As Europe’s food retail sector strives to improve its energy efficiency, Accelerate Europe compares how CO2 and hydrocarbons are helping to reduce energy consumption in supermarkets.
Supermarkets are estimated to be responsible for around 3-4% of the total energy consumed in an EU country, according to a 2016 report by the EU-funded SuperSmart project. As Europe’s food retail sector strives to improve its energy efficiency, Accelerate Europe compares how natural refrigerants CO2 and hydrocarbons are helping to reduce energy consumption in supermarkets.
The SuperSmart report, which was funded under the EU’s Horizon 2020 programme and put together by partners including shecco (publisher of this website), noted that a large proportion of the average European supermarket’s total energy costs come from lighting, heating, ventilation and air conditioning, with the biggest share coming from refrigeration.
Analysis collated by SuperSmart revealed that refrigeration typically takes up 35-50% of total energy use. Reducing the energy consumption of supermarket refrigeration systems, therefore, can deliver significant cash savings.
The efficiency debate
A study conducted by HVAC&R component manufacturer and solutions provider Emerson, in conjunction with German research institute ILK Dresden, purports to hold the answer. It compared the efficiency of CO2 and hydrocarbon systems. The research, published in January 2018 and conducted from 2015 to 2016, reveals that hydrocarbon integral (or self-contained) display cases with a condensing water loop are more efficient than remote CO2 transcritical rack systems.
To compare the CO2 and hydrocarbon (in this case propane; R290) setups, the study focused on a typical European discount store with 10 display cases and a vending area of approximately 1,000 m2 (which is within the most common size category for a European supermarket as identified by the SuperSmart report).
The analysis compared integral propane (R290) and remote CO2 systems and found that by opting for the propane setup, retailers could achieve savings on maintenance, energy consumption and refurbishment of €50,000 per store over a 10-year period. “Any operator with 10,000 stores could therefore achieve potential savings of more than €500,000,000 over a ten-year lifespan of their refrigeration systems,” said Emerson in a press release.
What about heat reclaim?
The Emerson/ILK Dresden study does not include heating or air-conditioning costs in its energy, installation or running costs breakdown, a factor readily acknowledged by Eric Winandy, director (integrated solutions) at Emerson Commercial & Residential Solutions and his colleague Thomas Tomski, vice-president (marketing).
Yet system integration can lead to cost savings. Instead of having separate HVAC and refrigeration systems, retailers are increasingly looking at combining them into one HVAC&R solution.
Delhaize Belgium, part of the Ahold Delhaize group, is using heat reclaimed from a CO2 rack installed in a Brussels supermarket to warm the greenhouse of a rooftop ‘Urban Farm’, as well as to provide heat and hot water for the store below (see Accelerate Europe, spring 2018 edition).
Research conducted by SuperSmart, citing several studies, contends that heat recovery can increase the total COP of a CO2 transcritical system by 20%.
The Colruyt Group’s Colin Bootsveld, a project engineer at the Belgian retailer, is in a good position to compare the performance of CO2 and hydrocarbons. The retailer has opted for propane chillers in its stores in Belgium and CO2 remote systems in its Colruyt Prix Qualité stores (one of the brand names under which the Colruyt Group operates in France).
“In France, our colleagues have opted for CO2 cooling,” Bootsveld told Accelerate Europe. “The main reason was that we did not have the engineering capacity in Belgium to support the introduction of hydrocarbon chillers in France, and CO2 was commercially available.”
“The first impression is a disappointment. The COP has gone down significantly and the energy savings are not as large as expected. We found that the integration on the hydraulic side needs improvement."
– Collin Bootsveld, The Colruyt Group, on CO2 heat reclaim
They used heat reclaim in these stores. “The first impression is a disappointment. The COP has gone down significantly and the energy savings are not as large as expected. We found that the integration on the hydraulic side needs improvement. In the end both CO2 and hydrocarbon systems need to transfer their heat to a water-based distribution system, so this part is essentially the same for both,” he says.
On the other hand, Bootsveld says, “a CO2 system can provide hot tap water, whereas our hydrocarbon chillers cannot. Theoretically it would be possible to use the superheat from the hydrocarbon chillers to provide 10% of the waste heat at high temperature levels”.
The Colruyt Group is currently testing CO2 heat pumps for tap water. “The nominal 3.5 kW heating power satisfies perfectly the needs of our butcheries in Colruyt supermarkets,” he explains. “The results are satisfying, but we are disappointed to see so few Japanese manufacturers bringing these heat pumps to the European market.”
“Also we have noticed that the CO2 heat pump is very effective in heating cold tap water to 65°C but that the efficiency drops when we introduce a recycle of hot water, which is necessary in larger systems. In that case hydrocarbons would become an interesting possibility,” he says.
Dealing with warm ambient climates
Efficient heating and cooling depends not just on the choice of refrigerant but also the location of the system. CO2 used to be seen as inefficient in warm climates as the refrigeration system gets closer to the transcritical point. But developments like ejectors, parallel compression and adiabatic cooling are helping to mitigate this.
“Thanks to the parallel compressor and the ejector, the summer COP is now very good and comparable with the HFC gases,” Enrico Zambotto, refrigeration director at Arneg (a leading provider of commercial refrigeration equipment using both hydrocarbons and CO2), told Accelerate Europe.
David Guthörl, head of the ‘Energy/CO2 Sustainability Unit’ at Swiss retailer Coop, agrees: “The difference in climate can be mitigated by the ejector which provides the necessary efficiency boost of the CO2 technology (in cold as well as in warm climates). In the cold climate more heat is needed for heating [through heat reclaim], which is comparable with cooling at high ambient temperatures.”
“[In hydrocarbon cabinets] the energy usage still is far from efficient as the waste heat emitted has to be dealt with separately."
– David Guthörl, Coop
In hydrocarbon cabinets, Guthörl asserts, “the energy usage still is far from efficient as the waste heat emitted has to be dealt with separately”.
Integral water-cooled systems cited in the Emerson/ILK study can solve this problem. “The study was based on self-contained hydrocarbon cabinets with a condensing water loop,” says Emerson’s Tomski. “Therefore, heat is transferred outside of the store.”
Emerson’s Winandy told Accelerate Europe that both of the tests done by ILK took place in Germany, in relatively low ambient temperatures. They conducted a sensitivity analysis showing that using hydrocarbon cabinets in Barcelona gains a 10% efficiency edge over CO2, as propane works better in warmer conditions. In the colder climate of Gothenburg, CO2 gained 4% over hydrocarbon technology.
AHT, who manufacturers hydrocarbon-based cabinets including integral water-loops, hails the energy savings from using the heat that is rejected by hydrocarbon cabinets. “During spring, autumn and winter, you can save energy, because the ‘rejected heat’ will be re-used to heat the store,” argues AHT’s laboratory manager Werner Schwaiger. “For us it is clear – hydrocarbons are the best technology in terms of energy saving (reduction of CO2).”
While comparisons between CO2 and hydrocarbon systems are difficult to make given the many variables in play, it is clear that many European retailers are opting for natural refrigerants.
To learn more about how retailers are deciding between one natural refrigerant and another, please read the full version of this Accelerate Europe ‘Technology Focus’ here.