Accumulation of frost on evaporator coil acts as insulator. As its thickness increases effectiveness of coil drops. Cooling capacity decreases. Frost deposit is the result of low air flow or some restriction to air flow.
Techniques used for removal depend on the size of the system. Simply shutting off the unit can melt this frost. But it takes lot of time, and conditions may go wild. Electric resistance heater can be used. It consumes lot of energy. Also time required is long hours of shutdown.
An energy efficient approach is to use hot gas bypass operation. In this operation, high pressure vapors from compressor discharge are passed through evaporator coil. For this purpose, when frost is detected by the unit, series of operations start. These operations may also be time scheduled. As a first step refrigerant from coil is removed to start defrosting operation. The entire liquid refrigerant is pumped out. Before full charge of hot gas, a small quantity is passed through coil. This is done to avoid any abrupt changes in temperature which may damage tube materials. After this full charge of high pressure gas is passed through the evaporator. Frost on the coil melts and it is drained through drain pan to disposal. After charging residual gas is removed. System is ready to start normal function again. This defrosting technique consumes minimum of energies and time. Operation can be performed without any additional components. It makes system functioning reliable and easy to operate. No complicated controls are involved. Simple steps complete this cycle and make operation failsafe.
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