Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system subjected to partial and unbalanced thermal loadings

Abstract

This paper shows the performance evaluation of the variable refrigerant flow (VRF) air-conditioning system subjected to partial and unbalanced thermal (cooling and heating) loadings. The one outdoor unit's and two indoor units' VRF system was used as a test specimen in the controlled outdoor chamber in which temperature and humidity were controlled. The indoor chamber thermal loading was controlled from full to partial thermal loadings and from balanced to unbalanced thermal loadings with respect to the specified rated capacity of the test specimen. The purpose of this study is to determine the real performance of the system when it is operating under actual operating situations. The general results show that the system coefficient of performance much depends on the partial and unbalanced thermal loadings. It is shown that the system maximum coefficient of performance occurred at around 50% of the rated thermal loadings. It is shown that as the load balance ratio decreases, the system coefficient of performance decreases, particularly for the cooling operation, due to the increase of compressor speed to support the refrigerant sub-cooling. In the heating operation, the compressor speed increase is very minimal which results in a very small decrease of the system coefficient of performance as the load balance ratio decreases. Based on this study, the system coefficient of performance becomes much different as the system is operating at partial thermal loadings. Also, during the unbalanced thermal loadings, the system coefficient of performance further decreases, particularly during the cooling operation. With the results of the study and analyses of the system operation, it is important to consider how the VRF system operates in an actual building when estimating the energy consumption of the VRF air-conditioning system to be installed in a new or in a retrofitted building.

Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system subjected to partial loadings at different outdoor air temperatures

“…In terms of the accurate evaluation of the new buildings or retrofitted buildings in energy consumption, it is very important to consider the outdoor air temperatures as they much affect the electric energy consumption of the system in delivering the needed indoor thermal environmental conditions. Moreover, when the VRF air-conditioning system is operating at different outdoor temperatures at unbalanced loading, the performance of the VRF airconditioning system is expected to be affected further as compressor speed changes to support both the effect of outdoor temperature and unbalanced loading (Enteria et al, 2016). Hence, the results of this study and of previous study on unbalanced loading are important in the realistic and actual electric energy consumption determination of the system in actual building installation and operation.…”

“…Hence, a performance evaluation of the VRF air-conditioning system subjected to different outdoor air temperatures while operating in different thermal loading ratios is needed. Based on the review of previous studies, the evaluation of the system based on different outdoor air temperatures and loading ratios is not yet fully completed (Enteria et al, 2016;Horie and Hihara, 2012;Watanabe et al, 2009;Watanabe et al, 2007). This paper shows the evaluation of the VRF air-conditioning system with one outdoor unit and two indoor units operated under different outdoor air temperatures for both cooling and heating operations.…”

“…The load balance ratio (α) proposed and introduced is shown in Eq. (1) (Enteria et al, 2016). In this measurement evaluation, α is equal to 1, the indoor chamber 1 load is equal to the indoor chamber 2 load.…”

Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system during the heating-defrosting cyclic operation

“…The results also show the importance to be considered when the system operates at a low outdoor air temperature since the heating-defrosting cyclic operation results in changes of the indoor environment temperature. The results of this and previous studies regarding the real performance of the VRF air-conditioning system and its impact on energy consumption and indoor environmental conditions at different conditions which happen during real operation is important to be considered both in energy consumption of buildings and in the maintenance of buildings required indoor thermal environment (Enteria et al, 2016a;Enteria et al, 2016b Greek letter α Load balance ratio (α = 1, Balanced; α < 1, Unbalanced)…”

“…As the VRF air-conditioning system is expected to encounter heating mode operation in locations with a winter season, the performance evaluation of the system in this climatic condition is important. The review of the previous studies shows that the evaluation of the VRF air-conditioning system occurring during the heating-defrosting cyclic operation has not yet been done in detail (Enteria et al, 2016a;Enteria et al, 2016b;Horie and Hihara, 2012;Watanabe et al, 2009;Watanabe et al, 2007). This paper shows the evaluation of the VRF air-conditioning system with one outdoor unit and two indoor units operated under different very low outdoor dry bulb temperatures and different wet bulb temperatures in which ice accumulation occurred in the outdoor unit heat exchanger.…”