Search

Contents

Skip to Main Content

• Introduction
• Sustainability & Housing
• Planning, Community & Sustainability
• The Site & The Dwelling
• Energy Use
  • Energy Surveying
  • The Basics Of Energy Efficient Design
  • Energy conservation in the building envelope
  • Daylighting and artificial lighting
  • Preventing heat loss through ventilation
  • Renewable Energy
  • Energy Efficient Delivery Systems
  • Communal Heating, District Heating and CHP
  • Geothermal Energy
  • Energy Efficient Systems In The Dwelling
• Resource Conservation
• Healthy Dwellings
• Maintenance & Rehabilitation
• Finance & Management
• Useful Addresses
• Bibliography
• Selected Reference Material
• Case Studies
• Acknowledgements

4. Energy Use

Housing providers have a role to play in helping local authorities to meet the energy targets set out in the Home Energy Conservation Act of 1995 by auditing their stock and establishing strategies to meet them. In the long term, the experience that RSLs gain in this area can be used to help all home owners and housing providers address energy efficiency.

Communities Scotland Sustainable Development Policy¹ also lays down specific energy targets to be met by all housing funded by them. The targets are easily achievable and should be taken as a minimum standard. In many instances it may be possible to increase the SAP rating level to nearer 100 using optimum design strategies.

Communities Scotland Sustainable Development Policy Energy Targets

• New build SAP rating no less than 85-90
• Rehabilitation SAP rating no less than 65-70

This Chapter outlines the basic principles for reducing energy use and offers guidance on the following:

• energy surveying
• the basics of energy efficient design
• energy conservation in the building envelope
• daylighting and artificial lighting
• preventing heat loss through ventilation
• renewable energy
• energy efficient delivery systems
• energy efficient systems in the dwelling

4.1 Energy Surveying

The basis of any strategic approach to saving energy must start with a careful survey of existing stock. Once this has been carried out a programme can be drawn up which targets housing in need of upgrading on a systematic basis². Apart from helping to form an energy strategy, energy surveys can give the following benefits:

• tailored energy advice to occupiers³
• identify energy grant eligibility for occupiers⁴
• inform maintenance strategy and life cycle costing
• provides base line for future energy auditing.

There are a number of different energy and environmental rating schemes available which are usually carried out by qualified assessors. The four most well known are:

• SAP (Standard Assessment Procedure)
• NHER (National Home Energy Rating Scheme)
• BREEAM (Building Research Establishment Environmental Assessment Method)
• BRE Environmental Standard Award

The SAP⁵ is a requirement under Building Regulations for all new build dwellings to ensure they are energy efficient. It has a rating from 1-100, the higher the better. It is a relatively crude assessment of annual energy costs which takes no account of local climate, occupancy patterns, or heating patterns. The rating is based on fuel cost rather than CO₂ emissions which can lead to distortions. It is also sensitive to boiler controls, favouring condensing boilers under any circumstance, even when they might not be required.

The NHER⁶ system operates at a variety of levels of sophistication and is more sensitive than SAP, taking into account local climate and location details. It operates on a scale of 1-10, again the higher the better. In addition NHER can also take account of occupant behaviour and the condition of the dwelling when used at a higher level. It is generally slightly more expensive to carry out than the SAP but yields more meaningful results.

The Environmental Standard⁷ is the current Version 3 of BREEAM (the Building Research Establishment Environmental Assessment Method) and it concerns new homes. This gives credits for a variety of environmental measures adopted, including energy efficiency, and offers a broader rating than either SAP or NHER.

It can be used to examine the overall environmental impact of housing stock. There is also an additional cost to receive the accreditation. It is currently being updated and will be launched as the new Environmental Standard for Homes.

4.2 The Basics Of Energy Efficient Design

Energy efficiency is an integrated approach to insulation, ventilation, solar gain, daylighting, thermal mass, heating and control systems. It is important always to consider these aspects in relation to each other.

Space heating counteracting heat loss through the external building fabric is the primary form of energy consumption in Scottish housing. The optimum use of energy is to get a balanced system which uses as much free heat gain as possible to offset minimised heat losses and energy consumption.

sources of free heat gain in dwellings

• sunlight
• occupants (80 watts each)
• cooking heat
• hot water usage
• waste heat from lights
• waste heat from domestic appliances

4.2.1 Energy conservation in the building envelope

Reducing energy demand in housing is the first priority, followed by the use of renewable energy sources for heating wherever possible. The retrofitting of proper levels of insulation to existing housing stock is the single most cost effective way to save energy and cut down on global climate change emissions from the housing sector in Scotland (see Section 8.1.3). Other benefits of retrofitting insulation are:

• financial payback to the housing provider through reduced service requirements
• preservation of building fabric
• condensation-free dwelling
• healthy and warm dwelling for the occupier
• low fuel bills
• increased air tightness and control of ventilation.

The following levels of insulation are appropriate for the UK, depending on the type of construction:⁹

• roof 300-450 mm
• wall 150-300 mm
• floor 150-250mm

These levels of insulation are not always achievable in retrofit schemes but the great majority of existing dwellings can be improved to at least 1990 Building Regulation levels within reasonable costs¹⁰.

It is preferable to use an organic, natural material for insulation where this is possible to minimise environmental and health impacts (see Table 4.2). Insulation materials are generally lightweight and bulky therefore long distance transportation should be avoided if possible.

Housing providers should assess their stock on the basis of individual dwelling type and orientation where possible (see Table 4.1)¹¹ and decide which form of insulation is most appropriate for them on balance. Effective guidance on the cost-benefits of retro-fitting different insulation systems in Scotland is available from the Scottish Executive as well as others.¹²

Table 4.1 Factors affecting choice of insulation strategy

Key factors	external insulation	internal insulation
ease of installation	requires scaffolding exposed to weather affects access to building	awkward detailing confined space occupants need to be decanted
type of construction	fixing system to suit construction preparation of external surfaces required	cavity fill best where possible in walling dry-lining detailing depends whether construction is solid ornot
type of heating regime requirements	suitable for constant slow response heating requirement with thermal mass	suitable for intermittent fast response heating requirement with no thermal mass
type of insulant	rigid boarding required complex systems: rainscreen cladding using sheet panels polymer render on mesh base difficult to use natural insulants	drylining walls suits natural insulants relatively simple system care required with solid flooring and sloping roofs
energy payback	relatively slow with complex systems varies between 5-30 years depending on detailing and materials used	relatively fast cavity fill and loft I year wall drylining 5 years
aesthetics	very effective for altering profile and exterior of building not always suitable for conservation areas or listed buildings	no effect on exterior of building can present awkward detailing internally to avoid cold bridging
financial payback	relatively slow varies between 17-55 years	relatively fast especially for cavity fill and loft 2-3 years
life cycle impact and health	tends to have high embodied energy with high environmental impact minimal health impacts for occupants	low embodied energy especially when using natural insulants care needs to be taken with certain foam insulants that off-gas into the dwelling
maintenance	requires re-painting for smooth render systems, otherwise as for external cladding	no additional maintenance beyond internal finishes. Loose fill fibres in walls may settle after a year and require topping up.

Table 4.2 Types of Insulation available¹³ for different dwelling elements

Material	Roof options	Wall options	Floor options
Organic Natural Renewable Reuseable Low embodied energy	loft: cellulose flax hemp sheeps wool wood wool wood fibre flat roof: cork	internal insulation or timber frame: cellulose cork flax hemp sheeps wool wood wool wood fibre cavity fill: none recommended	suspended: as for loft solid: as for flat roof
Inorganic Minerals Non-renewable Reuseable High embodied energy	loft: rockwool, fibreglass perlite vermiculite flat roof: foamed glass rockwool fibreglass	internal insulation or timber frame: rockwool, fibreglass cavity fill: foamed glass rockwool fibreglass	suspended: rockwool, fibreglass solid: rockwool, fibreglass perlite vermiculite
Fossil Organic Oil-derivatives Difficult to re-use High embodied energy Off-gassing present	loft: expanded polystyrene extruded polystyrene polyisocyanurate foam polyurethane foam urea and phenol formaldehyde foam flat roof: expanded polystyrene extruded polystyrene polyisocyanurate foam polyurethane foam urea and phenol formaldehyde foam	internal insulation or timber frame: expanded polystyrene extruded polystyrene poly-isocyanurate foam polyurethane foam urea and phenol formaldehyde foam cavity fill: expanded polystyrene extruded polystyrene polyisocyanurate foam polyurethane foam urea and phenol formaldehyde foam	suspended: expanded polystyrene extruded polystyrene polyisocyanurate foam polyurethane foam urea and phenol formaldehyde foam solid: expanded polystyrene extruded polystyrene polyisocyanurate foam polyurethane foam urea and phenol formaldehyde foam

Windows can account for up to 10% heat loss in a well insulated dwelling and should be specified with as much insulation as the housing provider can afford. Double glazing with low emissivity films and inert gas is now standard practice in many cases but this can be significantly improved on by the use of double casement windows. These have one frame with double glazing coupled to one with single glazing. The increased frame depth and air gap between the two glazing units can double the insulation value.

Box 4.1 Insulation strategy : pointers for good practice

• maximise insulation to roof, wall and floor
• use breathing, natural and low energy insulation products where possible
• combine adopted heating strategy with appropriate insulation system
• a little insulation retrofitted is better than none at all
• use windows with U-value range 0.6-1.2 using double glazing frame coupled to single glazed frame where possible

4.2.2 Daylighting and artificial lighting

Minimising energy used in lighting becomes a key issue once housing is more energy efficient than current building regulations. The aim should be to maximise daylighting while minimising artificial lighting (see Box 4.2)¹⁴. Glazing generally loses about six times as much energy as a well insulated wall or roof and a balance must be struck between providing daylighting and minimising heat losses.

Daylight is dependent on the amount of open sky available outside a window, the amount of sunshine available and the amount of reflectance of light from surrounding surfaces. The size, angle and shape of openings together with room height depth and decoration determine the distribution of the daylight (Figures 4.9 - 4.11).

Sun angles range from 10 degrees from the horizontal in the winter in the far north of Scotland to 60 degrees in the summer further south. Windows should be carefully designed to maximise sunlight penetration into rooms without glare. (see Figure 4.12) Given the low sun angles that mark the Scottish winter, glare can be a particular problem caused by strong contrast between light from a window and its surround.

Box 4.2 Daylighting and artificial lighting: pointers for good practice

• daylighting:
  • check site for daylight obstructions and position building form to overcome these
  • design form and layout of dwelling to maximise daylight penetration
  • design glazing and openings to optimise daylight in rooms
• avoid glare by:
  • external planting regimes and filtering devices
  • light colouring of internal decoration especially window frames and surrounds
  • splayed window reveals (Figure 4.12)
  • internal shading devices such as venetian blinds
  • introducing light from more than one direction
  • indirect lighting by reflectance from light surfaces
  • external self-shading offered by building form
• artificial lighting:
  • use low-energy light bulbs (can save up to 40 per cent on electricity bills in a well insulated house)¹⁵
  • use efficient lighting and specify high frequency control gear for flourescents
  • avoid internal rooms and stores which require artificial light
  • ensure all common areas are naturally daylit
  • use light colours on walls, floors and ceilings to increase efficiency of lighting

4.2.3 Preventing heat loss through ventilation

Ventilation can account for up to 25 per cent of heat loss in a typical house. Conventional housing has 3-5 air changes an hour which has to be warmed in winter. Effective detailing against air leakage and draughtproofing¹⁶ can reduce this to 0.5 -1 air changes an hour. Timber frame construction is easier to make airtight than masonry, and loose fill insulation, such as cellulose, can help fill in gaps between construction elements.

Mechanical heat recovery systems recover heat lost through ventilation by extracting heat from exhaust air and using it to pre-heat incoming fresh air¹⁷. They range in size from small air brick size units (Figure 4.13) to large systems housed in the

loft. The small units can be effective where mechanical extraction is required by regulation. The larger systems tend to involve substantial ductwork, are difficult to retrofit and can be noisy. They are not recommended for use in dwellings with over 1 air change an hour as efficiency is lost.

Passive stack ventilation allows exhaust air to rise up through the dwelling naturally using extract pipes that exit at the ridge of the roof. Its main advantage is that it uses no mechanical energy, has no moving parts and can replace mechanical ventilation for building regulation purposes¹⁸. It requires adequate height to create a steady flow. There are now a number of proprietary systems available which compare favourably to mechanical extract systems (Figure 4.14)

Box 4.3 Preventing heat loss through ventilation: pointers for good practice

• ensure adequate draughtproofing to all windows and doors
• use timber frame construction for better air-tightness
• pay attention to all jointing details and seal them
• use loose blown fibre insulation rather than rolls or batts
• use small heat recovery units where mechanical ventilation is required
• use passive ventilation systems where possible

4.3 Renewable Energy

Renewable energy is any source of energy that effectively replenishes itself and is inexhaustible. Currently most energy for housing comes from finite and unsustainable fuel sources such as natural gas, coal and nuclear power. Housing providers should aim to incorporate renewable energy into their new developments and existing housing stock wherever possible¹⁹. The use of renewable energy has the following benefits:

• minimises the use of non-renewable fossil fuels
• minimises air pollution
• a “clean” source of energy
• a “free” source of energy to the user

Renewable energy systems should not be used as a primary means of addressing energy efficiency. They come into their own once initial conservation measures have been taken and only a relatively small amount of water heating or electricity is required (see Case Study No.3). It is always more cost effective to conserve energy than to produce it in housing. Solar power is the easiest to use in urban situations, while rural sites can benefit from the other forms of renewable energy such as wind or water.

Table 4.3 Renewable Energy options

Key factors	active solar20	wind21	hydro22	biomass23
type of installation	photovoltaic (PV) panels for electricity or water/ evacuated air panels for heating/hot water	windturbines providing electricity from small diameter 50w to large commercial turbines providing 0.5mw or more	ranges from small micro-hydro turbine running off constant stream with a drop to large commercial dams and river installations	straw, wood or various fast growing crops can be harvested for burning to create energy.
ease of installation	can be installed as part of roof (new build) or retrofitted re-plumbing required for existing water tank only appropriate for south facing roofs with minimum pitch of 300	depends on size larger installations require large foundations and should be sited at a distance from any dwellings	easiest with small stream and high head of water requires pipework and concretework to house turbine	requires large amount of land sited near to fuel burning facility. 300-500m2 of coppice for space heating one dwelling
heating regime requirements	solar panels most effective in summer (up to 80% of hot water supply). best with low constant heating. PVs not effective for heating.	provides renewable energy for electrical heating -most effective in winter. heating demand should be relatively constant as there is an energy storage limitation.	provides renewable energy for electrical heating -most effective in winter. energy storage limitations. more reliable than either wind or sun.	best for hot water only rather than space heating. PVs not effective for heating. effective all year round but requires storage space (5m3 per dwelling per year for wood)
embodied energy payback	7-12 years	0.5 years	N/a	minimal
aesthetics	problems of integrating panels on existing stock in urban/conservation areas	needs careful siting in rural areas. does not affect dwelling	pipework should be underground ideally turbine house and dams need integration with landscape	monocultural cropping can look unsightly and out of place as well as restricting views
financial payback	10 -15 years for water panels photovoltaics do not payback over their lifetime yet	depends on size - larger installations pay back more quickly 7.5 ->12.5 years	small scale systems can pay back within 7 - 8 years	8-10 years depending on size of scheme and species planted
life cycle impact and health	minimal health impacts- clean technology. some environmental impact from products	beating noise can be intrusive if sited to close to housing- otherwise clean technology some environmental impacts from turbines	minimal health impacts -clean technology micro-hydro has minimal environmental impact larger schemes have more impact	fuel must be burnt cleanly to avoid toxic emissions possible impact on biodiversity
maintenance	life expectancy of panels 15-20 years servicing required	life expectancy of turbines can be 20 years or more servicing required	very long life expectancy turbines can run for 30-60 years minimal maintenance	requires intensive input for harvesting and maintenance of crops

4.4 Energy Efficient Delivery Systems

An understanding of how energy is delivered to a housing development allows the housing provider to take advantage of the most efficient delivery system for a particular site. The provider often has little control over the primary means of how energy is supplied to a site and most existing Scottish housing stock still relies either on gas, or electric heating from non-renewable fossil fuel resources.

Electric heating systems should be avoided because they generally produce between two to four times the overall amount of CO₂ emissions compared to gas central heating when the full production cycle is taken into account. If electric systems are to be fitted on grounds of availability, capital costs and maintenance, their efficiency should be optimised through the use of renewable energy or combined heat and power schemes where possible.

4.4.1 Communal Heating, District Heating and CHP (combined heat and power)

It is inefficient to install normal size boilers and central heating systems for well insulated individual dwellings. A common heat source can greatly reduce the number of boilers required and subsequent maintenance. The advantage of this form of supply is that it is highly flexible in terms of fuel source; renewable energy, waste heat, gas or electricity can all be used²⁴. Communal heating provides heating for one housing scheme whereas district heating supplies a whole area.

Combined Heat and Power generation (CHP) goes one step further than communal and district heating by maximising the efficiency of the production of electricity. The waste heat produced by an electricity generator is used to provide hot water for heating. The generator can be as small as a van engine (see Case Study No.12 and Figure 4.15) but CHP works best on a district basis, where there is a constant demand for both heating and electricity. Perthshire Housing Association is currently investigating a CHP scheme which will link up a hospital, school and housing; the different providers requiring heating at different times maximises the efficiency of the system.

Both communal heating and CHP schemes present issues in relation to fuel charging. Housing providers can choose between a flat rate charge or individual metering. The former can be wasteful and unfair on individual tenants, while the latter may be expensive to install and manage. Different housing associations have overcome these issues in different ways (see Case Study Nos. 3, 4 and 12 and Table 4.4).

Table 4.4 Options for Energy Efficient Delivery Systems

Key factors	individual dwelling heating	communal heating	district heating25	combined heat and power26
type of installation	central heating or point heating delivered by gas or electricity	single heating source can serve single housing development	single heating source can serve large area of town or city	single heating source can serve communal or district scheme uses waste heat from electricity generator to supply hot water for heating
installation requirements	re-wiring for electrical systems and re-plumbing for gas systems, individual point source heaters or radiators and a boiler	compact housing layout simple and accessible external pipe runs central plant room required	as for communal heating, pipe runs should run under public pavements	can be small combustion engine for communal heating27 or power station for district heating
heating regime requirements	convectors and radiators can be used for intermittent or fast response heating storage heaters are for slow response heating individually metered on fuel used	operates best with low temperature radiators	operates best with low temperature radiators	requires constant demand for heat and electricity for efficiency operates best with low temperature radiators
metering	individually metered and billed	can be individually metered (expensive) or charged on flat rate or mix of both (best)	as with communal heating most efficient option is to offer flat rate with individual top up supplied by individual electricity supply	as for communal and district heating with electricity metered (expensive) or operated on pre-payment card28
financial arrangements	installation paid and serviced by housing provider or owner occupier	installation paid and serviced by housing provider with service charge	as for communal heating or using 3rd party to install and service (partnership with energy supplier)	as for district heating requires partnership with others who might use heat and electricity on a more constant basis (hospital, sheltered housing etc)
maintenance requirements	maintenance of individual heating systems by housing provider. High for gas central heating, low for electric	maintenance of distribution network and central plant by housing provider with option of 3rd party maintenance	as for communal heating negotiation required with other authorities where pipework extends beyond site	as for district heating

4.4.2 Geothermal Energy

There is a particular opportunity for housing in the Central Belt area of Scotland where many old mine workings have relatively warm water sitting in them. The low-grade heat that exists deep under the surface of the Earth can be upgraded using heat pumps within a housing scheme situated on top of the mineworkings or immediately adjacent. There can be considerable savings on fossil fuels as the heat may be of the order of 13°C all year round, requiring a top-up heat input of only a few degrees to provide adequate central heating (see Case Study No. 3).

4.5 Energy Efficient Systems In The Dwelling

Once the sources of energy supply have been decided it becomes important to optimise elements within the dwelling for energy efficiency. A key component is the accurate sizing of heating systems. Many housing schemes fail to achieve energy targets because of the mismatch between high insulation levels and heating specifications. With high insulation, condensing boilers may not be necessary (Figures 4.16 - 4.17). In many instances, point sources of heating rather than the standard package of central heating, will be adequate and save on energy use, maintenance, cost and resource use in manufacture. There are now a number of smaller heating installations available for the low energy dwelling²⁹.

The lower the operating temperature of a heating system the wider the range of energy sources it can use giving the greatest upgradeability and flexibility. For this reason low temperature radiator systems or underfloor heating are preferable to high temperature radiator systems

Table 4.5 Energy efficient systems in dwelling

variables	individual gas central heating	individual point sources/electric heating	renewable energy systems
delivery mode	condensing boiler direct or indirect hot water system	electric heaters gas wall heaters	solar water panels linked into indirect system photoelectric panels (PV) feeding electrical mains
sizing	avoid oversizing of boilers and radiators may be unnecessary altogether	can be used for very small heating loads	solar hot water = 4m2 per dwelling photoelectric panels = 80 -100 watts each (600x1200mm panel)
controls	avoid overcomplex programmes ensure that condensing boilers can operate in condensing mode (low temperature)	controls tend to be very basic (thermostat but no timer) -may not be responsive to occupancy patterns	needs sophisticated programmer to balance solar gains against standard form of heating (occupiers need training in use)
flexibility	boiler position determined by layout	electric heaters are highly flexible gas heaters need positioning on an outside wall	panels only suitable for certain roofs (correct orientation and pitch)
upgrading	system may need downsizing replacement of boiler	simple replacement of point heaters	panels should be replaceable as efficiency increases

Energy Checklist-Key Areas

Form and fabric

• carry out energy audit on existing stock and adopt an achievable insulation programme (see Section 4.1)
• incorporate optimum levels of insulation to all fabric elements before anything else (see Box 4.1)
• design building envelope to ensure air tightness and avoid cold bridging (see Box 4.3)
• optimise daylighting (see Box 4.2)

Systems

• select appropriate delivery system for heating (see Table 4.4)
• specify high energy efficiency space and water heating systems - avoid oversizing
• realise full potential of renewable energy sources (see Table 4.3)
• incorporate effective and easily understood control systems
• ensure integration between the energy system proposed and other aspects of human comfort
• use natural ventilation or passive stack ventilation in preference to mechanical ventilation (see Section 4.2.3)
• specify gas heating in preference to electric heating where possible
• use low temperature radiators to allow for a variety of low temperature energy sources.
• check energy efficiency measures repay their embodied energy over the product lifetime (see Table 4.3)

Footnotes