How to reduce heat gain for cabinets and cold rooms

How to reduce heat gain
for cabinets and cold rooms
Minimising the heat gains on refrigerated cabinets and cold rooms cuts the
cooling load on your refrigeration system and saves you energy and money.
Any energy efficiency initiative dealing with refrigeration
should start by reviewing the heat gains on your system.
If you understand the nature of these gains, you’ll be able
to manage the amount of cooling that needs to be done
and make energy savings. Heat gains include warm air
entering the cabinet or cold room and heat produced by
electrical equipment within the cooled space. This guide
covers in detail two opportunities to reduce heat gains:
reducing cold air changes using strip curtains, and using
EC (electronically commutated) replacement motors
for evaporator fans.
The business case
You will find opportunities for reducing heat gains on
refrigerated cabinets and cold rooms in most applications.
Improving door management in cold rooms results in
substantial energy savings. For example, installing plastic
strip curtains to a cold room can give savings of up
to 30%, and have a payback period of around a year.
Replacing conventional shaded-pole fan motors with
equivalent EC motors can cut their energy use by
65%, as well as generating less heat and reducing
your maintenance replacements. You can maximise
the saving achieved by fitting a whole new fan assembly
instead of just replacing the motor. In most applications
the payback period for fitting EC motor fans is one to
two years, but it can be much shorter.
The technology
Refrigerated cabinets include catering fridges, bottle
coolers and retail display cabinets. Some, such as catering
fridges, have doors, while others, such as multi-deck display
cabinets are open-fronted. Cabinets are almost always
factory-built with no on-site assembly. Most cabinets are
cooled by an integral, hermetically sealed refrigeration
system located within the cabinet frame. Supermarket
cabinets may use centralised refrigeration systems.
Cold rooms are refrigerated spaces large enough for
the user to enter when loading or unloading the contents.
Cold rooms tend to be assembled on-site from insulated
panels and bespoke jointing systems. They may be
cooled by ‘mono-bloc’ or split refrigeration systems.
Mono-bloc systems consist of a single unit containing
the evaporator, compressor and condenser, arranged
so that the evaporator hangs inside the room and the
compressor/condenser hangs outside. Split systems
consist of a remote compressor/condenser assembly
connected to the evaporator within the cold room.
Heat gain sources in a cold store or cold room are usually:
• Heat gained through the insulated walls, ceiling and
floor (20%)
• Warm air and moisture leaking in through the doors
and gaps (30%)
• Evaporator fans (15%)
• Evaporator defrost (15%)
• Lights (10%)
• Occupants and associated equipment (10%)
How to reduce heat gain for existing cabinets and cold rooms
Heat gains
Figure 1 Typical heat gains for a cold store
The main sources of heat are similar for cabinets,
although the proportions differ.
The following table summarises your opportunities
for reducing the heat gain in existing cabinets and
cold rooms. You’ll find more detailed information
on fitting strip curtains and EC motors below.
Figure 2 Opportunities to reduce heat gains
Fit plastic strip curtains
Open-fronted display cabinets, cold rooms
Fit insulated strip curtains
Cold rooms
Use night blinds when not in use
Open-fronted display cabinets
Fit transparent doors
Open-fronted display cabinets
Repair door seals
Cabinets with doors, cold rooms
Improve door management
Cabinets with doors, cold rooms
Fit self-closing doors
Cold rooms and cabinets with hinged doors
Fit automatic doors
Cold rooms
Install efficient lights
Any cabinet or cold room with lights
Improve lighting control
Any cabinet or cold room with lights
Fit EC motors
Retail display cabinets or cold rooms
Optimise defrost control settings
Any cabinet or cold room with defrost heating system
Fit defrost-on-demand controller
Any cabinet or cold room with defrost heating system
Locate away from sources of heat
All cabinets, especially open-fronted and integral ones
The single largest gain is usually caused by warm moist
air getting in through openings – mainly open doors. Gaps
around doors, between panels and where pipes penetrate
the walls also allow a small but constant stream of warm
moist air to enter. For cabinets without doors, warm moist
air enters through the open front.
Where a cold room door is in frequent use, plastic strip
curtains can keep cold air in and warm air out. They can
also be used for open-fronted cabinets.
Figure 3 on the following page shows a small freezer store
temperature measured with and without a strip curtain.
Every time the door opened the air temperature in the
cooled space increased from -19ºC to -2ºC without the
strip curtain, but only to -16ºC with the curtain in place.
The time taken to return the store temperature back
to -19ºC was 12 minutes without the strips and three
minutes with.
How to reduce heat gain for existing cabinets and cold rooms
Figure 3 Effect of using a strip curtain for a freezer
cold room
Evaporator fan motors
Evaporator fan motors are another important source
of heat gain. Recent advances in fan design and motor
efficiency offer good savings for older cabinets or cold
rooms. Conventional shaded-pole AC motors can be
replaced with DC electronically commutated (EC) motors.
This can result in energy savings of up to 65% for the fan
motor. Since the fan motor consumes much less energy,
there is also less heat for the refrigeration system to
remove. For a large supermarket, replacing standard AC
evaporator fan motors with EC types will save 6% of the
running costs of the refrigeration equipment.
A fan assembly integrating the EC motor, impeller and
inlet ring mounting can be supplied as a simple drop-in
replacement for a standard evaporator fan and motor
unit fitted in cabinets. This increases the efficiency of
the fan, giving greater savings than replacing the motor
alone. Usually EC motors have a two-speed operational
option. By combining an EC motor with a suitable
controller, the fan can operate at a reduced speed when
the compressor is not operational or when night mode
is engaged. At half its full speed the fan motor will use
up to 87% less energy.
Strip curtains
Figure 4 Considerations for strip curtains
Do you have a cabinet with an
open front?
Consider fitting strip curtains. Recent merchandising studies have
found a transparent barrier doesn’t cause any noticeable loss of sales.
However, if the cabinet has a night blind fitted, this will reduce the savings
from installing a strip curtain and may make a curtain difficult to fit.
Is there evidence of ice build-up on
the ceiling, walls or the floor of
your cold room?
This is a good indication that a high level of air change is taking place and
that you’ll make significant savings by reducing the warm air ingress
through the door.
Do you have a cold room with a door
that needs to be frequently open?
If so, then consider fitting strip curtains to the doorway. Consider also
whether you could reduce the time the door is open through better
management or by automatically closing the door in some way.
Is the cold room used for chilled or
frozen products?
If the cold room is at a low temperature i.e. for frozen products, then
installing strip curtains will almost certainly be worthwhile. An insulated
strip curtain may be cost-effective depending on the average time the door
is open. If the cold room has a self-closing or automatic door the savings
from installing strip curtains will be reduced. In the case of a freezer, it may
still be worthwhile to install strip curtains if it is accessed frequently.
How to reduce heat gain for existing cabinets and cold rooms
Applications – strip curtains
• No gaps at the sides of the opening
You can easily apply strip curtains to open-fronted display
cabinets, deli-counters and cold room doorways. For cold
rooms, they are most applicable if the door is frequently
open or the room is at a low temperature for frozen goods.
• Strips are long enough to reach the bottom of the opening
Figure 4 on the previous page outlines points for you to
consider when installing strip curtains.
Common problems – strip curtains
Specification checklist – strip curtains
When specifying strip curtains you will first need to
decide whether they should be plastic or insulated.
Insulated curtains provide better heat retention than
conventional plastic strips, so are particularly applicable
to freezer cold rooms.
You will then need to consider how the strip curtains will
be attached to the doorway – some fixing methods may be
more suitable than others depending on the application.
Finally you will need to measure the dimensions of the
opening where they are to be fitted. Your supplier will
need this information before quoting for and supplying
strip curtains for your cabinets or doorways.
Commissioning checklist – strip curtains
When installing strip curtains you’ll need to check for
the following:
• Good strip overlap
• Detailed installation instructions should be provided
with the strip curtains.
Where strip curtains are fitted on cabinets or cold rooms,
you should regularly make sure that they:
• Are in good condition – replace any damaged or
missing strips;
• Are being used properly – operators should be
discouraged from holding open strip curtains
• To minimise heat gains through doorways in cold rooms
in general, you should regularly make sure that:
• Doors are kept closed whenever possible.
• Doors fit well with good alignment and seal when
closed. If a door is knocked, its hinges or slides may be
damaged, preventing the door from shutting properly.
If so, these should be repaired as soon as possible.
• Door seals are in good condition. Look for any gaps or
damaged rubber. For frozen food cold stores, faulty seals
may be indicated by ice or frost build up around the
door. Rubber seals commonly deteriorate and may need
replacing after a few years of use. Door seals should be
replaced by a suitably qualified service technician.
EC motors
Figure 5 Considerations for EC motors
What type of motor is used by the evaporator fans?
Are they shaded-pole AC motors?
Replacing shaded-pole AC motors offers the largest
What are the ratings of the evaporator fan motors
and how many are there per unit?
This will determine the potential power savings along
with the existing motor type.
Is it worthwhile to replace the whole fan assembly?
Fitting a new fan assembly will give efficiency savings
for both the fan and motor.
Do the fans run continuously?
The hours of use, along with the power saving of the
motor will determine the overall saving.
Could the evaporator fans run at low speed part of the
time, for example, at night or when the compressor
is off?
The fan can be run at either full or low speed if a
controller is installed. This will increase the energy
savings but also the cost.
How to reduce heat gain for existing cabinets and cold rooms
Applications – EC motors
Commissioning checklist – EC motors
You can fit EC motors to evaporator fans in retail display
cabinets and cold rooms. They can also be used in
vending machines and drinks coolers, but the payback
period will be longer.
There are many suppliers with experience in installing
EC motors replacements for conventional fan motors.
A good supplier should carefully specify a replacement
motor and fan to match the size and air flow of the
original, and then install and commission.
Figure 5 on the previous page outlines points for you to
consider when choosing whether to install EC motors.
You may need to ask the equipment supplier or your
refrigeration contractor to supply most of the information.
Specification checklist – EC motors
Your supplier will need to know the details of the existing
motors, such as their rating and electrical supply. If you
plan to replace the whole fan assembly, he will also need
the following:
• the design air flowrate of the fan and/or
• the diameter of the ring mount in the cabinet to
make sure the replacement is the same size.
If you want the fan to run at low speed part of the time
you will need to tell your supplier, who may need to
install a different controller. Your supplier will also need
to know how the fan will be controlled to run at reduced
speed e.g. when the cabinet is operating in night mode
or when the compressor is off.
The company supplying and installing the EC motors
should do a survey of your existing refrigeration systems
to ensure they select suitable replacements for the
existing evaporator fan motors and where applicable,
fan assemblies.
Common problems – EC motors
EC motors are relatively simple to install, have a 15-year
lifespan and are usually more reliable than conventional
types. Motors should be replaced by a suitably qualified
service technician.
Finding a supplier
Strip curtains come under the Government’s Enhanced
Capital Allowances scheme. You can see a list of ECA
approved suppliers at
You should be able to obtain a list of competent
contractors to supply and install replacement
EC motors from the following trade associations:
Institute of Refrigeration
020 8647 7033
British Refrigeration Association (BRA)
0118 940 3416
See the Carbon Trust website at
for further information to help you make your refrigeration
more energy efficient.
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