Imperial’s heatwave report on Sainsbury’s intensifies calls for doors on fridges

A study by Imperial College of the effects of the 2018 summer heatwave on Sainsbury’s refrigeration systems has recommended that doors on fridges should be made a legal requirement, because of their energy saving benefit.

They also discovered systems struggling to cope with the heat. An analysis of refrigeration system alarm data revealed that during July 2018, a threshold temperature was crossed, ‘after which systems began struggling estate-wide.’

They said that an analysis of refrigeration system alarm data revealed that during July 2018, a threshold temperature was crossed, ‘after which systems began struggling estate-wide.’

They said: “A pressing concern under prolonged high ambient temperatures is systems failing to provide adequate cooling for safe perishables storage. If an asset encounters a significant fault or is unable to maintain the set-point temperature, stock must be removed from cabinets resulting in labour costs and inhibited sales performance. Refrigeration systems must therefore be robust enough to withstand the summer 2018 temperatures into the future.”

The research looked at the retailer’s ‘energy penalty’, defined as the increase in 2018 refrigeration energy consumption relative to the 2016/17 baseline. This was calculated for a sample subset of 30-stores, spread across the UK, and extrapolated to a 600-store template estate.

Researchers found that the energy penalty for July alone - where average temperatures were 2.67 deg C higher than the previous year - was 5.1 per cent to 11.2 per cent, or additional carbon emissions of between 616 tCO2e and 1,353 tCO2e. Imperial noted that the latter measure will be of increasing importance as the UK moves towards the legally binding net-zero emissions target for 2050 .

They concluded: “As a general rule, a 2 deg C increase on today’s average summer temperatures will increase the estate’s refrigeration energy consumption by 6.1 per cent or 7,835 MWh across June-August. Interestingly, no correlation was found between system age and the energy penalty, implying site-specific factors tend to drive the response to elevated temperatures.”

Other findings also include that there was negligible performance difference between HFC and CO2 refrigerants. This builds on previous research which indicated there is no longer a financial case for installing new HFC systems, largely because of the restrictions of the EU F-gas regulations. But the researchers also found that ‘managerial and behavioural factors were…crucial’ and so will be a further focus of study.

On the basis of the study, the researchers make a vast number of recommendations for the retailer and its systems, both short term and long-term.

Based on the energy data analysis and discussions with key stakeholders, we set out a series of technological, behavioural, managerial and policy recommendations to help mitigate the negative effects of higher summer temperatures on refrigeration system management.

Its short-term recommendations to minimise the impact of the heat wave include: adiabatic cooling for gas coolers, bringing an 8-12 per cent energy benefit; load shedding via removing non-essential cabinets in heatwaves; adding doors to cabinets and plastic strip curtains to coldrooms; and adapting the alarm regime from reactive to predictive.

For the longer-term, Imperial suggests investigating a series of options for CO2 systems, drawing on experience in warmer climates. These include: oversizing the gas coolers to increase robustness in the face of temperature spikes; adding parallel compression, which has shown 10-15 per cent efficiency savings over standard booster systems, or ejector technology, which can save up to 30 per cent over boosters; and tackling the ‘serious issue’ of gas cooler corrosion, which currently requires component replacement every five years, via better fin spacing; and installing more heat recovery systems to the installations. Imperial estimates that 40 per cent to 100 per cent of supermarket heating demand could be met. A recent UK study indicated 32 per cent reduction in total supermarket energy consumption using heat recovery.

A further recommendation is to combine CO2 systems with a ground source heat pump to reject heat to the ground in summer, for later utilisation in winter. This, the researchers note, requires access to land, but could provide a 20 per cent energy reduction.

Imperial says that greater communication between retail staff and the engineers is crucial, affecting areas such as component placement, particularly gas coolers; correct use of nightblinds; and appropriate frequency of refrigerant top-up.

Imperial concludes by calling for mandatory doors on fridges, noting the 40 per cent potential energy reduction, saying ‘such massive consumption reduction must warrant action’.

More controversially, it also calls for cabinet maintenance to be made mandatory, on the basis of its contribution to energy consumption.