How We Do It
How it works
Heat pumps convert low-temperature heat into higher-temperature heat – even in winter when it is well below freezing.
This process takes place in a closed circuit and involves constantly changing the state of the working fluid (evaporation, compression, condensation, expansion). Refrigerators operate on the same principle to extract heat from inside and discharge it to the outside.
By contrast, heat pumps take stored solar heat from the environment around the house – soil, water or air – and release it together with the input energy in the form of useable heat to the heating and hot water circuit.
The Heat Pump Cycle
The heat pump operates on the basis of a working fluid (coolant) which changes state (liquid/gas) in a continuous cycle and absorbs and releases heat.
The heat pump cycle is essentially based on the Carnot cycle. This diagram illustrates the operating cycle of a heat pump:
In a heat exchanger the liquid refrigerant absorbs energy from the heat source (water, soil or air) and evaporates as the temperature rises.
In a compressor the introduction of electrical energy causes the vaporised but still cold coolant to compress and heat up. The coolant leaves the compressor as a hot gas.
3. Liquefaction / condensation
The hot gas flows into the liquefier, releases energy to the heating system, condenses and leaves the condenser as hot, liquid refrigerant. This energy heats the hot water for heating or domestic use to the desired temperature.
The hot, liquid refrigerant is transferred to the expansion valve. In the expansion valve the pressure is reduced very rapidly. The temperature of the coolant also drops very quickly without releasing energy. The cold, liquid refrigerant is transferred to the evaporator and the cycle begins again.
Here a loop of pipe is filled with a liquid antifreeze fluid and buried underground. The fluid continuously circulates inside the buried pipe absorbing heat energy from the earth and eventually transferring it to the home using the heat pump.
The pipe, or heat exchanger, can be laid in the ground as a horizontal loop or a vertical loop. The choice can depend on the amount of sp ace available or the soil type. A typical borehole depth for a vertical loop is 150 to 200 feet. The majority of geothermal installations are closed loop systems.
In an open loop system, water is used from a surface or underground source, such as a lake, pond or well. The water is pumped into the heat pump where the heat is extracted before the water is discharged back to its original source.
Well water designs are the most cost effective as the well can also be used for household water. Water quality is important as mineral deposits and organic matter can quickly clog up and damage a geothermal system.