Design, simulation and control of air- and ground-source variable refrigerant flow heat pump systems

可变制冷剂流量（VRF）系统是一种热泵系统，其中单个室外机（即加热模式的蒸发器）在单个制冷剂网络上连接到多个室内机（即加热模式的冷凝器）。室内单元分布在建筑物的多个区域，并为其区域提供必要的加热或冷却。与可变风量系统相比，VRF系统已被证明可以减少空间冷却的能源消耗，但很少考虑在寒冷气候中用于供暖为主的应用。在《巴黎协定》的背景下，VRF系统为减少加拿大的温室气体排放提供了巨大的潜力。***该研究项目涉及空气源和地源VRF热泵系统的设计、建模和控制。将开发一个模拟模型，并根据受控环境条件（空气温度和湿度）的实验室实验测量结果进行验证。这将允许开发新的控制方法，以根据系统配置（例如室内单元的大小，数量和位置）的知识来优化VRF系统的操作。对与地热热交换器耦合的VRF系统进行模拟时，必须考虑由于系统运行条件（如流体流速）的变化而产生的短期影响，以及部分由于单个地热热交换器之间的热干扰而产生的长期影响。地热热交换器模拟技术的改进将有助于评价地源热泵系统的能源性能以及使用这些系统的潜在能源、环境和经济效益。***在《蒙特利尔议定书》和《基加利修正案》的范围内，需要替代制冷剂来取代包括氢氟碳化合物在内的当前一代制冷剂。由于VRF系统的制冷剂充注量很高，使用二氧化碳（CO2）作为制冷剂可以显著减少生命周期的温室气体排放，尤其是泄漏和退役造成的温室气体排放。基于研究项目中开发的仿真工具，将设计、构建和测试一个跨临界CO2 VRF系统原型。该项目将有助于使用低影响制冷剂的下一代热泵系统的进步。

Variable refrigerant flow (VRF) systems are heat pump systems where a single outdoor unit (i.e. the evaporator in heating mode) is connected to multiple indoor units (i.e. the condensers in heating mode) on a single refrigerant network. The indoor units are distributed across the multiple zones of a building and provide the necessary heating or cooling to their zone. VRF systems have been shown to reduce energy consumption for space cooling when compared to variable air volume systems, but they are rarely considered for heating dominated applications in cold climates. In the context of the Paris Agreement, VRF systems offer a great potential for the reduction of Canada's greenhouse gases emissions.***The research program addresses the design, modelling and control of both air-source and ground-source VRF heat pump systems. A simulation model will be developed and validated against measurements in laboratory experiments with controlled environmental conditions (air temperature and humidity). This will allow for the development of new control methods to optimize the operation of VRF systems based on knowledge of the system configuration (e.g. size, number and position of indoor units). The simulation of VRF systems coupled to geothermal heat exchangers necessitates the consideration of short-term effects that arise due to changes of the operating conditions of the system (e.g. fluid flow rate) and long-term effects due in part by thermal interference between individual geothermal heat exchangers. Improvements in simulation techniques of geothermal heat exchangers will allow for the evaluation of the energy performance of ground-source heat pump systems and the potential energetic, environmental and economical benefits of using these systems.***In the context of the Montreal Protocol and the Kigali Amendment, alternative refrigerants are needed to replace the current generation of refrigerants, including hydrofluorocarbons (HFCs). With the high refrigerant charge of VRF systems, the use of carbon dioxide (CO2) as the refrigerant could significantly reduce the life-cycle greenhouse gases emissions, especially from leakage and decommissioning. Building upon the simulation tools developed in the research program, a prototype transcritical CO2 VRF system will be designed, built and tested. This project will contribute to the advancement of the next generation of heat pump systems using low-impact refrigerants.