Energy efficient cool rooms and refrigeration

[Click here to download a PDF version of this information paper]

The cold chain

New technologies in refrigeration allow for greater control over the quality of products and may enable significant energy savings as well.

Innovative methods, such as quick cool-down of meat products and pre-cooling of fruit and vegetables, can help farmers make energy savings along the ‘cold chain’, as illustrated in Figure 1, while maintaining product quality and food safety standards.

The cold chain
Figure 1: The ‘cold chain’ in agriculture.
Energetics

For many farmers, refrigeration makes it possible to get fresh produce to the market. Temperature control is critical, as are the control of humidity, water and air movement. Many crops also have short growing seasons, requiring products to be managed effectively at every stage in the cold chain: the quality of the end product is only as good as the weakest link in the chain.

In addition to lower energy bills and improved product quality, an investment in energy-efficient refrigeration technology may result in opportunities to differentiate your produce from that of your competitors.

This information sheet will guide you through the refrigeration process, discussing points in the process at which you can save energy and money without sacrificing quality control.

Quick wins

Prevent heat from entering your refrigeration system and you will save money.

  • Look at shading, positioning and the design of your facility. Does your refrigerator receive direct sunlight? Consider ways of avoiding heat gain from sunlight.
  • Reduce the temperature of products to be placed in storage by picking produce at night or early in the morning. Alternatively, an array of pre-cooling methods, such as hydro, vacuum or forced-air cooling, could be considered.
  • Organise restocking so as to minimise the number of times you need to access the coolroom.
  • Inspect the seals, insulation and door alignment of refrigeration units regularly. Seals wear and can be damaged, compromising food safety and wasting energy. Look at where forklifts and vehicles may damage the polystyrene shell of your coolroom and consider taking steps to prevent such damage.
  • Install insulated coolant pipes to limit heat absorption from the surroundings.
  • Inspect and clean heat exchangers to improve the performance of your refrigeration system. Ensure that dust and spider-webs are not clogging the fins; that no grass is growing in front of the outside exchanger; and that products are not blocking the fan inside. Your goal is to maintain a clear, unobstructed area for at least one metre in front of and behind the coil.

Assessing opportunities

In a typical refrigerated warehouse, 15 percent of electricity use is for running pumps, motors, fans, conveyors and lighting systems, five percent is for sanitation and cleaning, and the remaining 80 percent is used for cooling, freezing and refrigeration.1

Investment in energy efficiency is not only about technology upgrades. Innovation can be a great marketing tool and a driver of cost reduction. Engaging and working closely with customers can give you an edge over your competitors. For example, customers may place a premium on the temperature of produce being within a specified range before delivery. There may also be different – and more energy-efficient – ways to meet regulatory food safety requirements.

When assessing opportunities for boosting the energy efficiency of your cooling/refrigeration system, gain a better understanding of your system by considering the following:

  • What equipment do you already have? How old is it? Many studies suggest that units more than 10 years old are worth replacing. This also applies to control systems.
  • What’s your current electricity use? Measure your consumption, either by the whole system or by individual components. Ideally these will be sub-metered, but plug-in meters are also available. Alternatively, an electrician can install a temporary meter. Let the meter run for a week and work out your average use.
  • What lights do you have? How are they controlled?
  • How are your seals and insulation? Are the door seals of all cooling and refrigeration units in good order? Inspect the insulation of your cool rooms, paying particular attention to the edges and joins.
  • Is it better to replace the whole cooling/refrigeration unit or just components of it?

Once you have a basic understanding of the refrigeration system in your business, the next step is to compare various viable energy opportunities and choose those that best suit your operation. You should be familiar with how refrigeration uses energy. Electricity is used principally in compressors, fans and lights, as illustrated in Figure 2.

Technology across the agricultural sector varies from ‘integral’ units similar to those of the typical residential fridge, to mobile refrigerated transport and large coolrooms in distribution centres and on farms. Even with this range of scale, certain technological components – a compressor, an evaporator and a condenser, all linked by pipes – are common to all systems.

Refrigeration system components
Figure 2: Energy use by refrigeration system components
Energetics

As the technology is the same, the principles of efficient operation also apply. How energy is used and moved around a refrigeration system is illustrated in Figure 2. Every arrow represents a place in the system that can be made more efficient. The blue arrows show where electricity is used, the red arrows show heat flows.

Energy flow refrigeration
Figure 3: Energy flow through a refrigeration system
Energetics

Typical refrigeration systems will have two heat exchangers: one inside the fridge and one outside it. To maintain a constant temperature, the compressor must remove heat at the same rate as the rate at which it enters the cabinet. Reduce the rate at which heat enters the cabinet and you reduce all electrical usage.

Typical sources of heat load in coolrooms are the temperature of produce before it enters cool storage, forklifts, air exchanges, and heat transfer through the building shell.

Typical energy savings opportunities, applicable to the ‘whole of system’ and to key energy-use components of the system, are highlighted below. 

Technology innovation delivers energy saving

Many cost-effective energy savings opportunities exist in refrigeration systems, particularly in large systems such as coolrooms. Figure 4, below, illustrates the average payback in years and percentage reduction in energy use by the system or component to which the energy savings measure is applied.

Figure 4: Energy savings opportunities in order of payback.

Energy savings measure

Energy savings[1]

Payback

Night blinds

24–29%

0.28

High-efficiency compressor

4–10%

0.74

Inert gas-insulated glass doors

8–10%

0.74

Glass doors/lids

50–59%

1.33

Electronically commutated evaporator-fan motors

5–19%

1.37

Electronically commutated condenser-fan motors

3–8%

1.37

Variable speed drive (VSD) fitted
to the compressor

9–19%

1.54

High-efficiency lighting

<19%

1.59

Insulation (+25 mm)

1–6%

3.09

Energy management system
and/or controls

<60%

varies

Typical savings and paybacks will vary depending on the efficiency of the system being replaced and the choice of upgrade. Consequently, payback periods may be shorter or longer (e.g. many studies suggest payback periods of under a year for high-efficiency compressors).

Motors, compressors and fans

The big change in refrigerators over the past decade is an increase in the widespread use of electronically commutated (EC) motors. These motors use much less energy than traditional copper-wound induction motors.

A typical refrigeration system might have three motors: one for the compressor and one each for the evaporator and the condensor. Replacing these in an existing system could reduce energy use by half. System age is a good indicator and, in general, anything 10 years or older[1] is unlikely to be an EC motor. Buying a new complete system with EC motors could reduce your energy use by even more.

Typically, a compressor comes as a single, sealed unit. So the compressor and motor that drives it need to be replaced at the same time. These are ‘hermetically sealed’ units. Advances in both motors and compressors should make this a high-value opportunity. The savings from upgrading the compressor can be determined using information from suppliers. Work out how much energy your compressor uses now to supply a given pressure, then compare that figure to the energy a new compressor supplying the same pressure would use.  

Beyond changing the fan motor, you can upgrade the fan attached to the motor for very little cost. New, stiffer and lighter plastics push air more efficiently and often, one of these can be fitted to your existing motor.

Larger systems may also benefit from a variable speed drives (VSDs) or the addition of a variable speed controller. VSDs reduce the electrical load during low load periods, while controllers can be fitted to existing motors to reduce the current use during start-up.

Refer to supplementary paper, VSDs on fans.

Lighting

Significant advances have occurred in lighting with the introduction of LEDs. If your lights look like this traditional incandescent bulb, you can be certain that upgrading them to high-efficiency fluorescent bulbs or LEDs will save you money and improve the reliability of your lights.

LED solutions are available for a range of applications, from illuminating warehouse high-bays to providing cost-effective strip lighting for refrigeration. The payback period for LED is typically longer than for other energy-efficient lighting but a payback period of less than four years is still common.

If you are calculating the savings that these new lights can deliver, remember that lights inside a refrigerated space also contribute heat. LEDs are more efficient because they emit less heat. The impact of this will usually be small, but removing that heat load will make the whole system more efficient.

Refer to supplementary paper, Lighting.

Control system

The control system itself uses very little energy, but it controls how much energy the other components use, which makes it an important link in the system.

Modifications as simple as ensuring temperature settings are  correct can lead to significant savings over time, with one degree Celsius of temperature adding about five percent to the energy use. More advanced control systems can provide more accurate control of temperature, lighting and fans, leading to savings throughout the system.

Refer to supplementary papers, Refrigeration – Variable temperature control and Refrigeration – Variable head pressure control.

Replace the whole system?

Small integral systems similar to residential refrigerators and/or deep freezers close to 10 years old might be worth replacing. Some of these appliances will still have Energy Rating stickers attached and these are a great means of determining the system’s energy use. If no such stickers are attached, investigate ways of measuring the system’s energy use directly, using a plug-in meter or with an electrician’s help.

Work out how much energy the system uses in an average year. Once you have this, you can compare this energy use to those of new units, which have to be pre-tested and must meet Australian Standards. On its energyrating.gov.au website, the federal government has calculators that allow you to input your electricity price and compare various units to see which is likely to save you the most money.

Replacing coolrooms and other large, remote compressor refrigeration systems is much more complicated, with the price of upgrading driven by the labour costs associated with piping and installation as well as those of the components themselves. In cases like these, you will be better served by analysing the energy-using components individually than by measuring whole-system use. Apply the rules above for motors, fans, compressors and lights to see improvements across the whole system.

To get more out of your existing large refrigeration or coolroom system, consider the following:

  • Analyse the energy-using components individually rather than measuring the whole-system use. Apply the rules above for motors, fans, compressors and lights to see improvements across the whole system.
  • Change the timing of when the refrigeration system is used. This can impact the cost, depending on our electricity tariff structure. This can be difficult with perishable goods, but is feasible with large glycol-water systems like those used in dairies or poultry processing.
  • Inspect for damage to the wall panels. In cool rooms and other large installations, the panels are often made from polystyrene, a terrific insulator, but prone to physical damage. Periodically inspect the outer and inner perimeters for damage that may allow air flow into the coolroom.

Refer to supplementary paper, Refrigeration – upgrade or replace degraded compressor.

Consider refrigerant gases when upgrading

There are no opportunities to change the refrigerant of an existing system to another which will improve performance. However, under current Australian law, refrigerants are impacted by the amount they contribute to global warming, determined by their Global Warming Potential (GWP). Carbon dioxide, the most basic greenhouse gas, has a GWP of one. So, one tonne of carbon dioxide attracts one unit of carbon price, about $23. But for R404A, a common low temperature refrigerant, carbon price per tonne is 3,784 x $23 = $87,000.

Many businesses are now taking steps to reduce their exposure to these prices by shifting to lower-GWP refrigerants such as carbon dioxide and propane. It is a complex area but one worth considering when you’re replacing equipment, as it could lead to significant savings over the life of the equipment.

Table 1: GWP and the application of various refrigerant gases5.

 Designation

Applications

GWP

R22

Being phased out

1,810

R134A

Air-conditioning and higher-temperature refrigeration

1,430

R407F – a blend of R32, R125 and R134a

A wide range of refrigeration (designed as a swap for ozone-depleting R22)

1,705

R404A

Low temperature refrigeration

3,784

R290 – propane

Typical in ice-cream freezers, but appropriate for a wide range of refrigeration

3.3

R600a – isobutane

Small refrigerators

3

R744 – carbon dioxide

A wide range of refrigeration

1

Further information

Farm Energy Innovation papers

Refrigeration – Variable temperature control: Allowing and planning for temperature variation within refrigeration can increase energy savings.

Refrigeration – Variable head pressure control: Adjusting head pressure set points allows for optimal condenser operations and energy savings.

Refrigeration – Insulation on tanks: By ensuring that refrigeration tanks, coolroom storage and other climate-controlled areas are tight and well insulated, farmers can reduce cooling requirements and save energy.

Refrigeration – Upgrade or replace degraded compressors: Upgrading or replacing refrigeration compressors is an energy-saving opportunity.

Variable speed drives in agriculture: Fitting variable speed drives (VSDs) to motors can reduce their energy use. This includes evaporator and compressor fans in refrigeration.

Food safety effects of damaged fridge seals

NSW Food Authority, NSW food safety laws

NSW Food Authority 2008, potentially hazardous foods

Brewer, SJ, 2011, ‘Damaged and Soiled Refrigerator Seals (Gaskets) from Commercial Food Premises: A Potential Reservoir for Food Pathogens’, Bioproducts Technology Consultant 

Energy-efficient refrigeration technologies

Office of the Environment and Heritage, 2011, Energy Saver – Technology Report: Industrial refrigeration and chilled glycol and water applications, New South Wales 

Queensland Government, 2010 Refrigeration Efficiency – U5 

Mary’s Free Range Chicken product website 

Federal government, Industry Tourism Resources, 2003, A guide to energy efficiency innovation in Australia wineries, Australian Federal Government

Management of packing sheds and coolrooms

Growcom and the Queensland Government, Land and Water Factsheet. Energy efficiency: Packing shed and cool room, Queensland Government 

Alberta Agriculture and Rural Development, Fresh Fruit and Vegetable pre-cooling for market gardeners n Alberta 

Case examples

1. A typical vegetable coolroom, designed to handle between two and six pallets.

2. South Queensland fruit and vegetable supplier talks about the importance of temperature control and the additional benefits of humidity control.

3. Simplot at Bathurst in NSW discusses some of the more complex compressor upgrades and system modifications available for large systems.

References

  1. Australian Federal Government, 2013, Product Profile – Commercial Refrigerated Display and Storage Cabinets, E3 Committee, Department of Resources, Energy and Tourism.

[1] If you are unsure of a motor’s age, the motor plate should indicate whether that motor is a new EC; otherwise, an electrician or mechanical fitter should be able to help you.

[1] Energy savings are expressed as a percentage of savings against the equipment load or application load, whichever is applicable.

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