Experimental investigation of multifunctional VRF system in heating and shoulder seasons

The top three end uses which are space heating, space cooling, and water heating accounted for close to 41 percent of site energy consumption in U.S. building primary energy consumption. A multifunctional variable refrigerant flow (MFVRF) system is finding its way into buildings since it can simultaneously provide space cooling, space heating and hot water. The MFVRF system was installed in an office building and fully instrumented to measure the performance of the system under a wide range of outdoor weather conditions. The effects of a part-load ratio (PLR), a hot water demand and a heat recovery operation mode on the performance of the MFVRF system were investigated in a field test for the heating and shoulder seasons. As the hot water demand for the MFVRF system increased, the PLR was improved, which resulted in an increase in system heating performance. In the heat recovery operation mode, the heat absorbed from the indoor units operating in the cooling mode was transferred to other indoor units operating in the heating mode. The daily performance factor was 2.14 and 3.54 when the ratio of daily total cooling energy to daily total energy was 13.0% and 28.4%, respectively, at the similar outdoor weather conditions. This enhancement was attributed to the waste heat recovered during the heat recovery operation mode and the decrease in pressure ratio, which is a result of the improvement of the compressor efficiency. The performance of the MFVRF system for the heating and shoulder seasons was improved by transferring the recovered energy to the indoor space and supplying the hot water.