Cool ways to save

Boosting the efficiency of cold stores has been the subject of intensive research over recent years, because it can yield substantial cost reductions, says Rod Addy

A flurry of projects focused on reducing energy consumption and costs in the frozen and chilled sectors are yielding promising results.

Co-ordinating them is the Food Refrigeration and Process Engineering Research Centre (FRPERC), based at the University of Bristol, which claims UK frozen storage rooms alone use 900GWh of energy annually. But FRPERC is closing down on July 31 unless it can find a new home, so it's up to industry to take up its good work.

Research undertaken to date includes the development of interactive software by South Bank University enabling processors to tweak variables from outside temperature to new coolant types to increase cold store efficiency.

But there's so much more than that to FRPERC's labours. In one Potato Council study, ambient cooling, with air at a temperature of 20°C blown across products for five minutes, was found to reduce product temperature by 50 degrees Celsius before cold storage.

"This removes 562kJ of heat energy and stops 60kg/h of water freezing on the coils," said Mark Swain, FRPERC deputy director, at an April conference in Birmingham on developments in refrigeration.

Alternative food preparation methods prior to cold storage, such as deboning meat carcasses or flooding animals' circulatory systems with coolant could also lessen the work cold stores had to do, said Swain.

A swathe of other simple design features and practical measures could be applied to make cold stores more energy efficient, delegates at the event heard.

For example, proper door and seal maintenance and monitoring, improved strip curtains, installing automatic closing doors and simply keeping doors shut would stop air infiltration and increase efficiency, said Swain. FRPERC data suggests such tactics could achieve energy savings of more than one third.

Similarly, FRPERC senior research project manager, Judith Evans, said: "You could achieve a huge amount of saving if you improve insulation."

A trial involving three cold stores indicated that installing 33cm of insulation reduced their energy use by an average of 64%.

More efficient mechanics

The equipment used within cold stores was as important as cold store design, said Swain, with the biggest single energy saving - 40% - achievable through installing evaporative condensers.

However, he added: "Electric refrigerator fans can be really bad news. Fan power increases with the cube of its velocity." Controllers that varied fan speed relative to the optimum temperature or more efficient fan motors could help, he said.

Use of variable speed fan drives was a major tip that emerged from research conducted by environmental consultancy Enviros for the British Frozen Food Federation.

But the study, Improving the energy efficiency of the cold chain, found addressing attitudes to optimum temperatures was even more vital. Cold stores were often run at -22°C, whereas keeping them at -18°C was sufficient and saved significant energy.

However, all the eight processors studied did not use sub-metering. If they had, they could have controlled temperatures and targeted savings better, the study concluded.

Refrigerant usage and leakage was another huge area for improvement. Of 30 sites surveyed for the Refrigerant emissions and leakage zero project, funded by the Institute of Refrigeration, 30% leaked, according to Dr Graham Maidment of South Bank University, who spearheaded the study. Often new caps and seals were the simple answer.

"One leading retailer [with this problem] has now gone out and instructed service engineers to fit 1,000 new caps," said Maidment.

Even buying the right kit initially and using it correctly played a part. "If systems had the proper spec and design in the first place, half these things wouldn't be issues," said Swain. Evans added: "Some firms are doing odd things like running freezer stores as chillers."