HOW DOES A HEAT PUMP WORK?

At the heart of a modern heat pump is a refrigerant system. Paradoxically, the refrigeration cycle is an efficient provider of heat as well as cooling and the basics of its operation are quite easily understood.

There are two basic principle locations in the transfer of heat; the place where heat is absorbed (the source), and where it is rejected (the destination). The significant proportion of this can be recovered, thereby reducing running costs and the ultimate release of CO2.

The mechanical refrigeration cycle consists of an arrangement of heat exchangers; one that absorbs heat, the other that rejects it. All but the largest industrial systems are hermetically sealed and pressurised, thereby reducing noise, space and heat losses. This means that the compressor and the motor that drives it are encased in a welded shell.

This heat absorbed is transported through a sealed system of pipes by a fluid, the refrigerant, circulated by a compressor. The refrigerant is a fluid that has a low boiling point. A metering device to control the flow of refrigerant completes the arrangement and it is all connected by pipes. As the refrigerant works under pressure, the whole system is sealed for life.

In order to absorb and release the heat into and from the refrigerant, we exploit the ability of the refrigerant fluid to boil from a liquid to a vapour and then to condense back into a liquid. This is a continual process while the compressor is running and circulating the refrigerant.

For all volatile substances, there is a known relationship between its pressure and its boiling point; by controlling these in the refrigerant we can achieve cooling and heating in the same machine at the same time.

High pressure liquid refrigerant is fed through the metering device into the evaporator heat exchanger where it evaporated into a vapour by absorption of heat from the heat source (air, water, ground, other) passing through the heat exchanger.

The relatively cool return vapour is drawn back to the compressor. The compressor and the electric motor that drive it are constructed in a fully sealed hermetic shell. The cooled return vapour from the evaporator is passed over the compressor motor windings within the heat pump, thus cooling the windings of the motor.

Much of the energy absorbed by the electric motor driving the compressor is absorbed into the refrigerant.

The combined heat from the source, plus much of the waste energy from the electric motor is then compressed to a high temperature vapour and enters the condenser heat exchanger where it is cooled and condensed into a high pressure liquid ready to begin the cycle again.

The heat released during the process of condensing the refrigerant to a liquid is rejected via the heat exchanger directly into air or transferred to water to heat the building. The air or water temperature at this point could be 43 to 60 degrees centigrade, depending on the design of the system.

Although some systems are configured for heating only, reverse cycle heat pumps use an electrically operated reversing valve with four pipe connections to change the direction of refrigerant flow within the system so that the system is able to deliver both heating and cooling as desired.

Many commercial systems are capable of cooling as well as heating, with fully automatic control enabling the user to receive year round operational benefits.