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Heat pumps

A heat pump may be a viable option for heating in your home or church premises.

Heat pumps are increasingly being mooted as options for electrifying a building’s system, enabling it to reach the target of the Church of England and Diocese of London of net zero carbon by 2030.

This helps contribute to the struggle against climate change, part of our duty to care for God’s Creation.

Different types of heat pump are available; information is essential to assess whether your building might be suitable for a heat pump, and if so what type it should be.

Overview

Heat pumps include ground source and air source heat pumps. They work like refrigerators in reverse, cooling the ground or the air while warming inside the building.

The heat thus extracted is usually low temperature, therefore the system needs to be well deployed usually at low level, and in a well-insulated space.

Heat pumps are powered by electricity, but take much less from the grid than conventional electrical heating – therefore they can reduce a building’s costs, carbon emissions and contribution to global warming.

If the building is supplied on a genuinely renewable electricity tariff, it may be able to achieve net zero carbon status.

The benefit is greatest when the building also has solar panels, so the electricity used by the heat pump is itself renewable.

This remains a developing technology, which must be competently specified and installed by trained and qualified persons.

Heat pumps have been employed successfully on several sites in the Diocese, most notably the parsonages of St John Wembley and St John the Baptist Hoxton.

St Paul’s Church Hammersmith has heat piles, a kind of ground source heat pump. Other churches in the Diocese with heat pumps include:

  • St Andrew-by-the-Wardrobe in the City
  • Holy Redeemer Clerkenwell (in its Institute building)
  • St George Hanover Square (crypt restaurant)
  • Jesus Church, Forty Hill
  • St Cuthbert North Wembley.

Suitability

Ground source heat pumps are beneficial for new homes, and may be worth considering for some church halls and possibly churches especially new church buildings.

Air source heat pumps may also be beneficial in some cases, as well as cheaper and easier to install than a ground source heat pump.

The heat that is obtained from a heat pump low grade, in the case of a ground source system, at an average flow temperature of approximately 45 degrees C. However higher temperature heat pumps are now becoming available.

Even a high temperature heat pump is likely to deliver a cooler temperature than a traditional central heating system (which may have a flow temperature of 70 deg C).

A heat pump therefore needs to be matched to a heating system capable of working to this lower water temperature. Radiators and pipework will need to be larger than for traditional systems.

The temperature will usually not be sufficient to supply hot water for taps, and not for hot water storage which requires a temperature of 60 deg C, to prevent Legionella.

Heat pump systems are generally compatible with underfloor heating, because the gentle heat may be sufficient to keep the congregation or other occupants warm, before rising up inside the space.

It is important for successful functioning of a heat pump that the building should be well insulated, especially if under floor heating is not to be used.

Many if not most existing churches are not readily suited to upgraded insulation. An exception is where a roof void can be packed with insulation. However this may still not be sufficient for viable running of a heat pump – too much heat would still be lost through the walls before it reaches the ceiling.

For new churches or extensions however, a heat pump may well be worth considering. Any new building should be super-insulated; they are also likely to be smaller in height and volume than many historic churches.  Existing church halls (of modern construction) and also new church halls may also potentially be suitable candidates for a heat pump.

Research has not given consistent answers about the benefits of heat pumps in domestic premises. The modern net zero carbon Vicarage of St John Wembley has a ground source heat pump. Not all case studies are equally favourable – but a heat pump remains very well worth considering for many houses, and certainly for new houses.

Air source heat pumps

An air source heat pump consists of an external heat extractor, preferably located on a hidden elevation at the back of the building, within shrubbery perhaps – where it will not be too unsightly – especially for a church building.

The extractor sucks heat from the air, which is then pumped through a heat transfer medium to the internal heating system.

An air source heat pump is cheaper to install than a ground source heat pump, as it does not involve excavation. However the heat produced is at an even lower temperature, making super-insulation of the building even more necessary.

The economics are most likely to be favourable on a site without mains gas – the improvement relative to electricity is greater, and there may be no benefit over gas, economically speaking, in many cases. However this is more likely to be favourable for a new building, such as a new house, or a church extension.

Types of air source heat pumps

There are two basic types:

  • Air to water heating systems. The heat pump serves a traditional radiator circuit. However this requires the circuit and radiators to be suitably designed. In particular a two-pipe system is essential, with wide not narrow bore pipes, and larger radiators;
  • Air to air systems. These are very similar to the kinds of room aircon system (so-called) with a blower inside with a pipe to an external wall mounted unit. They are designed to offer winter warming as well as summer cooling.

Ground source heat pumps

Below 2-3m depth, the ground temperature should normally vary little over the course of a year, and remain at the approximate mean annual air temperature. As a result of these constant temperatures, the ground has the potential (via a heat pump) to provide heating during the winter, and/or cooling during the summer.

Ground-source heat pump systems are best applied in buildings that have both a heating requirement in winter and a cooling requirement in summer. This ensures that there is a net thermal balance over the year, so that the heat removed from the ground in winter is returned to the ground in the summer.

Almost all churches are heated only, therefore the economics are less favourable for this approach. Some other buildings eg homes may need summer cooling (even more in the future as climate change increasingly takes hold).

Where an application is being considered with a heating load only, local geology and ground water movement, as well as surrounding buildings which may also have heat pumps, will need to be considered. Otherwise the ground may be progressively cooled from year to year. This reduces the efficiency of the heat pump.

Also the disruption of excavating for a ground source heat pump is also significant – especially for a church. See Archaeology, below.

Types of ground source heat pump

There are two basic types of ground source heat pump:

  • Closed loop systems. These circulate water through a series of coils buried in the ground. The coils may be deep vertical bores, or shallow horizontal coils;
  • Open loop systems use the ground water through a single borehole for abstraction, and return water to ground once heat has been removed.

An open loop system needs at least 100m separation between abstraction and water return, to prevent short-circuiting of the heat – this amount of space is a luxury that is not available on many church sites.

As stated, closed loop systems are in turn of two types:

  • Horizontal coil systems. These are suited to small installations of no more than 30 kW. A large extent of open ground would be needed for horizontal heat exchangers. This is beneficial for example in new housing estates. It might also be a way of heating a church hall, say when the church car park needs to be re-surfaced anyway;
  • Vertical heat exchanger loops are also sometimes described as ‘energy piles’. There is an excellent example in the new Church Centre at St Paul’s Hammersmith.

Vertical boreholes are typically 80 to 120m deep, and spaced on a 6m grid for each loop. Each metre of installed pipe generates from 30 to 70 watts. The viability of deep piles is improved when piling is needed anyway for new construction.

Archaeology

Excavating for a ground source heat pump on a church site may disturb archaeological remains. A desk-based archaeological assessment will be a pre-requisite. The Diocesan Advisory Committee will need to consult its Archaeological Advisor. See Permissions, below.

Ground water

Open loop systems may require permission from the Environment Agency, due to heat transfer and the risk of aquifer contamination. This applies especially in proximity to any river or water course.

Any physical barrier between the system and a neighbouring water course may not make much difference – for example concrete is a good conductor of heat.

A water source heat pump also needs EA permission.

Supplementary heating

Some heat pump systems can be sized to take a base load of the heating demand through the year, with a gas fired boiler used as a top-up for peak demand.

This arrangement is referred to as a bivalent system.

If one third of the peak load is carried by the heat pump then this will reduce the capital cost of the system, but over the course of a heating season will contribute 60% of the delivered heat.

The supplementary heat can be made up with a gas fired boiler.

However as stated it is important to ensure that the water temperatures delivered by the boiler and heat pump are compatible with each other, and with circuit radiators and pipework.

This may improve economic viability. It may work well when a new heat pump is installed in series with an existing gas boiler which still has a few years to run – and whose life may thereby be extended.

Finance

Boiler Upgrade Scheme

The government’s Renewable Heat Incentive has been replaced with the Boiler Upgrade Scheme.

The Boiler Upgrade Scheme is mainly intended to encourage the installation of heat pumps in homes, but may also be suitable for some small churches and church halls.

The amount payable was increased from £5,000 to £7,500 by the Prime Minister in his speech on 20th September 2023.

VAT

Bear in mind that VAT at 20% will be added to installations costs of most projects, although this may be reclaimable under the Listed Places of Worship Grants Scheme (at least until March 2025).

Domestic heat pump projects will be zero rated from April 2022 – March 2027. However churches are sadly not eligible for this concession.

Permissions

Faculty

A faculty is also needed for any installation in a church, before which the Diocesan Advisory Committee (DAC) should be consulted.

Planning permission

Planning permission from your Local Planning Authority (Council) is also likely to be required, if there is a material change in external appearance and/or if the building is listed or in a conservation area.

There is no automatic bar to making changes which affect a church’s appearance – but it must be done well. You are likely to need to make every effort to mitigate the visual impact of any new installation, in order to gain permission.

The external unit of an air source heat pump is therefore likely to trigger the need for planning permissions. As well as appearance, the Council may want to consider any potential noise nuisance. There is a widespread perception that heat pumps are noisy, which isn’t necessarily the case but an assessment may be required.

Therefore it is especially necessary to check the position with the Local Authority at feasibility stage. If planning permission isn’t required, it is strongly advised that a certificate of lawful development be applied for and obtained before starting any works.

Engineers and consultants

Professional advice should always be sought.

It is important to retain the services of consultants and installers who are trained and technically proficient in the system to be installed.

In addition to an experienced engineer, you may need an architect to coordinate your project – he or she could be your Quinquennial Inspector.

Installers should be certified under the Microgeneration Certification Scheme.

More information and advice

Parish Property Support Team
Head of Environmental Challenge.

Generating your own energy
Climate Action Projects
Solar Panels.

Climate Action Finance
Getting a faculty.

Boiler Upgrade Scheme
Microgeneration Certification Scheme (MCS).

Environment Agency

Environment and Sustainability, front page.


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