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Energy efficient and sustainable refrigeration

18 June 2008

David Clarke, director of design consultants CDIS-KARM, member of the FCSI and the Catering for a Sustainable Future Group, offers advice on how to make your refrigeration equipment more energy efficient.

When looking at the energy consumption of the commercial kitchen and the CO2 emissions generated, the refrigeration equipment and plant used needs careful consideration, as the total energy used by the caterer for refrigeration is estimated to be 6% of the total energy used by the catering facility.

Major advances have been achieved in refrigeration technology over the past 10 years and it has become clear that commercial refrigeration has many untapped opportunities if we are serious about reducing the energy used and the harmful emissions discharged.

Using the technology that has been developed in recent years it is not unusual for up-to-date controllers to show energy savings of up to 15% and for refrigerated cabinets and counters that have been designed to achieve ECA approval to obtain energy savings of up to 40%.

To obtain the above savings it is important to consider the location of the cabinets, installing them in the coolest part of the kitchen that the working pattern will permit so as to reduce the working load on the compressors. It must also be remembered that each cabinet requires at least 50mm of space to the sides and rear with 200mm at the top for free air to circulate around the cabinet.

Consider base mounted compressors as the temperature in the commercial kitchen can often be less at low level as hot air rises. However the area in front of the cabinet must be kept clear at all times.

Don't overstock the units, although they will work more efficiently when loaded, remember to never block the circulation areas around the food as this will increase the energy usage.

Always cool hot food by blast chilling before placing it in the refrigerated storage unit as it is not only more energy efficient it also avoids any risk to food safety.

It's more applicable to cold rooms rather than cabinets and counters, but it is worth remembering the thicker the wall, ceiling, floor and door insulation, the more efficient the unit will be as temperature losses and gains are greatly reduced.

Unbelievably as it may seem, one of the most common problems is that kitchen staff leave doors to cabinets and cold rooms open and in some cases wedge them open, always shut the door and in the case of cold rooms fit a plastic strip curtain to keep the cold air in and the hot air out.

Planned preventative maintenance is essential if we wish to maximise the unit's efficiency, a partially blocked condenser will increase energy consumption by up to 23%, a faulty door seal by up to 11% and incorrect temperature settings by 6%. A 15% refrigerant leak will increase the energy usage by 100%.

Regular maintenance increases the unit's life, while reducing breakdowns with expensive repairs and food wastage which all have a heavy impact on the environment while increasing the running costs.

If you are replacing existing cabinets it is generally less costly to operate one larger unit than two smaller ones, to avoid unnecessary opening of doors which will increase energy usage you may wish to consider units with glazed doors so that the contents can be viewed without opening the doors or you may wish to consider a combination of drawers and half doors. If however the operation sees regular periods of low usage it may be more efficient to use two smaller cabinets so that during quiet periods individual cabinets can be switched off. One full cabinet is much more efficient to run than two half full cabinets.

Currently HydroFluoroCarbons (HFCs) are widely used in many commercial refrigeration applications, HFCs are the replacement refrigerant for ChloroFluoroCarbons (CFCs) which were the refrigerant of choice for many years, but they have been phased out due to their high Ozone Depletion Potential (ODP) characteristics. HFCs have zero ODP, but still have a high Global Warming Potential, today, the focus is shifting from ODP to global warming and HFCs are included on the Kyoto list of gases whose emissions need to be reduced.

Hydrocarbons (HCs) have been identified as one of the possible alternative refrigeration gases for HFCs as they are environmentally benign (zero ODP and negligible GWP) and give a good technical performance. HCs work on a simple vapour compression cycle in the same way as the current HFCs with working temperatures and pressures that are close to those of HFCs so no substantially different equipment is required.

HCs have already been used as refrigerants in the EU and Asia for a number of years, but mainly in domestic refrigeration. Hydrocarbons are now being introduced in commercial refrigeration as a commercially viable alternative for HFCs and are a key component of the Greenfreeze programme being run by Greenpeace.

While units running on HCs are in general terms 15% more energy efficient than comparable units that run on HFCs, because of its flammable properties certain requirements exist that limits its use. The maximum charge per sealed system is 2.5kg or 10kg in open air for indirect systems. The precautions for recharging are that staff have special training, no ignition source should be within a radius of 10m, no power supply to be located in the charging area, sensors are to be provided for detecting leaks and dry powder fire extinguishers must be provided. Also Hydrocarbons are heavier than air so special consideration must be given to the kitchen drainage details in areas were leaks can occur.

At the present time Hydrocarbons can be satisfactorily used in freezer and refrigeration cabinets, but general opinion suggests that the larger cold room installations need to have some further research and development work undertaken.

The Glycol secondary refrigeration system is capable of running a large number of different appliances, chilled areas and cold rooms on one system. It has outstanding rapid temperature pull down times; however it is not capable of dealing with freezer cabinets or rooms. A typical Glycol system will reduce the primary refrigeration gas used within a commercial kitchen by up to 72% which brings with it the obvious benefits for the environment; it will also reduce the energy usage by up to 25%, while in some foodservice applications caterers have achieved a 15% reduction in food loss through reduced wastage.

The Glycol secondary refrigeration system comprises of a pair of external chiller units circulating a food safe mixture of chilled glycol and water around a ring main connected to the independently controlled equipment. The chiller units run alternately, offering back-up, if one unit should develop a fault, an alarm sounds and the remaining unit comes into operation. As the units are in a remote location the kitchen and servery are not exposed to the heat and noise emissions that integral units can create.

On the larger type installation, the Glycol system has an added benefit in that it is easier to install a heat recovery system that can harvest the heat rejected and use it to preheat the cold water feed to the water heater supporting the kitchen.

When purchasing refrigeration equipment look for appliances that are ECA accredited, this means that they are recognised as being energy efficient and in certain cases you can claim 100% tax allowance in the first year. It is also worth talking to your consultant or supplier as Carbon Trust interest free loans may be available for projects that greatly reduce the CO2 emissions generated by your business.

David Clarke is a director of design consultants CDIS-KARM(01603 721961www.cdis-karm.com), a professional member of the Foodservice Consultants Society International UK (01483 761122,www.fcsi.org.uk) and a member of the Catering for a Sustainable Future Group (www.csfg.co.uk).

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Jacobs Media Group is honoured to be the recipient of the 2020 Queen's Award for Enterprise.

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