and 60 mm were used in the tests. The cold accumulator operated with a water–air heat pump. Based on the test results, the following parameters were calculated: the cooling capacity, cooling power, energy efficiency of the cold storage, and energy efficiency ratio (EER) of the accumulator. The obtained measurement results were described with mathematical relationships (allowing for measurement error) using criterial numbers and the developed “Research Stand Factor Number” (RSFN) index. It has been found that, for the prototype cold accumulator under investigation, the maximum values of the cooling capacity (17 kWh or 85.3 kWh per cubic meter of the accumulator), energy efficiency (0.99), and EER (4.8) occur for an RSFN of 144·10−4. The optimal conditions for the operation of the prototype cold accumulator were the closest to laboratory tests conducted for a bed with capsules with a diameter of 70 mm and a mass flow of the water–glycol mixture flowing between the accumulator and the heat pump of 0.084 kg/s. During the tests, no significant problems with the operation of the prototype cold accumulator were found.
Highlights
In the majority of European countries, the demand for cooling in residential and public buildings is unpredictable
The most common solution currently used in cold storage processes in the technical systems of buildings is ice water
The energy efficiency ratio was calculated as the quotient of the amount of heat collected from the accumulator to the amount of electric energy used for this purpose by all elements of the testing stand, following this relationship: EER = Qcs
Summary
In the majority of European countries, the demand for cooling in residential and public buildings is unpredictable. One of the directions for improving the energy performance of this type of installation is to use cold storage with a simultaneous reduction of the nominal cooling power of the cold source [2,3,4] This solution enables the storing of cold air when the cold demand is lower than the nominal power of the cooling devices and using it at times when peak loads exceeding the cooling device’s power occur [5]. Cold tanks producing ice on coil heat exchangers started to be employed [19] This enables the utilization of the heat of water–ice phase change for cold storage. The thermal expansion problem was eliminated by employing tanks using binary ice or a suspension of fine ice particles in a water solution. By utilizing the heat of the water–ice phase change, it is possible to achieve a high cold storage density [24,26]
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