Guide to Conversion of Traditional Buildings

6.3 Heating system

Mandatory Standard

Standard 6.3

Every building must be designed and constructed in such a way that the

heating and hot water service systems installed are energy efficient and

are capable of being controlled to achieve optimum energy efficiency; and

Limitation:

This standard does not apply to:

a) buildings which do not use fuel or power for controlling the temperature

of the internal environment, or

b) heating provided solely for the purpose of frost protection.

6.3.1 Application of standard to conversions

In the case of conversions, as specified in regulation 4, the building as converted shall meet the requirements of this standard in so far as is reasonably practicable, and in no case be worse than before the conversion (regulation 12, schedule 6).

6.3.2 Commentary

In most buildings, space and water heating represent the highest component of the operational energy or carbon footprint of the building. Therefore, it is important to seek to minimise this impact, and this section sets standards for the efficiency of all heating plant.

It is acknowledged that there may be limits to what can be achieved in terms of fabric improvements to traditional and culturally significant buildings. The burden of demonstrating efficiencies may therefore rely more heavily on the building’s services.

The section does not recommend one system or fuel type over another, but sets minimum efficiencies on all possible options, together with guidance on controls and a number of heating system-related devices. Practitioners should be aware, however, that minimising fossil fuel consumption and replacing where possible with renewable energy will inherently reduce energy consumption and carbon emissions, although doing so may not always be possible without impacting on the character and historic fabric of a building or its setting.

All guidance associated with Section 6.3 is now provided through a link to the Domestic Building Services Compliance Guide for Scotland. In this guide, Section 6.3 is largely represented by Sections 1 - 8, 12 and 14 - 17.

6.3.3 Issues to be considered

Typical risks in the conversion of historic/traditional buildings

1. Design and installation of services generally

There is a risk that new or upgraded service installations could damage or otherwise impact on a building’s historic fabric and character. Impacts can include:

• Covering or obscuring of historic features or details.
• Causing direct damage during installation or subsequent maintenance.
• Inducing staining through leaks or condensation of uninsulated or insufficiently insulated pipework or cold vessels.
• Creation of dirt traps where services are run close to the surface.

While the inclusion of renewables can help to minimise the carbon emissions of the building, their location and installation should be informed by the traditional characteristics or cultural significance of a building or its setting.

Impacts can come from the services installations themselves, but also from associated support and access / maintenance infrastructure.

Heating services can impact on a building in other ways. For example, acoustic performance of equipment must be considered, along with possible vibration, as well as the potential for discharge pipes to emit condensate, overspill or steam which can damage adjacent building fabric.

2. Compensating for reduced envelope insulation

Where opportunities for fabric improvements are limited, heating services and emitters may need to be larger and will potentially have more impact on culturally significant spaces. Careful design and planning become more important.

3. Replacement service installations

Where older systems are being replaced with more efficient modern systems, these may well be more compact, reducing the overall impact on the building.

However, the services themselves may be significant and worthy of retention, despite their possible inefficiency. A common example is the replacement of cast iron radiators with contemporary alternatives.

4. Design of routes

Design and routing of all services should not be left to site operatives who may not have the necessary understanding of the needs of historic buildings.

5. Closing open flues

Some guidance in the past recommended blocking off redundant flues and chimneys to reduce air leakage and cold internal surfaces. While this makes some sense thermally, it needs to be carefully considered in relation to the risk of moisture build-up. In general, it is recommended that, where feasible, redundant flues are ventilated at the top and bottom.

6. Heat pumps

Heat Pumps are increasingly specified due to their efficiency and ‘clean heat’ profile. Their efficiency increases with the size of emitters used, but these may in turn have a greater impact on the spatial quality and character of internal spaces, creating a direct tension between heritage and energy efficiency.

This tension can be resolved through the use of underfloor heating, which removes all visible heat emitters and is a healthy and efficient solution. However, underfloor heating infers extensive works to floor build-ups which can be costly and may not be appropriate in some situations.

7. Capital cost vs running costs vs impact

Where a new heating system is under consideration, a balance needs to be struck between capital costs, running costs and the physical and visual impact of any system on its surroundings. These three considerations rarely align such that all costs and impacts are low.

8. Service life of mechanical systems

The service life of mechanical systems can be relatively short, meaning that access for ongoing maintenance, repair and replacement must be considered.

6.3.4 Recommendations to meet the standard

Once a new heating system has been chosen, or an existing system partially upgraded, the relevant sections of the Domestic Building Services Compliance Guide for Scotland set out minimum levels of efficiency for all newly specified parts of the system deployed, along with some wider guidance. Note that a holistic appreciation of the building and all of its systems will be required to inform the design. In some cases, there may be additional design and procedural considerations if a building is of greater cultural significance.

Section 1.7 of the above guide clarifies the requirements for works to existing systems. Where only a part of a system is to be replaced (for example a boiler), there is no requirement to upgrade the remainder of the system. However, the guide identifies opportunities for upgrades in section 1.9 where these may be cost-effective. This is one area which may offer a way to demonstrate greater savings where fabric improvements are more difficult.

As noted, the technical standards do not offer guidance on what type of heating system to choose, acknowledging that the system will already be installed in many cases. The following provides some points for consideration where it may be possible to adopt a wider strategic approach in addition to the new heating system. These may be helpful for the purpose of demonstrating that savings have been achieved strategically, in addition to simple equipment efficiencies.

a) Reducing demand for heating.

In the drive to reduce carbon emissions and improve energy efficiency, reducing the demand for heating is the first step and is essentially the principal aim of Section 6.

i. Good building maintenance is the precursor for all energy efficiency works because without it, all subsequent efforts are at risk from spoiling due to rain ingress, water leaks or similar. Damp building fabric wicks heat at a greater rate than dry fabric and creates its own risks in terms of condensation and mould etc.

ii. Insulation and improved airtightness are the primary means to reduce heating demand and carbon emissions, as well as fuel bills and improving comfort. It is understood that these measures may need further consideration due to potential impacts on the of certain buildings and spaces, but all efforts made to improve a building will bring widespread benefits to the environment and occupants.

iii. Zoning. It is possible to reduce energy consumption and the need for heating by considering the patterns and types of use in each room of the building and then allowing for different spaces to be heated differently. TRVs (Thermostatic Radiator Valves) are a common example of this but many options are available. The key is to arrange the zoning in response to different occupation patterns to optimise the savings possible and this should be considered at the design stage and included either in designs and specifications, or in a performance specification for contractors.

iv. Timer and Programmers. Like zone controls above, these are fixed items which fall under consideration of the building standards. Wherever possible, these should be fine-tuned and operated in such a way to minimise unnecessary heating of spaces. Note that some ‘thermally massive’ buildings and slower response heating systems will not respond as well to either zone controls or timers so this will require consideration.

b) Free or incidental sources of heat.

Taking full account of ‘free’ sources of heat allows a heating system designed to reduce the amount of heat provided by the system and demonstrate efficiencies in a different way. Note this is only possible if the system is designed to account for these gains, and to be responsive to them.

i. Solar gain. Solar gain can provide a significant amount of heat to a building, and this can offset equally valuable levels of heat demand, as long as the heating system is able to respond to them. To achieve this, the system needs to be thermostatically controlled to recognize the solar gain and reduce heating input. The system also must be zoned so this only takes place where the solar gain is felt.

ii. Internal heat gains. Internal heat gains from fixed and portable equipment can be significant, especially for non-domestic uses with, for example, large amounts of computing or other machinery. This heat gain can be useful in colder weather if it is adequately accounted for and if the heating system can respond accordingly. However, it can also lead to overheating in warmer weather and is usually a costly way to produce heat. For this reason, it is usually best to try to minimise internal heat gains, but where these are unavoidable, it is worth making sure the heating system accounts for and responds to them.

c) Building and Occupant Characteristics.

Where a heating system is to be changed, efficiencies may be achievable by carefully considering the nature of the building and occupancy before opting for a specific heating system.

i. Occupancy and Lifestyle. The occupancy patterns of a building and the different spaces within it can be markedly different. These need to be properly understood, so that the heating system can most efficiently respond to them using the controls mentioned in the above sections.

ii. Property type. Beyond the energy efficiency of a particular building, its spatial and material characteristics can affect how well a heating system might work. For example, older buildings often have higher ceilings than is common in contemporary buildings. If radiators or other largely convective heating is used, warm air will tend to accumulate at high levels in the room and fail to heat people effectively or efficiently. In this way, inefficiency is ‘baked in’ to the system regardless of the efficiency of the equipment used.

iii. Thermal mass. Thermal mass is the ability of building materials to store heat. This can be a useful characteristic when used in conjunction with a responsive heating system. However, if occupancy levels of a building are low, there may be less value in keeping the whole building warm. It is important to bear in mind that thermal mass does not work well when the mass is separated by internal linings (such as lath and plaster) in draughty buildings. This is also the case where the heat is largely held in the air, as is the case with convective heating systems (including radiators). Some natural insulation materials have a degree of density that makes them potentially valuable components of a thermal mass and overheating reduction strategy.

d) Heating system characteristics.

Regardless of equipment efficiency, some heating systems are fundamentally more efficient by design or because of their fuel types, although these can be highly dependent on individual circumstances.

i. Fuel types and carbon intensity. This aspect can make the largest difference to the overall carbon emissions of a heating system, and it is important to aim to use renewable or ‘clean heat’ alternatives wherever possible. The situation is however fluid, and it is difficult to get a wholly unambiguous answer in many cases. In very broad terms however, the ‘worst’ fuels to use are fossil fuels, with coal tending to have higher emissions than oil, which has higher emissions than portable gases, which have higher emissions than mains gas.

ii. Timber and other renewable biofuels are almost always better, but this is only where the potential for replanting is being realised in practice, and where sources are relatively local. Electricity was considered the worst of the fuels until relatively recently and is still a poor choice where it comes from areas of high carbon intensity of the grid.

iii. Scotland now has significant and increasing supplies of renewable electricity, or electricity that is locally renewably sourced. Therefore, where a heat pump is being used to ‘upgrade’ the electricity, it is now considered the best choice environmentally. Regularly updated carbon intensities for different fuels and heating systems are given within the supporting tables and documentation associated with SBEM, RdSAP and SAP, as well as other energy modelling tools.

iv. Combined heat and power (CHP). CHP-generated heat can be efficient because it is the by-product of electricity generation, although the fuel used may not be particularly sustainable. With an increasingly decarbonised grid, the CO2 emissions of CHP are likely to exceed that of grid electricity, but CHP remains an option and may suit circumstances where both electricity and heat are required. This is particularly the case where a large ‘base load’ is needed, such as in swimming pools, hospitals, or where developments are large, varied and relatively compact.

v. District heating. Like CHP, district heating is considered efficient not necessarily because of its fuel type, but because of the inherent efficiencies in generating heat in a large, centralised system. District heating is to be rolled out across parts of Scotland. Where these networks make sense (due to the demand profiles locally) homes and other buildings will be obligated to connect to them in due course.

vi. Centralised vs Dispersed. While the efficiencies of larger centralised systems can be helpful, heating demand may in some cases be dispersed across a building or site and may also be needed at very different times. In these cases, the most efficient solution may be a series of heating ‘hubs’ dealing with heat demand locally (with reduced distribution losses) or at specific times. It may also help efficiencies (and the visual impact on a sensitive environment) to replace one large heat source with a series of smaller or modular heat sources which can respond to different heating demands more efficiently.

vii. Instantaneous vs stored heat. Fundamentally, all heating systems operate either by providing a boiler or other heat source large enough to respond to any load (e.g. a ‘combi boiler’) or by having a store which allows for a smaller heat-generator. The smaller heat sources can be set up to work more efficiently using the storage as a buffer between peak demands and the efficient working of the heat source. Whilst storing heat can make the heat source smaller and more efficient, there are usually inefficiencies associated with the ‘standing losses’ of stored systems. In short, therefore, each option has its own advantages and disadvantages. The key is to choose a system that works best for the particular building, occupancy and use profile of the project. If using renewables, for example, their heat input cannot be controlled and so a storage-based system is almost inevitable.

viii. Controls. Controls are critical because, whilst they need to be set up to effectively control the system in a technical sense, they are also the interface with occupants and need to be simple to understand and largely intuitive. In attempting to deliver the range of options discussed above, controls can often be complicated to understand. Another common problem is the incorrect location of sensors which are not in the most occupied rooms, so they are not responding to changing temperatures being experienced by people in that space.

e) Water heating

While the relevant sections of the Domestic Building Services Compliance Guide for Scotland provide minimum efficiencies for a range of water heating equipment, there is significant potential to reduce energy associated with water heating through strategic design. The following points may be worth consideration.

i. Reduce hot water consumption. Hot water consumption can be reduced in several ways without seeking to adjust occupant behaviour. Standard 3.27 of the Technical Standards addresses this in situations where the standards need to comply. Ensuring that pipe runs between a boiler and taps are as short as possible means standing and distribution losses from hot water sitting in those pipes are reduced. It also means hot water arrives more quickly at taps which is generally appreciated. Insulation of pipework is also relevant and is covered in section 6.4. Some hot water taps are inevitably a long way from a boiler and it may make more sense to employ local, instantaneous, heaters. Another technique is to employ aerated taps and showers heads which reduce the actual flow of hot water without reducing the ‘feel’ of a suitable flow of water.

ii. Waste Water Heat recovery. Several companies provide systems that will recover some of the heat of outgoing water to pre-heat incoming cold water. Efficiencies of around 40% are claimed. These are primarily used for showers but can also be deployed in other areas and on a larger scale. These systems have the advantage of working whenever hot water is being drawn and are not seasonal.

iii. Solar thermal. Solar thermal panels can collect ‘free’ solar heat and send it to an internal water tank, offsetting large amounts of energy. Solar thermal systems are not without their own system losses, and only work well when the sun is shining, but they can contribute up to half of the hot water demands of some properties, depending on system design and demand profiles.