In the commercial context, refrigeration is used to extend the life of products such as food stuffs and chemicals. Applications include refrigerated cabinets, walk-in cool rooms, industrial and chemical cold storage, beverage cooling, vending machines and ice makers.
Refrigeration can be responsible for 25% to 85% of total company energy use. As many refrigeration systems are ageing and inefficient, there is often potential to reduce consumption by a large amount. Energy savings can often be made through actions requiring little or no investment.
General principles and practices
There are several easy, low-cost practices to minimise refrigeration energy use in any existing system.
- Avoid overstocking and ensure air grills are kept clear of products and obstructions.
- Don’t allow products to warm up during transfer.
- Switch off lighting and anti-condensation devices after hours.
- Check thermostat and defrost settings match conditions.
- Reduce heat gain from other equipment and sunlight.
Optimise system layout
Paying attention to layout and planning can deliver substantial energy savings.
- Avoid excessive pipe lengths and uninsulated pipework.
- Reduce the time personnel need to spend in (or passing through) cool areas.
- Ensure cooling equipment is as far as possible from heat sources.
- Optimise lighting layout and specifications, using LED where possible.
- Arrange the evaporator so cold air does not blow straight out the door.
- Locate condensers and heat exchangers where there is good air flow and waste heat can be discharged.
- Optimise routing of suction lines to avoid excessive pressure drop, liquid retention or unstable flow.
If the refrigeration system is more than 10 years old, it should be considered for replacement. Energy savings of up to 30% could be realised by selecting the most efficient new system.
A whole-of-system approach is critical to incorporating energy efficiency throughout the whole process without the constraints imposed by older equipment.
Understand your business needs now and into the future when designing a new system. Oversizing the rooms will impose an initial capital-cost penalty and ongoing energy-cost penalty. Ask your expert to pay particular attention to part-load energy performance during the design stage.
Refrigerated display cabinets
Refrigerated display cabinets (RDCs), refrigerated storage cabinets (RSCs), ice cream freezer cabinets and scooping cabinets are used in a variety of locations ranging from supermarkets to gelato shops.
Installing aerofoils along display shelves can be a cost-effective way to reduce cold air losses from open cabinets. In some cases, placing transparent doors to open cabinets is a cost-effective measure, though not as effective as a brand-new system.
In 2019, a new efficiency standard for RDCs was implemented by the Australian Government, improving the average energy efficiency of new refrigerated cabinets, and extending the range of cabinets covered under the previous standard. For more information, see the Energy Rating website.
Walk-in cool rooms and freezers are predominantly operated by small-to-medium enterprises, and the potential energy waste of an average unit is well over 25%.
Cold rooms are often constructed onsite using insulated panels. Even small gaps between panels or where pipes penetrate walls can allow a stream of warm, moist air into the room. With effective sealing, energy savings can be substantial.
Automatic rapid-close doors should be fitted to cold rooms where regular access is required. Strip curtains can help minimise heat gain through doors.
Many refrigeration units would benefit from improved insulation. Ensure potential areas of heat gain are well insulated.
- Poorly insulated coolant pipes can seriously affect performance of the refrigeration system.
- Insulation panels for walls, ceilings and doors should have an R-value of at least 4.5 which equates to 140mm of rigid foam insulation. For freezer rooms, panels should be at least R6 (175mm thick).
- Transparent windows and doors should be double-glazed on cool rooms and triple-glazed on freezers, with heat-reflective (low-emissivity) external treatments.
Upgrading system controls enables more sophisticated energy-efficiency strategies.
Normal design temperatures are typically 0 to 4°C for cool rooms, and -18°C to -20°C for freezer rooms. The operating set-point should be selected on the optimum temperature and humidity, and no colder.
Check the accuracy of temperature sensors by calibrating gauges against independently tested instruments. Ensure timer settings on automatic defrost are not excessive.
Most large-scale industrial refrigeration plants use several compressors. The system controlling the compressors maintains capacity without necessarily optimising efficiency. Automated sequencing and capacity control optimised for energy efficiency can save substantial energy.
Optimised defrost management can also improve efficiency, as the frequency and duration of defrosts are typically fixed, regardless of room temperature and workload between defrosts.
Fans, pumps and compressors
Compressors have different properties. Reciprocating compressors are generally used for small-to-medium sized chillers, while larger capacity chillers incorporate centrifugal or screw compressors. Compressors are the most energy-intensive part of the refrigeration process, so choose the most efficient compressor for the purpose and the load.
More efficient pumps and fans can repay themselves in energy cost savings within a few years. With DC inverter technology, newer compressors, fans and electronic controls can mimic air conditioning split systems technology to achieve flatline temperature control. This can save more than 25% of energy consumption.
See the Motors and variable speed drives page for more information.
Adjustable and variable speed drives on pumps
Older refrigerant pump systems use throttling or bypass pumping control methods. More efficient flow control can be achieved by using adjustable speed drives (ASDs), variable speed drives (VSDs) or by installing multiple pumps. VSDs are the preferred option when pumps operate for at least 2000 hours per year and process flow rate requirements vary by 30% or more over time.
See the Motors and variable speed drives page for more information.
In a conventional plant, head pressure is fixed and the plant control system attempts to maintain that fixed value. Variable head pressure control (VHPC) aims to optimise the head pressure of a refrigeration plant at any given time while taking into account operational factors, ambient conditions and plant load. When head pressure is optimised, the combined power consumption of the high-stage compressor and the condenser fan is minimised.
Evaporator/expansion valve adequate sizing
Evaporators are located inside chiller or cold rooms and must be large enough to support the needs of the system. When an evaporator is too small, the compressor must work harder and for longer. Defrosting also occurs more frequently in this case. This results in an overall increase in energy use.
In chillers, heat from the refrigeration process is expelled into the environment via air-cooled condensers or cooling towers. At the same time, hot water requirements are separately met by means of a dedicated water heater.
Some heat recovery is possible from oil coolers on the compressor, superheat from the compressor or the system condenser. Lower grade heat can be beneficial for pre-heating hot water, supporting space heating, or underfloor heating in cold or dry good stores.
Modern chillers, in particular those using ammonia (R717) or CO2 (R744) refrigerant, offer significant potential to recover waste heat at useful temperature levels (greater than 50°C). This recovered heat can offset the energy consumption of other operations, such as heating water, thus reducing site energy consumption.
See the Waste heat recovery page for more information on heat recovery.
Measurement and maintenance
Procedures should be established for the regular monitoring and testing of overall performance, as well as servicing of all components as recommended by the manufacturers. Regular scheduled cleaning and maintenance will help ensure efficiency and temperature control, as well as minimising system problems or failure.
Installing sub-metering of electricity consumption is an important step towards monitoring energy use and savings. Logging refrigerant use is also possible. Once refrigeration energy use is understood, future goals can be established and performance tracked.
See the Metering and monitoring page for more information.
Refrigerant selection is important, as the type of refrigerant can affect the efficiency of a system. Most refrigeration systems leak refrigerant gases, and many are known to cause significant environmental damage due to their high global warming potential (GWP).
A regulated gradual phase down - by about 85% by 2036 - of hydrofluorocarbons (HFCs) is underway in Australia and worldwide as these refrigerants have high GWP. New refrigerants with low GWP and high efficiency are expected to become increasingly available as the market responds to the new regulations. Many of these are based on ammonia or CO2. Ask your service provider about the best available products for efficiency and environmental performance.
There are widespread opportunities in the food industry and retail applications to store energy via refrigeration in cold storage to take advantage of existing thermal mass. Also, thermal mass can be added to using phase change materials, including ice.
Frozen storage tends to allow greater thermal temperature swings than cool rooms, though product considerations are important. Frozen meat for example is quite insensitive to overcooling, though this is not the case with ice cream.
Phase change materials (PCM) store a large amount of energy for heating, cooling or refrigeration by melting/freezing at a specific temperature. PCM thermal energy storage together with a refrigeration system can be used to store substantial renewable energy generated by solar PV.
The market is increasingly implementing storage strategies with rooftop solar PV that can reduce or eliminate peak demand. There is also likely to be an increase in the integration of electric batteries into refrigeration systems, as the economics of batteries steadily improves.
The use of onsite solar PV to power refrigeration facilities is increasingly common. Solar PV is well suited to higher daytime loads that typical refrigeration systems are subject to. Extensive PV arrays on warehouse roofs can also help reduce heat gain into the premises. Mobile prefabricated cold room modules with solar PV included within the package are becoming a popular solution to addressing business growth and rapid deployment scenarios.
Internet of things (IoT) and predictive control
The application of intelligent, cloud connected IT systems to refrigeration systems promises to enable even greater energy costs savings. CSIRO, for example, has recently designed a system utilising ‘self-learning’ model predictive control (MPC) techniques from control theory and computer science domains.
By taking into account forecast external conditions, electricity tariffs and adaptively learning the thermal response of the system, cost control is much improved. Strategies can be tailored to operating objectives, including minimising total cost and reducing energy consumption.
See the Industry 4.0 page for more information.
Cool room efficiency fact sheet (PDF 1MB) Australian Institute of Refrigeration, Air Conditioning and Heating
Commercial Refrigeration Energy Rating
Energy Efficiency Best Practice Guide - Industrial Refrigeration (PDF 663KB) Sustainability Victoria
Refrigeration guide UK Carbon Trust