HEATPUMPS - THE NATURAL SOLUTION FOR SUSTAINABLE HEATING
A range of legislation tackling climate change means the pressure’s on in the construction industry to meet carbon emission reduction targets, and heat pumps can help gain valuable ‘green’ points, delivering carbon savings as well as reduced running costs.
Although relatively new to the UK, heat pumps are accepted as one of the most energy-efficient forms of heat generation available today.
They can extract up to 75 percent of the heating energy they produce from the environment, with the only running cost being the electricity needed to drive the compressor. Put another way, for every kWh of energy needed to run the heat pump, 3-4kWh of useful heat is produced, giving the heat pump an ‘efficiency’ of 300-400 percent - also expressed as the Coefficient of Performance (CoP).
Heat pumps operate by drawing a high volume of low grade warmth from the ground, a water source (such as underground water) or the ambient air. The energy from the heat source is transferred to a refrigerant inside the heat pump, which is then compressed (using an electrically driven compressor), causing its temperature to rise significantly. A good analogy is the effect of putting your thumb over the end of a bicycle pump – when compressed the air gets hot as it is squeezed into a smaller space. A heat exchanger then extracts the heat energy from the hot refrigerant to heat water for central heating, underfloor heating or domestic hot water.
- 75% of the energy is taken from the environment i.e the air or ground and transfered to the heat pump.
- 25% of the energy is sourced from the national grid in the normal way of supplying your electricity. This is used to operate the heat pump but with very low consumption
- The energy from the air or ground is transfered to the refrigerant inside the heat pumps evaporator. This causes the temperature of the refrigerant to rise and change state from liquid to gas.
- The refrigerant gas is then compressed, using an electrically driven compressor, reducing its volume but causing its temperature to rise significantly.
- A heat exchanger (condenser) then extracts the heat energy from the hot refrigerant to heat water for central heating, underfloor heating or domestic hot water.
- After giving up its heat energy the refrigerant turns back into a liquid and is able to absorb energy from the environment, allowing the cycle to begin again.
In retrofit situations, heat pumps are ideal for use in off-gas areas, creating a cost-efficient alternative to oil or LPG systems, and insulating the property from fluctuating prices. In addition, a heat pump system has an estimated lifespan of 20+ years, with no annual safety inspection required, making the lifetime ownership costs extremely competitive. For new build installations, heat pumps can provide a significant CO2 saving over gas systems, while the introduction of the Renewable Heat Incentive in 2011 will also provide a compelling pay-back argument.
Air source heat pumps like this Dimplex LAB M are ideal for retrofits
In the UK, specifiers generally select ground source or air source systems. Ground source heat pumps use collectors filled with a mix of water and antifreeze buried either horizontally in trenches or vertically in boreholes to harvest the heat stored in the ground. At just 1m below the surface, the earth provides a stable source of heat throughout the year.
High output ground source heat pumps can produce flow temperatures of up to 70 degrees Celsius
Air source heat pumps use the freely available heat in the ambient air and as a result do not involve the installation of ground collectors, making them ideal for retrofit projects. However, air source heat pumps do not benefit from stable heat source temperatures (i.e. the heat source is at its lowest when heating is needed the most!), so the overall efficiency of an air source heat pump system will be slightly lower than with ground source systems.
Heat pumps are best suited to low temperature heat distribution systems, typically underfloor heating or fan convectors, since heating water to higher temperatures requires more energy from the compressor and reduces the CoP. Systems with radiators are possible, but still need to be operated at lower temperatures than conventional boiler systems, meaning radiators have to be oversized accordingly.
With indisputable reductions in carbon emissions leading to planning advantages for specifiers, grants available towards capital costs, the planned introduction of Renewable Heat Incentive’s guaranteed income for each kWh of energy produced from renewable heat, and heat pumps available for domestic and non-domestic installations, both refurbishment and new build, heat pumps are a low carbon, high efficiency option.
Want to find out more about the range of heatpumps available from Wolseley? Visit our Ground Source Heatpumps or Air Source Heatpumps pages.