This past December, when Australian supermarket chain Woolworths commissioned its latest transcritical CO2 system for a new 3,200m2 (34,444 ft2) supermarket in Fulham Gardens, a western suburb of Adelaide, it faced two major challenges: a lack of skilled technicians and very hot weather.
Both challenges have been overcome, according to Dario Ferlin, National Sustainable Engineering Manager for Woolworths.
Woolworths has installed more than 40 transcritical CO2 systems but this was its first in the state of South Australia, where CO2 systems are relatively new. So the chain had to help establish the local support for skilled technicians and technology supply.
“In areas of Australia with very few or no natural refrigerant installations, we need to support the project team and help them upskill,” said Ferlin.
To do this, the Woolworths project team, technology suppliers and local Adelaide-based contractors all collaborated to hold transcritical CO2 technology master classes over the course of several days.
“We started with transcritical cycle fundamentals right through to navigating the system controllers in the plant room,” said Ferlin. “By creating a solid local support crew, we are setting up the site for the best possible start.”
The local Adelaide-based installation contractor was Sims Refrigeration. The transcritical CO2 system was supplied by SCM Ref Australia, the Australian manufacturing arm of Swedish refrigeration system manufacturer Beijer Ref.
The system consists of two of SCM Ref Australia’s Kirby branded eCOBoost transcritical CO2 racks.
The racks use Emerson’s Copeland brand of CO2 semi-hermetic compressors and iProRack brand of electronic controls. The transcritical CO2 system serves around 180kW (51TR) of medium temperature or chilled capacity and 40kW (11TR) of low temperature or freezer capacity.
Designing for 45°C (113°F) ambient
The second biggest challenge after establishing local skillset and technology support was dealing with Adelaide’s climate.
The city experiences some of Australia’s hottest temperatures, regularly seeing heat waves during the summer with temperatures exceeding 40°C (104°F) for several days in a row.
According to Ferlin, this year is no exception (it is currently mid-summer in Australia).
“Whilst the east coast of Australia is dealing with the effects of La Niña this year (wet and mild summer), Adelaide seems to be ploughing into another hot summer with 38°C (100.4°F) forecast for this Friday,” Ferlin said this past December.
“So most definitely we need to design the system to account for ambient temperatures as high 45°C (113°F).”
Ferlin explained that the system design takes these conditions into account by making use of adiabatic pre-coolers for the gas coolers, appropriately sized coils and fans to account for high gas-cooler exit temperatures, and parallel compressors.
Ferlin has explained extensively in the past that adiabatic cooling systems are key to managing the energy use of transcritical CO2 systems in high ambient temperatures.
In 2019, Ferlin detailed how a Woolworths transcritical CO2 system in Prestons, New South Wales managed stable operation during a heat wave in January in Sydney with adiabatic cooling.
“We had seven consecutive days over 35°C (95°F) — of which five days were over 40°C (104°F),” said Ferlin said during a presentation at AIRAH Refrigeration in March 2019.
“The final day was our peak day, where we hit just over 46°C (114.8°F) on the condenser deck. Adiabatics are fundamental to transcritical CO2 if we are to make any inroads on abating energy consumption.”
At the same time, however, the availability and sustainable consumption of the water supply for the adiabatic cooling system is a very important consideration.
Ferlin spoke about how this created another challenge for the installation at Fulham Gardens in Adelaide – treating the water.
“Untreated water in many Australian regional areas, as well as some capital cities, is not suited to processes such as adiabatic cooling of gas-coolers,” said Ferlin.
“Calcium chloride quantities can be higher than maximum allowed thresholds, so water treatment systems need to be provided for,” he noted. “Again, these need to be robust and reliable with minimal maintenance requirements.”
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