General

HVAC Fundamentals: Heat Pumps

A heat pump is a refrigeration device used to transfer heat from one room or house to another. The heat pump is designed to take heat from a medium-temperature source, akin 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 working principle is typically referred to as reverse cycle conditioning or reverse-cycle refrigeration. The latter term is not correct because there are fundamental differences between the operating ideas of a heat pump and a real refrigeration unit. The confusion probably stems from the fact that during the cooling cycle, the operation of a pump is equivalent 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 out of doors coil is condenser, in which the new refrigerant gas releases Heat pump installation to the outside air.

Heat Pump Operating Rules

The two principal phases of heat pump operation are the heating and cooling cycles. A third section, the defrost cycle is used to guard the coils from excessive 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 but it surely quickly absorbs enough heat from the outside air to raise 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 below high pressure and temperature by means of 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 device and back by way of the coils the place the heating cycle begins all over again.

Cooling Cycle

Within the cooling cycle, the reverse valve causes he circulate of the refrigerant to be reversed. Because of this, the compressor pumps the refrigerant within the opposite direction so that the coils that heat the building or space in cold climate cool it in warm weather. In other words, the heat is extracted from the interior, cycled through the heat pump and then expelled outside the building or area throughout the condensation of refrigerant.

Defrost Cycle

Because the outside air is comparatively cool when the heat pump is on the heating cycle, and the outside coil is appearing as an evaporator, frost types on the surface of the coil underneath sure conditioners of temperature and relative humidity. Because this layer of frost on the coils interferes with the environment friendly operation of the heat pump, it must be removed. This is completed by placing the pump by a defrost cycle.