UK: Tests carried out by a major supermarket have shown that refrigerated display cases are at their most efficient when specifically designed for use with doors.

As part of a rethink of its refrigerated display case tender programme, Central England Co-operative recently conducted tests on four cases with independent consultants Mistral Technical Services.

“We decided that procurement of refrigerated display cases warranted a more vigorous process than was previously being conducted,” explained Central England Co-operative’s facilities and administration manager Kevin Collins.

“A test programme was devised in collaboration with Central England Co-operative’s independent consultants Mistral Technical Services, to benchmark a 2500mm medium temperature display case fitted with wardrobe style doors to our specification from four short-listed case providers.”

The supplier short list was produced based on traditional metrics; capital cost, ability to deliver to the store development programme and energy figures based upon the manufacturers’ published data in line with the testing methods in ISO23953:2014 Climate Class 3 (25°C/60%RH).

Keen to understand the energy performance in a store environment, Central England Co-operative portioned off a non-trading section of a store for a one month test period during the summer of 2017.

This ensured a consistent baseline and comparison of how four cases compared under the same conditions. The four cases were each piped to independent condensing units of the same manufacture and model. Performance was logged using an energy monitoring system with factory-fitted case probes supplemented with a product probe installed in the identical position in each case.

The Co-op’s existing refrigerant – the lower GWP R404A replacement R407F – was used for the tests. Tests were also carried out with its new refrigerant R448A.

Testing looked at aspects such as energy monitoring, air-flow, insulation, structural integrity and the Society’s retail colleagues were invited to assess any merchandising issues and score the cases.

The clear winner as the best energy performing case was the model that had been designed specifically for use with doors and a corresponding evaporator coil design. As well as being 43% more efficient than the worst performing, it also required a 25% reduction in refrigerant charge compared to the other cases.

All other cases were designed for open application and fitted with doors. According to the supermarket, smoke testing revealed these designs suffered from excessive air spillage – even when some of the doors were closed. Air spillage was described as “significant” when the doors were opened.

These same issues were also said to have been evident in thermal imagery as was the superior insulation properties of the best performing case which was the only one of dual carcass design.

The tests also contradicted the generally accepted notion with open cases that the larger the total display area, the larger the penalty in energy performance. The best performing cabinet also had by far the largest total display area.

The Central England Co-operative now realise that its traditional tendering approach of prioritising in favour of initial capital expenditure would have arrived at the wrong buying decision.

It now recommends that any retailer standardising on a selection of medium temperature cases with doors should investigate to ensure they are buying equipment designed specifically for door applications. It also says that the best energy performer needs to be judged against air flow efficiency, evaporator design, component selection and thermal integrity.

And, whilst ISO23953:2014 Climate Class 3 data is an invaluable benchmark tool and not in dispute, the Central England Co-operative says it is also important to test against typical store conditions, eg ISO23953:2014 Climate Class 0 (20°C/50%RH) to optimise on capital spend and energy usage.

Central England Co-operative is one of the largest independent retail co-operative societies in the UK. Employing over 8,000 staff, it achieved gross sales of £927m in 2016/17.