Putting a freeze on energy wastage


The cold storage and industrial refrigeration sectors can be richly rewarded by the implementation of just a few simple energy-saving technologies. Shaun Evers, managing director of Stonegate Instruments, one of the UK’s leaders in refrigeration and temperature control systems, explains how cost efficient devices can save companies substantial amounts of money and help to reduce greenhouse gas emissions.

Efficient refrigeration is crucial to the food industry which is worth £96.1bn to the UK economy and is responsible for at least 12% of the country’s energy use. Changing trends in food consumption and the way that we shop has driven forward growth. Over 4,000 supermarkets and most larger food retail outlets have an average of five cold rooms each, all with their own cooling and lighting facilities, and smaller food stores, butchers and food storage also, of course, use refrigeration.

This goes some way to explaining why energy consumption in the refrigeration sector costs British industry approximately £300m each year with the average site energy bill for a cold store totalling £0.5m. Between 1,500 and 2,000 food and drink manufacturing sites in the UK are major users of refrigeration and cold storage facilities, many using inefficient cold stores designed and built over 20 years ago, and refrigeration costs represent over 50% of the energy bill for some organisations.

A study by the Food Refrigeration and Process Engineering Research Centre (FRPERC) found that significant energy savings of at least 30% can be achieved by implementing low cost technologies that address the four key areas where energy is wasted; running equipment at the incorrect temperature, leaving doors open too long, through gas leaks, and due to raised moisture levels.

Temperature control

Keeping food at exactly the right temperature is, of course, not only fundamental to hygiene and the longevity of foodstuffs, but also to keeping energy bills down and cutting carbon emissions. Overcooling by just 1˚C can lead to a significant increase in energy consumption of up to 3%, with temperature differences of 5˚C proven to increase electricity consumption by 10-20%.

Efficient thermometers linked to audio and visual alarms that warn staff of variants are essential to both monitor the temperature of the cold store and the temperature of its contents. At its most basic this could be a compact digital thermometer designed to be used with a thermistor probe across a range of plus or minus 50˚C which will constantly display the temperature. Probes can be wall mounted or hand-held and chosen for their suitability in washdown areas.

A significant amount of energy wastage is caused purely by the incorrect operation of equipment and poor use of controls – simply leaving the cold storage door open makes the system work harder to maintain low temperatures. Research carried out by Stonegate indicates that an average of 32 visits per day are made to frozen food cold rooms, with the door open for, on average, more than 30 minutes five times a week.

Open doors can also lead to moisture control problems. Each time the door is open, moist air is drawn in as a result of the difference in air density between the outside and inside of the cold store. The water vapour forms ice which, over time, reduces the efficiency of the store and requires it to use more energy. Eventually the store will have to be defrosted, leading to more wasted energy.

To address these issues Stonegate Instruments has developed its Door Open Alarm system for food industry refrigerators, the Cold Room Logger for temperature monitoring and the Transducer Trip Module to measure moisture content. The Door Open Alarm system is a large and loud warning device using a flashing Xenon Beacon and up to two 100dB sounders which, when fitted to a cold room door, provides both audible and visual warnings that it has been left open for an extended amount of time. Data loggers have inputs for measuring temperature, door contacts and the amount of current used. Data is stored at regular intervals for access by USB connection to computers to ensure that systems are working to maximum efficiency.

Gas leaks

Gas leaks can be a serious matter. According to the Institute of Refrigeration working with the Carbon Trust, a leak of just 1kg of refrigerant gases causes approximately the same environmental damage as driving a van 10,000 miles. They report that leaks of up to 30% of the charge during a year are not uncommon in commercial and industrial refrigeration. If a gas leak occurs, a cold store’s energy consumption will increase to maintain the equipment’s cooling capacity. It is estimated that £40 million per annum could be saved on energy costs in the cold storage industry if gas leaks were dealt with correctly. Leaks are expensive in terms of downtime, service costs, refrigerant, electricity and CO2 emissions. This can be counteracted by applying best practice in leak testing, servicing, maintenance and repair.

No matter how good the manufacture, given time, vibration, temperature and environmental stress, tiny flaws in joint fittings, seams or welds are likely to become leaks. These could be at the tail end of a weld fracture or a microgroove between fittings. Leaks larger than 0.5oz a year can be detrimental to the operation of any refrigeration system.

Leak detection

The most effective method of finding gas leaks is with an electronic detector able to identify a wide range of refrigerant gases including CFCs, HCFCs, HFCs and CO2. Under European legislation, detectors must have a sensitivity of 5g/year and should be checked annually. For optimum reliability, they should be checked after 25 hours’ use.

Stonegate Instruments has developed a new improved gas detection system which can accommodate up to 24 remote refrigerant sensors linked to a compact central monitor unit. Both audible and visual alerts for alarm conditions and sensors can be included. The sensors are arranged in three zones of eight channels with four relay outputs for signalling an alarm, one for each zone. Each sensor contains a control for users to adjust the sensitivity according to individual requirements and the system has also been designed to accommodate a logger function that can record one week of logs for each of the 24 channels.
Refrigerant gas leaks are not only expensive but also intrinsically hazardous to the environment. Man-made fluorinated gases (F-gases) can remain in the atmosphere for thousands of years and contribute to a global greenhouse effect. They account for just 2% of the European Union’s overall greenhouse gas emissions but have risen by 60% since 1990 in contrast with all other greenhouse gases, which have been reduced.

As part of its policy to combat climate change, the EU passed legislation in 2006 to control F-gases. Under these regulations there is a legal obligation to test systems for leaks once a year if the charge is between 3 and 30kg and twice a year for systems with more than 30kg. Systems containing over 300kg of HFC must have permanent fixed leak detectors. Leaks must be repaired and the system retested at the point of repair within one month.

Corporate responsibility

Reducing energy wastage saves money and helps companies to show corporate responsibility in promoting green practices. The UK is the first country to set legally binding carbon budgets which place a restriction on the total amount of greenhouse gases that the UK can emit over a five-year period, leading to the target of reducing the UK’s greenhouse gas emissions by 80% by 2050.

The government introduced a mandatory corporate reporting regulation which came into effect October 2013, requiring all quoted companies to report on their greenhouse gas emissions. Another new initiative, the Energy Savings Opportunity Scheme (ESOS) will require all businesses with more than 250 employees or an annual turnover of more than €50 million (£41,322,450) to undertake an energy audit by 5 December 2015.

Implementing energy saving technologies in commercial refrigeration is straightforward and, with a payback of less than two years, offers long term savings which will help businesses to keep their energy costs at a minimum and meet their green targets. Putting a freeze on energy wastage couldn’t be simpler.