Integrating a building glycol loop to a supermarket transcritical CO2 (R744) system in Canada yielded “superior” results, according to Phillip Walker, Arneg’s Director of Refrigeration Solutions, who spoke during the ATMOsphere America 2022 conference on June 7–8.
ATMO America was organized by ATMOsphere (formerly shecco), the publisher of R744.com.
The integrated CO2 glycol loop provides subcooling for the gas cooler, heating for domestic water and maximum heat recovery – making it significantly more efficient than a comparable system without the integrated loop.
The result was that the integrated supermarket system, installed in a Montreal supermarket, needed 13.79% less horsepower than one without a glycol loop, said Walker. The reduced power demand resulted in 8.1% energy savings. The integration also reduced flash gas in the system by 35.55%.
“Supermarkets have unique requirements, and unification between HVAC and refrigeration yields favorable results,” said Walker, referring specifically to Canada, where the ambient temperatures can vary greatly but tend to be cooler on the whole than other North American regions.
Arneg has adopted a holistic approach to designing refrigeration systems, using heat recovery to subcool the gas cooler outlet in the summer and for dehumidification. The return temperature in the glycol loop is 85°F (29.4°C), meaning it can be used to regulate the temperature in the gas cooler outlet, Walker explained. With pumps and valves “I can subcool it, I can heat it, I can control it, I can induce flash tank stability,” he said.
“For every degree you can reduce the gas cooler outlet, the impact is significant, so if we can knock off 3–4°F (1.6–2.2°C) it has a significant impact, and the cost consideration is minimal,” Walker added.
In the winter the glycol loop can also be used for heating freezer floors, radiant floor heating, and air-to-air heat recovery in the ventilation units.
The Montreal system is designed for a dry gas cooler with a delta T of 3 to 4.8°F (1.6 to 2.7F) which is typical for Arneg systems in Canada. Most of Arneg’s systems have hot gas defrost and variable frequency on the lead compressors.
There are currently two stores using the integrated glycol loop system in Canada, with a third coming into operation shortly. In total, Arneg has more than 20 transcritical CO2 stores in Canada, though none in the U.S. so far. Globally Arneg has about 1,000 CO2 systems in operation, more than half of which are transcritical booster systems.
“For every degree you can reduce the gas cooler outlet, the impact is significant, so if we can knock off 3–4°F (1.6–2.2°C) it has a significant impact, and the cost consideration is minimal.”Phillip Walker, Arneg
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