| Popis: |
Commercial food outlets in the UK are responsible for 3% of the UK total energy consumption, with refrigeration systems account for 29% of this total. In this paper, a validated model that simulates a commercial refrigeration system installed over 2000 sq. ft to mimic a real express store installed at the Riseholme Refrigeration Research Centre at the University of Lincoln, UK, is presented. Investigations are conducted to examine the different failures of air conditioning (AC) systems and their impacts on the indoor store temperature, and hence on the refrigeration performance and energy consumption. Three different scenarios were examined: gradual increase in store temperature caused by an AC system with reduced performance, sudden increase in store temperature caused by a drastic AC failure and fluctuations in store temperature caused by a faulty AC system. The results of the investigation for different failure scenarios of the AC system during 3 h of continual operation showed an increase in the energy consumption of the refrigeration system by 17.4% as a result of gradual AC failure, 33.6% for the sudden failure and 5.3% for the intermittent failure. It is concluded that the AC failures caused the power drawn to increase due to spending a prolonged period of time at higher temperatures than during the normal AC operation. Also, the frequency which the compressors switch on and off increases the level of wear on the compressors. Both gradual and sudden failures of the AC system show a sustained increase in temperature that leads to a greater duty cycle for the expansion valve to increase the amount of refrigerant available. It is found that the sudden failure of the AC system had the greatest impact on the system, as the temperature of the store rises quickest, the display cases are exposed to higher temperatures for a longer time; this causes the greatest demand on the system and so lead to the largest power consumption. It is notable that for all three failure types that the product temperature experiences, there are no noticeable fluctuations and they remain comfortably within the temperature boundaries between 3 and 1 °C, as the system is able to provide an adequate cooling. |
