What are the basic workings of a heat pump

Heat Pumps

A heat pump is a relatively new technology in the UK although they are widely used in Scandinavia and many parts of Europe where there is an abundance of renewably sourced electricity.

A heat pump takes energy from outside and transfers it into heat to be circulated around a heating and hot water system.

A heat pump uses electricity to run the components of a heat pump, principally a fan, compressor and circulating pumps to transfer the energy from the heat source into the heat sink or heating system.

What are the advantages and disadvantages of the different types of heat pumps?

There are debates over which system is the most efficient however, an air source heat pump is reliant on the outside air temperature which can be a lot cooler than the ground temperature which by comparison is relatively stable.

Consequently, a ground source heat pump tends to be more efficient in all outside temperature situations however, they are significantly more expensive to install and are therefore less popular than an air source heat pump.

How does the operation of a heat pump differ from a boiler?

A heat pump is at its best when it is circulating low temperature water around the heating system in a “steady state” mode.

The heat pump is best run from a weather compensation system and allowed to run at all times as dictated by the external weather temperature and the internal room temperature.

Because of the low temperature of the heating system water it is not best suited to be operated intermittently like a boiler.

A boiler is typically turned on for a couple of hours in the morning, switched off all day and then turned back on at night for 5 or 6 hours. 

The high temperatures that a boiler can generate result in it heating the house more quickly than a heat pump can hence the need to run the heat pump in a “steady state” mode and avoid the need to heat the house quickly and from a low base temperature.

What are the servicing requirements of a heat pump?

The servicing requirements of a heat pump are not as onerous as a boiler however, there are disagreements as to whether the homeowner can undertake this or a service engineer is required.  

With a Ground Source heat pump the requirements are more of a check than an activity, the closed loop collection system needs to be checked for the correct levels and efficacy as the fluid also serves as an anti-freeze.

The heating system water pressure needs to be maintained and, if the installation has a mains pressure unvented hot water storage cylinder, the servicing requirements of that needs to be considered.

An Air Source heat pump requires the external unit to be kept free of leaves and debris, any filters within also need cleaning or replacing as specified by the manufacturer.

And similar to a Ground Source heat pump, any unvented, mains water pressure cylinder needs to be serviced to the manufacturer’s instructions.

What are the annual running costs of a heat pump system?

The running costs of a heat pump will vary from house type to house type.

A well-insulated house built to new building regulation standards will generally be less expensive to run than a gas or oil fired boiler system providing the heating system flow temperatures are kept relatively low, ideally around 40ºC.

A heat pump will be less efficient and more costly to run when generating higher temperatures, either because the house isn’t well insulated, the radiators are insufficiently sized for the lower temperatures or when generating higher temperatures to produce hot water.

Can I connect a heat pump to an existing heating system?

The short answer is yes. This is called a hybrid heat pump and typically consists of gas boiler and air to water heat pump outdoor unit.

It works using an outdoor heat pump with an existing or new boiler to provide heating and hot water to the home.

Unlike a standalone heat pump, remedial changes such as resized radiators and fabric improvements are less likely to be required to ensure performance.

The hybrid heat pump may utilise the existing system and fabric improvements can be installed over a longer period. 

The heat pump would be able to heat the house comfortably during most months but when it reaches colder temperatures, the boiler would support the heat pump to get the house up to temperature.

A combi boiler can also provide hot water whilst the heat pump warms the property.

How much does it cost to install a heat pump?

The installation cost of a heat pump will differ from house to house and from size and type of heat pump chosen.

As a rule of thumb, an air to water heat pump will cost around £8k to install and a ground source heat pump could be anything up to and around £20k.

This though is very dependent on the site and as to whether the existing heating system can be used and the position of the equipment etc.

There are grants available to assist in the investment, sometimes locally and regionally, as well as the Renewable Heat Incentive (due to end March 2022) which will pay an annual sum to the purchaser of the system for 7 years.

Are heat pumps noisy?

An air source heat pump has an outdoor unit that contains a fan to induce the external air into the unit and consequently, they are noisier than a ground source heat pump.

Generally, there are few complaints about the noise from a heat pump and when compared with the normal ambient external noise are quite acceptable.

SOURCE: www.worcester-bosch.co.uk

Dave Stroud
Author: Dave Stroud