Energy efficiency evaluation of multiple split-system air conditioners with unbalanced load operation for building energy simulation

The number of buildings that adopt the multiple split-system air conditioners is increasing, especially for small and medium-sized buildings. Many researches have been done on the energy consumption performance of the multiple split-system, but there are still many unclear points about its actual performance, in particularly, with regard to performance under partial load condition. It is important to understand the partial load performance and set the reliable performance characteristics when we perform building energy simulation because it will have a significant influence on annual energy consumption of the system. In order to clarify the efficiency under partial load condition, we have analysed the measurement data of actual buildings and found that there is a range of the efficiency even at the same load ratio. We assume that the cause of this range is due to bias (unbalance) in the heat amount handled by multiple indoor units. The efficiency tends to be higher when the heat amount of all indoor units of the system are equal, which is same as the test condition specified by ISO 15042:2017, but the efficiency tends to be lower when the heat amount handled by the indoor units is highly unbalanced. This research clarifies the influence of the unbalanced heat load to the system energy efficiency. We measured fundamental data on the energy efficiency of the multiple split-system air-conditioner in an experimental facility that connects multiple constant temperature and humidity chambers. We found that the unbalanced load operation caused about 20% energy loss in maximum and concluded that the indoor units should be arranged so that extreme unbalanced heat load does not occur.