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Abstract
This article presents a comprehensive research review on variable refrigerant flow systems. The content includes four main parts: (1) a comprehensive introduction of variable refrigerant flow systems; (2) a review of recent experimental studies, including testing of the heat pump variable refrigerant flow system, heat recovery variable refrigerant flow system, and new variable refrigerant flow systems under various operation modes; (3) a review of steady-state modeling of variable refrigerant flow systems, including history, modeling approach, and model accuracy; and (4) a review of a dynamic modeling study of variable refrigerant flow systems, including modeling approach, control design, and fault detection and diagnosis techniques. It is suggested that the experimental study of variable refrigerant flow systems should include occupants’ thermal comfort. In addition, it is recommended that the steady-state simulation should take the internal gain of buildings into consideration. To improve the accuracy of the steady-state variable refrigerant flow model, more field testing would also be necessary. For dynamic modeling research, it is suggested to include heat recovery variable refrigerant flow and new variable refrigerant flow systems. Development of advanced controllers and effective fault detection and diagnosis algorithms would also be necessary.
Nomenclature
| BLAST | = | Building Loads Analysis and System Thermodynamics |
| COP | = | coefficient of performance |
| DPF | = | daily performance factor |
| DOE-2 | = | Department of Energy Simulation Tool -2 |
| DVM | = | digital variable multiple |
| DX | = | direct expansion |
| EER | = | energy efficiency ratio |
| EEV | = | electronic expansion valve |
| eQUEST | = | Quick Energy Simulation Tool |
| ERV | = | energy recovery ventilator |
| FDD | = | fault detection and diagnosis |
| GSHP | = | ground source heat pump |
| HP | = | heat pump |
| HPVRF | = | heat-pump-type variable refrigerant flow |
| HR | = | heat recovery |
| HRU | = | heat recovery unit |
| HRVRF | = | heat-recovery-type variable refrigerant flow |
| HX | = | heat exchanger |
| IAQ | = | indoor air quality |
| IDVS | = | integrated solid desiccant heat pump and variable refrigerant flow system |
| IPLV | = | integrated part-load value |
| IU | = | indoor unit |
| JHVS | = | joint heat recovery ventilation and variable refrigerant flow system |
| JIS | = | Japanese Industrial Standards |
| LQR | = | linear quadratic regulator |
| LTI | = | linear time invariant |
| MCU | = | mode change unit |
| MEAC | = | multi-evaporator air conditioning |
| MFVRF | = | multi-functional variable refrigerant flow |
| MIMO | = | multiple-input–multiple-output |
| MPC | = | model predictive control |
| OA | = | outdoor air |
| OAP | = | outdoor air processor |
| OU | = | outdoor unit |
| OUHX | = | outdoor unit heat exchanger |
| PID | = | proportional-integral-derivative |
| PLR | = | part-load ratio |
| PWM | = | pulse-width modulation |
| RH | = | relative humidity |
| SCHX | = | subcooler heat exchanger |
| SDHP | = | solid desiccant heat pump |
| SHR | = | sensible heat ratio |
| SISO | = | single-input–single-output |
| THIC | = | temperature and humidity independent control |
| TRNSYS | = | Transient System Simulation Tool |
| VAV | = | variable air volume |
| VRF | = | variable refrigerant flow |