A heat pump is a device that provides heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one.
Whether installing a heat pump in a new or existing dwelling, the initial capital investment will generally be greater than for a conventional boiler system. The concept of a heat pump might be relatively new to you, it is possible you have already gathered some very useful information with regard to specific products and systems. The aim of this guide is to provide you with a fundamental knowledge of heat pump so that you can make more informed decisions in choosing the correct system and once installed how to operate the system efficiently. (Source: SEAI)
Heat energy flows naturally from a hot place to a cold place. The main task of a heat pump is to move heat energy in the opposite direction i.e. from a cooler to a hotter place but energy is required to achieve this! There is a lot of natural energy available in our surroundings which can be tapped into, but in order to do that, we need some way of collecting and moving it to where it’s needed – that’s the role of the heat pump.
There are two sides to a heat pump system: the heat source for example the ground, air or water and the heat sink where the heat is sent and used. In simple terms the heat pump is the machine which drives this cycle of heat collection and release. A heat pump is similar to a fridge in the way it works. In a fridge, the heat is taken away from the storage section of the fridge and released at the rear. In a heat pump the process is opposite - the heat is taken from the air, ground and water and released into the building.
A heat pump uses an electric compressor which moves a fluid (called a refrigerant) around in a closed pipe circuit. A heat exchanger takes the heat from the surroundings, transfers it to the refrigerant circuit passing through the compressor, where its temperature is raised. The heat then passes through another heat exchanger, where it is transferred to the dwelling, and the cycle can start again. Electrically driven heat pumps are the most common type of heat pump available with electricity used to drive the compressor. The collector, the heat pump unit, the heat distribution system and the control system all make up the heat pump system.
The three main types of heat pump systems are:
Air Source - energy is extracted from the external air
Ground Source - energy in the soil is extracted either by transferring heat from a horizontal bed of pipes laid flat in the soil or by transferring heat from pipes laid in a vertical borehole
Water Source - energy in the water is extracted directly, either from wells or from rivers, streams
Air source heat pumps
Air source heat pumps use the outside air as a heat source. Air temperatures vary seasonally and moisture content fluctuates also so an air source heat pump will always be at the mercy of the climate. The colder the air temperature, the harder the heat pump must work to lift the temperature up to what is required for heating. Also, as heat energy is taken out of the air, droplets of water can freeze on the heat pump heat exchanger which then means the heat pump must “defrost” so the cycle can begin again. For this reason, air source heat pumps are slightly less efficient than their ground and water source counterparts, however this slight loss of efficiency is reflected in costs – they are typically less expensive to install. The most common type of air source heat pump used in dwellings is an air to water heat pump – the water referring to the method of heat distribution, i.e. through an under floor heating system (which uses water).
Other types of air source heat pumps include exhaust air heat pumps, which are usually fitted to ventilation systems to provide hot water / hot water and heating, air to air heat pumps, which use the ventilation system instead of water systems such as under floor heating or radiators.