Demonstrating the increasing viability of transcritical CO2 systems in warm climates, leading Australian retailer Woolworths recently presented data showing stable performance of one of its transcritical CO2 systems in a supermarket near Sydney during one of the country’s most severe heatwaves in January.
“On 25 January, we had a significant heat event in Sydney,” said Dario Ferlin, Woolworths’ sustainability engineer, at the recent AIRAH Refrigeration 2019 conference, held on 25-26 March in Melbourne.
“We had seven consecutive days over 35°C — of which five days were over 40°C. The final day was our peak day, where we hit just over 46°C on the condenser deck.”
The store, located in Prestons, New South Wales, was commissioned on 6 December 2018 and is the first transcritical CO2 system to fully serve a store’s entire HVAC&R needs for the retailer.
Ferlin presented temperature data for low temperature, medium temperature, and store ambient temperature versus outdoor ambient temperature for the period 25 January through 1 February 2019.
“The outdoor ambient temperature profile is represented by the black line,” explained Ferlin.
“Now, just as a reminder, we are controlling three climate zones with this transcritical [CO2] system. The low-temperature system, which are the freezers, the medium-temperature system, which is the chilled product, and the ambient store conditions,” he said.
The green line, Ferlin explained, is the saturated suction pressure profile for the low-temperature system. The grey line represents the same for the medium-temperature system, and the red line reflects the store’s ambient conditions.
“We had satisfactory climate control conditions in all three climate zones throughout the seven-day heatwave,” said Ferlin.
The use of adiabatic cooling plays a key role in managing the system’s energy use in extreme heat, Ferlin said.
“Adiabatics are fundamental to transcritical CO2 if we are to make any inroads on abating energy consumption,” said Ferlin.
Ferlin added, however, that the company is conscious of the fact that it does not intend to accept gains in energy efficiency in exchange for excessive water consumption.
“Mind you we’re being careful about how we use adiabatics,” he said. “We don’t want to be offsetting energy at the expense of water.”
Ten natural systems by 2020
This is Woolworths’ third installation of a transcritical CO2 system in Australia.
In its ‘Corporate Responsibility Strategy 2020’ report, the company states that, “by 2020 we will install ten natural systems employing technologies such as transcritical CO2 or water loop”.
The Woolworths installation in Prestons follows the installation of another fully integrated HVAC&R transcritical CO2 system at an IGA in Melbourne in March of this year.