Installing Air Source Heat Pumps in Listed Buildings and Historical Properties
Overview of installation considerations for an air source heat pump implementation in a listed building or historical property.
Britan has an an arrray of of listed buildings and historical properties, which come in a variety of architectural shapes, ages and sizes. The one thing they often have in common however is that they are generally difficult to heat.
Improving energy efficiency lowers carbon emissions and fuel bills and often increases comfort, but it also might be necessary to ensure that a building complies with legal requirements and more broadly, improving energy efficiency forms a part of the wider objective to achieve a sustainable environment, so there are various incentives to exploring the viability of renewable air source heating in a listed or historical building.
Striking the right balance between benefit and harm is not easy when it comes to any heritage project. The unintended consequences of getting energy efficiency measures wrong (or doing them badly) include: harm to heritage values and significance, harm to human health and building fabric, and failure to achieve the predicted savings or reductions in environmental impact. So firstly a ‘whole building approach’ should be taken for any listed or historical buildings in such an undertaking considering :
The context for the project
Construction of the building
Condition of the building
The building's historical significance
An understanding of all the factors that affect energy use
How to devise an energy efficiency strategy for the building
This approach will ensure that energy-efficiency measures are suitable, robust, well integrated, properly coordinated and sustainable. Plus provides an effective framework for communication and understanding between all involved in the process; assessors, designers and installers as well as those who occupy and manage the building.
Air source heat pumps can be sized to cover the entire peak heating demand with no other heat generation source; known as monovalent systems. Or air source heat pumps can be sized to just provide the base heating load, with gas boilers (or another heat source) used to meet the peak load. These are known as bivalent or multivalent systems, and normally implemented to reduce the size of the heat pump for space and cost reasons.
Renewable Energy Heating
To assessing the advantages of renewable energy heating for listed buidings or historic premises, we would help you to evaluate :
Whether air source heat pumps would suit the building and its use
Carbon reduction benefits
Potential savings and whole-life energy costs
System installation and any impact on the building and its historic fabric
Visual impact on the building setting or heritage asset
Planning controls that may affect choice and positioning of the installation
Low or zero carbon technology options that we can assist with include:
Solar photovoltaic panels for electricity generation, solar thermal batteries for energy storage and solar thermal panels for water heating
Air source heat pumps (air-to-water and air-to-air), ground source heat pumps and water source heat pumps.
Air source heat pumps are most effective within buildings with a highly energy-efficient make-up, where heat demand and loss have been reduced to a minimum.
The output of energy supplies can fluctuate with heating, although lesser with high temperature heat pumps. They will often need to be balanced with electricity supplied from the National Grid, importing or exporting as required, unless incoporated within a greater renewable energy technology infrastructure, e.g. with solar panels, solar storage or a combined heat and power network. .
Further apart from the initial set-up, operation and maintenance costs, the de-commissioning of redundant systems need to be considered. This can be higher than for conventional supplies e.g., if a large property with a number of gas or oil boilers.
Its is recommended to evaluate whether any improvements could be made to the buildings demand for heating and its heating loss. Minimising heat losses will not only reduce the size of the heating plant required, but also the costs of running the heat pump and its carbon impact.
Building condition strongly influences energy performance too and maintenance is vital. For example, draughts from cracks and poorly maintained doors and windows will contribute further to heat loss. Also when designing any heating system, it is essential to understand the usage patterns of a building, e.g., what times different areas are used, who by, and whether any particular activities take place. This information will help our engineering designers to ensure the air source heating heating system is capable and suited to the needs of the people using the building's areas and spaces.
Air source heat pumps need to be sized to match the heating demand of a property, so we would calculate the peak heating load and extent of heat loss in order to be able to determine the amount of heat energy required to maintain comfortable conditions.To avoid ending up with an over- or under-sized air source heat pump system, the heat loss would need to be assessed incrementally; calculating loss through the walls, ground, roof, and windows, so as to maximise system efficiency. Understanding the proportion of the heat loss through each component enables us to appraise the impact of any proposed fabric improvements.
It is important to thoroughly understand the building’s environmental performance also, so monitoring and modelling through on-site measurements are highly recommended - such as U-value measurements, hygrothermal and dynamic thermal modelling, air pressure testing, thermal imaging, and on-site weather data collection should be considered.
Many historic buildings will have existing heating systems with pipework and emitters that are in good condition. It should not be assumed that these systems will need to be entirely replaced. Reusing heating systems should always be considered, as the embodied energy originally used to make the equipment can be considerable. An assessment of the existing heat emitters and pipework would be be undertaken. However, it may be that radiators need to be supplemented or replaced with larger versions in order to be suitable to work with the lower water flow temperatures that some heat pumps require.
Also early examples of heating systems and emitters are likely to be of historic interest and should be conserved.
Pipework and Underfloor Heating
The efficiency of most air source heat pumps increases as the water supply temperature is decreased, so to maximise efficiency, reduce running costs and carbon missions, air source heat pump systems are designed to operate at lower flow temperatures. General air source heat pumps pumps circulate heated water up to temperatures of 55°, which is a lower than a conventional gas or oil boiler, so often radiators and and pipework needs to be large enough to provide adequate heat to rooms, which can resiult in additional cost. The type of most appropriate air source heat pump, the size of radiators and existing pipework infrastructure would always be assessed by one of our engineering designers. There are however high temperature air source heat heat pumps that can provide supply water temperatures of up to 110°C. While more expensive than conventional air source heat pumps, there is usualy less requirement to address any radiator or other heat emitter changes.
Underfloor Heating Systems
The lower flow temperatures of most air source heat heat pumps makes them particularly suited for integrating with underfloor heating systems. Underfloor heating systems respond slowly to heating and may take a long time to reach the desired room temperature, however owners do find that they can quickly adapt to the change required to be able to control the system and reach effective heat levels when required. This can make underfloor heating systems well suited to a building that is used frequently during the week due to the lower temperature difference between flow and return pipework than that of conventional heating systems. This means that the flow rate through the pipework will increase in order to provide the same amount of heat. It is important to consider that raising floor levels, changing or replacing them, to accommodate an underfloor heating system installatio may likely need listed building consent due to the impact of the alterations not only to the floor and substrate, but also to changes to skirtings, doors, and steps.
Air source heat pumps use electricity to generate heat, so require a power supply - be it National Grid, solar, CHP or turbine. Domestic sized installations will normally only need a single-phase electrical supply, but larger installations will require a 3-phase supply. (A single phase supply is smaller and most domestic houses with gas central heating need single phase and have this as standard. If you require two or more electricity meters then you need a three phase supply. As we have electrical engineering specialists in house, we would assess all the equipment you will be running and determine how much power you need) Also early engagement with your energy provider would be essential to check that, if a new supply is required, that it can support the electrificaton of heating, as in some rural communities in the UK, this may be challenging where there has not been upgrades to the electricity network (to support heating electrification).
Buffer vessels, which are specifically for low temperature heating systems and not for domestic hot water production, can be added to increase the heating system volume, maximise air source heat pump run times and efficiency, and buffer any discrepancy between the heat pump flow rate and the heating system flow rate. Buffer vessels also have a role in defrost cycles. Buffer vessels are not required in all heating systems, as the management of the minimum system volume has been incorporated within the design of some air source heat pumps.
An air-water air source heat pump can also be used to heat domestic hot water. The heated water is transferred to a hot water cylinder, much the same as with a conventional indirect hot water system. Domestic hot water has to be stored above 60oC to prevent Legionella bacterial growth and associated health risks. As most general air source heat pumps provide hot water at 55°C, an internal or external electric immersion is needed to increase the temperature of the water to a safe temperature of 60oC. Again we would help calculate the consumption patterns so that the air source heat pump is correctly sized to meet the heated water demand.
Generally, the installation of air source heat pumps are considered permitted development. However, these must comply with conditions listed on the UK Planning Portal website. Similarly the installation of a ground source heat pump or a water source heat pump at domestic premises is usually considered to be permitted development, not requiring planning permission. However consents are likely to be required for installing any type of air source heat pump in a listed building or buildings in a conservation area, scheduled monuments, or installations that affect designated wildlife sites. Installation works need to take into account wildlife, particularly protected species and wildlife licenses may be required. Also there are a range of ecological considerations when it comes to water source heat pumps, and specialist advice should be sought when installing heat pumps.
All heat pump installations have to comply with Building Regulations, and guidance is set out in the Approved Documents. Ground source and water source closed-loop systems generally do not require a permit from the Environment Agency. Where they are installed adjacent to or in a watercourse, consent may be required. Owners are liable for any adverse effects that may be caused by their system (such as a leak that could cause pollutants to enter the groundwater).
For open-loop systems, groundwater investigation consent from the Environment Agency is needed before drilling or test pumping any abstraction boreholes. If work proceeds, you will require an abstraction licence and a permit to discharge. For further advice, see Open-loop heat pump systems: permits, consents and licences.
Other Air Source Heating Installation considerations
An air source heat pump works by the evaporator extracting heat from the outside air to warm the liquid refrigerant and turn it into a gas, which is then compressed to further raise the temperature (see : how air source heat pumps work diagram). This allows heat to be extracted from the air, even on the coldest of days. The condenser is the part of the heat pump that delivers the heat into the building. All ASHPs house the evaporator in the outdoor unit.
The difference between the two types is the location of the condenser - with a monobloc heat pump, the condenser is located inside the outdoor unit; and in a direct expansion heat pump, the condenser is located remotely from the outdoor unit.
With ASHP installations, there are rarely any groundwork issues compared to other types of heat pump. However, the visual impact of the outdoor condenser unit and the need for a clear unobstructed air path will need to be considered. Although there is an increasing range of designs, colours and and external casing units to choose from that asist with the unit blending into surroundings. It is also possible to screen the unit or place them in plant rooms, but manufacturers guidance needs to be followed to not interfere with the air intake.
To ensure that the external unit will not be damaged by flood water, the unit must not be sited anywhere near a risk of flooding now and in the future.
Any change in the number or size radiators or heat emitters (to cope with the lower water flow temperatiures) needs to be carefully planned so as to carefully and considerately site them in keeping with the interiors are of historic interest. They can in fact be sited lower than a conventional radiator, with the chassis removed and fitted into a decorative wooden or metal enclosure to match the interior.
We would also evaluate the manufacturer’s noise data to consider the positioning of any units. A professional noise assessment will take into account background noise levels, the characteristics of the noise, volume on all settings including defrost, distance from the air source heat pump to the nearest neighbour, and any noise barrier/mitigation present
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