Sustainable heating and cooling

APPLICATION NOTE
SUSTAINABLE HEATING AND COOLING
James Parker, Reginald Brown, Nic Wincott
November 2017
ECI Publication No Cu0155
Available from www.leonardo-energy.org

Publication No Cu0155
Issue Date: November 2017
Page i
Document Issue Control Sheet
Document Title: Application Note – Sustainable Heating and Cooling
Publication No: Cu0155
Issue: 02
Release: Public
Content provider(s) James Parker, Reginald Brown, Nic Wincott – BSRIA Ltd
Author(s): James Parker, Reginald Brown, Nic Wincott – BSRIA Ltd
Editorial and language review Bruno De Wachter
Content review: Creara
Document History
Issue Date Purpose
1 June 2013 First publication, in the framework of the Good Practice Guide
2 November
2017
Second edition after revision
3
Disclaimer
While this publication has been prepared with care, European Copper Institute and other contributors provide
no warranty with regards to the content and shall not be liable for any direct, incidental or consequential
damages that may result from the use of the information or the data contained.
Copyright© European Copper Institute.
Reproduction is authorized providing the material is unabridged and the source is acknowledged.

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CONTENTS
Summary ........................................................................................................................................................ 4
Introduction.................................................................................................................................................... 7
Part 1 – Alternative Low Carbon Technologies................................................................................................ 8
Passive Building Options.........................................................................................................................................8
Passive solar design..................................................................................................................................8
Atria..........................................................................................................................................................9
Passive thermal storage .........................................................................................................................11
Earth tubes and labyrinths .....................................................................................................................13
Solar Thermal Technologies..................................................................................................................................15
Solar thermal panels ..............................................................................................................................15
Solar cooling...........................................................................................................................................16
Transpired solar collectors .....................................................................................................................19
Wind to Heat ........................................................................................................................................................21
Biofuels ................................................................................................................................................................23
Biomass systems for buildings................................................................................................................23
Heat Pumps ..........................................................................................................................................................25
Heat sources for heat pumps .................................................................................................................25
Heat distribution for heat pumps...........................................................................................................27
Multi-generation Systems ....................................................................................................................................30
Combined Heat and Power ....................................................................................................................30
Trigeneration..........................................................................................................................................33
Summary of Part 1................................................................................................................................................36
Part 2 – Improving Existing Systems.............................................................................................................. 42
Controls ................................................................................................................................................................42
Building management system................................................................................................................42
Optimum start/stop ...............................................................................................................................42
Occupancy sensors.................................................................................................................................43
Carbon dioxide sensors ..........................................................................................................................43
Distribution of Heating and Cooling .....................................................................................................................44
Benefits of low flow temperatures.........................................................................................................44

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Heat emitters for low temperature heating distribution.......................................................................45
Thermal Storage ...................................................................................................................................................45
Lower temperature storage ...................................................................................................................46
Higher temperature thermal storage.....................................................................................................47
Heat Recovery.......................................................................................................................................................47
Evaporative Cooling..............................................................................................................................................49
Free Cooling..........................................................................................................................................................51
Night purging..........................................................................................................................................51
Free cooling from the ground ................................................................................................................51
Electric Motors .....................................................................................................................................................53
Summary of Part 2................................................................................................................................................54
Strategy selection tools ................................................................................................................................ 57
References.................................................................................................................................................... 58
Useful Information Sources..................................................................................................................................60

Issue Date: December 2017
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SUMMARY
In many non-residential buildings across Europe the energy consumed for heating and cooling is more than
half the total energy consumed by the building. This is not inevitable since the introduction of some simple
design concepts and currently available technologies which can lead to significant reductions in the energy
consumption, operating costs and carbon emissions of both new and existing buildings.
This guide discusses some of the technologies and systems that can be installed into new buildings to provide
more sustainable heating and cooling. It also considers how existing systems can be improved through
retrofitting improved technology or simply adjusting control strategies to reduce waste. Watchpoints are
included after each section to assist specifiers in assessing whether these technologies and systems might be
feasible for their building.
The guidance is arranged in two parts:
 Alternative low carbon technologies
 Improving existing systems
The subjects that have been considered are summarised with comments in the in the table below.
Sustainable heating and cooling option Comments
Passive building
options
Passive solar design New buildings should be designed with the optimum
orientation and glazing ratios for passive solar design to
reduce heating and cooling loads. Changes to solar
transmission and shading devices are possible to improve
the performance of existing buildings.
Atria Atria act as solar collectors, drive natural ventilation and
add useful space to the building. Atria are usually
considered as an option for new buildings but can depend
on the climate. They can also be retrofitted between
existing buildings and over courtyards.
Passive thermal storage Phase change materials can provide passive thermal
storage in both new and existing buildings to reduce
cooling loads and improve comfort. They are particularly
useful for meeting rooms and other intermittently
occupied spaces.
Earth tubes and
labyrinths
Ground cooling and labyrinths can be integrated in the
construction of new buildings, particularly to reduce
ventilation cooling loads.
Solar thermal
technologies
Solar thermal panels Solar thermal panels can be fitted to most buildings to
provide sanitary hot water for most of the year. The
optimum area of collector is defined by the daily hot
water demand.
Solar cooling Solar cooling, using thermally driven chillers linked to
solar collectors, may be viable for large mechanically
cooled buildings in sunny climates.

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Transpired solar
collectors
Transpired solar collectors can preheat the ventilation air
for new or existing buildings. The technology is
particularly suitable for buildings with a low glazing ratio
on the south aspect.
Wind to heat Wind turbines Excess electricity that cannot be used, exported or stored
in batteries can be stored as heat. This is a useful option
for communities not connected to the electricity grid.
Biofuels Biomass Wood pellets or chips from sustainable forests can be
used as an alternative to gas or oil fired boilers.
Heat pumps Heat pumps Heat pumps produce lower carbon emissions than fossil
fuel boilers per unit of heat supplied. Heat pump options
are available for all building types, both new and existing.
The choice of heat pump depends on the available heat
sources and of the heating/cooling distribution system.
Multi-generation
system
Combined heat and
power
Combined heat and power (CHP) is the simultaneous
generation of heat and power. Carbon emissions are
lower than for the same amount of heat and power
supplied from a conventional boiler and power station.
CHP in buildings is provided by internal combustion
engines, small gas turbines or fuel cells. The maximum
size and running hours for sustainable operation of the
CHP is limited by base load heat demand of the building.
Trigeneration Trigeneration is CHP plus cooling. The cooling is provided
by an absorption chiller running on waste heat from an
internal combustion engine or gas turbine. Since the
cooling demand extends the running hours of the CHP,
the economics of trigeneration can be better than CHP
alone.
Controls Building management
system and Building
Energy Management
Systems (BEMS)
All buildings need controls to provide efficient operation
of the heating and/or cooling systems. Building
management systems (BMS) integrate the control of
different building systems and allow for more
sophisticated control strategies and data gathering.
Building Energy Management Systems (BEMS) specifically
control all aspects of the energy system to optimise
performance and energy efficiency. Modern BMS & BEMS
systems may use wireless sensors and controls to
minimise installation costs.
Optimum start/stop Optimum start/stop is a form of dynamic predictive
control that allows the heating or cooling system to
operate for the minimum time necessary to achieve the
comfort objectives of the building. It can be implemented
via discrete controllers or as a control function in the
BMS.
Occupancy sensor Occupancy sensors save energy by reducing the heating
and cooling of areas of the building that are unoccupied.
They are usually linked to a BEMS (or BMS but can also be
used with local controls.

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Carbon dioxide sensor Carbon dioxide sensors save energy by controlling the
ventilation rate for different areas of the building
according to the level of occupancy. They are usually
linked to the BMS but can be used with local controls.
Distribution of
heating and cooling
Low temperature heat
emitters
Low temperature heat emitters allow condensing boilers
and heat pumps to operate at their maximum efficiency
and reduce distribution losses.
Thermal storage Lower temperature
thermal storage
Ice storage provides a convenient and compact method of
storing cold during periods of low demand. The ice can
be utilised to reduce peak loads on chillers for air
conditioning systems. Operating chillers to produce ice at
night can result in cost savings.
Higher temperature
thermal storage
Liquid water is not the most compact form of thermal
storage, but it is inexpensive and easy to implement.
Many heating technologies can benefit from
incorporation of thermal stores and buffer vessels to
improve system performance or capture energy at the
most convenient time
Heat recovery Ventilation heat recovery Heat recovery ventilation reduces the heat and cooling
losses associated with ventilation air.
Evaporative cooling Evaporative cooling Evaporative coolers can provide very efficient cooling (or
pre-cooling) of fresh air using nothing more than the
evaporation of potable water. Indirect evaporative
cooling does not increase the humidity of the air entering
the building.
Free cooling Night purging Operating ventilation systems at night can remove
residual heat and pre-cool the building to reduce the load
on the cooling systems for the next day.
Ground cooling Heat pump ground loops and boreholes can produce cold
water for cooling at minimal cost without operating of the
heat pump.
Electric motors Fans and pumps Air and water distribution systems should be designed to
minimise unnecessary pressure losses. Variable speed
fans and pumps allow significant energy and cost saving
through optimisation of commissioning and dynamic
system control.
High efficiency electric motors (or equipment
incorporating these) should be always selected for new
applications and used as replacements whenever
possible. Variable speed drives can be retrofitted in some
circumstances, but this may require changes to the
system design and control strategy to achieve significant
energy savings.

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INTRODUCTION
Forty percent of Europe’s energy use and a third of the greenhouse gas emissions can be attributed to
buildings with much of this relating to heating and cooling. For example, in the UK 38% of all CO2 emissions
are related to space heating [1]. These emissions can be avoided or significantly reduced through a
combination of holistic design, integrated renewable energy and high efficiency systems that can be described
as sustainable heating and cooling.
The options for reducing the energy consumption and carbon emissions from a building should be considered
in the following order of priority:
1. Reduce heating and cooling loads
a. Optimise the building fabric to reduce the need for heating and cooling
b. Minimise internal heat gains through selection of efficient lighting, equipment and processes
2. Incorporate passive solutions in the building design
3. Maximise the energy efficiency of installed systems
4. Capture and use renewable energy
The aim of this document is to give the reader an overview of the technical opportunities to reduce energy
consumption and lower carbon emissions from buildings by implementing sustainable heating and cooling.
We assume that all new buildings will be constructed with a good standard of fabric insulation in accordance
with the local implementation of the Energy Performance of Building Directive (EPBD) so this aspect is not
discussed. For existing buildings, the cost benefit of fabric improvements should always be considered at the
same time as investments in new heating and cooling technologies since they are inextricably linked.
This guide is in two parts:
 Part 1 looks at alternative low and zero carbon technologies for heating and cooling that should be
considered for new buildings and major refurbishments.
 Part 2 looks at improving the operation and performance of existing systems.
We know from comparisons of building performance across Europe that there is enormous scope for reducing
the energy consumption of buildings by improving design and implementing the “best available technology not
entailing excessive cost”. However, we should not forget the human factor. A large part of the energy
consumption any building is determined by the behaviour of the building occupants. The best technologies will
not achieve the best result unless the occupants understand how the building is supposed to work and are
committed to making it work.

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PART 1 – ALTERNATIVE LOW CARBON TECHNOLOGIES
PASSIVE BUILDING OPTIONS
The best way to reduce the impact of energy consumption on the environment is to consume less. The passive
building approach focuses on using the fabric of the building to help do to this. Passive systems are usually
low-maintenance and intrinsically reliable as there are few, if any, moving parts.
A prerequisite to passive design is a well-insulated and airtight building envelope. This reduces the amount of
heat escaping from the building in winter, or entering the building in summer, and therefore reduces the
amount of energy required to heat or cool the occupied spaces. Airtight does not mean that the building
should be under-ventilated, but that uncontrolled ventilation should be minimised e.g. by careful sealing of
gaps between construction elements.
Passive design has been championed through the Passivhaus Institute in Germany (http://passiv.de/en/) and
their Passivhaus certification scheme, operated though national Passivhaus institutes throughout Europe.
PASSIVE SOLAR DESIGN
The sun is the best and most widely available source of free heat. Even in the winter, solar gains can provide a
useful proportion of the space heating requirement.
Optimising solar heat gain depends on the architecture and orientation the building. Passive design solutions
may incorporate large areas of glazing on the south face of the building to maximise the solar gain with less
glazing and more insulation on the north face of the building to reduce heat losses. However, a poor design
could increase cooling loads and the risk of overheating during the summer. It could also reduce the usable
occupied space if areas next to the glazing are uncomfortable during some periods of the year.
Many new buildings now incorporate external shading features such as “brise soleil”. These are fixed devices
that control glare while still allowing the occupants to benefit from diffuse solar radiation and high daylight
factors. Brise soleil can be retrofitted to existing buildings, instead of solar reflective film or tinting of the
windows that can lead to excessive use of electric lighting.
Figure 1 – Brise Soleil.
(Source : AB Glass)

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On the east or west faces of the building, vertical shading fins (on the south side of the window openings) may
provide the best effect.
It is essential to consider the wider implications of all the design decisions for the whole year to ensure the
visual and thermal comfort of the occupants. Building thermal modelling software allows a rapid assessment of
the effect of changing the glazing area, light transmission and thermal properties of the glazing as well as the
effect of external and internal shading.
WATCHPOINTS FOR PASSIVE SOLAR DESIGN
Optimise the solar design to the
local micro climate, precise
location, elevation and aspect.
The building should be designed to maximise the useful solar gain in
winter but avoid summer overheating. External solar shading devices are
already used for many low energy buildings and can be fitted to existing
buildings. Modelling is essential to design the best balance between
heating and cooling.
Maximise the daylight
contribution while avoiding
glare
Maximising the daylight factor can reduce dependence on electric lighting
but the low sun angle in winter can produce glare on sunny days.
Consider both external shading (horizontal and vertical) and internal
blinds in the modelling. Also consider fitting automatic lighting controls to
maximise energy savings.
Consider the implications of
attaching the brise soleil to the
facade of the building
Brise soleil are typically lightweight structures made from wood or tubular
aluminium sections, but aerodynamic effects can produce unexpected
loads.
Also consider the effects of thermal bridging between the shading device
and the building structure which can significantly increase the U-value
(thermal transmission) of the wall. Many brise soleil manufacturers
provide specialist design and modelling services to evaluate these effects.
Brise soleil may also obstruct the window cleaning strategy for tall
buildings so discuss the options for window access with the supplier.
ATRIA
Well-designed atria can help both the heating and cooling strategy of the building. Atria are glazed spaces that
are thermally separated from the conditioned spaces of the buildings they are connected to. The classic central
core atrium is often found in shopping centres (as shown below), but other possibilities include linear atria
covering one elevation or completely enveloping the building.

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Figure 2 – Classic shopping centre atria in Oslo.
(Source: BSRIA)
The atrium acts as a buffer between the indoor and outdoor space and as a solar collector [2]. In the schematic
shown below, the “stack effect” induced by warm air in the atrium draws air through the occupied spaces and
out through vents at the top. Ventilation rates are controlled by opening or closing the vents and using internal
shading to control the solar gain.
Atrium
Occupied Space Occupied Space
Vents
Figure 3 – Principle of ventilation driven by a central atrium.
(Source: BSRIA)
While atria are frequently incorporated in modern shopping centres around the world they can be equally as
useful for smaller buildings. There are also a few examples where atria have been created for existing
buildings, particularly schools, by covering over courtyards and spaces between the buildings.

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Note that while passive atria (without heating or cooling) can reduce the energy consumption of the building,
those atria simply added as tall, fully conditioned glazed spaces at the front of some hotels and offices could
unintentionally increase it.
WATCHPOINTS FOR ATRIA
Can air move freely through the occupied
space?
During moderate weather conditions, natural ventilation
provides relatively small pressure differences to drive the air
flow through the building. Obstructions to air flow, such as
internal partitions, will reduce the available ventilation rate.
Where natural ventilation of the building may not be sufficient
under all weather conditions, a hybrid ventilation solution
(natural ventilation with fan assistance) can be considered.
Can the air move through the occupied
space without disturbing occupants?
During high wind conditions, air velocity through the occupied
space should be controlled to less than 0.3 m/s to avoid
discomfort to occupants.
Are the various controls linked? For atria to work effectively it is important that all the control
elements (atrium vents, fresh air vents and heating system)
are linked together by an integrated control system.
Modelling Modelling the airflow is an essential part of the design process
to make sure that the ventilation strategy will work under all
weather conditions.
PASSIVE THERMAL STORAGE
Thermal storage in buildings depends on a property known as thermal mass. This is the capacity of the fabric
and structure of the building to absorb and store heat. Thermal mass releases heat as the building cools down
and absorbs heat as the building warms up. This helps to even out the effect of fluctuations in heating and
cooling loads, whether from occupant activity or variations in outside air temperature. Thermal mass gives the
building thermal inertia.
Thermal mass can be provided by dense construction materials such as stone, concrete and brick in contact
with the ambient air. Unfortunately, modern high-rise offices with glazed walls, raised floors, suspended
ceilings and few internal walls provide limited scope for incorporating thermal mass. Phase-change materials
(PCMs), in the form of wall and ceiling coverings, are increasingly being used as an alternative. These products
absorb large amounts of heat compared to the conventional materials they replace.
Most commercially available PCMs are based on micro-encapsulated waxes that have a melting/freezing
temperature in the range of comfortable room temperature (21 to 26 °C). As the temperature rises, the wax
changes from a solid to liquid, absorbing heat in the process. That heat is released when the temperature falls
and the wax changes back from liquid to solid. Many of the available PCM construction products are based on
the BASF Micronal® PCM range [3] in which the PCM powder has been mixed with the conventional material.
Typical gypsum plasterboard heated from 22°C to 25°C would absorb around 3.3 kJ/kg, while PCM
plasterboard with a transition temperature of 23°C could absorb 15 kJ/kg.

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Consider a conference room with the air conditioning switched off. At the start of the first meeting of the day,
the room is cool but the temperature gradually increases due to the activity of the occupants. At some point
the air conditioning may be activated to prevent the room becoming uncomfortably hot. If, however the room
has surfaces with PCMs, these will absorb heat at the transition temperature, delaying the use of the air
conditioning and therefore saving energy. If the meeting lasts long enough then all the PCM may melt and the
temperature will begin to rise again so the air conditioning must eventually be used. For shorter meetings, the
use of air conditioning might be avoided altogether. When the room is vacated, the temperature will gradually
fall back below the transition temperature and the PCM will solidify ready for the next meeting.
PCMs can be incorporated into many common construction elements such as plasterboard wall panels, ceiling
panels and concrete blocks or mixed with wall plaster. PCMs can also be integrated with other cooling or
heating systems to increase the thermal storage capacity of those systems. Remember that PCMs only work
when the ambient temperature crosses the transition temperature of the PCM. If the ambient temperature
stays above or below the transition temperature there will be no latent heat effect so the selection of PCM
with the appropriate transition temperature is fundamental to the design of the system. Thermal modelling of
conditions in the room is strongly recommended as part of the design process.
WATCHPOINTS FOR PASSIVE THERMAL STORAGE
What if the room already has significant
thermal mass (exposed concrete,
stonework etc.)?
PCMs are most useful in cooling applications for lightweight
buildings with minimal exposed thermal mass. If the room
already has significant exposed thermal mass, the benefits of
installing PCM will be limited.
What form of PCM is most suitable? It is important that the PCM product is exposed to air so that it
can transfer heat to and from the space. PCM products can be
used as wall and ceiling linings in the room or as duct linings in
the ventilation system.
Some PCM products may be inflammable. This will have to be
considered when the product is specified.
The PCM product should be chosen for an
appropriate temperature range of the
room.
Phase change materials absorb or release heat over a small
temperature range (the transition temperature) related to the
melting point of the embedded PCM. Manufacturers provide a
range of products with different transition temperatures. Most
products are designed to reduce cooling loads so that the phase
change temperature is at the upper end of the comfort
temperature range
Can the PCM products recharge? Remember that there must be an opportunity for the material to
“recharge” when the room is not occupied. This must be
considered in the control strategy i.e. if the PCM is included for
cooling then the room must continue to be ventilated after the
occupants have left so that the PCM can cooled to below the
transition temperature.
In buildings without mechanical cooling, the PCM can be
recharged by operating the ventilation system at night to provide
free cooling.

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EARTH TUBES AND LABYRINTHS
Several metres below the surface undisturbed ground remains at a stable temperature throughout the year.
This is approximately equivalent to the average annual air temperature at that location. In the UK this is in the
range of 8°C to 14°C. In earth tube systems, the outside air is drawn through large diameter buried plastic or
concrete pipes or ducts before entering the building. These cool or warm the air entering the building
depending on the relative temperatures of the air and ground. In summer, there can be useful pre-cooling and
in winter pre-warming of the incoming fresh air.
The tubes are 30 m up to 100 m long (per tube) and buried about 2m below the surface of the ground. The
diameter of tubes for commercial building applications ranges from 0.5 m to 1.5 metres. The air velocity is
typically 6 to 10 m/s.
Although the heating or cooling effect obtained from the ground is free, and exploits natural convection as far
as possible, additional fan power may be required to drive the system. The useful heating or cooling effect
divided by any fan power gives a “coefficient of performance” for the system. In Northern Europe, the
seasonal CoP for cooling could be in the range 20 or more (compared to a CoP of 4 – 5 for heat pumps).
Although earth tubes can be costly they are low maintenance. Access should be available for surface cleaning
and sanitisation. They may be impregnated with Silver to prevent the growth of mould and other
microorganisms.
A sophisticated implementation of concrete earth tubes is part of the Earth Ranges Centre in Canada. The
current performance of this system can be interrogated at http://earthrangers.energyoperation.schneider-
electric.com/direct/Earthrangers/earthtubes.
Figure 4 – Earth Rangers Centre earth tube ventilation system.
(Source: Earthrangers.org, Canada)
While earth tubes are generally located outside the building footprint, labyrinth systems are usually positioned
under the building and used for diurnal (night/day) thermal energy storage. The labyrinth consists of a series of

Page 14
underground pathways with concrete walls that provide the thermal mass. The surface of the walls may be
profiled to increase the surface area and improve heat transfer with the flowing air. The labyrinth may have
some ground coupling, but it is the thermal storage effect that is most important.
Labyrinths are most common in areas of the world where there is a big day/night temperature difference (the
Middle East and Australia). There, the labyrinth can be purged with cold night air to store “cold” for the
ventilation during the following day.
Figure 5 – A PLAN VIEW of an earth labyrinth.
(Source: BSRIA [4])
WATCHPOINTS FOR EARTH TUBES AND LABYRINTHS
Is it possible to install earth tubes? On a small site, it may not be possible to install a useful length of earth
tubes. The condition of the ground and conflicts with other buried
services (drains, water pipes, cables etc.) also needs to be considered.
Discussions with a specialist installer may be useful to understand if
the site has potential.
Air quality Locate the intakes to the system to minimise ingress of air pollutants.
Intakes near parking areas should be located at least 2m above ground
level and away from standing traffic.
Air can be filtered at the entry to the earth tube system or the entry to
the building. Some systems also include UV treatment to sanitise the
air, but this will add to the operating and maintenance costs.

Page 15
Protect the system against water
ingress
Debris, condensation and water ingress could lead to mould and fungal
growth resulting in smells. The tube system should be hydraulically
sealed from the surrounding ground. Intake louvers with screens
should provide protection from rain and insect penetration. The tubes
should be laid with a fall (to a sump with a drainage pump) to allow for
efficient drainage.
Contaminated land Expert advice should be taken when considering the installation of
earth tube systems on brownfield sites where there may be
contaminated land or in areas with a geological radon hazard.
Systems resistance It is important to minimise air flow resistance to save fan power.
Intake screens, tube bends and filters will all add resistance and the
effects should be considered when estimating the CoP.
SOLAR THERMAL TECHNOLOGIES
SOLAR THERMAL PANELS
The sun, either directly or indirectly, is the source of all renewable energy. Solar water heating with glazed flat-
plate collectors or evacuated-tube collectors is the most common form of solar energy harvesting. In warmer
climates, simple passive thermosiphon systems are used, while in more temperate regions fully pumped
systems using flat-plate or evacuated tube collectors are normal. Evacuated tube collectors are more efficient
than the flat-plate collectors during the winter and produce higher temperatures.
To maximise the exposure to the sun, the ideal location of the panels is on south facing walls or roofs, but solar
thermal panels do not need direct sunlight to function. This is because the Infra-Red wavelengths that power
the panels can penetrate cloud so even diffuse sunlight can produce useful amounts of hot water for much of
the year.
Evacuated tube and flat plate solar systems in northern Europe are usually indirect, meaning that a heat
transfer fluid is circulated through the collector and then to a heat exchanger where heat is transferred to a
thermal store or the sanitary hot water. The heat exchanger can be a plate or a coil. The latter is used within a
multi-coil hot water cylinder that allows inputs from different heat sources to be combined e.g. from gas
boilers or other renewable technologies such as heat pumps.
The total installed capacity of solar thermal systems in Europe (2012) is equivalent to 26.3 GWth, generating
18.8 TWh of solar thermal energy while contributing to savings of 13 Mt CO2 [5].
WATCHPOINTS FOR SOLAR THERMAL PANELS
Orientation In Europe, solar panels are most effective when facing south
although the optimum installation angles will change with latitude.
Shadowing can be a problem and should be avoided.

Page 16
Is the roof capable of supporting the
weight of the system?
Some roof structures may need strengthening to carry the
additional weight of the panels and mounting. Wind loads, and
particularly lift produced from the angled panels should also be
considered. Expert advice should be obtained from a structural
engineer.
Sizing the panels There is no benefit in fitting more panels than needed to meet the
usual hot water demand for the building.
Is there sufficient hot water storage? Peak hot water generation may be at a different time to peak
demand. Hot water storage should be sized to help to match
supply and demand.
Can the system be integrated with other
hot water producing equipment?
Often solar thermal systems are not capable of meeting the full
hot water demand in winter, so top up systems such as gas boilers
or other renewables will be needed to meet the demand.
Integration is often done through multi coil cylinders.
In colder climates, is there adequate frost
protection/drain down systems in place?
In northern Europe, freezing of pipework in winter can be a big
problem causing pipes to burst. The system may be drained when
the panels are not in use, or a heat transfer fluid with antifreeze
properties may be specified as possible solutions.
Further information about solar thermal systems can be found at:
 European Solar Thermal Industry Federation (ESTIF): http://solarheateurope.eu/welcome-to-solar-
heat-europe/.
 IEA solar heating and cooling programme: www.iea-shc.org.
SOLAR COOLING
Solar cooling systems use the sun as an alternative to mechanical cooling powered by electricity.
Solar absorption cooling is not new technology. Augustin Mouchot produced the first ice block with solar
energy using a solar concentrator and the periodical absorption machine of Edmund Carré at the Paris
exhibition of 1878. The equivalent modern system would be conventional adsorption chiller supplied with high
temperature hot water from a solar concentrator. Absorbtion chillers have low CoP’s, but this is irrelevant in
most cases since the sun is providing free energy.

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Figure 6 – Augustin Mouchot solar absorption demonstration at the Paris exhibition 1878.
(Source http://de.goldenmap.com/Augustin_Mouchot)
BACK-UP
BOILER
G
C
A
E
CHILLED WATER
CIRCUITS
COOLING TOWER
HEAT
STORAGE
SOLAR
COLLECTOR
DESORBER
CONDENSER
ABSORBER
EVAPORATOR
Figure 7 – Solar collector linked to an absorption chiller.
Solar concentrators focus direct sunlight to produce high temperatures and are ideal for absorption cooling.
Smaller scale systems, including those mounted on buildings, use reflective parabolic troughs to concentrate
solar radiation onto a blackened absorber tube containing a heat transfer fluid (Figure 8). Some solar
concentrators are able to follow the path of the sun to maximise the energy capture. The fluid in the tube can
reach temperatures of up to 400 °C, and so can be used for high grade heating applications, even for steam
production and combined heat and power systems [6].

Page 18
Figure 8 – Diagram of a parabolic trough solar collector.
(Source: Wikipedia Commons)
Solar concentrator technology is best suited to areas that experience consistently high levels of solar radiation,
which unfortunately excludes much of northern Europe.
Other systems use desiccant cooling. In the liquid desiccant system, moist air is dehumidified by contact with a
water absorbing liquid while in a solid desiccant system moist air is dehumidified by contact with a water
absorbing solid. The air then passes to the next stage of the process, where it is re-humidified with a water
spray producing the cooling effect. The desiccant is regenerated (water removed) by the application of solar
heat.
In one form of the solid desiccant system, air passes through a desiccant matrix in the form of a rotating
wheel. One sector of the wheel absorbs moisture while the remainder is being regenerated. In another form
the airflow can be periodically switched between two absorbers so that one will be dehumidifying while the
other is regenerating.
More details on solar chillers are contained in the multi-generation section below and the following sources:
 The International Energy Agency’s (IEA) Technology Roadmap Solar Heating and Cooling:
www.solarthermalworld.org/content/global-roadmap-iea-calls-stakeholders-realise-vision
 IEA solar heating and cooling programme: www.iea-shc.org/ & http://task53.iea-shc.org/
 International Conference on Solar Heating and Cooling for Buildings and Industry - Abu Dhabi -
November 2017 http://www.shc2017.org/
WATCHPOINTS FOR SOLAR HOT WATER
Can the panels produce enough hot
water at the required temperature for
the ‘sorption chiller?
Single effect absorption chillers require a heat source temperature
of at least 80 °C and the double-effect chillers one of at least 140
°C. Adsorption chillers typically require heat source temperatures
of 60 °C to 95 °C.
Is thermal storage required to dampen
the fluctuations in source
temperature?
A review of the demand and supply patterns should be carried out
to make sure that heat will be available when the chillers require it.
Payback Unless there are other objectives (e.g. meeting Carbon reduction
targets), lifetime costs implications should be carefully considered.

Page 19
TRANSPIRED SOLAR COLLECTORS
Transpired solar collectors (TSC) use solar radiation to heat the ventilation air supplied to the building. The TSC
is a perforated metal sheet that heats up when exposed to sunlight. This in turn warms the layer of air in close
contact with its outer surface (the boundary layer). The warmed air of the boundary layer (up to 30°C above
ambient on a sunny day) is then sucked through thousands of tiny perforations into a cavity between the
collector and the structural wall of the building. The warmed air is distributed, after further heating if
necessary, via building ventilation system.
The thermal collection efficiency of the TSC (useful heat collected divided by solar irradiation) depends on the
flow rate per unit area, emissivity of the sheet and wind speed. Under ideal conditions this can reach 70%.
The typical TSC material is a perforated version of the plastic coated galvanised steel sheet (flat or profiled)
used for thousands of modern industrial and commercial buildings. Dark colours are preferred for higher
emissivity. Non-TSC areas can be clad with a lower-cost non-perforated version of the same sheet and will be
visually indistinguishable.
Figure 9 – Transpired solar collector cavity.
(Source: BSRIA)

Page 20
Ventilation
distribution
Supplementary
heating coil
Fan
Building structure
& insulation
Solar radiation
Perforated
TSC sheet
Figure 10 – How a transpired solar air collector works.
(Source: BSRIA)
TSC is a simple low cost technology (100 - 150 €/m
2
installed price) that has been demonstrated to save up to
40% of the space heating demand of suitable buildings. If the building is being re-clad already for other
reasons, then the marginal cost of incorporating TSC is even less. TSC is particularly suitable for warehouses,
large retail outlet and factories with large south facing wall areas with a low glazing ratio. There have also been
demonstration schemes for other buildings (Figure 11) and individual houses.
Figure 11 – Transpired solar collector demonstration (green façade) at SBEC Research Centre.
(Source: BSRIA)

Page 21
WATCHPOINTS FOR TRANSPIRED SOLAR COLLECTORS
Can the warm air be used effectively to
heat the building?
TSC is used to preheat fresh air for ventilation. The peak energy
collection is in the middle of the day, so a conventional system
is needed to heat the building at the start of the working day,
particularly during Winter. Overall energy savings in an ideal
application could be 30-40%.
A building with a south facing wall with
less than 50% glazing.
TSC can be fitted around windows, but it is much easier and less
expensive to install if there are large areas of continuous wall as
in many out-of-town retail outlets and warehouses.
The optimum area of TSC will depend on the required
ventilation rate for the building. Typical TSC installations are
designed with an airflow rate of 50-100 m³/h per m² of
collector. The area covered by TSC does not need to be any
larger than needed to supply the ventilation requirement.
If it is not possible to find sufficient wall area, then TSC can be
installed as a purpose- designed roof mounted solar collector.
Can the TSC be easily connected to the
building ventilation system?
Ideally the duct connection should be taken straight through
the inner wall into the space, but external insulated ducts can
be fitted on the roof if this is not possible.
Controls TSC is used with a variable speed fan to optimise the solar
energy collection and supply temperature. A fresh air bypass (or
separate fresh air supply) should be fitted for summer
operation when the heat from the TSC is not needed.
Other features If warm air from the TSC is distributed at high level into a large
space (such as a warehouse) then destratification fans may be
needed. It may be used as input air to feed an Air Source Heat
Pump thus improving its performance, often significantly.
WIND TO HEAT
The wind is a 100% renewable energy source. Many parts of Europe have average winds speeds high enough
to make the installation of wind turbines viable.
While the excess electricity from small wind turbines is usually exported to the grid, this may not be an option
for isolated communities. If battery storage is also satisfied then the remaining energy can be economically
stored as heat.
Heat storage can use conventional electric storage heaters, sanitary hot water cylinders or purpose designed
thermal stores, with the heating elements directly connected to the wind turbine. Direct connection avoids the
need for an inverter and the associated energy losses. Wind turbines are useful for space heating as stronger
winds tend to occur in the colder months of the year. An example of a small wind turbine used for heating is at
the community hall of Berneray (one of the islands off the west coast of Scotland) [7]. This has a 10kW turbine
linked to storage heaters and a hot water cylinder.

Page 22
Figure 12 – Berneray Hall, Western Isles, Scotland.
(SOURCE: BSRIA)
WATCHPOINTS FOR WIND TURBINES
Does the site have a sufficiently high
average wind speed throughout the year?
Most turbines need an average wind speed of around 4m/s to
start generating so for large projects, it is worthwhile carrying
out a long-term survey with an anemometer mounted at the
same height as the proposed turbine hub.
Does the wind turbine have a clear and
unobstructed exposure to the prevailing
wind?
Wind turbines should be situated as high as possible, the hub
height should be at least 10 m.
Local obstructions including trees, buildings and other structures
can reduce wind speed and energy collection.
Is there sufficient space for maintenance
of the turbine?
Some turbines are hinged at the base for maintenance. A
distance equal to the height of the turbine (including blades)
should be kept clear of obstructions so that the pole can be
dropped.
Could the wind turbine create structural
vibrations?
Small wind turbines have been mounted directly on buildings,
but this must take account of the structural loads and the
possibility of turbulence induced vibration
Could the wind turbine create noise or
visual disturbance?
Turbines inevitably produce some noise and this must be
considered during the planning process. Blade passing shadows
from large wind turbines can disturb occupants of nearby
buildings.

Page 23
BIOFUELS
Biofuels are fuels that have been produced from plant material. The primary source of the energy in those
fuels is the sun. Photosynthesis converts atmospheric carbon dioxide into carbonaceous plant material, the
derivatives of which can be burned. Biofuels are available in all three physical states i.e. solid fuels, liquid fuels
and gaseous fuels.
Bioethanol is produced by fermenting sugar or starch based crops. This can be blended with gasoline for use in
automobile engines.
Biodiesel is produced by transesterification of vegetable oils. Most biodiesel is produced directly from
rapeseed oil. Restaurants and food manufacturers are increasingly collecting waste cooking oil to process into
biodiesel for transport.
Some diesel engines, including those used in CHP systems, can be run on 100% biodiesel although they may
require modification to avoid problems with lubrication and the build-up of carbon deposits internally. Most
biodiesel for use in engines is therefore blended with petroleum diesel to reduce these effects.
Biodiesel can also be burned in oil heating boilers with only minor changes to the burner e.g. different burner
nozzle. If unmodified vegetable oil is burned, the equipment may need to be started and stopped on
petroleum diesel to avoid carbon build up.
Biogas is methane produced by anaerobic digestion of organic material. Biogas can be collected as a waste
product from landfill sites, or made through controlled digestion of food or farmyard waste. In some areas of
the UK biomethane is injected into the natural gas grid, but there are large CHP plants using biomethane with
reciprocating engines or gas turbines.
BIOMASS SYSTEMS FOR BUILDINGS
Mankind has been burning wood for heating for thousands of years, but using biomass in a modern building
can be much more complicated than an open fire. Modern biomass boilers are designed to replace traditional
gas or oil boilers and are of a similar size. However, wood has a low energy content compared to fossil fuels, so
finding the space to receive and store sufficient can be a problem and the fuel feed system (usually based on a
mechanical screw) needs regular maintenance (Figure 13).
Figure 13 – Schematic of a biomass boiler with screw auger feeding woodchips.
(Source: BSRIA [4])
Processed wood pellets are easier to handle than woodchips or logs and have a higher calorific content, so
need less storage volume, but are more expensive per unit of heat.

Page 24
An alternative to direct combustion of wood chips is gasification. The wood is processed through a gasifier,
where a controlled combustion process occurs at over 1000 °C, partially oxidising the wood to produce
methane, carbon monoxide, carbon dioxide and hydrogen [4]. The gas released is then exported or burnt in a
gas boiler (or engine in the case of CHP units). An advantage is that the gasification process does not produce
NOx (nitrogen oxides) or dioxins, often a problem related to traditional biomass installations. Gasification
systems are complex and are most commonly found at present as part of large scale district heating and some
CHP schemes.
Biomass boilers are not suitable for all applications. Although biomass boilers can modulate their output they
are not as flexible as a gas or oil boiler and cannot be started and stopped instantly. This means that a careful
assessment of the heat demand profile is required to select the optimum size of boiler.
One approach to the design of biomass boiler systems is to size the boiler to meet the base heat load of the
building. This allows the boiler to run for long periods at full load. Frequent cycling of an over-sized boiler will
reduce its life. The remainder of the heat load can be met through traditional gas or oil boilers (or even liquid
biofuel boilers) which can also be used as back up when the biomass boiler is undergoing maintenance.
Installing several small biomass boilers rather than a single big boiler may improve flexibility and boiler life
though this will increase capital costs. Adding a thermal store may also help to reducing cycling under part load
conditions.
It is important to ensure that a secure supply of suitable good quality biomass fuel is available, and will remain
available over the medium to long term, otherwise the system may be unsustainable.
WATCHPOINTS FOR BIOMASS
Does the building have sufficient base
heat load to enable continuous operation
of the boiler?
Consider several small boilers rather than one big boiler to allow
output flexibility (modulation) and reduce cycling.
Does the building have sufficient space
for biofuel storage facilities near the
boiler?
Biomass can require large fuel storage facilities, especially boilers
with higher capacities. Typically, the fuel stores are sized to
match the delivery size, i.e. a truck load.
Check there is good unobstructed access for delivery vehicles.
Is there a good quality and reliable supply
of fuel?
A good quality fuel supply is important to maintain efficiency.
Cheap but poor quality fuel can work out more expensive if it
contains contaminants or the moisture content is too high.
Security of supply must be considered when sizing the fuel
storage capacity. Long term contracts for fuel supply should be
put in place as failures to deliver fuel on time may shut the
system down.
Can the biomass boiler be integrated with
other technologies?
It is important to have an alternative supply of heat when the
biomass boiler is not running and/or to meet peak loads.
Biomass can work well with heat pumps as part of a bivalent-
alternative system. The heat pump is used during periods of low
space heating demand and the biomass is used during cold
weather.

Page 25
HEAT PUMPS
Heat pumps are devices that transfer heat from a lower temperature heat source to a higher temperature heat
sink. The process is driven by an external energy source.
An example of a heat pump is the domestic refrigerator or freezer where the heat energy is moved from the
food compartment into the room. This process uses a refrigerant within a vapour compression cycle illustrated
below.
Figure 14 – Schematic of a closed cycle vapour compression heat pump.
(Source: BSRIA)
Refrigerants used in heat pumps include: propane (R290) Isobutane (R600a) hydrofluorocarbon (HFC)
refrigerants such as R134A (1,1,1,2-tetrafluoroethane), ammonia (R717) and carbon dioxide (R744).
It is also possible to drive a heat pump process with high grade heat, the ‘sorption refrigeration cycle. This uses
a different operating principle and a different kind of refrigerant (e.g. aqueous solutions of ammonia and
lithium bromide). The amount of heat (or cold) produced is several times the amount of energy used to drive
the process. The ratio of the heat produced to the input of driving energy is known as the coefficient of
performance (CoP). A heat pump with a CoP of 4 produces 75% renewable heat as that is the proportion that
comes from the environment or other renewable source, the other 25% being the energy used to drive the
cycle. A conventional electric heater has a CoP of 1.0 as all the electrical energy input is converted to heat.
Sometimes the objective is to produce cold rather than heat. In that case, the ratio of cold produced to the
driving energy is called the cooling CoP or the EER (energy efficiency ratio).
HEAT SOURCES FOR HEAT PUMPS
Heat pumps are categorised by heat source. The main sources are the natural heat, originally derived from the
Sun found in the ground, the water on or under it, or in the air. Waste heat created by human activity can also
be employed e.g. heat found in sewage water or industrial processes.

Page 26
Ground source heat pumps use the solar energy stored in the ground to heat water or air for the building.
Undisturbed ground below about two meters has a stable year-round temperature approximately equal to the
average annual air temperature at that location.
The main methods used to collect ground heat are:
 A Closed Loop Ground Heat Exchanger(GHE/GHX)
 An Open Loop where the water is physically pumped out of the ground or a surface water body.
Ground Heat Exchanger (GHE/GHX) are typically loops of pipework installed in vertical drilled boreholes or
buried horizontally in the Earth
Vertical loops are fitted into boreholes usually between 70 and 150 metres deep with a horizontal spacing of
between 5 and 10 metres. An average 100 metre borehole should extract around 6 kW depending on the
geology and hydrogeology. Assuming a heat pump CoP of 4.0, 10 boreholes could provide 75 kW of heat (the
energy extracted from the ground plus the energy used to drive the heat pump).
To achieve the same output with the same heat pump using a horizontal ground loop would, depending on the
ground conditions particularly moisture content and require a land area of approximately 3000 m
3
i.e.
equivalent to half a professional football pitch. Therefore, while shallow horizontal ground loops are relatively
common for single houses with large gardens, most social housing and commercial projects tend to use
vertical bore holes.
Groundwater source heat pumps use water drawn directly from aquifers or other underground resources e.g.
mines, and are nearly always Open Loop whereas Surface Water source systems use canals, rivers, lakes or
other large surface bodies of water as the heat source, and may be open loop or closed loop, where
prefabricated heat exchangers may be deployed.
Groundwater source systems are generally more efficient as the supply temperature from the ground remains
almost constant throughout the year whereas the temperature of surface water can fluctuate significantly and
sometimes quickly because of Solar insolation, rainfall or melt water.
Another advantage of open loop groundwater as a thermal resource is that the approach temperature is
relatively unaffected by the volume drawn. This affords considerable flexibility in energy availability and hence
design flexibility.
Air source heat pumps use the energy in the ambient air, ventilation extract air etc. The big disadvantage is
that when the outside temperature is at its lowest is inevitably when most heat is required.
This has two effects:
 The CoP falls because the delta T (temperature difference) between the source and sink temperature
increases.
 The power of the heat pump falls.
Note too that an ASHP will require defrosting more frequently in cold weather and the defrost cycle reduces
efficiency.
Either system can be used to produce hot water for space heating or sanitary use or to produce warm air for
space heating.

Page 27
Some ground heat pumps are reversible, so they can be used for cooling as well as heating. Alternatively, it
may possible to obtain sufficient cooling merely by circulating water through the ground loop as the ground
will be relatively cold. This is called “comfort” or “free cooling”.
This strategy effectively uses the ground as a heat store as some of the dissipated heat will be recovered
during the next heating season.
HEAT DISTRIBUTION FOR HEAT PUMPS
The CoP of the heat pump varies depending how it is operated. Ideally the temperature difference between
the source and the sink will be minimised. Using a heat pump to generate high temperatures or trying to
extract heat from cooler heat sources will lower the CoP. For example, a heat pump will be more efficient
when providing heat for an underfloor heating system at 35°C flow temperature than for radiators at 55°C or
sanitary hot water at 60°C. Therefore, the installation and application of the heat pump needs to be carefully
considered to make sure it is operated efficiently and supplying heat at the minimum temperature necessary.
Certain kinds of heat pump perform better in particular applications while the use of others may be restricted
within buildings for practical reasons e.g. because of refrigerant toxicity or flammability concerns. Carbon
dioxide heat pumps are good for sanitary hot water because they can provide high flow temperatures. Gas
engine heat pumps may be preferred where electrical supplies are limited. Absorption heat pumps are
particularly good for use with high temperature waste heat from CHP plants when they may be used for
trigeneration i.e. Electricity, heating and cooling.
Sales of heat pumps across Europe now exceed 1,000,000 units per year [8].
WATCHPOINTS FOR HEAT PUMPS
All heat pumps
Energy Cost & Carbon Content The relative cost and carbon content of the motive energy input
(usually electricity) must be considered carefully as it will vary from
Country to Country and have significant impact on system viability.
Some Countries are making the Carbon Content of their electricity grid
available live online. www.gshp.org.uk/Gridwatch.html and
www.electricitymap.org/?wind=true&solar=false&page=map
Minimise the distribution
temperature
Heat pumps are most efficient when the output temperature is low.
Surface heating, of which Underfloor is most common but wall and
ceiling heating enjoying increasing popularity, is ideal for use with
hydronic heat pumps (those providing hot water).
Consider alternative sources of heat when high temperatures are
required e.g. biomass for peak winter heating loads and/or domestic
hot water.

Page 28
Provide full heating coverage at
external design temperature
Monovalent systems with electric heat pumps should ideally be
designed to provide 100% of the space heating load at the local winter
design conditions without any direct electric heating.
Alternatively, non-electric heating can be used as part of a bivalent
system operating above the design temperature.
Ground Source Heat Pumps
Measure the thermal conductivity of
the ground as part of the site
investigation and design process
The size of the ground collector (area associated with the buried loops
or total length of the boreholes) has a major impact on the cost and
future performance of the project. If the ground collector is under-
sized, then the heat pump will not achieve the design output and
efficiency may deteriorate over time due to ground cooling. If the
ground collector is over-sized, then it will cost more to install.
Although some information on ground conditions may be available
from previous geological reports, it is always advisable to carry out
ground investigations to optimise the size of the collector.
NB: Some redundancy should be included in large systems to offset the
possibility of an individual loop or borehole being taken out of service
due to leakage.
Boreholes Boreholes must be grouted to improve the thermal contact between
the tubes and the surrounding ground and prevent cross
contamination of aquifers.
The use of a high-performance grout and clips designed to push the
tube to the periphery of the borehole will improve thermal
performance by up to 20%.
Pressure testing Ground collectors should be made of High density polyethylene
(HDPE). All ground loops must be thoroughly tested for leakage,
preferably in accordance with EN 805. The procedure described in this
standard accounts for the possibility of residual air in the system and
the creep of the plastic when the tube is pressurised.

Page 29
Water Source Heat Pumps
Direct water source Open Loop Water source boreholes usually require permission from the
regulatory authorities and may not be permitted where the
aquifer is also used to supply drinking water. The supply of
water from boreholes must be “proved” before installation of
the heat pump. The energy required for pumping the borehole
should be considered in the operating costs.
Rivers and lakes can be used as a water source, but heat
exchangers must be protected from debris and the
accumulation of biofilm. The maintenance of the filtration
system can be a significant part of the operating cost.
Water source systems must avoid the risk of freezing. Exposed
pipes linking the source to the heat pump should be insulated.
Indirect water source Closed Loop Indirect water sources (from heat exchangers in rivers and
lakes) are less thermally efficient than direct water sources but
require less maintenance. Pollution risk from leaks must be
considered.
Air Source Heat Pumps
Is there supplementary heating for periods
of very cold weather i.e. below the
external design temperature?
Some heat pumps contain an electric heater for supplementary
heating. However, this can run excessively if not carefully
controlled. Other possibilities depend on the heat distribution
system. For wet heat distribution systems, a supplementary
boiler may be the simplest option.
Air recirculation The outdoor unit should be located to minimise recirculation.
This can reduce performance and increase the frequency of
defrosts. The coil-to-wall separation distances recommended by
the manufacturer should be respected and the area around the
coil kept free of obstructions. Groups of coils should be
arranged in accordance with the manufacturer’s
recommendations. Locations such as narrow passageways
between buildings should be avoided.
Could external fans create a noise
nuisance?
External units contain a fan and often a compressor. The noise
impacts on neighbouring properties must be considered and
there may be specific requirements imposed by planning
regulations. Shrouded or ducted outside air coils may be used
in sensitive areas, but these will be less efficient than an open
coil.
Further information about heat pumps can be found at
 Leonardo Energy: Application Note “Heat Pumps for Larger Buildings” (http://www.leonardo-
energy.org/heat-pumps-larger-buildings#.UYe9CFfwBXs)

Page 30
 Leonardo Energy: How to manual for heat pumps www.leonardo-energy.org/how-manual-heat-
pumps
 IEA Heat Pump Centre: www.heatpumpcentre.org
 European Heat Pump Association: www.ehpa.org/
MULTI-GENERATION SYSTEMS
Multi-generation systems simultaneously provide electricity and heating and/or cooling, and may be described
by one of the following terms:
 Combined heat and power (CHP) or Cogeneration
 Combined cooling heat and power (CCHP) or Trigeneration
COMBINED HEAT AND POWER
CHP (cogeneration) plants are available in a range of sizes, from one kilowatt for domestic properties to
several megawatts for a district energy centre. All fuels can be used either directly or indirectly with the prime
mover being a reciprocating internal combustion engine, gas turbine or steam turbine. A combined cycle CHP
plant uses both a gas turbine and a steam turbine.
Small and medium scale CHP systems (10 kWe to 1 MWe) are mostly based on gas and diesel engines
developed from those used for road transport or shipping. Micro-CHP systems (<1 kWe) are based on Stirling
engine technology. Heat is provided in the form of hot water, steam or hot air (for building heating
applications).
CHP plants are rated according to the electrical output expressed as kW electrical (kWe). The thermal output is
expressed as kW thermal (kWth). The heat to power ratio varies according to the technology. Most CHP
installations are electrically led as electricity is usually more valuable than heat. Since the heat is often
considered a waste product, a high power to heat ratio is preferred. However, there are other factors to
consider such as the temperature of the heat and nearby demand.
A CHP plant cannot produce electricity without heat so ideally there should be a local and constant demand for
this heat to avoid shutting down the plant or discarding the excess. Dumping heat is wasteful and the value of
the electricity alone may not even cover the cost of the fuel. The CHP plant in buildings should therefore be
sized so that it meets the base heat load of the building to maximise the running time without dumping heat.
Peak loads should be covered by a combination of thermal storage and boiler plant. The CHP plant should then
be operated as the “lead” boiler so that it is used as much as possible to help recover the investment.
Operating a CHP when there is demand for heat but not for electricity is much less of a problem as the surplus
electricity can usually be exported to the grid.
The suitability of CHP for a property is dependent on the use of the building. Carbon Trust suggests that the
minimum run time for CHP to be economically viable is 4500 hours per year [8]. In ideal applications, this could
provide energy cost savings of up to 20% compared to a system with conventional boilers and electricity
purchased from the electricity grid. Any building with large hot water consumption (laundries, commercial
food preparation etc.) or swimming pool (leisure centre, health club, school etc.) is potentially a good
candidate for CHP, but those with small or seasonally dependent heating requirements such as offices are not
ideal. Hotels can be good applications as they have year-round hot water demand but sufficient thermal
storage to cope with daily peaks in demand.

Page 31
The European Directive on the promotion of cogeneration based on a useful heat demand in the internal
energy market (CHP directive) supports CHP as the most efficient means of utilising fossil fuels in power
generation. This is reflected in national policies, targets and incentives for CHP. Although the Directive is
aimed at large scale CHP for public power generation and industry, incentives may be available for smaller
district heating schemes and individual buildings.
The UK’s Association for Decentralised Energy (ADE) provide a range of case studies for CHP in buildings and
industry together with guides on how to plan CHP and assemble the business case for the investment:
www.theade.co.uk/case-studies?/case-studies_19.html.
FUEL CELLS
The future of micro and small-scale CHP systems is the fuel cell. Fuel cells convert chemical energy into
electrical energy as does a battery. The difference is that the chemical reactants are continuously replenished,
so the fuel cell never runs out of energy. The reason that fuel cells are mentioned here is that some fuel cells
produce not only electricity (with up to 60% efficiency) but also heat. That heat must be removed to prevent
the fuel cell overheating, but is also a useful resource.
Most fuel cells use the simple reaction between hydrogen and oxygen to generate electricity, water and heat,
first demonstrated by William Grove in 1839. If natural gas (methane) is the fuel, it is first passed through a
reformer to produce hydrogen. Some fuel cells operate at high enough temperatures to be able to reform the
gas within the fuel cell itself, such as molten carbonate fuel cells (MCFC) and solid oxide fuel cells (SOFC).
Figure 15 – Hydrogen fuel cell reactions.
(Source: Wikipedia commons)

Page 32
Figure 16 – The arrangement of components in a typical fuel cell with integral reformer.
(Source: BSRIA [4])
Carbon dioxide gas is produced during the reforming process though the emissions are lower relative to the
amount of electricity produced than for other CHP technologies.
The downside of fuel cell CHP is cost. At the present state of development, the capital costs of fuel cells per kW
installed is much greater than for comparable engines. Even with wide scale deployment, the cost of small
fuels cells is unlikely to drop below €3000/kWe installed (Staffell 2012) [9].
The high cost means that the current market for fuel cells is confined to critical applications wherees the cost
can be offset against conventional standby power systems.
A good source of information about current developments and commercially available systems can be found at
Fuel Cell Today website (www.fuelcelltoday.com/).
WATCHPOINTS FOR COMBINED HEAT AND POWER
Does the building have a sufficient base
load heat demand for a CHP plant?
CHP plants are usually sized according to the base load heat
demand (with boilers providing for peak demands) so that they
can run for the maximum time. Ideally CHP should run for at
least 4,500 hours per year to provide efficient operation and a
reasonable return of the investment. Over-sized CHP plant will
be inefficient and expensive to run.
The annual operating hours can be increased if CHP is combined
with, ‘sorption cooling to create a trigeneration system.

Page 33
Heat rejection If it is intended that the CHP should generate electricity without
a concurrent heat demand, then the heat produced will need to
be rejected to atmosphere. This requires a cooling tower or dry
cooler to be incorporated in the design of the system. Usually it
is not cost effective to run the CHP without utilising the heat, but
there may occasions where this is preferable to stopping the
generator for a brief period and then restarting. Thermal storage
or buffer tanks will also increase the flexibility of operation.
Island operation Most CHP plants for buildings can only operate while connected
to the electricity grid. If there is a power cut, then most stop
immediately. Although it is technically possible to design a CHP
system to run in island mode, it is complicated to comply with
safety standards and the engines may not be suitable for on-load
starting. Many buildings therefore have conventional standby
power generators in addition to CHP. In some of those systems,
the CHP may be restarted in support of the standby power
generator.
TRIGENERATION
Trigeneration can improve the function and economics of large CHP plants by extending the application of the
heat produced. In trigeneration, high temperature heat is used as the energy source for an absorption chiller
to produce useful cooling. Due to the low efficiencies of absorption chillers, the efficacy of the system will
need to be considered carefully, but if the heat used to drive the chillers would otherwise go to waste then
there will be benefits e.g. by enabling the system to generate in the summer months.
Large scale trigeneration is popular for data centres and airports where there is a high base load for cooling
and electricity. Also, large systems can usually operate in “island mode” if there is an interruption to power
from the electricity grid.
ABSORPTION AND ADSORPTION COOLING
A liquid absorption chiller operates using two fluids – a refrigerant and an absorbent. These fluids are
separated and re-combined in the absorption cycle. The refrigerant is absorbed into the absorbent releasing
heat. This solution is then pumped into a generator with a high operating pressure, where heat is added. This
causes the refrigerant to desorb from the absorbent and vaporise. The vapours flow to the condenser where
the heat is rejected, and the vapour is condensed to a high-pressure liquid. The liquid is then throttled through
an expansion valve to a lower pressure in the evaporator where it evaporates by absorbing heat. This
absorption of heat is used to provide the useful cooling effect.

Page 34
Figure 17 – A schematic of an absorption chiller.
(Source: BSRIA [4])
Adsorption chillers are like absorption chillers because the process is driven by heat rather than
mechanical/electrical input. They consist of a pressure vessel divided into four chambers – the evaporator, the
generator/receiver and the condenser. The generator and receiver are linked by valves that automatically
open depending on differential pressure. Water is used as the cooling medium with silica gel as the adsorbent.
At low pressures water vaporises at low temperatures. Silica gel can bond large amounts of water without loss,
reversibly, releasing the water again when heat is applied. See Figure 18.
Figure 18 – Schematic of an Adsorption Chiller.
(Source: GBU MB-H/BSRIA [4])

Page 35
The process works as follows:
1) Water is brought into the evaporator and evaporates; through this the cooling circuit cools
2) The evaporated water is then adsorbed in the receiver
3) The adsorbed water is de-absorbed with the supply of heat; the receiver turns into the generator
4) The de-absorbed water is condensed in the condenser
The collector and generator are alternately heated and cooled with the chiller. During the heating of one side,
the receiver is chilled by the cold-water flow from the condenser. This draws off the heat created through the
adsorption process. After the cycle time expires, the chiller switches over via a pneumatically actuated valve.
Adsorption chillers are more efficient than absorption chillers at low driving temperatures. The required input
temperature is between 60°C and 95°C, making them ideal for use with solar hot water collectors. They also
have few moving parts, meaning reduced maintenance costs, but are larger, heavier and more expensive than
absorption chillers.
The IEA has established a new Task 53 - New Generation Solar Cooling and Heating to support international
research into use of new refrigerants and processes to improve the efficiency of these systems.
WATCHPOINTS FOR TRIGENERATION
Is there sufficient cooling demand to
make trigeneration viable?
Trigeneration is most cost effective where there is a large cooling
demand (> 1 MWth cooling). The potential loads and
optimisation of the system over at least a year need to be
carefully modelled at the design stage to ensure that the system
will be economically viable.
Backup systems A successful trigeneration system will cover a large proportion of
the total heating, cooling and electrical loads. The implications
of maintenance downtime or system failure and the consequent
increased electrical demand from the grid must be carefully
considered.

Page 36
SUMMARY OF PART 1
There are numerous options for the sustainable heating and cooling of buildings. The advantages, limitations, environmental benefits and cost factors of the key low
carbon technologies are summarised below.
Technology Advantages Limitations Environmental Benefits Costs
Solar passive
design
Operating costs (heating, cooling
and lighting) are significantly
reduced.
Higher levels of controlled natural
daylight improve occupant
comfort.
No mechanical parts. Low
maintenance and long life.
Requires good orientation of
the building to maximize the
benefits.
It is difficult change the passive
solar design of existing
buildings apart from shading
and glazing.
Minimisation of energy consumption
and carbon emissions for heating
and cooling.
If designed to Passivhaus standards,
the overall energy consumption
should be < 120 kWh/m²/year.
More work needs to be put into the
design stage, but the reduction in
heating and cooling loads should
reduce the capital cost of heating
and cooling equipment.
Atria Few moving parts. Reduced
heating and cooling costs.
Increased space and comfort for
occupants.
It is not always possible to
retrofit.
Reduced energy consumption and
carbon emissions for heating and
cooling.
Glass is heavy and expensive but
avoids the rain-noise and fire safety
issues associated with lightweight
roofing.
Roofing over a space may increase
the official occupied area of the
building leading to higher taxes.
Occasional window cleaning may be
required.

Page 37
Passive thermal
storage
Produces more stable internal
temperatures and a more
comfortable environment.
PCM based products can be
retrofitted. No maintenance
requirements.
carbon emissions for cooling.
Monitoring of some projects using
PCM has shown up to 55% reduction
in CO2 emissions [11]. Another
example states a saving of over 100
tons of CO2 per year [12].
Vegetable based PCMs are fully
biodegradable.
PCM powder or granules costs
around €10 per kg.
A study of an office in Germany using
PCM gypsum plaster yielded a
€25,000 annual cost saving
compared to concrete core
activation [12].
The payback period based on energy
savings can be less than 5 years.
Earth tubes and
labyrinths
Pre-cools ventilation air in summer
and pre-heats ventilation air in
winter.
Reduces the need for mechanical
cooling equipment.
Low maintenance requirements.
Only feasible for new build
and/or where sufficient space is
available.
The area over the tubes can be
landscaped or used for parking
but should not be built over.
carbon emissions.
There are several systems based on
concrete or plastic tubes, but the
capital cost is dominated by the
excavation works required. This
depends on the site and stage of
construction.
Ventilation through ground tubes
increases fan energy consumption,
but the effective coefficient of
performance (cooling effect/fan
power) should be between 10 and
20.

Page 38
Solar thermal Simple and robust technology.
Evacuated tubes can provide
higher temperatures than flat-
plate collectors.
Many products and installers.
Yield decreases in winter,
particularly in more northern
climates, leading to potential
supply/demand mismatch.
There is no benefit in installing
a system that produces more
heat than you can use.
carbon emissions for heating. A 4m²
collector could produce annual
energy savings of approximately
2,000 kWh [13] .
A typical 4m² to 6m
2
solar hot water
installation for a house costs 2,000€
to 3,000€ in materials but the price
per unit area decreases for larger
systems [13]. Installation costs
depend on the location and type of
building and roof.
Solar cooling Can be used to utilise the hot
water produced by solar systems
during the summer when they are
at their most efficient.
Peak building cooling load occurs
at the same time as peak solar
thermal energy production.
Operation of the absorption
chiller may need to be boosted
by gas or oil consumption
during warm but cloudy
weather.
carbon emissions for cooling
Solar cooling is still developing so
prices and paybacks are uncertain. It
is best evaluated as solar assisted
absorption cooling, in which case the
investment decision would be based
on the marginal cost of the collector
and an estimate of useful heat at the
temperature required by the chiller.
Transpired solar
collectors
Efficient capture of diffuse solar
radiation to heat ventilation air.
Durable and low maintenance.
Best for buildings with a low
glazing ratio on south facing
walls.
carbon emissions for heating.
Transpired solar collectors are
comparable in cost to conventional
steel cladding solutions. The
installed cost is 110€ to 190€ per m
2
.
This includes the cost of the fan
system and controls.

Page 39
Wind to heat Suitable for isolated communities
that cannot use, export or store all
the electricity that is generated.
Storing heat is less expensive than
storing electricity.
Limited demand for heat
(mainly hot water) during the
summer months.
A well-sited 6kW turbine can
generate around 10000kWh per
year. This would save over 5 tonnes
of CO2.
Small wind turbines (6-12kW) cost
from 2,000€/kW installed. Grid
connected inverters (not required for
heating only) cost from 1,000€ to
2,000€. [13]
Biomass Produces high grade heat from
renewable combustion resources.
Can produce renewable heat
consistently all year round.
Fully scalable from single houses
to power stations.
Fuel supply can be a problem in
some areas. Installation may
also be restricted city areas to
avoid particulate air pollution.
Biofuels have a lower energy
density than traditional fossil
fuels volume. Fuel storage and
handling can be a significant
part of the costs.
Work most efficiently at peak
output.
Biomass is renewable but don’t
forget non-renewable inputs to
agriculture and transport.
Small biomass boiler cost from 500€
to 1,000€ per kW installed including
fuel storage. [15]
Fuel cost savings (for commercially
supplied fuels) can be up to 60%
relative to oil [15] but this is highly
dependent on the location and
supply chain.

Page 40
Heat Pumps
(see also
Application Note
“Heat Pumps for
Larger Buildings”)
Heat from heat pumps is
considered as partly renewable.
Heat pumps can utilise
environmental heat sources or
recover waste heat.
Reversible heat pumps can be
used for both heating and cooling.
Heating & cooling & UTES
The coefficient of performance
(CoP) of all heat pumps reduces
as the output temperature
increases. Heat pumps using
conventional refrigerants are
limited to around 55°C.
The CoP of air source heat
pumps reduces as the outdoor
temperature decreases.
Consequently, a supplementary
heat source may be required
during cold weather.
There are different installation
constraints on air and ground
source heat pumps that need to
be considered.
carbon emissions for heating and
cooling.
Ground source heat pumps cost from
800€ to 1,200€ per kW (installed)
[17]. Air source heat pumps are
approximately half the cost on a
comparable ground source system
when installed.
However, the air source system will
have a much shorter life (10-12
years) than the ground source
system (15-20 years for the heat
pump and >50+ years for the ground
heat exchanger) so this should be
considered in any whole life costing
calculation.
CHP Generates both electricity and
useful heat.
A range of technologies available.
Can be set up to run as backup
power supply in the event of a
power failure.
Fuel cells are quiet and have no
moving parts.
Requires constant loads to
achieve optimum performance.
Cannot generate electricity
without generating heat.
Small scale CHP (< 1 MWe) costs
1,000€ to 3,000€ per kWe installed
[13].
Fuel cell CHP is not yet cost effective
for normal building applications, but
prices are expected to come down in
the future.

Page 41
Tri-generation Generates electricity as well as
useful heating and cooling energy.
Absorption chillers are quiet,
vibration free and have low
maintenance costs.
Absorption chillers are
relatively expensive and most
suitable for medium to large
scale cooling applications (>200
kWth cooling).
Reduced primary energy
consumption and carbon emissions
for heating and cooling.
Absorption chillers cost from
70,000€ for 400kW unit to 180,000€
for a 2,000kW unit. This does not
include the cooling towers or
installation.
One US supplier of packaged
trigeneration solutions suggests a
1 MWe micro-turbine trigeneration
plant including an 875kWth
absorption chiller would cost around
$2.8 million.

Page 42
PART 2 – IMPROVING EXISTING SYSTEMS
Many of the technologies to improve the sustainability of heating and cooling listed in Part 1 are most cost
effective when included in new buildings, but they can also be viable to retrofit to existing buildings. This is
important as only a small proportion of the existing building stock is replaced each year and we cannot afford
to wait for new buildings alone to solve the problem of carbon emissions.
Even where major investment is not possible, there may be many low-cost opportunities to improve the
sustainability of existing systems and buildings.
CONTROLS
Poor control of heating and cooling systems leads to wasted energy and uncomfortable occupants. It is the
first area that should be reviewed in any system where savings are sought. The UK’s Carbon Trust claims that it
is possible to save up to 30% of heating fuel consumption by simple improvements to controls [10].
Temperature set-points and time clock settings (if present) should routinely be reviewed and validated to
ensure that the building is not unnecessarily heated or cooled. Optimisation of existing control systems is
covered in more detail in Energy efficiency self-assessment in buildings [11] but there are several possibilities
for extending the functionality of a basic heating and cooling control system.
BUILDING MANAGEMENT SYSTEM
A building management system (BMS) is more than just a control system. A BMS can be thought of as a brain
of a building, taking inputs from sensors and then controlling installed equipment. The BMS may also be able
to log (record) sensor data, control outputs, alarms and metered energy usage for future analysis. The caveat
is that it can only record what it is connected to. If the existing energy meters (electricity and gas) are not yet
connected to the BMS, it is well worth doing so to enable automated data collection. Where additional sensors
or new metering connections are needed, it is increasingly cost effective to implement these using wireless
technologies to simplify installation and minimise cabling costs. Monitoring energy consumption has been
proven as an effective way to highlight waste and reduce consumption.
The BMS is provided with an interface (usually web-based) that allows the operator to alter control
parameters, set up logs and retrieve data. Unfortunately, this may not allow the operator to change or
enhance the programme that was set up by the installer or add new hardware. Changes to the programme or
hardware will usually require another visit from the installer, so the labour cost needs to be considered.
OPTIMUM START/STOP
An optimum start/stop is an advanced form of time control for a heating system. It can be implemented
through a building management system, as a stand-alone controller or within a programmable time clock. The
optimum start algorithm learns how quickly the building reaches the desired temperature under various
internal and external temperature conditions and uses this knowledge to switch on the heating system so that
it just reaches the desired space temperature at the start of occupancy. Without optimum start, the heat or
cooling system will be activated at a fixed time each day, and the building may reach the desired temperature
long before it occupied. This wastes energy. At the end of the day, optimum stop can switch off the heating or
cooling before the end of occupancy but without allowing the temperature to become uncomfortable.
Optimum start/stop can be applied to individual zones and linked to the main heating and cooling plant e.g.
boiler, chillers, heat pumps, circulation pumps and ventilation fans.

Page 43
OCCUPANCY SENSORS
A big waste of energy in many buildings is caused by the unnecessary heating and/or cooling of unoccupied
spaces. Sensors allow the heating or cooling of unoccupied zones to be reduced or switched off. The available
sensors include passive Infra-red (PIR) sensors (also used lighting controls and burglar alarms), acoustic
detectors and key-cards (as in hotel rooms).
Systems controlled by occupancy sensors have two modes. In occupied mode, the space is heated or cooled to
the normal operating temperatures. In unoccupied mode, sensed by a period of inactivity, the heating or
cooling system is controlled to a set-back temperature or turns off completely and any mechanical ventilation
is reduced. Some systems have window sensors which simply turn everything off when a window is opened.
CARBON DIOXIDE SENSORS
All buildings require ventilation to provide fresh air for the occupants and remove the old stale air and indoor
pollutants. However, excessive ventilation will lead to higher costs for heating or cooling this replacement air,
and in the case of mechanical systems, higher costs for operating the fans.
People exhale carbon dioxide so the levels in buildings are directly related to occupancy. Designers usually
calculate a ventilation rate for maximum occupancy of each space and therefore over-ventilate most of the
building for most of the time. Carbon dioxide (CO2) sensors allow ventilation to be controlled at a lower rate
when the space is not fully occupied, thereby reducing heating/cooling costs and fan power.
Note that the background level of CO2 in the atmosphere is already over 400 ppm in city areas. Ventilation
rates are boosted when the CO2 concentration in the occupied space reaches 1200 ppm. Higher levels of CO2
could cause drowsiness and loss of concentration. CO2 sensors are often installed in schools to keep the pupils
alert by increasing ventilation to occupied classrooms and reducing ventilation to unoccupied class rooms.
Bear in mind that CO2 is not the only air pollutant in the indoor environment. In some situations, it may be
appropriate to use other air quality parameters to control the ventilation system. For example, humidity or
indoor air quality (IAQ) sensors are responsive to a wide range of pollutants including volatile organic carbons
(VOC) that may be released into the air during work activity.
WATCHPOINTS FOR SENSORS AND CONTROLS
Control strategy The control strategy should be properly designed so that
different control loops do not conflict. It must be fully
documented.
Sensor location The correct placement of sensors is important to the correct
operation of the associated controls. Environmental sensors are
often located where it is convenient to the installer rather than
where they can sense the true condition of the space. Wireless
sensors are easier than hard-wires sensors to locate in the ideal
position and much less expensive for retrofit.

Page 44
Commissioning Commissioning is vital to the efficient operation of all building
systems. The sensors and controls should be designed to be
easily commissioned. Adequate time for commissioning must be
allowed in the construction programme.
If as installed commissioning differs in any way from “as
designed” this must be explained and formally recorded.
Calibration of sensors Sensors must be checked and calibrated before use to ensure
an effective control system and rechecked on a regular basis.
Some sensors (CO2 and IAQ) are subject to drift and may have a
relative short life.
User controls Occupants should be aware of and understand the function of
the sensors and controls.
Manual override of controls should be limited in effect and
duration e.g. a button (electronic or physical) to prolong the
operation of heating or cooling system should only provide a
one-time effect, after which the system reverts to the normal
schedule.
Consideration should be given to the way a space is used to
avoid unintended consequences. e.g.: movement detectors
should not be used in classrooms where the occupants may be
sitting still for long periods as this will cause the sensor to think
the room empty.
DISTRIBUTION OF HEATING AND COOLING
BENEFITS OF LOW FLOW TEMPERATURES
Low temperature heating distribution has several benefits over higher temperature heating distribution:
1. Improved efficiency of the primary heating equipment such as condensing boilers, heat pumps and
chillers.
2. Reduced distribution losses.
3. A wider range of renewable energy sources can be utilised, especially Heat Pumps.
A condensing boiler will be much more efficient when operating at flow temperatures of less than 50°C as it
benefits from the latent heat of condensation of moisture in the flue gases. A heat pump will benefit through
the higher CoP at low flow temperatures and low T.
Distribution losses can be minimised the thorough competent insulation of all components, but for a given
system losses are proportional to the temperature difference between the fluid in the pipe and the ambient
air.
These benefits are only possible if the heating system uses low temperature heat emitters.

Page 45
HEAT EMITTERS FOR LOW TEMPERATURE HEATING DISTRIBUTION
The flow temperature required for underfloor heating (35°C - 45°C) is much lower than for a traditional
radiator (> 50°C). The exposed floor surface is kept below 29°C [12] for safety and to provide a comfortable
temperature profile in the space.
Underfloor heating used to be difficult to retrofit to existing buildings (except as part of a major
refurbishment) because of the change in floor height. However, there is now a wide choice of low profile
underfloor heating systems for retrofit. These are laid on the existing floor and increase the floor height by less
than 50 mm. Other surface heating systems for walls and ceilings are gaining popularity.
If underfloor heating is not feasible then low temperature radiators can be considered. These have a larger
surface area, including fins, to operate with surface temperatures up to 45 °C compared to up to 70°C for
traditional radiators. Traditional steel panel radiators can be used at lower heating water temperature, but the
radiator may need to be oversized by a factor of three to produce the same output [13].
If there is insufficient wall space for low temperature radiators then a fan convector radiator may be
considered. In a fan convector, a small fan drives air through fins on the back of the radiator panel or through a
matrix of finned tubes similar to a fan coil. This forced convection boosts the output of the panel or coil so
that the package can provide a high output from a small heating unit operating at low flow temperature.
WATCHPOINTS FOR DISTRIBUTION OF HEATING AND COOLING
Can the system emit enough heat to meet
the heating demand in all areas of the
system?
Heat emission from underfloor systems is limited by the
unobstructed floor area and maximum allowable surface
temperature (29°C for general areas, 33°C for shower rooms).
50 - 100 W/m
2
is typical. The effect of additional surface
coverings such as carpets and rugs must be considered at the
design stage.
Does the space need fast heating
response?
Low temperature heat emitters may have a longer response
time than traditional radiators and may be unsuitable for areas
that experience rapid fluctuations in air temperature.
Is cooling required? Underfloor heating systems can also be used for underfloor
cooling, particularly when coupled to reversible heat pumps.
Free cooling may also be possible for non-reversible heat
pumps. The flow temperature must be set or controlled to
avoid the possibility of condensation in the floor structure.
Distribution pipe may also need to be lagged to prevent
condensation.
THERMAL STORAGE
The incorporation of thermal storage in heating and cooling systems has several benefits. Heat stores can:
 Absorb the output of primary heating and cooling equipment to avoid short cycling at periods of low
load. This improves efficiency through the reduction of start-up and shut-down losses. Also, some
equipment (chillers, heat pumps, CHP, biomass boilers) have a restriction on the number of starts per
hour and/or a minimum run time per operating cycle.

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