Utvärdering av innpvativ värmeväxlare i kyldisk : för effektivare energianvändning i butiker

In this study, a new innovative type of air-to-liquid heat exchanger, called HEALEX (which stands for High Efficiency Air to Liquid Heat Exchanger), has been tested and demonstrated in an open display cabinet at a supermarket. HEALEX is adapted for obtaining good heat transfer performance even at a laminar flow regime on the liquid side, which is often the case in indirect cooling systems in supermarkets. The heat exchanger consists of parallel plates, with liquid in every second passage and air in the other passages. The purpose of the demonstration was to show the potential of increasing the energy efficiency by replacing the conventional cooling coils by HEALEX. On the long term, the purpose of the project was to raise the interest and acceptance for this type of heat exchanger, and through raised acceptance increase the amount of energy efficient heat exchangers in supermarkets, which in turn would result in energy savings. One of the objectives of the project was to confirm results from a previous study where tests had been performed in a laboratory. The results from the laboratory tests showed that the same cooling capacity and average temperature of the “food packages” could be obtained with around 6 K higher inlet temperature of the liquid, -7°C with the traditional coil and ‑1°C with HEALEX. The project was not intended to directly compare the performance of the original heat exchanger and the one of HEALEX regarding efficiency. A field study is not well suited for direct comparisons of different heat exchanger performances, since there are too many hard-to-control variables (ambient climate, customer behavior etc.) that affect the performance of the cooling system. Studies for direct and exact comparisons should always be carried out in a laboratory, where parameters that affect the result can be controlled. The first tests were made with the original heat exchanger placed in the bottom of the display cabinet, and thereafter the heat exchanger was replaced with HEALEX. The data collected in the project were air- and liquid temperatures before and after the heat exchangers, air temperatures and humidities in the display cabinet, liquid and air pressure drop and liquid volume flow. Temperature and humidity of the ambient air is also measured. The results from this study show that there is a potential of energy savings by using HEALEX in display cabinets at supermarkets instead of conventional cooling coils. The inlet temperature of the secondary refrigerant could be raised 6°C after the installation of HEALEX and almost the same cooling capacity and average temperature in the display cabinet as for the original heat exchanger could be obtained. These results confirm to a large extent the results from the laboratory tests. The results from this study also indicate that the need for defrosting will occur much more seldom for HEALEX compared to a conventional cooling coil. Defrosting was initiated by time control at 6.00 am and at 7.00 pm. Since the pressure drop is constant during the measurement period it is likely that there is no frosting and thereby no need for defrosting. In order to find out if defrosting is needed or not, the it would have been necessary to increase the intervals between the defrosts, which was not possible in this study. Earlier studies have shown that COP increase with approximately 2.5% per oC increased liquid temperature. Thereby an increase of the liquid temperature with 6oC implies energy savings of about 15% for the compressor drive energy