A Novel Low Energy Defrost Process for Aircoils
Dr Tom Davies, Emeritus Professor
University of Exeter, UK
Time & Place
Tue, 13 Mar 2018 16:00:00 NZDT in E5 (Engineering Core Bldg)
Aircoils used in freezer systems and air source heat pumps need periodic defrosting, a process which consumes significant amounts of energy (often electrical) and commonly creates undesirable effects in frozen food storage equipment and a reduction in COP of heat pumps.
The talk describes the operation of a low carbon method of defrosting aircoils which does not require extra energy (it stores and then uses surplus energy in the liquid refrigerant leaving the condenser) and also reduces side effects such as large temperature variations in frozen food and “steaming”.
Experimental results obtained from controlled laboratory tests on retail display cabinets, walk-in cold stores and an air source heat pump will be presented showing typical energy reductions of around 20%.
Retrofitting in several operational supermarkets revealed that a typical commercial aircoil operating well as an evaporator does not usually perform well when operating as a condenser, an essential requirement of the new defrost system, in which a thermosyphon flow of refrigerant transfers heat from a heat store to the frosted aircoil.
There is now a need to design aircoils which will uniformly distribute a two-phase mixture of refrigerant between the multiple pipe sections connected to the inlet manifold so that defrost is uniform over the entire tube bank.