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，其中单个室外机组(即供暖模式下的蒸发器)与单个制冷剂网络上的多个室内机组(即供热模式下的冷凝器)相连。室内单元分布在建筑的多个区域，并为其区域提供必要的供暖或制冷。与变风量系统相比，VRF系统已被证明可以减少空间冷却的能耗，但它们很少被考虑用于寒冷气候下以供暖为主的应用。在《巴黎协定》的背景下，VRF系统为加拿大减少温室气体排放提供了巨大的潜力。该研究计划涉及空气源和地源VRF热泵系统的设计、建模和控制。将开发一个模拟模型，并在控制环境条件(空气温度和湿度)的实验室实验中对照测量结果进行验证。这将允许开发新的控制方法，以基于对系统配置的了解(例如，室内单元的大小、数量和位置)来优化VRF系统的运行。对耦合到地热换热器的VRF系统的模拟需要考虑由于系统运行条件(例如流体流量)的变化而产生的短期影响，以及部分由于各个地热换热器之间的热干扰而产生的长期影响。地热换热器模拟技术的改进将有助于评估地源热泵系统的能量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》的背景下，需要替代制冷剂来取代当前一代的制冷剂，包括氢氟烃(HFCs)。在VRF系统制冷剂充注量较高的情况下，使用二氧化碳(CO2)作为制冷剂可以显著减少全生命周期温室气体的排放，尤其是泄漏和退役。在研究计划中开发的模拟工具的基础上，将设计、建造和测试跨临界CO2 VRF系统的原型。该项目将促进使用低影响制冷剂的下一代热泵系统的发展。

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.