An analysis of the feasibility and characteristics of photoelectric technique applied in defrost-control

Developing a new frosting map to guide defrosting control for air-source heat pump units

“…Furthermore, it was not verified by experiments or field tests. 12 According to the field test results [15], the outdoor heat exchanger in an ASHP unit 13 may also be frosted in the non-frosting region. Therefore, the frosting map should be 14 further improved.…”

“…8 9 2 The developed new frosting map 10 11 A frosting map based on a temperature-humidity chart indicates frosting situations 12 and levels on the outdoor heat exchanger surface in an ASHP unit. The procedure to 13 develop the new frosting map is shown in Fig. 2, and is explained in this section.…”

“…Therefore, by comparing the values of T w , T d and T f , the frosting map can be 9 divided into three regions: a non-frosting region, a condensing region and a frosting 10 region. 11 12 3) Determination of T w and T d 13 Based on the above analysis, two crucial parameters, T w and T d , need to be determined 14 first. 15 T w can be estimated by the following correlation: Fig.…”

“…In the previous studies by 10 Wang et al [5], the heating capacity of an ASHP unit was decreased by 29 % to 57 % 11 when its outdoor heat exchanger was covered by frost. Frosting not only increased the 12 heat transfer resistance and reduced coil's efficiency [6], but could also lead to the 13 shutdown of an ASHP unit [7].…”

Defrost Temperature Termination in Supermarket Refrigeration Systems

“…The system was laboratory-based, and not optimized for field or commercial use. Xiao et al (2009) and Xiao et al (2010) characterize the performance of a photoelectric device for determining frost layer thickness. It was found that the photoelectric device could accurately estimate frost height.…”