EXPERIMENTAL EVALUATION OF A MULTIFUNTIONAL VARIABLE REFRIGERANT FLOW SYSTEM IN AN EDUCATIONAL OFFICE BUILDING

Abstract

The top three end uses - space heating, space cooling, and water heating - accounted for close to 41 percent of site energy consumption in U.S. building primary energy consumption. Therefore, energy efficient heating, ventilating and air-conditioning (HVAC) systems in buildings is essential for energy savings in the building sectors. A multifunctional variable refrigerant flow (MFVRF) system is finding its way into residential and commercial buildings since it can simultaneously provide space cooling, space heating and hot water.

The MFVRF system was installed in an educational 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) on the daily performance factor (DPF) and total energy consumption were experimentally investigated in the field performance tests. Although the higher PLR represents a more effective cooling and/or heating the system, the DPF is not always increased with PLR because the system is optimized at a certain range of PLR. Furthermore, the effects of the hot water demand and the heat recovery operation modes on the performance of the system were investigated in a field test for the heating and shoulder seasons.

Integrating the water heating functions into the heat recovery type variable refrigerant flow (HR-VRF) system, not only supplies hot water year-round, it also improves the system performance. As the hot water demand for the MFVRF system increased, the PLR was improved, which resulted in an increase 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 DPF was 2.14 and 3.54 when the ratio of daily total cooling energy to daily total heating 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.

Energy saving potential of the MFVRF system in a building with high internal heat gains, resulted in a high cooling load for the cooling season and a low heating load for the heating season, was verified through the field performance test. 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.