Investigation of the performance of a heat pump under frosting and defrosting conditions

A flexible heat pump cycle for heat recovery

“…Notably a study on reverse defrost cycle using vapour injection concludes that the main improvement would be a shortened defrosting duration by 7.75% 48 . The defrosting of current ASHPs could consume 5-17% of the systems' heat production annually, e.g., in the UK [43][44][45]49 .…”

Control strategies for defrost and evaporator fans operation in walk-in freezers

“…Along the experimental study done by da Silva et al [19], which tested the system with different evaporator geometries, it was noticed that increasing the time between successive defrosting processes improves the thermal performance of the system, so the pair fanevaporator must be designed as a coupled system. Moreover, Votsis et al [20], reached similar conclusions demonstrating that defrost cycles should be kept to a minimum.…”

“…By means of detecting the frost formation, defrost process can be launched just on demand, hence the energy consumption will be reduced no matter the defrost method used. Different parameters were measured and used to determine the amount of frost in the evaporator, such as air pressure difference across the evaporator [20], temperature difference between room air and evaporator [¡Error! No se encuentra el origen de la referencia.-24], fan power [25], frost thickness by measuring frost thermal conductivity with optic sensors [26,27] or with acoustic oscillators [28], refrigerant flow instability [7,29], air humidity [30,31], measuring the heat transfer rate on the air and refrigerant side of the evaporator [32], or use of photo-electrical sensor [33][34][35][36][37].…”

Frost detection method on evaporator in vapour compression systems

“…Moreover, it was pointed out that the time between two consecutive defrost processes affects the overall system efficiency as the system thermal efficiency improves when this time increases. Same conclusion, that defrost processes should be the lesser as possible, was achieved by Votsis et al (Votsis et al, 1989). Melo et al (Melo et al, 2013) tested three different electric heaters used for defrosting purposes, focusing on improving the defrost efficiency.…”

“…Thus, some studies are focussed on frost detection and estimation of frost level. Several different parameters were gauged to evaluate the thickness of the frost layer built-up on the evaporator such as, for instance, temperature difference between the evaporator and the indoor air (Buick et al, 1978;Ciricillo, 1985;Kim and Lee, 2015), air moisture (Tassou et al, 2001;Zhu et al, 2015), air pressure difference on the evaporator (Votsis et al, 1989), flow stability on the refrigerant flow (Lawrence and Evans, 2008;Lawrence and Parker, 2001) or fan energy demand (Muller, 1975). Other researchers developed optic (Paone and Rossi, 1991;Woodley, 1989) and acoustic (Llewelyn, 1984) sensors to measure heat transfer on frost, linking it with frost thickness.…”