Energy Performance
Certificates
Building Services - Cooling
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SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Cooling Systems
Local air conditioning systems include through-the-wall packaged
units and split systems to provide comfort cooling, or heating and
cooling, but not humidity control.
Ventilation air needs to be handled separately, and thus there is little
scope for controlled free cooling. Whilst it is not common to base a
major new design on individual local air conditioning units, they are
commonly used to introduce air conditioning in major refurbishment
of naturally ventilated buildings.
Individual local units have lower CoPs than centralised plant and
often lack a coherent control strategy
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
However, they provide scope for energy savings through:
Avoiding multiple heat exchange (into/out of chilled water and
condenser water) and fouling at each water heat transfer surface.
Avoiding pumping large volumes of chilled and condenser water
Simpler heat rejection equipment (i.e. direct air cooled condensers
instead of cooling towers with their energy consumption and water
treatment consequences)
Plant operating only in those areas that need cooling at a given time.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Although more localised plant may increase maintenance costs, this
approach may provide greater standby in areas served by a number
of local units.
Where it has been decided that air conditioning is unnecesary in the
building as a whole, it may be appropriate to use highly localised
units to cool hot spots in a mixed-mode approach, thus avoiding
larger cooling systems. A similar approach may be appropriate
where cooling requirements are more stringent in one small area
than in the building as a whole.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Through-the-wall’ packages
These units are difficult to integrate into a coherent system, but may
be applicable where a single room within a building needs to be
cooled, either to different temperatures, or at different times, from
the remainder which has a co-ordinated system. Cooling CoP lies in
the range 1.5 to 2.3.
Heating is sometimes provided by electric resistance heaters, which
should be appraised carefully in life cycle cost terms. Care should
be taken to ensure that they do not operate in conflict with any
separate space heating system, or with other similar units in the
same zone, and that they are time controlled to function only when
required.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
• Through-the-wall’ packages
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Individual reversible heat pumps
Packaged heat pumps have much the same limitations as throughthe-wall packages except that heating can be provided more
efficiently by reversing refrigerant flow through the indoor and
outdoor coils.
This saves energy in comparison with electric resistance heating,
but care needs to be taken to compare the total running cost of heat
from this source with other alternatives such as a separate central
heating system.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Split unit packages
Split units have a separate outdoor unit to house the compressor
and condenser thus avoiding noise problems in the space being
served. Some units offer variable speed compressors that enable
cooling to be modulated, and thus the energy use can be matched
more closely to cooling requirements. Split systems provide cooling
CoPs of 2.5 to 3.0 whereas through the wall units only give 1.5 to
2.3.
Otherwise, they should only be used in the same context as
individual packaged units, with extra care taken to avoid the
prospect of leaks from the connecting refrigerant lines. Most typically
used in refurbishments, they often lack a coherent control strategy
when multiple units supply the same space leading to simultaneous
heating and cooling.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Variable refrigerant flow rate
Variable refrigerant flow rate (VRF) multi-split systems are generally
regarded as local systems but are increasingly used as distributed
cooling systems. More than one indoor unit can be connected to the
same outdoor unit.
However, it is important to comply with the manufacturer’s
recommendations on horizontal pipe runs, number of bends and
vertical lift, in order to minimise energy losses.
In each circulation loop, the refrigerant flow rate can be varied to
match the heat transport requirements, thus making energy savings.
Some suppliers offer heat recovery between zones on the same
circulation loop, and it is in this mode that the system operates at its
peak CoP of 3.1
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
In heating only, or cooling only, modes the best system CoPs lie in
the range 2.3 to 2.5.
In some installations, several outdoor units for individual refrigerant
loops have been located in a bank adjacent to each other, but not
connected, which can give the false impression of a co-ordinated
system. Care should be taken to ensure a coherent control strategy
with this approach.
In particular, controls for multiple units serving the same space
should be linked to avoid simultaneous heating and cooling. Deadbands between heating and cooling set points should be adequate
to avoid individual units cycling between heating and cooling modes.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Ducted Installations
Ducted split heat pump units work under the same principles as the
ceiling or wall mounted units only they are located within ceiling
voids or bulkheads and the conditioned air is transported to the
occupied zone by means of a system of ductwork, this type of
system would prove difficult to assess as all the items of plant are
hidden with the only visible items of plant being grilles or diffusers.
The assessor must view the installation to take records of the type of
plant installed so efficiencies may be determined.
Ducted units generally have a system of ventilation working
alongside this installation. this may be viewed as being outside the
requirements of a Level 3 assessment, however some simpler more
common systems are described below.SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
Other Forms of Cooling
There are numerous other types of mechanical cooling available which
would be outside the realms of a Level 3 assessment. The following are the
most common used and are for reference purposes.
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Constant volume
Dual duct
Variable air volume
Partially centralised air/water systems
Centralised air with reheat
Induction
Fan coils
Chilled beams and ceilings
Displacement ventilation
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
LEVEL 3
BUILDING SERVICES TRAINING
End of Section
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3