NHBC guide to renewable energy

19 Pages·3.385 MB·English

by  Farookhi I. (Ed.)

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