Modeling Variable Refrigerant Flow (VRF) systems in building applications: A comprehensive review

Wang, Junke; Lu, Xing; Adetola, Veronica; Louie, Edward

doi:10.1016/j.enbuild.2024.114128

Cited by 2 publications

(1 citation statement)

References 63 publications

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“…The integration of heat pump technologies into ventilation systems is a less widespread solution. In recent years, the situation has been changing, with more manufacturers introducing air handling units with integrated heat pumps [13]. However, the operating range of heat pumps integrated into ventilation units is often limited by the outdoor air parameters.…”

Section: Introductionmentioning

confidence: 99%

Experimental Studies and Performance Characteristics Analysis of a Variable-Volume Heat Pump in a Ventilation System

Frik,

Bielskus,

Džiugaitė-Tumėnienė

et al. 2024

Applied Sciences

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Air-to-air heat pumps are used in today’s ventilation systems increasingly often as they provide heating and cooling for buildings. The energy transformation modes of these units are subject to constant change due to the varying outdoor air state, including temperature and humidity. When choosing how to operate and control energy transformers, it is important to be able to adapt effectively to the changing outside air conditions. Nowadays, modern commercial heat pumps offer two levels of control flexibility: a compressor with a variable speed and an electronic expansion valve. This combination of control elements has boosted the seasonal energy efficiency of heat pumps. For a long time, cycle control possibilities have been dominated by electronic controls. The authors of this paper aim to present an additional element to the traditional heat pump controls, which provides a third level of control over the cycle. To achieve the objective, experimental investigations of a heat pump integrated into a ventilation unit have been carried out under real-life conditions. The experiments involved varying the operating modes of the unit by adjusting the compressor speed, the position of the expansion valve, and the volume of the system loop. The study examined the performance characteristics of the heat pump and found that the performance of a variable-volume heat pump is comparable to that of a conventionally operated typical constant-volume heat pump system. In addition, the study found that by adding a third level of volume control to the active heating circuit, in combination with conventional controls, the heat pump’s heat output range could be extended by 69.62%. The study determined the variation of the heat pump cycle in the p-h diagram with the variation of the loop volume. The benefits and drawbacks of a heat pump with a variable-volume loop are discussed in this study.

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Section: Introductionmentioning

confidence: 99%

Experimental Studies and Performance Characteristics Analysis of a Variable-Volume Heat Pump in a Ventilation System

Frik,

Bielskus,

Džiugaitė-Tumėnienė

et al. 2024

Applied Sciences

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Energy-Saving Effects of the Intermittent Control of Pumps in Ground Source Variable Refrigerant Flow Systems with a Buffer Water Tank

Tanaka,

Kindaichi,

Kawasaki

et al. 2024

Energies

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Variable refrigerant flow (VRF) systems are common air-conditioning systems used in regions with moderate climates that have cooling and heating demands. Unlike typical air-source VRF systems, ground-source VRF systems require heat-source water circulation, and reducing the pumping power remains a significant problem. Herein, the intermittent pump control for circulating heat source water was achieved by installing a buffer water tank between the ground heat exchangers and VRF units. An intermittent control methodology was developed based on the indices of water transport efficiency and incorporated into a system simulation model with 72 boreholes, a cooling capacity of 252 kW, and a buffer water tank of 30 m3. Results indicated that intermittent control was achieved at heat load ratios lower than 40% as expected. This intermittent control allowed more efficient water transport with 38% lower pumping power than conventional inverter controls. Although the proposed system equipped more pumps and heat exchangers than conventional systems, it exhibited higher energy efficiencies for most measurement days than the conventional air-conditioning systems. The annual energy consumption was thus reduced by 34% and 8% compared to air-source VRF systems and conventional ground-source VRF systems, respectively.

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Modeling Variable Refrigerant Flow (VRF) systems in building applications: A comprehensive review

Cited by 2 publications

References 63 publications

Experimental Studies and Performance Characteristics Analysis of a Variable-Volume Heat Pump in a Ventilation System

Experimental Studies and Performance Characteristics Analysis of a Variable-Volume Heat Pump in a Ventilation System

Energy-Saving Effects of the Intermittent Control of Pumps in Ground Source Variable Refrigerant Flow Systems with a Buffer Water Tank

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