Heat pumps

DEFINITION: A device that transfers heat from a colder area to a hotter area by using mechanical energy

Ground or air source heat pumps are growing in popularity due to their efficiency and relatively low cost. Ground pumps use pipes to extract heat from the ground, while air pumps absorb heat from the outside air – both provide heating and hot water and are suited to applications where there’s a demand for steady, low temperature heat such as underfloor heating or radiators.

Air source heat pumps are usually easier to install as they don’t require any trenches or drilling, but are often less efficient than ground source heat pumps.

How do heat pumps work?

Heat pumps transfer heat by circulating a substance called a refrigerant through a cycle of evaporation and condensation. A compressor pumps the refrigerant between two heat exchanger coils. In one coil, the refrigerant is evaporated at low pressure and absorbs heat from its surroundings. The refrigerant is then compressed en route to the other coil, where it condenses at high pressure. At this point, it releases the heat it absorbed earlier in the cycle.

What are the business benefits of heat pumps?

Heat pumps can deliver a number of benefits such as reduced fuel bills and lower carbon emissions. They can produce up to three to four times more heating or cooling than the energy it takes to operate them, saving around 30-40% of electricity. The level of efficiency depends on the temperature of the heat source the pump is drawing on – if the air is very cold outside, this is good for ground pumps as the earth beneath is warmer, but not so good for air pumps. If the heat pump is providing hot water this also can reduce its efficiency.

What's the cost and ROI?

Ground pumps are more expensive than air pumps, but as a rule of thumb, the cost per kW installed for a ground pump ranges between £2,500-£2,000 while cost per kW for an air pump is between £1,000-£500. The larger the pump, the lower the cost per kW. Payback is between 5-8 years if self-funding, sometimes less for larger systems. Energy bill savings of 5-10% can be achieved with a PPA.

Some pumps may be eligible for support under the Renewable Heat Incentive (RHI) scheme. These incentives guarantee certain prices for the heated generated for seven years.

Are there any other key considerations for heat pumps?

The main consideration is whether to go for ground or air. Businesses with access to land, such as a country estate or football club, may opt for the former, while an office that owns roof space but no carpark might go for the latter. A ground pump requires pipework, buried in the soil, and ground conditions must be surveyed to ensure suitability. Ground pumps can be installed horizontally or vertically depending on space constraints.

Heat pumps usually work for 20 years or more, although they do require regular scheduled maintenance. Poorly designed heat pump systems increase the risk of getting Legionnaires’ disease if water is stored below 65°C for long periods. Either an immersion heater or fresh water system will remove this risk. 

See also: Air-source heat pump

See also: Ground-source heat pump

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