18 May 2017
In the US, more than 40% of the primary energy is consumed by buildings. In the building sector, more than 45% of the primary energy is used in space cooling, space heating and water heating. Variable refrigerant flow (VRF) system is a popular building air conditioning solution. Modern VRF systems such as multi-functional VRFs are also able to provide simultaneous space cooling, space heating and water heating to the building. Therefore, the performance improvement of VRF system becomes a key research topic. In this paper, a thermodynamic model of multi-functional VRF is proposed and implemented in simulation engine EnergyPlus. The model is validated in cooling season. The model agrees with the experimental data with an hourly cooling capacity deviation within ±10% and an hourly energy consumption deviation within ±5%. Due to low utilization rate of water heating operation when compared with space cooling and heating, an integrated VRF system with chilled water storage capability is thereafter proposed. The integrated system uses the water storage component in multi-functional VRF systems as a chilled water storage unit. The integrated system is able to switch between the air-cooled and water-cooled modes based on the ambient temperature. The integrated system is also modeled in EnergyPlus. The performance of the integrated system and the baseline VRF system is compared and the calculated seasonal cooling energy savings for a target building in Tampa, FL is 11.5%.