We are now researching various heat pump systems that can provide heating and cooling capacity for the commercial buildings and houses. The heat pump system is an essential mechanical system in the HVAC market. Especially, we focus on the variable refrigerant flow (VRF) and vapor-injection (VI) heat pump system. The heat pump technology using vapor-injection cycle with R410A refrigerant is a prominent technology that can provide heating and cooling capacity with showing better performances than a conventional heat pump system. By injecting fully vaporized refrigerant into the compressor’s middle state of compression, the compression efficiency can be improved. Now, the heat pump system is getting attention for the renewable energy system, because the heat pump technology is the most efficient technology that can provide the heating and cooling energy for the b