Table Of Content

May 2007 NHBC guide to renewable energy NHBC guide to renewable energy May 2007 INDEX Index Page 1. Introduction 3 2. Solar thermal (solar water heating) 4 3. Solar electric (photovoltaic) 6 4. Heat pumps (ground source and air source) 8 5. Wind turbines (small scale, building mounted) 11 6. Biomass (domestic biomass heating systems) 13 Appendix A – Annual total UK solar irradiation map 15 Appendix B – Typical system costs 16 Appendix C – UK Microgeneration Certification Scheme 16 Appendix D – Relevant standards and additional information 17 Appendix E - Acknowledgements 18 NHBC Technical Page 2of 19 NHBC guide to renewable energy May 2007 INTRODUCTION Introduction The UK government is calling for registered builders specifying or necessary for systems to work well and carbon dioxide emissions to be cut in installing renewable energy technology. deliver environmental benefit, without order to address climate change and It covers the most commonly used giving rise to unexpected problems. has identified housing as a sector that ‘microgeneration’ technologies: Renewable energy is an emerging field can make a significant contribution. The consultation document ’Building A (cid:2) Solar thermal (solar water in the UK and there are currently few Greener Future: Towards Zero Carbon heating systems) systems that have been independently assessed and certificated. BRE is Development’1suggests challenging (cid:2) Solar electric (photovoltaic) working with the Department of Trade energy efficiency targets for new build homes, which will require the use of (cid:2) Heat pumps (ground source and and Industry to develop the ’Microgeneration Certification Scheme‘. renewable energy technologies. air source) Further information is available at Already, planning authorities are (cid:2) Wind turbines (small scale, Appendix C, and up-to-date information implementing the ’Merton Rule‘, building mounted) can be obtained from the Scheme’s requiring some of the energy demand website: www.ukmicrogeneration.org. in new developments to be met by (cid:2) Biomass (domestic biomass) renewable energy and the heating systems. implementation of the Code for It brings together useful information Sustainable Homes2will give This guidance does not form part of the from a variety of sources, and presents further encouragement. NHBC Standards. it in a single, concise publication that This guide, prepared with assistance will help readers identify those aspects 1 & 2Communities and Local Government, from BRE, provides guidance to NHBC of specification and installation December 2006 N Building mounted Solar electric wind turbine (PV panels) W E S Solar thermal Biomass heating system Heat Pump Garage Garden contains Wood store buried coils for for biomass heat pump system heating system 1.1 Domestic scale renewable energy technologies NHBC Technical Page 3of 19 NHBC guide to renewable energy May 2007 SOLAR THERMAL Solar thermal (solar water heating) The technology sheet incorporating fluid channels conspicuous. Alternatively panels inside a weatherproof insulated can be mounted out-of-sight Solar thermal systems harness energy enclosure with a glazed cover. The on outbuildings. from the sun to heat domestic thermal tile is an ultra-low-profile, Some installations feature separate hot water. modular variation of the flat plate. solar pre-heating and back-up cylinders There is also an evacuated tube type but the most common configuration is collector which has an array of narrow to use a single twin coil cylinder where strip collectors fitted inside glass the lower coil connects to the solar vacuum tubes, which minimise heat system and the upper coil connects to loss. These are more efficient at the back-up system or boiler. absorbing the sun’s energy but tend to Alternatively some systems use a be more expensive. thermal store, the content of which is Systems can be designed to blend in heated by the collector; cold water with the building - for example, roof- then passes through a coil located in integrated collector panels have a low the store and is heated instantaneously profile design and can be less as required. Flat Plate Collector Black heat Reflective absorbing surface material Hot water out 2.1 Flat plate and evacuated Insulation tube solar collectors Box Glazing Cold water in Various systems are available, but generally a solar thermal collector, Evacuated Tube Collector installed at roof level, absorbs the sun’s energy and transfers it into a liquid (normally a water/antifreeze solution). Heat exchanger which sits in the manifold This liquid is circulated through a heat exchange coil in the hot water cylinder where its heat is transferred to the Connecting screw cooler water in the lower part. Glass tube Most UK systems have a ‘back-up’ system (normally the central heating boiler) which heats the water further to reach the desired temperature as Metal fin necessary, depending on the availability of sunshine and the demand for hot water. The system operation is controlled by an automatic electronic unit, which compares the temperatures of the collector and Metal tube cylinder or store. Many systems use a ’flat plate‘ 2.2 Flat plate and evacuated tube solar collectors collector - a specially coated metal NHBC Technical Page 4of 19 NHBC guide to renewable energy May 2007 SOLAR THERMAL Solar thermal (solar water heating) Thermosiphon Pumped Expansion Vent Roof Roof Vent Header cistern Air vent Hot water Header store cistern Solar Expansion Solar collector vessel collector Hot water Hot water store store Pressure gauge Solar Check valve Check valve collector Pump Pump Safety valve 2.3 Three types of solar water heating system Solar thermal systems can be used to the collectors – it may be necessary to (cid:2) Ensure that the system is provide pre-heated water to solar seek the advice of a structural engineer commissioned properly and test for compatible combination boilers. Water or the designer of the roof-structure. correct operation. preheated by the system is stored in a small cylinder and feeds the boiler to Additional space will need to be (cid:2) Provide operating instructions and available inside the building to reduce the energy needed from gas or maintenance recommendations for accommodate the larger cylinders or oil. The boiler manufacturer should be the homeowner. thermal stores necessary and the floor asked to confirm suitability. construction will need to be capable of Health and safety Solar thermal systems reduce the withstanding their load. consumption of fossil fuel for domestic The system control panel and display Care should be taken to address all water heating, and systems can typically provide between 55 and 70% should preferably be located in a issues, including: prominent position, such as in the of the hot water requirement. A solar kitchen or alongside the central (cid:2) the potential for excessive collector area of 3-4m2is normally heating programmer. An electrical temperature and pressure in heat required for a three-bedroom house. fused spur outlet will normally be transfer fluids and stored water required. Pumps and controls should Design considerations (cid:2) the risk of Legionnaires’ disease - be located so that they are accessible this is a potentially fatal form of for maintenance. The solar energy resource varies pneumonia that can thrive in across the UK (see ‘Annual total solar Planning permission may be required purpose built water systems unless irradiation’ map at Appendix A). The for solar collectors. they are properly managed. Further further north, the less solar energy guidance can be found at there is and the greater is the collector Installation tips www.hse.gov.uk/legionnaires/index. area required to capture it. htmand in the HSE’s Approved (cid:2) Ensure solar collectors are securely Collectors should be sited on Code of Practice & Guidance fixed to withstand wind loads, etc. unobstructed roofs, ideally facing document, L8 south, southeast or southwest. It is not (cid:2) Weatherproof all penetrations advisable to install them on north- through the roof covering with (cid:2) working at height facing roofs. Shadows from adjacent suitable flashings, purpose-made (cid:2) electrical safety. buildings, trees and chimneys, etc. will tiles, etc. Sealant is not suitable for reduce the amount of energy collected. this purpose and will not be Collectors should be located so that Additional information sufficiently durable. they can be safely accessed for cleaning and maintenance, although at (cid:2) Install pipes to falls and provide See Appendix Cfor information on the a pitch of more than 15° they are insulation to them as required by Department of Trade and Industry’s normally self-cleaning. the design. ’Microgeneration Certification Scheme’. The roof structure will need to be (cid:2) Fix permanent labels and flow See Appendix Dfor relevant standards designed to accommodate the load of arrows to pipework, valves, etc. and additional information. NHBC Technical Page 5of 19 NHBC guide to renewable energy May 2007 SOLAR ELECTRIC Solar electric (photovoltaic) The technology Solar electric systems harness energy from the sun to generate electricity. Solar electric panels or modules, which incorporate photovoltaic cells made from semiconductor material, are installed at roof level. When sunlight reaches the semiconductor material, direct current is generated. In most systems, this is then converted into alternating current by means of an inverter, which is fed into the dwelling’s mains electrical system. There are two main types of photovoltaic cell: (cid:2) Monocrystalline cells offer the highest conversion of sunlight to electricity but are expensive to produce. (cid:2) Thin film cells are considerably 3.1 Roof-mounted solar electric panels cheaper, but less efficient and so larger panel areas are needed to generate significant power. The traditional ‘building block’ of solar electric power generation is the photovoltaic panel or module. This comprises a weatherproof double glazed metal frame, enclosing a toughened glass front plate and a metal or plastic back plate with solar cells sandwiched in between. Typically, solar electric panels are mounted onto a metal support frame fixed to the roof (or walls) of a building. Alternatives to photovoltaic panels are photovoltaic slates and tiles, which make up the complete photovoltaic ‘array’. These are interchangeable with ordinary roofing components and can be used to produce a solar electric 3.2 A grid-connected system installation, which is fully building- integrated. Photovoltaic cells can also be incorporated into glazing and cladding, skylights, conservatory panels and external shading louvres. across the UK (see ‘Annual total solar standard formula. Typically 10m2of Dedicated wiring is used to collect the irradiation’ map at Appendix A). The monocrystalline cells are needed per power generated by the solar electric further north, the less solar energy kWp. The energy yield rule of thumb panel or array. In mains-connected there is and the greater is the area of for the UK is 750 kilowatt hours of installations, the electricity generated solar electric panel required to electricity generated per kWp is fed to an inverter, which is connected capture it. per annum. to the electrical consumer unit. The rating of a solar electric Solar electric should be considered installation is given by its peak power from the outset in order to maximise Design considerations output measured in kilowatts (kWp), the benefits. Ideally, systems should be The solar energy resource varies which is defined according to a designed integrally with the building NHBC Technical Page 6of 19 NHBC guide to renewable energy May 2007 SOLAR ELECTRIC Solar electric (photovoltaic) layout and electrical services. This will totally flush with the roof to be wiring should not be thought of as make the system more cost effective. less conspicuous. ‘only low voltage’ as solar electric panels can generate DC electricity Solar electric panels should be sited on To install a grid-connected system, the at over 100V. The photovoltaic DC, unobstructed roofs, ideally facing south, local Distribution Network Operator mains, ELV and signal cables should southeast or southwest. It is not advisable (DNO) will need to be notified if the to install them on north-facing roofs. system output exceeds 16A per phase be segregated. For south-facing panels, an inclination (Engineering Recommendation G83/1). (cid:2) Fix permanent labels to wiring, of 45° offers optimum spring-summer- The DNO is the company which junction boxes, etc. autumn overall performance. operates the distribution network in the local area, and may not be the (cid:2) Ensure that the system is It is possible to have separate east and electricity supplier. To find out which commissioned properly and test for west-facing arrays at additional cost. company the local DNO is, visit the correct operation. Shadows from trees and chimneys, etc. will reduce the amount of energy British Photovoltaic Association (cid:2) Provide operating instructions and website (www.pv-uk.org.uk). collected although it may be possible maintenance recommendations for for panels to be mounted on Space will be required for the the homeowner. outbuildings, etc. to avoid this. installation of the inverter and control Because their output reduces when equipment, which is normally wall Health and safety they are dirty, solar electric panels mounted adjacent to the electrical should be inclined as steeply as consumer unit. Ventilation should be Care should be taken to address all possible to ensure that rain and dirt provided around this equipment. issues, including: run off quickly. As photovoltaics are (cid:2) electrical safety (noting that some based on solid-state technology their Installation tips wiring may be live when the main maintenance requirement is minimal. (cid:2) Ensure solar electric panels are switch on the consumer unit is in The roof structure will need to be securely fixed to withstand wind the “off” position). designed to accommodate the load of loads, etc. (cid:2) working at height. the panels – it may be necessary to seek the advice of a structural (cid:2) Weatherproof all penetrations engineer or the designer of the through the roof covering with Additional information roof structure. suitable flashings, purpose-made tiles, etc. Sealant is not suitable for See Appendix Cfor information on the Planning permission may be required this purpose and will not be Department of Trade and Industry’s for solar electric panels, although sufficiently durable. ’Microgeneration Certification Scheme’. systems can be designed to blend in with the building. For example, ‘low’ or (cid:2) Locate and install cables carefully See Appendix Dfor relevant standards ‘no profile’ arrays are designed to be to minimise the risk of damage - the and additional information. NHBC Technical Page 7of 19 NHBC guide to renewable energy May 2007 HEAT PUMPS Heat pumps (ground source and air source) The technology Heat pumps upgrade low temperature heat extracted from the ground or air into higher temperature heat that can be used for space and water heating. Heat pumps work on the same principle as a refrigerator’s cooling circuit - they absorb heat at a low temperature (from the surrounding ground or air) and ‘upgrade’ it to a higher temperature. Most heat pumps are electrically driven and work by absorbing ambient heat from the air or ground surrounding the building and depositing it inside at a high enough temperature to provide space heating and/or hot water. In a typical system, for every unit of energy used to drive the system, between 3 and 4 units of 4.1 Ground source heat pump unit 4.2 Horizontal trench heat are produced. Because heat pumps require energy to drive them, the energy produced is not strictly renewable. However, the pump can be run from a “green” source (electricity generated from renewable resources or purchased from a supplier on a “green” tariff) to minimise carbon emissions. Heat pump performance is measured in terms of Coefficient of Performance (COP), which is the ratio [heat delivered ÷compressor power input]. Ground source heat pumps Ground source heat pumps (GSHPs) extract ambient heat from the ground 4.3 Heat collection loop around the building. The key components of the installation are: (cid:2) a heat collection loop of continuous plastic pipe (containing antifreeze solution) and a circulating pump Only one type of ground loop would be used in a system (cid:2) a factory-built packaged heat pump (cid:2) a low pressure hot water system, Ground source similar to a standard central heat pump heating system. There are two types of GSHP Vertical bores collection loop: ‘Slinkies’ in trenches (cid:2) Vertical loops, lowered into deep (60m-100m) boreholes which are then backfilled with suitable grout to prevent undesirable groundwater migration, and (cid:2) Horizontal loops, laid out in slit 4.4Ground source heat pump unit trenches, (average depth 1.5 m) NHBC Technical Page 8of 19 NHBC guide to renewable energy May 2007 HEAT PUMPS Heat pumps (ground source and air source) which are then backfilled with soil. One or two trenches up to 40m in length may be needed with the necessary length of pipe. Air source heat pumps Air source heat pumps (ASHPs) extract ambient heat from the air outside the building. The key components of the installation are: (cid:2) a packaged heat pump and circulating pump (cid:2) a low pressure hot water system, similar to a standard central heating system (the system may be charged with antifreeze solution to avoid the risk of freezing). ASHPs are either installed externally on roofs or in gardens. Alternatively they may be located inside the building with the outside air circulated via louvres and ducts. They are generally 4.4 External air source heat pump unit less expensive to install than GSHPs although their day-to-day performance is dependent on weather conditions. Where the heat pump is to be backed to allow the higher temperature output Design considerations up by another heat source, the control only when in domestic hot water of that source must be interlocked to heating mode. The heat pump and heating system ensure that it can never operate as the The position of all equipment including should be designed from the outset in priority or ‘lead’ device. the heat pump, hot water cylinder and order to optimise performance. The best COPs are achieved by running thermal store (where fitted) should be Heat pumps are best suited to systems at low temperatures - the carefully considered. Adequate space, buildings with a high thermal mass, lower the flow and return design load-bearing capacity and access for which tends to smooth the demand for temperatures (e.g. +40°C/+30°C), the maintenance should be provided. heat and allows the device to operate better. For this reason, they are ideally The rating of the mains electrical power as a ‘base load’ heat source. A high suited for use in conjunction with supply may need to be increased to thermal mass also allows the heat underfloor heating systems, although accommodate the electrical current pump to be run on cheap rate they can also be used with ’low drawn by the heat pump. electricity overnight before the temperature‘ radiators. building ‘coasts’ for a while after the The COP of a heat pump running Ground source heat pumps peak daytime rate period begins. sufficiently hot to deliver domestic hot Heat pumps do not work well in water at 50°C - 60°C will be The type and design of the collection buildings with low thermal mass unless considerably lower than its COP in loop used with a GSHP will depend on a thermal store is incorporated in the space heating mode. In view of this, the nature of the subsoil and geology. low-pressure hot water system circuit. there is a view that heat pumps should This should be established by only be used for space heating and undertaking an investigation to Because of the relatively high capital that domestic hot water should be determine the geotechnical and ground and running costs of heat pumps, they heated by a solar thermal system with water conditions. may not prove cost-effective when a an auxiliary backup. Conversely, an mains natural gas supply is available. The layout of horizontal collector loops alternative view is that, because of should be designed to suit the shape of Heat pumps are not generally sized to their capital costs, heat pumps should the house plot and boundaries. meet the peak heat demand, on the be used for both space and domestic assumption that any heat shortfall will hot water heating, but never for both Where land has been remediated care either be met by incidental gains (from duties at the same time. If a heat pump should be taken to ensure that capping electrical appliances, etc.) or satisfied is used for both duties separate layers, etc. (where present) are not by a ‘boost’ heater. temperature controls should be fitted damaged or compromised. NHBC Technical Page 9of 19 NHBC guide to renewable energy May 2007 HEAT PUMPS Heat pumps (ground source and air source) Air source heat pumps (cid:2) Test all pipework after installation purpose built water systems unless and backfilling to ensure that it they are properly managed. Further The location for the installation of an is sound. guidance can be found at ASHP needs to be considered carefully as they can generate significant noise (cid:2) Fix permanent labels and flow www.hse.gov.uk/legionnaires/index. htmand in the HSE’s Approved in operation. arrows to pipework, valves, etc. Code of Practice & Guidance Consideration should be given to their (cid:2) Ensure that the system is document, L8 aesthetic appearance of external commissioned properly and test for ASHPs and planning permission may correct operation. (cid:2) electrical safety be required. (cid:2) Provide operating instructions and (cid:2) for GSHPs, damage to services maintenance recommendations for below ground, membranes, capping Installation tips the homeowner. layers, etc. (where present). (cid:2) Consider drilling vertical bore holes Additional information and installing the pipework loop at Health and safety an early stage in the construction of the homes – heavy plant is needed Care should be taken to address all See Appendix Cfor information on the and it can be a messy operation. issues, including: Department of Trade and Industry’s ’Microgeneration Certification Scheme’. (cid:2) Install the pipework loop carefully (cid:2) the risk of Legionnaires’ disease - and protect it from damage during this is a potentially fatal form of See Appendix Dfor relevant standards backfilling and after installation. pneumonia that can thrive in and additional information. NHBC Technical Page 10of 19