Application of the water loop variable refrigerant flow air-conditioning system in large-scale buildings in cold climate

Traditional variable refrigerant flow (VRF) air-conditioning system is popular in buildings for several key benefits. First, VRF system is capable to meet the requirements of simultaneous heating and cooling. Second, it is easy to start, stop, maintain precise temperature control, and realize household metering. However, the performance of VRF air-conditioning system deteriorates when it increases in size. The capacity and efficiency falls sharply when the pipe length and height difference increases. Moreover, the performance is seriously affected by outdoor temperature. Such deficiencies result in the limitation to applications of VRF air-conditioning systems in large-scale buildings in cold area. Water loop variable refrigerant flow (WLVRF) air-conditioning system is introduced here to fit large-scale buildings in cold area and offer a more efficient option that provides both performance and environmental benefits. It is an integrated system based on VRF air-conditioning unit, water loop and air source heat pump. It uses water rather than refrigerant as its main energy transfer medium. VRF air-conditioning units are linked together by neutral temperature water loop to form a complete system. The water loop transports energy among different areas in the building instead of refrigerant pipes, decreasing the scale of VRF air-conditioning unit and improving the performance. The outlet water temperature of air source heat pump is lowered, leading to a good operating condition for it. Previous models for refrigerant and building load are cited in this investigation. Mathematical models of major equipments and other elements of the system are established using lumped parameter method based on DATAFIT and MATLAB. The performance of WLVRF is simulated and initial investments, and running costs are calculated through a market-research. A contrast is carried out between WLVRF system and traditional VRF system. The results imply that WLVRF system has better working condition and lower running costs than traditional VRF system. It will offer a better choice in terms of air-conditioning systems, especially in large-scale buildings in cold area.