Technology overview

Air conditioning
Maximising comfort, minimising energy consumption

enter
 Air conditioning 2

Preface

Menu

Reducing energy makes perfect business sense; it saves

money, enhances corporate reputation and helps everyone
in the fight against climate change.

The Carbon Trust provides simple, effective advice to help

businesses take action to reduce carbon emissions, and the
simplest way to do this is to use energy more efficiently.

This technology overview introduces the main energy

saving opportunities for lighting and demonstrates
how simple actions can save energy, cut costs, improve
conditions and increase profit margins.

help
 Air conditioning 3

Introduction
Around 40% of commercial floor space is expected to be air-conditioned
by 2020, compared with only 10% at the end of 1994.

Menu
The demand for air conditioning1 in UK buildings is investment in energy efficiency measures. This has Who is this publication for?
growing rapidly in response to more intensive building influenced the recent UK building regulations
This guide will help energy managers or facilities
use, increased demands for comfort by occupants, amendments which deal specifically with ventilation
managers to:
business and market pressures and the expectation and the conservation of fuel and power but provide
of a warmer climate. Around 40% of commercial floor challenging targets to meet in terms of overall energy • Understand the process that should be undertaken
space is expected to be air-conditioned by 2020, performance of new and refurbished buildings. in the early stages of design when it may be possible
compared with only 10% at the end of 1994. to minimise or avoid the need for air conditioning
Meeting the requirements of the new regulations is just
This continual growth in the use of air conditioning, one reason to examine the use of air conditioning. • Review the best choice of air conditioning systems
along with a corresponding increase in electricity Keeping down energy costs, ensuring adequate comfort and highlight opportunities for energy savings.
consumption and power station carbon dioxide and considering the carbon footprint of a business are all
emissions is at odds with the Government’s energy factors to take into account.
goals. These include reducing emissions of carbon Did you know?
Although demand for air conditioning is high, there are
dioxide the main contributor to global warming – by
increasing opportunities to exploit ‘free cooling’ and for Comfort cooling is very expensive. In the UK,
some 60% by 2050. Energy efficiency measures are
adopting simpler and more cost-effective technology. there are relatively few days per year where the
expected to deliver half of the necessary improvements.
Building operators and those who are involved in temperature is very high (over 28ºC). Using
Furthermore, a new EU directive, known as the Energy purchasing should be aware of these opportunities and comfort cooling for just this short time can cost
Performance of Buildings Directive (EPBD), came into understand the options available to them before as much as a whole year’s heating.
force in January 2006 which is designed to increase investing in air conditioning systems.

help The true definition of an ‘air conditioning system’ is one which has the ability to control temperature, humidity and air quality, yet the term is often applied
1

to systems which only provide cooling. These cool air systems are more correctly referred to as ‘comfort cooling’. This guide will use the general term ‘air
conditioning’ to refer to both types of system.
 Air conditioning 4

Energy consumption
The energy consumed by air conditioning systems in commercial buildings is
expected to double from current levels by 2020. In a typical office, air conditioning
can account for over 30% of annual electricity consumption.
Menu
Recent years have seen a shift in energy consumption It is imperative that designs for future buildings and Figure 1 Air conditioning energy use by UK sector
patterns in the UK. In the past, energy consumption major refurbishments account for a changing climate
was significantly greater in winter due to heating to ensure that buildings can provide comfortable and
demand. However, the summer demand has been healthy internal environments over their lifetime, whilst
growing dramatically which is primarily due to the minimising energy use and greenhouse gas emissions.
increased use of air conditioning. As air conditioning
uses electricity, which is responsible for higher CO2
emissions than the equivalent amount of fossil fuel Did you know?
energy, its impact on the carbon footprint of a building
The energy costs and associated CO2 emissions
can be significant.
of a typical air-conditioned building are 30%
Changes in climate will affect energy use in buildings. higher than a naturally ventilated building. It is
Average annual temperatures in the UK are predicted to also more likely to have increased capital and
increase by a few degrees over this century particularly maintenance costs.
Commercial office 22%
in the south-east of England. Naturally ventilated Communication and transport 4%
buildings are likely to overheat more frequently in Further and higher education <1%
extreme conditions and air conditioning systems may Government estate 1%
fail more regularly. It is probable that full air conditioning Hospitality 1%
Leisure 6%
will be demanded in more buildings to control summer
Other government <2%
temperatures and humidity, leading to an increase in Other service sector 2%
energy usage. Retail 41%
Warehouses 7%

help
 Air conditioning 5

Air conditioning energy use

Building performance Did you know?
There are a number of important factors that determine
the energy use of an air conditioning system: The performance of buildings with full air Energy efficient buildings need not cost any
conditioning depends critically on three things: more to build than a conventional building. In
• The design, layout and operation of the building
fact, building fabric and services design can be
– this affects how the external environment impacts 1. Good design
integrated effectively to even reduce capital
on internal temperatures and humidity 2. Suitable commissioning
costs. For example, the cost of adding external
3. Effective maintenance and management.
• The required indoor temperature and air quality shading can be offset by minimising or avoiding
Menu – cooler temperatures, greater precision and more Unfortunately, this is not often achieved in air conditioning plant.
refined air quality all consume more energy practice. Many buildings with complex service
systems are awkward to operate and they
• The heat generated internally by lighting, equipment
underperform in terms of occupant satisfaction
and people – all of these have an impact on how
and operating costs. Some of the best
much cooling a building requires
performing buildings are those with simpler,
• The design and efficiency of the air conditioning passive or free cooling systems. Such buildings
plant – this provides cooling and moisture control are also easier to operate and maintain,
exactly where it is needed in the building which in turn reduces costs and breakdowns.

• The operating times of the air conditioning equipment

and ability of the controls – these limit operation
to exactly when it is needed

• The amount of fresh air provided per person.

Reducing the air conditioning load allows alternative

ways of cooling to be considered that are simpler
and less energy intensive. This can reduce energy
consumption whilst providing cost savings and
maintaining a healthy and comfortable environment
for staff.

help
 Air conditioning 6

Technology overview
The components of an air conditioning system, as well as the way they are set up and controlled,
have a big impact on energy use and the levels of comfort provided for occupants. By examining
the existing system, it should be possible to highlight areas for potential energy saving opportunities.
Menu

The primary mechanism central to all mechanical coil by a fan. This fan can either be next to the coil Figure 2 Components of an air conditioning unit
cooling systems is the refrigeration cycle, in which or at a more remote point of a ductwork system. Outside air
heat is moved from one place to another. Systems that Blower
The air that has passed over the coil then mixes with the Fan motor
include the refrigeration cycle may be called a ‘chiller’
air in the room, cooling it down and achieving the
or ‘refrigeration machine’. In smaller systems, it may Condenser
required temperature. The amount of cooling given to the
be called an ‘air conditioner’.
space can be varied by changing either the temperature
In essence, a refrigeration machine operates in the difference between the incoming air and the room, or by
same way as a domestic refrigerator, where heat is changing the volume of air entering the room, or both.
absorbed from inside the cabinet and rejected outside,
There are three generic types of air conditioning Cooled Condenser
but on a larger scale. This takes place either directly via room air discharge
system, each with many variations: air
an air-cooled pipe coil or via an intermediate ‘condenser’
Filter
water circuit at a remote cooling tower (see Figure 3). • Centralised air systems, where all the heating
and cooling is carried out in a central plant room Warm Flow
The cold fluid can be either refrigerant or chilled water. room air restriction
and conveyed to the rooms by ductwork
Where chilled water is provided, pumps are needed to Compressor
move it around the building to where cooling takes place. • Partially centralised air/water systems, where Evaporator
centrally cooled or heated air is further heated
The cooling generated has to be transferred into the air
or cooled at entry to the rooms This diagram shows the major components of an air conditioning unit in
in the room where cooling is required. The heat transfer a packaged system. Most air conditioning systems have these components;
however, they will be arranged differently in every application.
often takes place in a ‘pipe coil’, which consists of rows • Local systems, where all operations are Packaged systems are discussed further on page 9.

of parallel pipes through which the cold fluid passes. performed locally.
Metal fins at right angles to the pipes aid the heat
Each of these is discussed in the following sections.
help transfer from the air, which is usually blown over the
 Air conditioning 7

Centralised air systems Types of centralised air systems Figure 3 A centralised air system
Cooling tower
These systems typically supply cooling from large Constant volume (CV) single zone systems are simple, Central air-handling plant

central chillers that generate chilled water. This water relatively low cost and easy to commission, Central
is then pumped around the building through pipes to but cannot provide adequate control for areas or ‘zones’ plant
wherever cooling is required. with different/simultaneous heating or cooling needs.
Several separate systems may be required to serve
Centralised systems are often based around a packaged
different zones, increasing capital costs and plant space.
air handling unit (AHU), which typically contains heating
and cooling coils, a humidifier, filter and fan to move the Variable air volume (VAV) systems address the Extract air
Menu Variable air
air. The incoming air is drawn into the AHU and passed problem of zones with different requirements by varying through volume Distribution
light fitting terminal unit
over the coils to heat or cool the air as required. This the quantity of air (and hence the amount of cooling) system,
ductwork
‘conditioned’ air is then supplied by ductwork to the supplied to each space.
Condensed water and
rooms within the building. The equipment is normally pipework
VAV systems can be particularly energy efficient as Hot water
located in central plant rooms but may be roof-mounted
they are able to operate the main supply and extract Terminal Fan
(see Figure 3). unit with coil
fans at reduced speeds. This can yield significant reheat unit
The chillers (the refrigeration equipment) provide chilled energy savings from reduced fan power and a reduction
Chilled water
water for the cooling coil(s) within the AHU. The chiller in the costs associated with heating and cooling air.
may be water cooled (with a cooling tower) or cooled Central
VAV systems are primarily for buildings with a year- plant
by outside air. Hot water for the heating coils is provided
round cooling demand. They can be smaller than
by boilers, which may be located in another plant room.
the equivalent multi-zone system because their design
Heating and cooling can be distributed to the occupied Chiller plant Boiler
does not provide full cooling simultaneously in all zones.
spaces via air ducts, or through pipes that provide
This complexity makes them an expensive solution
heated and cooled water to terminal units in each room.
which requires careful commissioning.
When outside air is cooler than the internal temperature,
Displacement ventilation systems provide cool Further information
fresh air can be introduced and chilling is not required. In
air from a central plant and supply it at low velocity to
the UK, temperatures are often below 19ºC, so exploit For more information, order
ventilation terminals. The supply temperature is slightly
this ‘free cooling’ to minimise the need for refrigeration. Heating, ventilation and air conditioning
cooler than the room temperature and so the air rises
(CTV003) from the Carbon Trust
to ceiling level by natural convection as it picks up heat
from occupants and equipment. The warm air is then
removed. Displacement systems are energy efficient
and give good indoor air quality and thermal comfort.
help
 Air conditioning 8

Partially centralised systems Types of partially centralised air systems Chilled ceilings and beams consist of ceiling-mounted
panels of pipes that are cooled by chilled water. They
A central AHU provides the common factor in partially Some systems give extra control to existing centralised
transfer their cooling effect to the space by radiation or
centralised systems although further conditioning in air systems. The air from the central supply is further
natural convection without using fans to encourage air
the room may be locally controlled. These systems heated or cooled to room requirements by additional
movement, hence these systems are referred to as
can supply a high level of localised control making them heating or cooling coils (known as batteries). In constant
‘static cooling systems’. Since they use water as the
flexible to individual user’s needs. If controlled correctly, volume systems, this increases controllability and the
main medium for the distribution of cooling around the
this results in energy savings by ensuring that heating ductwork can be configured to serve rooms with quite
building, they make considerable savings in fan energy.
and cooling only operate where required. different requirements. Heating and cooling coils can be
Menu located either within ceiling voids (partially centralised Room-based reversible heat pumps are individual
system) or in the plant room (fully centralised system). units which can be floor standing or concealed in the
Figure 4 A partially centralised air system ceiling void, linked together by a piped water circuit
Four-pipe fan-coil units typically comprise a fan,
that runs around the building. Each unit operates
Cooling tower heating coil, cooling coil and air filter, all housed in a
independently and is able to heat or cool the air in the
metal casing. Fan-coil systems can satisfy the individual
Central-mounted
Central immediate area. This is achieved by means of a small
unitary heat pump plant heating and cooling requirements of multi-zone
heat pump in the unit, which takes heat from the
buildings and enable good building flexibility. They are
water circuit and uses it to heat the room. To cool
only partially centralised since fresh air is usually ducted
the room, the heat pump works in reverse to remove
to each unit from central plant along with piped heating
heat from the space and transfer it to the water circuit.
Common
and chilled water.
Distribution This type of system is often referred to by the trade
water circuit
system, Fan coils provide good environmental control and air name ‘Versatemp’.
ductwork and movement yet require a lot of maintenance, as they are
pipework The key benefit of this system is its ability to save
in essence, mini air handling units. Providing only
energy by transferring heat from an area where
minimum fresh air from the central AHU means that a
it is not needed to an area where it is, via the piped
Wall-mounted much lower volume of air is ducted around the building
heat pump water circuit. It is most beneficial in zones which have
compared to the equivalent multi-zone system.
different heating and cooling periods to each other.

Central
plant

Heat Supplementary
exchanger heating (boiler)

help
 Air conditioning 9

Local systems Types of local systems

Did you know?
Local systems are not linked to any centralised plant Packaged and split systems provide a convenient
and only provide cooling in the immediate space way to air condition small buildings or specific areas All air conditioning systems require specialist
where they are placed. They are commonly used within a building. Typical applications include shops, service engineers for repairs and maintenance.
to serve a single zone or small proportion of a building restaurants and office areas. Packaged air conditioners They must be installed to a high standard to
(see diagram below). They may or may not provide have all their components in a single box, which can ensure good performance and reliability, and
ventilation depending on their level of sophistication. be installed, ready-tested. ‘Split systems’ separate the simple occupant controls should be provided to
Local systems are often used to provide ‘comfort room units, with their fan and heating/cooling coils, avoid wasting energy and money.
Menu cooling’ and can be useful where some areas require from the compressor and condensing units. The latter’s
cooling for a different period from the rest of the noisy components can then be placed outside the
building. For example, using them can allow the building. The room units can be mounted in the wall,
main centralised system to be turned off outside in an enclosure, or in the ceiling.
working hours.
Variable refrigerant flow systems (VRF) are
essentially sophisticated split systems. The difference
is their ability to provide heating or cooling on an
Figure 5 A localised system
individual basis. This is particularly useful in applications
Compressor/ such as office blocks, hotels and large retail stores etc,
condensing unit
which may need cooling in some areas and heating
Split system in others.

Refrigerant circuit VRF systems can be very flexible and energy efficient
when used as a heat pump, that is, for heating and
Room unit
cooling. Where air conditioning is necessary, using
VRF for heating and cooling incurs a marginal extra
cost but could save the cost of a separate boiler plant.

Packaged
air conditioner

help
 Air conditioning 10

Low-energy cooling
Once established, low-energy solutions can keep a building cool for
no additional capital outlay.

Menu
There are a number of strategies and technologies that Generally, an exposed ceiling slab is required to provide Stack ventilation and wind scoops can also be utilised
have the potential to reduce energy consumption and sufficient storage of cooling energy. The movement of – these are more sophisticated natural ventilation
costs associated with the use of air conditioning. Many cool night air may be natural or fan-assisted. This free techniques, often integrated with a simple yet effective
of these are tried and tested, but application will depend cooling of the building reduces energy consumption structural design. They generally have to be designed
on the individual circumstances presented in a building, otherwise used by mechanical cooling and ventilation, into new buildings but are often well worth the effort
as well as the requirements of occupants. leading to cost savings. in terms of cost savings and comfort for occupants.
See Figure 6 (below) for an illustration on how this
Reduce unnecessary heat gains Natural ventilation and free cooling can work.

Before installing cooling equipment, always identify As simple as it sounds, natural ventilation and free
where the excess heat is coming from. Sunlight, cooling relies on natural airflow between openings
Figure 6 Detail of stack-induced crossflow ventilation
equipment, lighting and refrigeration are often main on opposite sides of a room or building – or rising
causes. As a general rule, the more energy efficient warm air being replaced with cooler air sucked in
equipment is, the less heat it produces. So installing through windows or vents. This technique relies on
low-energy lighting and keeping equipment operating moving air through a building under the natural forces
at peak efficiency reduces cooling costs. caused by outside wind pressure and the buoyancy
effects of temperature differences. The most
Night cooling effective air paths are simple and generous.

Night cooling is an established technique where cool It may be possible to use windows and doors to provide
night air is passed through the building to remove heat good levels of natural ventilation, allowing mechanical
that has accumulated during the day. When the building ventilation to be switched off or turned down to save
fabric has cooled, it will absorb more heat, meaning money. When opening vents, doors and windows,
lower internal temperatures the following day. always consider security implications.
help
 Air conditioning 11

Mixed mode Free cooling in tower-based systems Consider using local renewable
resources
Some buildings use what is known as a ‘mixed mode’ There are several approaches that are based on cooling
system; a combination of both natural and mechanical towers. These systems can shut the chillers down and Some renewable energy options are outlined below.
systems. Natural ventilation and cooling are used where allow the towers to supply chilled water providing free The suitability of each of these is heavily reliant on
possible, with mechanical systems being used only cooling during the cooler months of the year. The the physical conditions of the proposed site.
when absolutely necessary. There are various popularity of systems like chilled beams/ceilings that
Ground water cooling essentially consists of two
advantages of such a system: use higher chilled water temperatures has significantly
wells drilled into the ground, where water is pumped
increased the period when free cooling is available each
• The building becomes more adaptable to a wide from one well to the other via a heat exchanger to
Menu year. Often a bespoke solution is called for which can
range of requirements provide useful cooling. Only certain sites have suitable
lead to increased design costs and higher operational
ground water sources at convenient depths so
• The occupants have more control over their risks than standard systems. See the box below for
careful investigation is required.
environment safety considerations with bespoke systems.

• Businesses can cut down on energy spend and

carbon emissions. Figure 7 Ground water cooling
Top tip
There are several variations/combinations of mixed
When installing air conditioning systems,
mode systems. Ultimately, they offer the security of
make sure you ask about design and operational
improved environmental conditions by using mechanical
risk, particularly regarding Legionnaires’
ventilation/cooling when needed without having to Supply air or water
disease. For most systems, this will not be an
operate fans and chillers throughout the year. to the building –
issue but always pay particular attention when
commissioning a bespoke solution and ensure
cooled by ground water
Chillers with free cooling coils Pumped Discharge
the system is regularly maintained. If in doubt,
There are now chillers available which incorporate a consult an expert. water
‘free cooling’ coil. These operate when the outside air
temperature drops below the temperature of the water
Heat exchanger
returning from the system. At this point, the compressor
in the chiller stops and free cooling begins. With the
changeable UK weather, particularly in cooler regions,
this option could have significant payback.

Well (low temperature water) Soakaway

help
 Air conditioning 12

Ground coupling using air utilises the natural storage Figure 8 Ground source heat pumps
of the earth to cool air passed through underground
pipes. The cooled air can be used directly, or for
buildings that demand strict internal conditions, it can
be used to pre-cool the air in a conventional system.
Heat transfer depends upon soil type, moisture content
and ground water movement and only some sites
are suitable.

Menu Ground source heat pumps use the ground for cooling Heat pump
or heating via a reversible heat pump. They consist of
a continuous loop of pipe filled with a water/antifreeze
mix, buried in the ground and connected to the heat
pump. In winter, the same system can be operated to
transfer heat from the ground to the building, typically
via a low temperature heating system such as
underfloor heating. This system is best suited to a site
with appropriate space and soil type for digging a trench
or borehole to accommodate the loop of pipe.

Did you know?

The energy consumed by cooling systems can Water flow
be reduced significantly by using chilled water
or refrigerant instead of air as the medium to
transport cooling around the building.

Depth
150-200ft

Water loop system

help
 Air conditioning 13

Delivery considerations
The way that cooling is delivered to occupied spaces
can have a significant impact on the effectiveness of
Myth Myth
the various low-energy cooling options. Systems that
can operate with higher chilled water temperatures
Leaving air conditioning on Turning air conditioning
(for example, chilled beams) or supply air (for example, overnight reduces energy costs thermostats as low as they can go
displacement ventilation systems) are far more likely
to make low-energy cooling solutions viable.
as the system stays at the required cools the building more quickly.
Menu
Many of the ‘passive’ and ‘free cooling’ technologies
temperature. Reality
which offer reductions in refrigeration load can cause an The temperature drops at the same rate but then
Reality
increase in fan or pump power requirements. A balance overshoots, using more energy than necessary and
The result is much higher energy consumption
must be struck between this additional fan or pump making it uncomfortable for occupants. If controls
than necessary.
power and reduced refrigeration loads. are not coordinated, the temperature could even go
low enough for the heating system to be switched
Remedy
on. Both systems then operate at the same time.
An office building only needs a fraction of overnight
Further information
energy to reach adequate temperatures for the start
Remedy
For more information about low-energy cooling of the day. Air conditioning may not be needed at all
Set thermostats correctly and educate staff to dispel
options contact the Carbon Trust. at this time if ‘night cooling’ is used.
this myth. As a last resort, protect thermostats to
prevent tampering, where possible.

Did you know?

The energy consumed by cooling systems can
be reduced significantly by using chilled water
or refrigerant instead of air as the medium to
transport cooling around the building.

help
 Air conditioning 14

Existing buildings
A building working at optimum performance will Review building operation Are there increasing complaints from building
provide a safe, comfortable working environment whilst occupants about being too hot, cold, draughty?
Ask the following questions to troubleshoot problems
delivering maximum productivity. However, even when A significant number of grievances should trigger an
in an air conditioning system. These may highlight a
Menu new, few buildings achieve this level of performance. in-depth investigation of the system to fully understand
need to review building controls and services, or
This is often due to poorly specified systems that any problems. The solution may be a combination
possible replacement of plant and equipment.
have not been set up to work correctly. of the points described on this page.

The key to understanding an existing building is to: Has energy consumption been increasing?
Has building function/layout changed since
This may be a sign that building and air conditioning
• Appreciate how the building has been designed original design?
plant are not operating as efficiently as originally
to work in its environment This could mean re-setting control zones, time
intended, or that air conditioning components and
and temperature settings and air flows. For example,
• Identify the current status of the building and assess control settings need to be reviewed.
conversion of a standard open plan office into a 24-hour
its performance
call centre might double occupation levels and require
Are maintenance costs increasing and is plant
• Ensure that the building and its systems are well an increase in air conditioning operating time.
and equipment regularly failing through wear?
documented in a language and format that is easy
This can be identified from maintenance log books
for managers to understand
and records. Ensure that a comprehensive preventative
Energy surveys
• Identify and address problem areas. maintenance plan is in operation and consider investing
in new, more efficient plant. Your company may qualify for a free energy
Optimising internal conditions in the work place can
efficiency survey from one of the Carbon
result in improvements in productivity and other
Was the system set up properly in the first place? Trust’s expert consultants. Contact the
substantial returns. For example, hospitals may
This may only be discovered as a result of other Carbon Trust www.carbontrust.co.uk/
experience improved patient recovery and hotels
operational problems such as overheating or overcooling. freesurvey for more details.
often report increases in guest satisfaction.
Compare settings with the original design figures
specified in the operating and maintenance manuals.

help
 Air conditioning 15

Are controls fine-tuned to suit current building Problems should be investigated and resolved promptly. Adapt carefully
operation? In all of the above areas, commissioning activities such
Many interior environments are designed to be easily
Controls are often set only once at installation before as resetting controls and/or re-balancing air flows could
adaptable for changing business needs, occupant
occupancy or work habits have been identified. The make a significant difference to building performance
requirements or a different use of the space. It is
result is a system that does not meet the current needs and reduced operational costs.
often during these changes that system controls and
of staff. To avoid this, walk around the unoccupied
operation go awry; for example, control zones and
building outside core business hours and check whether Conduct a building health check
times are incorrect for the new occupational hours
the air conditioning plant is in operation. Also examine
If necessary, ask a qualified technician to investigate in a reconfigured area of a building.
energy usage data from meter readings. This will help
Menu and provide a building health check. This will provide
identify if there is unnecessary energy consumption Moreover, building changes can introduce new
recommendations for:
which can then be easily resolved by resetting time structures that might interfere with efficient use of
controls to suit hours of occupation. • Restoring the optimal operation of building systems building services. For example, office partitions may
prevent good air distribution or natural cross-ventilation
• Saving energy
Are heat gains from internal equipment and cause temperature sensors to become separated
and lighting lower than expected in the • Improving comfort conditions from the zones they control.
original design?
• Achieving cost savings.
This can result in air conditioning running inefficiently
at low load. Compare current operation with the original Top tip
Keep a log book
design figures specified in the operating and
Building managers should continue to seek
maintenance (O&M) manuals. Review the arrangement Many existing buildings have either inadequate or
opportunities for improving existing buildings
for the chiller(s) and supplied air volumes and determine missing O&M manuals and commissioning records.
whilst ensuring that the installation of energy
if these can be revised. It is important that this information is readily available
saving technologies does not work against the
on-site or summarised in the form of a log book.
building’s original design. Always seek specialist
Has occupancy changed significantly since design? Preparation and use of a comprehensive but easily
help where required.
This can result in either over- or under-provision of fresh understood log book will help develop a better
air. Under-provision may lead to occupant complaints appreciation of the building and system design resulting
and over-provision will result in additional heating/ in improved building management. Ongoing use of
cooling costs. Compare operation with the original the log book will provide a means of recording building
design figures specified in the O&M manuals or in performance, enabling building occupiers to understand
the building logbook if available. The solution may and operate the building in an energy efficient manner.
be as simple as resetting the main air handling unit to
regulate the amount of fresh air entering the system.
help
 Air conditioning 16

Opportunities for energy saving

Simple actions on existing systems can save energy and costs.

Menu
Building fabric Basic control If possible, also ensure workspaces are shielded from
draughts and direct sunlight to help improve the comfort
Improve the building fabric Set appropriate internal temperatures
of the entire work area. These are no-cost solutions that
Well-maintained buildings with good insulation save on Most people feel comfortable in a temperature range save money and help maintain comfort.
heating and cooling costs. If there are any gaps in the of between 18–26ºC, provided the temperature is in line
fabric, heated or cooled air can escape which wastes with outdoor conditions. It is common sense that staff
energy and money. It therefore makes sense to improve and visitors will be dressed for the weather conditions, Did you know?
the building fabric prior to improving or replacing an so when it is hot outside, they will be wearing cooler
Energy efficiency measures such as turning
existing cooling system. In particular, gaps or holes in clothing. Make sure this is factored in when setting air
air conditioning equipment down or off can
walls, windows, doors and skylights should be repaired conditioning. It is recommended that the temperature
increase the lifespan of equipment and reduce
as soon as they become apparent. set point for cooling in, for example, an office is ideally
maintenance and replacement costs.
no more than 3ºC below the external temperature.
So, with an outside temperature of 27ºC, the cooling
Redirect heat from the sun
set point should be set at 24ºC.
Overheating due to high levels of glazing is a growing
Observe staff behaviour. If people are bringing in
problem in buildings. Consider fixed or moveable Further information
warmer clothing to wear whilst working, this may
external shading for windows, or replacing window
be a sign that the air conditioning is set too high. Set For more information on how to
panes with special heat-reflective glass to prevent heat
internal temperatures appropriately and encourage staff improve your building fabric, download
build-up. Alternatively, internal blinds can be angled to
to dress in a way that suits the setting. If uniforms are Building fabric (CTV014)
redirect useful light on to the ceiling whilst cutting out
provided, make sure they are suitable for their purpose,
much of the sun’s heat. This will allow more daylight
considering extreme temperatures if necessary.
into the space, whilst minimising glare.

help
 Air conditioning 17

Train staff to use controls Maintenance Keep it clean

Staff should receive guidance on recommended Maintain plant Filters in ventilation systems should be regularly
operating temperatures and on how to set heating checked to ensure they are not blocked. Blocked filters
Ensure cooling plant are regularly maintained to avoid
or cooling units correctly. ‘Louvres’ (movable slats to lead to reduced airflow and increased operating costs.
operating at reduced levels of efficiency. Check for
guide the cool or heated air) are a feature on most air Consider fitting gauges to indicate when replacement
refrigerant charge and leakage. Replace insulation
conditioning units and staff should be trained to operate of filters is required.
on refrigerant pipework as poor condition will affect
these to maintain a comfortable temperature. Display
the temperature of the refrigerant flowing through the
instructions on individual units and ensure that remote
system and thus consume more energy in maintaining Do spot checks
Menu controls have accessible and obvious storage spaces.
the required temperature. Pay specific attention
Provide instructions for systems that provide cooling Air conditioning plant may well be wasting energy for
to pipework located outside a building.
to separate function rooms or areas, such as meeting some time before it fails completely. Do not wait for
rooms off an open plan office. equipment failure or rely on the maintenance company
Check condensers to identify problem areas – preventive maintenance
makes better business sense.
Do not let heating and cooling operate Condensers are usually located on the outside of
at the same time buildings and eject heat that has been removed from
inside. Always ensure condensing and evaporating
Most air-conditioned areas need not be cooler than
devices are clean, well maintained and free from
24ºC (unless for a specific process requirement).
any obstructions.
Similarly, the maximum temperature recommended
for heating is 19ºC (the temperature in an area can
be comfortably above 19ºC but a system should not
Figure 9 Diagram of ‘dead band’ control recommended temperatures
be providing heat when it is over 19ºC).

It is common to find heating and cooling operating at

0ºC 5ºC 10ºC 15ºC 20ºC 25ºC 30ºC 35ºC 40ºC
the same time which wastes large amounts of energy
and money. A good solution is to set a gap, say
between 19-24ºC, to create a comfortable ‘dead band’ Heating is on until Cooling is on when
where no heating or cooling is operating. This will help temperature reaches 19ºC temperature exceeds 24ºC
to keep occupants happy and increase cost savings.
Unless this is implemented, both systems may operate Heating and cooling both off between 19ºC and 24ºC — a ‘dead band’ of 5 degrees
simultaneously and waste energy and money.

help
 Air conditioning 18

Efficient maintenance contracts Upgrading existing plant Replace old, inefficient plant
Day-to-day maintenance of equipment and control Sub-meter the system Advances in technology mean that more efficient,
settings can have a significant impact on energy modern equipment is available to replace older,
Chillers can account for up to a third of electrical
consumption, yet few maintenance contracts inefficient components in air conditioning systems.
consumption in a building. Installing sub-metering
explicitly include energy efficient operation This includes pumps, motors and fans, and payback
and collecting energy data enables inefficient areas
of systems as a requirement. As a result, the plant on these can be relatively quick. Investigate all
to be identified, investigated and eliminated. By gaining
is often run constantly and at maximum settings components in relation to the equipment, application,
an understanding of the energy used by air conditioning
that waste energy. Consider using a performance-based hours of use and the life cost. Spending time
components, performance targets can be set
Menu contract where the maintenance contractor and staff considering the options will help make the most
and monitored regularly. Sub-metering and the
are obliged to operate building systems efficiently energy efficient purchase.
corresponding monitoring and targeting can save
to minimise energy consumption whilst providing
up to 5% of the energy consumed by the equipment
an optimum internal environment.
that is being metered. Therefore, sub-metering can Fit variable speed drives (VSDs)
be a good investment if the costs of its installation
Fans and pumps do not always need to operate
are less than 5% of the yearly energy used by the air
Top tip at full speed all of the time. VSDs can help to reduce
conditioning system.
costs by enabling the output speed of the motors
Heat exchangers and cooling towers must be
to match requirements at different times of the day.
kept clean and water treatment processes
Review zoning arrangements This reduction in speed saves energy and there are
carefully maintained. This saves energy and
corresponding cooling cost savings too. More
prevents health problems such as Legionella. Many air conditioning systems are set up in ‘zones’
information can be found in the Carbon Trust’s
to provide different levels of cooling to specific areas
technology guide to Variable speed drives (CTG006).
within a building. Whenever building use changes,
these zones should be reviewed to ensure that they
are still delivering required conditions without wasting
Did you know?
energy. In addition, a yearly review of zoning
arrangements should be carried out to ensure that Energy consumption can increase by up
systems are operating to peak efficiency. to 30% if regular maintenance is not undertaken.
Cleaning fans, filters and air ducts can improve
efficiency by up to 60%.

help
 Air conditioning 19

Retrofit and system changes Reduce fan energy Review the suitability of the
Cooling control measures Fans used to move cool air around a building consume locations of any zone control
a major part of the energy used by conventional
In the UK, cooling is generally only required for parts
centralised air conditioning and comfort cooling
sensors. For example, make sure
of the year. However, the refrigeration plant used
to provide the cooling is often found operating
systems. The amount of energy used by the chiller that they are not in a location
is generally much lower than the fan energy in
unnecessarily or inefficiently to supply such small loads.
air-conditioned buildings in the UK.
exposed to sunlight and heat.
There are significant energy savings in upgrading
refrigeration systems and controls, or installing smaller Fan energy can be reduced by:
Menu
plant to serve such loads. To maximise performance
• Asking for systems to be designed to a low ‘specific
and reduce energy consumption:
fan power’. This means reducing the resistance to
• Review refrigeration controls and ensure they are airflow through the ductwork, which in turn means
coordinated with the rest of the building’s plant and making the ducts as large and as short as possible,
equipment with smoothed rather than sharp bends

• Review the sequencing of chillers (and boilers) and • Using efficient fans and motors
check they are operating at maximum efficiency
• Installing fan speed control. This reduces the airflow
• Check that free cooling is maximised in winter and at part load or part occupancy
switch off chillers where possible
• Improving the ventilation effectiveness; for example,
If there is a continuous small cooling load for 24 hours using ventilation to deal with specific areas of heat
a day, consider installing a separate small chiller so load rather than by conditioning the whole space.
that main chillers can be switched off outside
occupancy hours.

help
 Air conditioning 20

Building Energy Management Systems

Did you know? Top tip
Businesses with an energy bill of more than £10,000
a year could benefit from installing a Building Energy Option appraisal. Before making a change Don’t be afraid to ask! If you think your system
Management System (BEMS or BMS). This would to an existing system, it is important to consider is not operating correctly, or if staff members
be particularly beneficial for businesses considering all the available options, particularly where complain about problem areas in your building,
investing in a control upgrade. A BEMS is a computer- new investment is involved. An option appraisal act on it immediately. Always contact your
based system which can control any building service compares different possible solutions to a maintenance technician with any concerns.
– including air conditioning. Intelligent controllers or particular problem in order to determine the
Menu ‘outstations’ monitor conditions throughout the building best option.
and determine the operation of plant such as chillers,
The appraisal includes capital and operating
pumps and fans in response to changing conditions
costs and environmental impact, as well as
such as time, temperature and air quality.
practical issues like plant location, weight
To make the most of a BEMS, ensure that it is well and access and the flexibility to cope with
maintained and that staff are trained to operate it changes in building use and occupancy.
properly. Used correctly, BEMS can reduce total
energy costs by 10% and increase comfort so
they are well worth considering.

Integrating the measures

An energy survey or health check should highlight
areas that require action. These can be prioritised in
line with investment policy or as part of a general
upgrade or major refurbishment. This may vary from
simply resetting control points to complete new heating,
ventilation and air conditioning systems. It is essential
that the proposed changes are co-ordinated to avoid
conflict between one measure and another.

help
 Air conditioning 21

Specifying new systems

When specifying new air conditioning systems, it pays to buy the most efficient equipment possible.
Day-to-day running costs may quickly outweigh any additional installation costs and so installing
a more efficient system will ultimately be less expensive to run.
Menu
Always: Is close control of humidity required?
Top tip
• Select the most appropriate cooling system For most people, humidity is acceptable within the
for your requirements range of 40–70% relative humidity (RH). If humidity If new or refurbished buildings are over specified
is too low then problems can occur, such as static and complex, they may put themselves beyond
• Prioritise energy efficiency in the design and
electricity (below 40% RH) and health problems the competence of the building management
installation stages from the very beginning
associated with the drying of the respiratory tract team to achieve high standards of performance.
• Implement and maintain good system controls (below 30% RH). However, as most buildings in the Even if controls are set up and commissioned
UK sit within the 40%–70% range, they do not often correctly, they may be overridden in an attempt
• Carry out effective commissioning of the system
require the additional expense of humidification plant to improve occupant comfort. Always ensure
• Develop a maintenance plan to ensure that the accompanied by excessive energy costs. Unless users fully understand the best way
system continues to run efficiently, once installed humidification is required for a process, question to use controls.
(this may be through a maintenance contractor) whether it is really necessary.

• Provide suitable training for all system users.

Does the building need to be sealed against
Is air conditioning required? noise and pollution?
The choice of a passive or a mechanical cooling Noise and pollution can be caused by a number
approach can be determined by answering a series of factors and it can be a nuisance for a building’s
of relatively straightforward questions about a building occupants. It is often possible to provide ventilation
and its internal environment: from the back or to the side of a building where air
quality may be better. Remember that people prefer
to open windows for fresh air, so sealing the building
should be avoided unless absolutely necessary.
help
 Air conditioning 22

Are there high internal heat gains?

Is close control of
Internal heat gains are caused by building occupants, humidity needed?
sunshine, lighting, computers and other electrical Yes
equipment. Strategies to reduce heat gains can reduce No
the need for cooling and make natural ventilation a Does the building have
viable option. For example, replacing an inefficient to be sealed against
noise or pollution?
tungsten lighting system with a more efficient system Yes
can significantly reduce the heat in the lit space. No
Menu See the Carbon Trust’s technology overview to
Lighting (CTV021) for more details. Are there high
internal heat gains?
Yes
No
Is there a need for limiting internal
temperatures? Will it be acceptable for
the occupied space to
Temperature fluctuations may occur in a number of exceed 28ºC for a few hours
buildings but as the UK’s climate is generally moderate, on a few days each year? No
excessive temperatures are relatively uncommon. Yes Investigate Investigate
whether full air
Consider whether it would be acceptable for the whether
comfort cooling conditioning
occupied space to exceed 28ºC for a few days each (comfort cooling
is needed
year. If so, then a low-energy, naturally ventilated Try plus
(without
passive cooling humidification)
solution may be a viable option. humidification)
is needed
The flow chart opposite presents a summary of these
questions and indicates whether comfort cooling or full
air conditioning may be required.
Options Energy efficient mechanical options
• Natural ventilation • Chilled ceilings or beams
• Mechanical ventilation • Displacement ventilation
• Mixed mode • Fan-coil units
(a combination of the above) • Mixed mode
• Night cooling (any combination of the above
and natural ventilation)

Cost, complexity and maintenance all increase when mechanical cooling is installed
help
 Air conditioning 23

Consider the options Developing a brief for a new system

Did you know?
Careful specification of a new air conditioning When specifying a new air conditioning system,
system will help ensure that it meets the building’s a comprehensive brief should be developed that Building occupants generally have an
requirements while being both efficient and describes both the user and the client requirements, increased tolerance to higher temperatures
cost effective. including foreseeable changes. when they are able to take some personal
action to make themselves more comfortable,
Most air conditioning systems are made up of separate The activities within the building will dictate:
such as opening windows. Of course, take
pieces of equipment, working together to deliver a
• The amount of individual control required care that windows are not opened when air
comfortable internal environment. When new air
Menu • Whether temperature and humidity need to be conditioning or heating is on.
conditioning is proposed, the efficiency of each
controlled to a tight tolerance
component should be examined – not only in isolation
• The level of internal heat gain from office equipment,
but also in relation to how it will work with the other
lighting, etc.
components that make up the whole system.
• The amount of ventilation air that needs to be
Energy-Efficiency Loans
Manufacturers are a valuable resource when provided (usually derived from current and potential
considering equipment requirements. Many have a occupancy density) Small or medium-sized enterprises (SMEs)
selection of appropriate systems and often have • Zoning requirements and flexibility in spatial changes in England or Scotland and all businesses in
software which can provide an analysis of running • The proposed use of the building and its opening Wales that have been trading for at least
costs. This can cover aspects such as the choice of heat hours, occupancy patterns etc. 12 months could borrow* from £3,000 to
pump and the impact that controls can have. It may also £500,000. It is unsecured, interest-free and
As a general rule, it is important that the brief stipulates
be worthwhile considering leasing possibilities and repayable over a period of up to four years.
how ventilation and cooling systems should:
maintenance agreements when calculating the lifetime There are no arrangement fees and applying
costs of the system. • Be easily maintained is straightforward.
• Provide the required internal conditions
All businesses in Northern Ireland* that have
• Operate with minimal detriment to the external
Consider the level of expertise environment
been trading for at least 12 months may be
eligible for an unsecured interest-free loan.
or competence required to look • Have a reasonable operating cost.
Visit www.carbontrust.co.uk/loans.
after and operate the equipment Comparisons between different options should be on
*Subject to eligibility. Regional variations apply.
the basis of the whole life cost and not just on simple
as this could influence your payback of initial capital costs. Whole life costs (or
purchasing decision. life-cycle costs) take account of estimations of the annual
recurring costs for energy, maintenance, replacement
help and repair, as well as capital costs and interest charges.
 Air conditioning 24

Tender evaluation Commissioning Handover

Handover is a very important stage in the process.
During the tender evaluation, it is advisable to assess To ensure that a building operates correctly and meets
It is unwise to accept a new system until all the
the proposed systems together with the answers given the design requirements, the specification needs to
commissioning and testing has been completed
by tendering companies. include a commitment to properly documented and
satisfactorily. When a new system is handed over,
independently- verified commissioning and testing.
it should be accompanied by a Health and Safety file
Is it as simple as possible? The objective is to set up and test the equipment
including the O&M manuals together with the building
When considering the schemes, assess whether the and controls to make sure that they work together
log book required by the Building Regulations.
complexity of a system is appropriate to the user’s as designed. Results from this process should
Menu requirements – the best maxim is to ‘keep it as simple be included in the Operations and Maintenance
as possible’. Ensure that operators can understand (O&M) manuals and log book to show how the building
Air conditioning 2

Writing a
how the system should be controlled for an energy services were handed over in terms of equipment and
tender? Tender submission

efficient performance. control settings. A requirement for the building to be

Below is a list of issues to consider when tendering for air conditioning.

A detailed description of the operation and control of the proposed air conditioning system and its integration
with the rest of the building’s systems.

revisited for ‘system fine-tuning’ at a different time Download our

A detailed prediction of energy consumption (kWh/m2/year) and carbon dioxide emissions (kgCO2m2/year).

An explanation as to how the system will avoid simultaneous heating and cooling.

Is zoning considered? of year should also be included. For example, if the handy list of issues
An explanation of the role and scope building users will have in controlling their own environment.
For example, is the system reliant on occupants controlling windows and/or blinds?

An indication of the maximum fan power. This should be in line with the level of service requested
(ie not over-specified).

Ensure the scheme has taken into account areas system was set up in winter, it should be checked to ask any bidders
Use of variable speed control of fans — how their full benefits are to be achieved.

Use of variable speed control of pumps — tendering companies should identify the peak energy consumption
of pumps and indicate how energy will be saved through the application of variable speed control.

requiring different environmental conditions and those for satisfactory operation in the summer months. to cover.
How adequate ventilation will be achieved during occupancy.

Chiller efficiency — tendering companies should provide part load performance information and confirm what
the estimate of peak cooling load is, as this will influence selection of the chillers.

with different occupancy periods.

Confirmation that noise levels in the conditioned space will not exceed the requirements of the organisation
or any applicable regulation.

Energy efficiency — tendering companies should detail all energy efficient technologies and options that have
been included and specify those that are on the ECA energy technology list (ETL). See www.eca.gov.uk/energy

Whole life costing — use this to identify the appropriateness of all equipment and its integration into energy

Maintenance
efficient systems.

Flexibility of the system to adapt to changes in the level of cooling needed and zoning requirements.

How the system will be commissioned. Tendering companies should give examples of simplified descriptions

Has maintenance been considered? Maintenance is key to running an efficient and

and instructions that will be supplied at handover.

Maintenance and access requirements for the system — including provision for a programme of planned
preventative maintenance.

Ensure that there is adequate space and access to carry problem-free system. Determine whether maintenance
Download
out regular maintenance of plant, cleaning of ventilation work is to be contracted out or provided by in-house staff.
air paths, etc.
Users
Does it represent best value? Include reference to the importance of users in
Assess the whole life costs of the equipment and any specification and make it a requirement for
determine which gives best value for money, taking suppliers to provide all users and facilities managers
into account the available budget for the project. with information, training and guidance on how
to operate building services effectively.

help
 Air conditioning 25

Next steps
There are many easy low and no-cost options to help save money
and improve operation of the air conditioning system within your building.

Menu
Step 1. Understand your energy use Step 3. Prioritise your actions Step 6. Continue to manage the site’s
energy use
Look at the air conditioning system components and Draw up an action plan detailing a schedule of
check the condition and operation of all pieces of improvements that need to be made and when, along Enforce policies, systems and procedures to ensure
equipment. Monitor the energy consumption of the with who will be responsible for them. Where funding that the building and air conditioning system operates
building over, say, one month to obtain a base figure is limited, focus on energy intensive areas or those efficiently and that savings are maintained in the future.
against which energy efficiency improvements can that are performing badly first.
be measured.
Related publications
Step 4. Seek specialist help
Step 2. Identify your opportunities The following publications are available
It may be possible to implement some energy saving
from the Carbon Trust:
Compile an energy checklist. Walk round the building measures in-house but others may require specialist
and complete the checklist at different times of day assistance. Discuss the more complex or expensive
Technology overviews
(including after hours) to identify where energy savings options with a qualified technician.
Heating, ventilation and air conditioning
can be made. Compare different buildings to determine
(CTV003)
how they are performing in relation to each other.
Step 5. Make the changes and measure
Building fabric (CTV014)
You can build a walk-round checklist based on the the savings
information on page 28 and on page 14. For a complete Motors and drives (CTV016)
Implement the energy saving actions and measure
guide to conducting an energy walk round), contact the
against original consumption figures. This will
Carbon Trust and request a copy of Assessing the Technology guides
assist future management decisions regarding
energy use in your building (CTL003). Variable speed drives (CTG006)
energy priorities.

help
 Air conditioning 26

Glossary
Air handler Chiller sequence control Condenser coil
The component of heating and cooling systems A control or switching of two or more chillers in order A series or network of tubes filled with refrigerant,
that forces air through the ductwork of a building. to achieve the desired cooling temperature. This helps normally located outside the premises, that removes
Menu Air handlers usually consist of a sheet metal box to maximise chiller efficiency. heat from the hot, gaseous refrigerant so that the
housing fans and other equipment such as heating refrigerant becomes liquid again.
and cooling coils. Commissioning
The process of testing, checking or calibrating the Cooling capacity
Ambient temperature function of any building services component. A measure of the ability of a unit to remove heat from
The temperature of the outside air. an enclosed space.
Compressor
Batteries A device that moves refrigerant from an evaporator Dead band
(In air conditioning systems) Additional heating to a condenser and back to the evaporator again. This is established when heating and cooling controls
or cooling coils in a system. are set to give a wide gap between the temperatures
Condenser at which they cut in, to prevent heating and cooling
Building Energy Management System A heat exchanger in which a gas, such as a refrigerant operating at the same time.
(BMS or BEMS) vapour, cools and then condenses to liquid form.
A computerised system based on a network of In heating, ventilation and air conditioning (HVAC) DX coil
controllers offering closer control and monitoring systems, condensers are usually located on the outside The direct expansion (DX) coil contains the refrigerant
of building services performance, including heating, of buildings and reject heat that has been removed in a packaged air conditioner.
ventilation, air conditioning and sometimes lighting. from inside.
This is shown on a computer screen in real time and
allows the performance of plant to be monitored
and settings to be changed easily.

help
 Air conditioning 27

Ductwork Packaged air-conditioners Terminal units

This distributes the air from air handlers to conditioned A type of local air conditioning system with all its Devices at the end of a duct or pipework that transfer
spaces. In many buildings, this is hidden behind components in a single box which can be installed heating or cooling to the conditioned space. The most
suspended ceilings and within walls. ready tested. commonly found types include fan-coil units, induction
units and convectors.
Evaporator Passive heating, ventilation and cooling
A heat exchanger in which a liquid refrigerant absorbs The use of available natural energy such as heat from Time controls
energy from its surroundings and vaporises, producing the sun and wind-assisted ventilation, in order to benefit These ensure systems only operate when and where
a cooling effect. a building and maintain optimum comfort temperature. the building is occupied.
Menu

Interlocking controls Refrigerant Variable speed drive

Controls that prevent two or more systems operating The working fluid of the refrigeration system A device that controls the rotational speed of a piece
at the same time. which absorbs heat in the evaporator and rejects of motor-driven equipment such as a fan or pump. In an
it in the condenser. HVAC system, this can help to reduce costs by enabling
Louvres the output speed of fans to match requirements.
Movable slats to guide cool or heated air. These are Refrigerant leakage
a feature on most air conditioning units. Most types of refrigeration system are prone to some Water cooled condenser
degree of refrigerant leakage. This can cause a loss of A heat exchanger used to condense refrigerant vapour
Mixed mode systems cooling performance, excessive energy consumption using cooling water.
A combination of both natural and mechanical systems. and damage to the environment.
The building uses natural ventilation, heating and cooling Zoning
where possible, with mechanical systems being used Split air conditioning system Allows a building to be separated into individual areas
only when required. A local air conditioning system that separates the based on different requirements. Each zone may have
in-room unit, with fan and heating/cooling coils, from separate time and temperature controls, allowing
Night cooling the compressor and condensing unit which can be conditions in each area to be provided with heating
An established technique where cool night air is passed placed outside the building. or cooling appropriate to its individual needs and
through the building to remove heat that has thus achieving energy savings.
accumulated during the day. When the building fabric is Temperature controls
cooled, it will absorb more heat the following day, These ensure systems provide the correct
meaning lower internal temperatures. required temperatures.

help
 Air conditioning 28

Appendix
Action checklist

Air conditioning 2

Menu
Action checklist

Action Progress

Reduce the need for cooling. Turn off unnecessary equipment

during the day and especially out of hours to reduce heat
build-up in the space

Check the building fabric for gaps where air could be escaping

Minimise heat gains — shade glazed areas from sunlight, and

reduce energy usage in the space as much as possible

Consider low-energy solutions such as natural ventilation and

night cooling. If it is not possible to completely rely on low-
energy cooling, integrate these into the existing regime to
lighten the load on cooling plant

Check location of time and temperature controls and

understand what job they do. Poorly maintained controls and
permanently overridden controls affect comfort conditions and
energy efficiency levels

Adjust settings when building usage or occupation patterns

change and ensure zones are set up correctly

Turn off mechanical air conditioning and ventilation systems

out of hours. Consider installing automatic controls to ensure
equipment stays off when it is not required

If the building is rented or leased, ask the property owner or

managing agent where the controls are and how to use them.
If any controls are labelled ‘do not touch’, explore why — there
may be a valid reason but it could just be for the convenience
of the maintenance technician

Walk around the site at different times of the day and during
different seasons to see how and when cooling equipment is
working. Check time and temperature settings

Set higher switch-on temperatures for cooling and lower

switch-off temperatures for heating. Set a gap or ‘dead band’
between heating and air conditioning control temperatures
of about ºC. This improves staff comfort, cuts operating costs
and reduces wear and tear on both systems

Devise a maintenance schedule for cooling plant

Plan the upgrade or replacement of old or inefficient plant

The Carbon Trust can provide further guidance and support on improving energy use.

To start saving energy and reducing your

costs now, download and print our air
conditioning action checklist

Download

help
 Air conditioning 29

Go online to get more

The Carbon Trust provides a range of tools, services and information to help you
implement energy and carbon saving measures, no matter what your level of experience.

Menu
Carbon footprint calculator – Our online calculator will help you Case studies – Our case studies show that it’s often easier and less expensive
calculate your organisation’s carbon emissions. than you might think to bring about real change.


www.carbontrust.co.uk/carboncalculator 
www.carbontrust.co.uk/casestudies

Interest free loans – Energy Efficiency Loans from the Carbon Trust are a cost Events and workshops – The Carbon Trust offers a variety of events
effective way to replace or upgrade your existing equipment with a more energy and workshops ranging from introductions to our services, to technical energy
efficient version. See if you qualify. efficiency training, most of which are free.


www.carbontrust.co.uk/loans 
www.carbontrust.co.uk/events

Carbon surveys – We provide surveys to organisations with annual energy bills Publications – We have a library of free publications detailing energy saving
of more than £50,000*. Our carbon experts will visit your premises to identify energy techniques for a range of sectors and technologies.
saving opportunities and offer practical advice on how to achieve them.

www.carbontrust.co.uk/publications

www.carbontrust.co.uk/surveys

Action plans – Create action plans to implement carbon and energy Need further help?
saving measures.
Call our Customer Centre on 0800 085 2005

www.carbontrust.co.uk/apt
Our Customer Centre provides free advice on what your organisation
can do to save energy and save money. Our team handles questions

ranging from straightforward requests for information, to in-depth
help technical queries about particular technologies.
*
Subject to terms and conditions.
The Carbon Trust is a not-for-profit company with the mission to accelerate the move to a low CTG005v2
carbon economy. We provide specialist support to business and the public sector to help cut
carbon emissions, save energy and commercialise low carbon technologies. By stimulating
low carbon action we contribute to key UK goals of lower carbon emissions, the development
of low carbon businesses, increased energy security and associated jobs.

We help to cut carbon emissions now by:

• providing specialist advice and finance to help organisations cut carbon

• setting standards for carbon reduction.

We reduce potential future carbon emissions by:

• opening markets for low carbon technologies

• leading industry collaborations to commercialise technologies
• investing in early-stage low carbon companies.

www.carbontrust.co.uk
0800 085 2005

ACT ON CO2 is the Government’s initiative to help

individuals understand and reduce their carbon footprint.
Visit http://actonco2.direct.gov.uk for more information.

The Carbon Trust receives funding from Government including the Department of Energy and Climate
Change, the Department for Transport, the Scottish Government, the Welsh Assembly Government
and Invest Northern Ireland.

Whilst reasonable steps have been taken to ensure that the information contained within this publication
is correct, the authors, the Carbon Trust, its agents, contractors and sub-contractors give no warranty
and make no representation as to its accuracy and accept no liability for any errors or omissions.
Any trademarks, service marks or logos used in this publication, and copyright in it, are the property
of the Carbon Trust. Nothing in this publication shall be construed as granting any licence or right to use
or reproduce any of the trademarks, service marks, logos, copyright or any proprietary information
in any way without the Carbon Trust’s prior written permission. The Carbon Trust enforces infringements
of its intellectual property rights to the full extent permitted by law.

The Carbon Trust is a company limited by guarantee and registered in England and Wales under Company
number 4190230 with its Registered Office at: 6th Floor, 5 New Street Square, London EC4A 3BF.

Published in the UK: May 2010.

© Queen’s Printer and Controller of HMSO.