Refrigeration technology efficiency

Refrigeration technology efficiency and reducing environmental impact

Refrigeration technologies all work by transferring heat from one location to another, away from the area being cooled and into the surrounding environment. This Knowledgebase article explains the refrigeration technologies relevant to commercial catering appliances and gives you an insight into those that may be most efficient and most environmentally friendly.

Mechanical force, heat pumps, magnetism, electricity or lasers can all be used to move heat, and methods of refrigeration can be classified as non-cyclic, cyclic, thermoelectric or magnetic depending on what force they use and how they use it.

You can forget most of these technologies; only mechanical non-cyclic and heat pump cyclic technologies are sensibly and cost effectively applied in a commercial catering refrigeration appliance.

 

Mechanical non-cyclic refrigeration.

Mechanical non-cyclic refrigeration means physically moving something that is already cold, like ice, and putting it near the thing you need to be cooled. Melting ice, frozen carbon dioxide or any other low freezing point substance, as used in portable coolers or in pre-freeze bowl and ice and salt ice cream machines, must absorb energy to melt. The energy it absorbs is the heat of the thing or volume of air you are trying to chill. We say this is non-cyclic because once the ice is melted the cooling process ends; you would need to start the process with new ice.

Mechanical refrigeration of this kind is useful in certain catering appliances because you don't need anything but the ice - good for portability and compact units where it would be difficult to fit other refrigeration components.

 

Heat pump cyclic refrigeration

Cyclic refrigeration is the most common type of refrigeration technology used for commercial fridges or freezers, and providing a flow of energy is maintained (you keep the appliance plugged in to your electricity supply), refrigeration is a constant cycle.

Commercial fridges and freezers use a refrigerant substance, usually a fluid that changes between liquid and vapour, in a heat pump cycle. The particular type of heat pump cycle used in commercial refrigeration is the vapour-compression cycle.

The vapour compression cycle works by using a compressor and then a condenser to convert refrigerant vapour into a cooled liquid, that experiences a sudden drop in pressure after passing through an expansion valve. The drop in pressure cools some of the liquid even further, with the remainder evaporating into a cold vapour. Up to this point everything has been generating and dissipating heat and has therefore happened outside the insulated refrigeration chamber, but at this stage the cold liquid-vapour mix passes into the refrigerator. There it absorbs any warmth from the air, blown by fan over the evaporation coil or tubes it moves through. The warmth absorbed by the refrigerant provides the energy it needs to turn back into a vapour, which is then fed back into the compressor to continue the cycle.

During this process, the condensor acts to remove and dissipate some of the heat absorbed from the refrigerant's passage through the evaporator and condensor. Vapour compression refrigeration, done well, is therefore an elegant, carefully balanced system.

 

 

Types of refrigerants and their properties

Refrigerant fluids used in vapour compression cycles must be noncorrosive, free from toxicity and flammability, should not cause ozone depletion and contribute as little as possible to global warming. They also need to have very specific thermodynamic properties such as boiling point, vaporization point, moderate density in liquid form and high density as a gas. Refrigeration manufacturers are able to adjust operating pressures to some extent to alter the thermodynamic properties of a given refrigerant, which broadens the range of substances that are considered suitable.

A long list of undesirable refrigerant technologies predate the modern refrigerants, beginning with hazardous, flammable or toxic chemicals like ammonia or sulfur dioxide before moving on to chlorofluorocarbons (CFCs) like Freon, with their well documented, devastating ozone-depletion and global warming effects. Other fluorocarbons are less damaging but still have environmental effects - hydrofluorocarbons (HFCs) are common refrigerants in modern refrigerators but are significant contributors to the greenhouse effect. In summary, the refrigerants to avoid or seek out are as follows:

Chlorofluorocarbons (CFCs), for example R-12 or "Freon" - very harmful to ozone layer, banned.

Hydrochlorofluorocarbons (HCFCs), for example R-21 or "Freon 21" - very harmful to ozone layer, being phased out worldwide.

Hydrofluorocarbons (HFCs), for example R-134 A, R 404A - do not harm the ozone layer much but contribute significantly to global warming. These are still commonly used by many manufacturers and are present in fridges manufactured after 1990, including many of those stocked by Catering Appliance Superstore. It may be difficult to avoid these but there are other options on the market at not significantly more cost.

Non-halogenated hydrocarbons, or "hydrocarbon natural refrigerants", for example Isopropane (R-290A), Isobutane (R-600A) - negligible ozone depletion potential and very low global warming effects, currently the optimum replacements for CFCs, HCFCs and HFCs.

The type of refrigerant used in a refrigeration or freezing unit will be clearly listed under the product description on the Catering Appliance Superstore website, to enable you to make an informed decision.

 

What else makes a refrigerator efficient?

Features other than the refrigerant technology can make a difference. Air circulation, the efficiency of the compressor, and the depth and quality of the insulation and door seals are the main factors.

 

Air circulation

Any refrigerator that circulates cooled air effectively around the unit will achieve a more consistent temperature, and in theory this means that the unit doesn't need to work as hard. To achieve a given temperature in all parts of the refrigerator, a unit without air circulation has to make one area even colder and rely on convection to bring the warm air towards the point of heat exchange.

For example, /true/bottle-coolers use a forced air distribution system, and many models in the /gram range makes use of a directed cold air flow down the rear mounted distribution plate to maintain a correct an uniform temperature. Both are regarded as highly efficient in their class.

 

Compressor efficiency

The compressor, powered by electricity, generates the energy needed to maintain your vapour compression heat pump cyclic refrigeration system (your commercial fridge or freezer). The less energy the compressor has to use to achieve the same amount of work, the less your electricity bill will be. Sadly, not much information is generally available from refrigeration manufacturers on compressors, but as a user there are things you can do to improve efficiency. Positioning the refrigerator in an area where the compressor is well ventilated, even placing a fan near the compressor to carry away the warmed air, will reduce the amount of energy it uses noticeably - a cooled compressor means less heat will be being transferred back into the refrigerator compartment, so cooling is maximised in each cycle, and the compressor will not kick in as frequently.

 

Insulation materials and positioning

Effective insulation will also reduce the energy needed to bring the refrigerator or freezer to temperature and keep it there. Remember, a vapour compression cycle relies on transfer of cold refrigerant into the evaporator, which then absorbs any heat in the chiller compartment. A poorly insulated refrigerator will need colder refrigerant or more frequenct refrigerant cycling to maintain temperature (more frequent compressor use).

The insulation materials and depth have a very definite impact on this. A standard material for fridge or freezer insulation is polyurethane bonded to an external skin of plastic or metal, and 50mm is an acceptable depth for a fridge; although you can get by with 40mm or sometimes even less, expect to pay less for the product (you'll need to save some money to pay for the higher energy bills). Add 20mm at least for a freezer, and the lower the minimum freezer temperature the thicker the insulation needs to be.

Of course, there are other insulation materials and production methods, often with trademarked names, that have better or worse insulation properties, such as CO2 blown foam, cyclopentane blown foam, or polystyrene. Different insulators need different depths to achieve the same level of insulation. Polyurethane is used the most common worldwide at the moment because it is the cheapest and simplest material to work with. If the refrigerator or freezer doesn't specify an insulation material, assuming polyurethane is a safe bet.

There are other things you can do to maximise the efficiency of your insulation. Reducing ambient temperature, by keeping your entire refrigeration unit in a colder area than your kitchen in the first place, or at the very least away from appliances that kick out heat like ovens and grills, will help reduce heat transfer through the walls and door of the unit.

 

Industry standards for energy efficiency in commercial fridges and freezers

There are various industry standards for the overall energy efficiency of refrigeration and freezing units in the UK and Europe - unfortunately, while there is often clear comparative information for domestic appliances, there is not always a standard approach by commercial manufacturers and information on energy efficiency for some models can be very difficult to find.

In 2016 there will be a mandatory energy labelling scheme for commercial refrigerators and freezers sold in the EU, an easy to understand reference system based on the well-recognised A to G letter scale.

 

Energy efficiency and environmental profile of refrigeration manufacturers

We're proud to stock a very broad range of energy efficient refrigeration manufacturers. There are energy efficient models available from all brands, but some manufacturers go the extra mile to ensure the highest standards of efficient running and environmental responsibility.

Gram use really efficient, energy-optimised refrigeration technology and lay claim to the lowest energy consumption of comparable models on the market. As well as having a lot of models that come with hydrocarbon natural refrigerants as standard, Gram are also able to upgrade an even broader selection of their HFC R-134A and R-404A refrigerated models to more environmentally friendly hydrocarbon natural refrigerants if this is a particular concern for your business. Gram are experienced manufacturers of Isobutane and Isopropane refrigerators.

Foster were the first commercial refrigeration manufacturer in the UK to be awarded the Carbon Trust Standard, for their programme of reducing the carbon footprint of their manufacturing process over a three year period and the footprints of the units they make. Foster were also first in the UK to obtain ISO 14001 standard for Environmental Management Systems. Foster offer a hydrocarbon natural refrigerant option at no extra cost.