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Analysis of Air Side Cooling and Dehumidification Performance in Evaporator in Direct Expansion (DX) Variable Refrigerant Flow (VRF) Air-Conditioning (A/C) System

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Variable Refrigerant Flow Systems

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Abstract

Direct Expansion Variable Refrigerant Flow Air-Conditioning (DX-VRF-A/C) units can be seen in buildings of all sizes. The evaporator in a DX-VRF-A/C unit (or DX air cooling coil), normally generates heat and mass transfer in the form of cooling and dehumidifying of hot and humid air flowing through the cooling coil. DX air-conditioning unit with single speed compressors and forced draft fans usually rely on switch control to maintain only the indoor dry bulb temperature which results in an uncontrolled balance of indoor humidity and reduces thermal comfort, and consequently causes poor indoor air quality (IAQ) as well as produces low energy efficiency. Thus, DX air-conditioning unit with variable-speed compressors and forced draft fans are increasingly adopted in pursuit of higher energy efficiency and thermal comfort indoor environment. Hence, study the simultaneous heat and mass transfer performance in DX air cooling coil of DX air-conditioning unit with variable-speed compressor and forced draft fan is essential, however, research work is still lacking in regards to this A/C system. A comprehensive analysis of the airside cooling and dehumidification process in DX cooling coil and its application are illustrated in this chapter. It commences with introducing the calculation of an important dimensionless parameter, namely steady state Equipment Sensible Heat Ratio (SHR) of DX air cooling coil, which is defined as the ratio of the output sensible cooling capacity of DX cooling coil to the total output cooling capacity. An experimental study on estimating on the dehumidification effect on the airside of the superheated region (SPR) in a DX cooling coil is given. The development of the modified Logarithmic Mean Enthalpy Difference (LMED) method for evaluating the total heat transfer rate in a wet air cooling coil operating under both unit and non-unit Lewis Factors (Le2/3) conditions is reported at the end of this chapter.

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Acknowledgements

This research was funded by the Ningbo Natural Science Foundation Project, Project references: 2019A610094 and Beijing University of Technology, Project references: E01210300004. The research study was also supported by the Ningbo Science and Technology Bureau under Grant no: 2021S141.

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Authors and Affiliations

  1. Research Centre of Fluids and Thermal Engineering, University of Nottingham Ningbo China, Ningbo, 315100, China

    Liang Xia

  2. Center for Sustainable Energy Technologies, University of Nottingham Ningbo China, Ningbo, 315100, China

    Liang Xia & Isaac Lun

  3. Research Centre of Sustainable Built Environment, University of Nottingham Ningbo China, Ningbo, 315100, China

    Isaac Lun

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  1. Liang Xia
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  2. Isaac Lun
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Correspondence to Isaac Lun .

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Editors and Affiliations

  1. Department of Mechanical Engineering and Technology, College of Engineering and Technology, Mindanao State University—Iligan Institute of Technology, Iligan, Philippines

    Napoleon Enteria

  2. Building Research Institute, Tsukuba, Japan

    Takao Sawachi

  3. Waseda University, Tokyo, Japan

    Kiyoshi Saito

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Xia, L., Lun, I. (2023). Analysis of Air Side Cooling and Dehumidification Performance in Evaporator in Direct Expansion (DX) Variable Refrigerant Flow (VRF) Air-Conditioning (A/C) System. In: Enteria, N., Sawachi, T., Saito, K. (eds) Variable Refrigerant Flow Systems. Springer, Singapore. https://doi.org/10.1007/978-981-19-6833-4_4

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  • DOI: https://doi.org/10.1007/978-981-19-6833-4_4

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  • Online ISBN: 978-981-19-6833-4

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