Investigation on Current Control Defrosting Method of Multi-split Variable Refrigerant Flow System

There are many indoor units in the multi-split variable refrigerant flow (VRF) system. The continuous operation of heating in winter is longer than that of ordinary household air conditioning, so that the precise defrosting control is energy-saving and improves the comfort for users. In this paper, during the experiment, the indoor temperature was 20℃, the outdoor dry bulb temperature was 7℃, 0℃, -5℃ and -7℃, and the wet bulb temperature was 6℃, 0℃, -6℃ and -8℃ respectively. The defrosting temperature, liquid pipe temperature, defrosting time and the current value change rate of the condenser fan were compared when the heating capacity was reduced by 15%. The experiments showed that the current change rate was little affected by the outdoor temperature. It was only related to the frost mass, which could reflect the real frosting situation. Then through the maximum cycle heating capacity, air supply temperature and capacity decay rate, the most reasonable defrosting time could be seen when the fan current change rate was 15% - 20%. Compared with the traditional defrosting, the current control defrosting had a higher heating capacity. Under the four working conditions, the heating cycle capacity was increased by 2.3%, 4%, 2.8% and 5.8% in turn. At the same time, the control was precise. The phenomenon of thermosensor falling off and the uneven frost formation had little impact on the current control defrosting.

Keywords:

VRF, defrosting, current control, optimization,

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[1] P. Byrne, J. Miriel, Y. Lenat, “Experimental study of an air-source heat pump for simultaneous heating and cooling – Part 2: Dynamic behaviour and two-phase thermosiphon defrosting technique,” Appl. Energy, 88, 3072-3078, 2011.
[2] M. Wang, R. Q. Zang, E. Hu, A. W. Ezzat, “Investigation of air cooler fan start-up delay in liquid refrigerant defrosting system,” Appl. Therm. Eng., 143, 302-307, 2018.
[3] M. L. Qu, L. Xia, S. M. Deng, Y. Q. Jiang, “A study of the reverse cycle defrosting performance on a multi-circuit outdoor coil unit in an air source heat pump – Part I: Experiments,” Appl. Energy, 91, 122-129, 2012.
[4] K. Laeun, H. Yunho, R. Reinhard, K. Byungsoon, “Field performance measurements of a VRF system with sub-cooler in educational offices for the cooling season,” Energy and Buildings, 49, 300-305, 2012.
[5] T. N. Aynur, “Variable refrigerant flow systems: A review,” Energy and Buildings, 42, 1106-1112, 2010.
[6] B. Shen, C. K. Rice, “Multiple-zone variable refrigerant flow system modeling and equipment performance mapping,” Ashrae Transactions, 118, 420-427, 2012.
[7] P. Parida, F. H. Mei, J. Jiang, W. J. Meng, S. V. Ekkad, “Experimental investigation of cooling performance of metal-based microchannels,” Heat Transfer Eng., 31, 485-494, 2010.
[8] S. A. Tassou, D. Datta, D. Marriott, “Frost formation and defrost control parameters for open multideck refrigerated food display cabinets,” Proceedings of the Institution of Mechanical Engineers Part A Journal of Power & Energy, 215, 213-222, 2001.
[9] J. Xiao, W. Wang, Y. H. Zhao, F. R. Zhang, “An analysis of the feasibility and characteristics of photoelectric technique applied in defrost-control,” Int. J. Refrig., 32, 1350-1357, 2009.
[10] Z. Y. Wang, H. X. Yang, S. Chen, “Study on the operating performance of cross hot-gas bypass defrosting system for air-to-water screw heat pumps,” Appl. Therm. Eng., 59, 398-404, 2013.
[11] K. M. Hwan, L. K. Soo, “Determination method of defrosting start-time based on temperature measurements,” Appl. Energy, 146, 263-269, 2015.
[12] W. Wang, J. Xiao, Y. Feng, Q. Guo, L. Wang, “Characteristics of an air source heat pump with novel photoelectric sensors during periodic frost–defrost cycles,” Appl. Therm. Eng., 50, 177-186, 2013.
[13] M. J. Song, X. J. Wang, L. Y. Liao, S. M. Deng, “Termination Control Temperature Study for an Air Source Heat Pump Unit During Its Reverse Cycle Defrosting,” Energy Procedia, 105, 335-342, 2017.
[14] Y. Q. Jiang, J. K. Dong, M. L. Qu, S. M. Deng, Y. Yao, “A novel defrosting control method based on the degree of refrigerant superheat for air source heat pumps,” Int. J. Refrig., 36, 2278-2288, 2013.
[15] H. H. Tan, G. H. Xu, F. T. Tao, X. Q. Sun, W. D. Yao, “Experimental investigation on the defrosting performance of a finned-tube evaporator using intermittent ultrasonic vibration,” Appl. Energy, 158, 220-232, 2015.
[16] Y. C. Yoon, H. J. Jeong, K. S. Lee, “Adaptive defrost methods for improving defrosting efficiency of household refrigerator,” Energy Conversion & Management, 157, 511-516, 2018.
[17] J. Allard, R. Heinzen, “Adaptive defrost,” IEEE Transactions on Industry Applications, 24, 39-42, 1988.
[18] Y. Hayashi, A. Aoki, S. Adachi, K. Hori, “Study of frost properties correlating with frost formation types,” J. Heat Transfer, 99, 239, 1977.
[19] J. H. Zhu, Y. Y. Sun, W. Wang, Y. J. Ge, L. T. Li, J. D. Liu, “A novel Temperature–Humidity–Time defrosting control method based on a frosting map for air-source heat pumps,” Intern. J. Refrig., 54, 45-54, 2015.
[20] J. B. Zeng, X. L. Guo, J. H. Huang, “Experimental study on pulse defrosting of variable frequency air conditioner,” Refrig. & air conditioning, 14, 107, 2014.
[21] L. Li, W. F. Jin, H. Li, “Analysis of the influence of air temperature on indoor comfort,” Green technology, 2, 274-276, 2014.

International Journal of Thermodynamics-Cover

ISSN: 1301-9724
Yayın Aralığı: Yılda 4 Sayı
Başlangıç: 1998
Yayıncı: -

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