HVAC Fundamentals: Heat Pumps

HVAC Fundamentals: Heat Pumps

A heat pump is a refrigeration system used to switch heat from one room or space to another. The heat pump is designed to take heat from a medium-temperature supply, similar to out of doors air, and convert it to higher-temperature heat for distribution within a structure. Via a specifically designed reversing valve, the pump also can extract heat from the indoor air and expel it outdoors.

Because a heat pump system makes use of the reverse-cycle principle of operation, its operating precept is usually referred to as reverse cycle conditioning or reverse-cycle refrigeration. The latter time period will not be appropriate because there are fundamental variations between the operating ideas of a heat pump and a real refrigeration unit. The confusion probably stems from the truth that during the cooling cycle, the operation of a pump is similar to that of the mechanical refrigeration cycle in a packaged air conditioning unit. The indoor coil operate as an evaporator, cooling the indoor air. The outside coil is condenser, in which the hot refrigerant gas releases heat to the outside air.

Heat Pump Operating Rules

The two principal phases of heat pump operation are the heating and cooling cycles. A third part, the defrost cycle is used to protect the coils from extreme frost buildup.

Heating Cycle

The heating cycle of a heat pump begins with the circulation of a refrigerant by way of the out of doors coils. Initially, the refrigerant is in a low-pressure, low-temperature liquid state nevertheless it quickly absorbs sufficient heat from the outdoor air to boost its temperature to the boiling point. Upon reaching the boiling level, the refrigerant modifications right into a scorching vapor or gas. This gas is then compressed by the compressor and circulated under high pressure and temperature through the indoor coils, the place it comes into contact with the cooler room air that circulates around the coils. The cooler air causes the gas to cool, condense and return to the liquid state. The condensation of the refrigerant vapor releases heat to the interior of the structure. After the refrigerant has returned to a liquid state, it passes through a special pressure-reducing machine and back by means of the coils the place the heating cycle begins throughout again.

Cooling Cycle

Within the cooling cycle, the reverse valve causes he flow of the refrigerant to be reversed. In consequence, the compressor pumps the refrigerant within the opposite direction so that the coils that heat the building or house in cold climate cool it in warm weather. In different words, the heat is extracted from the interior, cycled through the heat pump after which expelled outside the building or area during the condensation of refrigerant.

Defrost Cycle

Because the out of doors air is comparatively cool when the heat pump is on the heating cycle, and the outdoor coil is appearing as an evaporator, frost varieties on the surface of the coil under certain conditioners of temperature and relative humidity. Because this layer of frost on the coils interferes with the efficient operation of the heat pump, it should be removed. This is accomplished by putting the pump by way of a defrost cycle.

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