What can the service technician do to keep the refrigeration system operating at peak efficiency

[toc]

Refrigeration can be responsible for 25% to 85% of total company energy use. Many refrigeration systems are ageing and inefficient, so there is often potential for major energy-saving improvements.

Quick wins

Metering and monitoring

Establish regular monitoring and testing of overall performance. This will help understand how much, when, and under what conditions energy is being used. It will also provide a baseline of current performance.

High frequency sub-metering of electricity consumption is a foundation for optimising system performance. Logging refrigerant use and system temperatures is also good practice. Once the energy use is understood, goals can be established and performance tracked.

To read more, see the Metering and monitoring guide.

Maintenance

Regular scheduled cleaning and maintenance will help ensure optimal energy efficiency and temperature control. It also minimises system problems or system failures.

Ensure regular servicing of all components as recommended by the manufacturers.

Minimise refrigeration energy use

There are several easy options for minimising refrigeration energy use:

Avoid overstocking and ensure air grills are clear of obstruction.
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.

Insulation

Many refrigeration units would benefit from improved insulation. Ensure coolant pipes and potential areas of heat gain are well insulated.

Insulation panels for walls, ceilings and doors should have an R-value of at least 4.5, which is 140 mm of rigid foam insulation.

For freezer rooms, panels should be at least R6 (175 mm thick). Transparent windows and doors should be double-glazed on cool rooms and triple-glazed on freezers, with heat-reflective (low-emissivity) external treatments.

Optimise and upgrade

New systems

If the refrigeration system is more than 10 years old, it should be considered for replacement. An efficient new system could save up to 30% in energy use.

A whole-of-system approach is critical to incorporating energy efficiency throughout the whole process. This should be free of 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. Pay particular attention to part-load energy performance during the design stage.

Optimise system layout

Attention to layout and planning can deliver substantial savings.

Avoid excessive pipe lengths and uninsulated pipework.
Reduce the time personnel need to be in cool areas.
Ensure cooling equipment is away from heat sources.
Optimise lighting by using LED where possible.
Arrange evaporator so cold air doesn’t blow straight out the door.
Locate condensers and heat exchangers where there is good airflow and heat can be discharged.
Optimise routing of suction lines to avoid pressure drop, liquid retention or unstable flow.

Refrigerated cabinets

Refrigerated display cabinets (RDCs), refrigerated storage cabinets (RSCs), ice cream freezer cabinets and scooping cabinets are commonly used in food retail.

Installing aerofoils along display shelves can be a cost-effective way to reduce cold air loss from open cabinets. Placing transparent doors on open cabinets can be effective, though not as effective as a brand-new system.

In 2019, a new efficiency standard for RDCs was implemented by the Australian Government. The standard raises the average energy efficiency of new refrigerated cabinets, and extends the range of cabinets covered under the previous standard. To read more, see the Energy Rating website.

Evaporator/expansion valve

Evaporators are located inside chiller or cold rooms and must be large enough for the needs of the system. If an evaporator is too small, the compressor must work harder and for longer. Defrosting also occurs more frequently, using more energy.

Cold rooms

Walk-in cool rooms and freezers are mostly operated by small-to-medium enterprises. The average potential energy waste of a unit is over 25%.

Cold rooms are often constructed onsite with insulated panels. Even small gaps between panels or pipes entering walls can allow warm, moist air into the room. With effective sealing, energy savings can be substantial.

Automatic rapid-close doors should be fitted to cold rooms needing regular access. Strip curtains can reduce heat gain through doorways.

Fans, pumps and compressors

Compressors have different properties. Reciprocating compressors are generally used for small-to-medium sized chillers. Larger capacity chillers incorporate centrifugal or screw compressors. Compressors are the most energy-intensive part of refrigeration, so choose the most efficient compressor for the purpose.

New 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 reduce energy consumption by 25%.

To read more, see the Motors and variable speed drives guide.

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 with adjustable speed drives (ASDs), variable speed drives (VSDs) or multiple pumps. VSDs are preferable when pumps operate for at least 2000 hours per year and process flow rate requirements vary by 30% or more over time.

To read more, see the Motors and variable speed drives guide.

System controls

Upgrading system controls enables more sophisticated energy-efficiency strategies.

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 no colder than the ideal temperature and humidity.

Check accuracy of temperature sensors by calibrating against independently tested instruments. The frequency and duration of defrosts are typically fixed, regardless of room temperature and workload between defrosts. A more tailored approach is preferable, but ensure timer settings on 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 bring substantial savings.

Pressure control

In a conventional plant, head pressure is fixed and the plant control system attempts to maintain that fixed value. Variable head pressure control (VHPC) optimises the head pressure of a refrigeration plant at any given time. It accounts for 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 reduced.

Heat recovery

In chillers, heat from the refrigeration process is expelled outside 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.

To read more, see the Waste heat recovery guide.

Renewable energy

The use of onsite solar to power refrigeration facilities is increasingly common. Solar is well suited to higher daytime loads that typical refrigeration systems are subject to. Extensive PV arrays on warehouse roofs can also reduce heat gain into the premises. Mobile prefabricated cold rooms with solar included are a popular solution in rapid deployment scenarios.

To read more, see the Renewable energy guide.

Innovations

New refrigerants

Refrigerant selection is important, as the type of refrigerant can affect the efficiency of a system. Most refrigeration systems leak gases, and many are known to cause significant environmental damage due to their high global warming potential (GWP).

A regulated phase down - about 85% less by 2036 - of hydrofluorocarbons (HFCs) is underway in worldwide. New refrigerants with low GWP and high efficiency will become available as the market responds to the regulations. Many new refrigerants will be based on ammonia or CO2. Ask your service provider about the best products for efficiency and environmental performance.

Storage strategies

There are widespread opportunities in food and retail to store energy via refrigeration in cold storage to take advantage of existing thermal mass. Also, thermal mass can be added to phase change materials (PCM), including ice.

Frozen storage tends to allow greater thermal temperature swings than cool rooms, though product considerations are important. For example, frozen meat is quite insensitive to overcooling compared with ice cream.

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 energy generated by solar PV.

The market is implementing storage strategies with rooftop solar that can reduce or eliminate peak demand. There is likely to be more integration of electric batteries into refrigeration systems, as the economics of batteries steadily improves.

Internet of things (IoT) and predictive control

Intelligent, cloud-connected technology integrated with refrigeration systems promises greater energy savings. CSIRO, for example, has designed a system with ‘self-learning’ model predictive control (MPC) techniques from control theory and computer science domains.

Cost control is improved when accounting for external conditions, electricity tariffs and adaptively learning the thermal response of the system. Strategies can be tailored to operating objectives, including minimising total cost and reducing energy consumption.

To read more, see the Industry 4.0 guide.

Desiccant-enhanced cooling

Development of hybrid cooling systems that combine desiccant-based dehumidifiers with conventional compressor refrigeration equipment is ongoing.

In these systems, desiccant is used to remove the latent heat load (the heat in water vapour) from the air to be refrigerated, leading to substantial energy savings.

IT cooling

With the growth in data generation, transmission and storage, the need for better performing IT cooling systems continues to drive innovation. In some data centres, air cooling is being replaced with specialised refrigerant fluids.

Liquid is passed through computer components via tiny heat exchanger channels, or components are immersed completely in a dielectric fluid that is electrically non-conductive.

To read more, see the Data centres guide.