Two CO2 (R744) systems from the OEM Arneg, coupled on one skid, are providing a 13-story mixed-use building in Montreal, Quebec (Canada), with supermarket refrigeration as well as heating, 140°F (60°C) domestic hot water and air-conditioning throughout the structure.
The design and performance of the integrated HVAC&R systems, based on data gathered from March 1 to October 31, 2022, were the subject of a presentation at the ATMOsphere America Summit 2023, held June 12–13 in Washington, D.C. The event was organized by ATMOsphere, publisher of R744.com.
Presenters included Phillip Walker, Director of Refrigeration Solutions at Arneg Canada; Charles Vanelslande, Vice-President of Engineering at Vaudreuil-Dorion, Quebec-based contractor TechnoRef4; and Steven Bruneau, President of Montreal-based contractor Frigo-Zone.
The first floor of the building, called Elogia, contains an IGA grocery store. The remainder of the building houses condos, with office space on the 13th floor. The building required a safe, non-synthetic refrigerant with system piping sharing corridors with human traffic. “For obvious reasons, it came down to using CO2 refrigerant,” said Walker.
Because of the variable cooling and heating loads, “we decided to use two flash tanks – two different systems on one skid” in the central system, explained Vanelslande. Total capacity is 70TR (246.2kW). “The synergy between the two systems is very important,” said Bruneau
To manage the different loads, “we have VRF [variable refrigerant flow] on the first compressor, and we used two-stage compression on each unit to make sure we could manage the dew point properly for the grocery store.” said Bruneau.
Refrigeration runs 24/7 with a 65TR (228.6kW) capacity, but with HVAC the story changes. The HVAC (air-conditioning) had its first startup on March 17 for the 3TR (10.6kW) office-space load on the top floor. “Creating enough pressure change in the 70TR system to pump gas up 13 stories to meet the HVAC demand was the biggest challenge,” said Walker
The challenge was met by coupling the systems to maximize efficiencies, said Walker. “The refrigeration system maintains the pressure in the HVAC flash tank when the HVAC is idle, and when the refrigeration is in transcritical operation, the HVAC is cooling the refrigeration gas cooler outlet,” said Walker.
In addition, generating the pressure for the HVAC startup is easier at small temperature differences, said Vanelslande. “With a small differential, you have a better flow and no problems taking 3TR up 13 floors nor returning oil to the compressor.”
“We’ve heard a lot of people in the industry say that HVAC CO2 doesn’t exist, but we are doing it,” said Walker. He hoped next year to have more data concerning the HVAC system supporting the refrigeration system in transcritical mode from an ongoing test of a “specialized” heat exchanger.
Besides this building, the same three companies have installed a CO2 HVAC and refrigeration system in another multi-use structure, said Walker – what he believes are the first such installations in North America. Both have been in operation for a year and a half. He noted that the group has five more multi-use buildings with CO2 systems coming in the next year.
“We have a good array of testing data on this machine [in the Elogia building]”, said Walker. The data was based on Montreal ambient temperatures as hot as 94°F (34.4°C) with a dew point around 68°F (20°C) and winter temperatures as low as -30°F (-34.4°C).
The dehumidification load kicked in on April 26 when the dew point outside went above 44°F (6.7°C). The supermarket requires the sales floor dew point to be controlled between 47.3–55°F (8.5–12.8°C). “We got the bin data to show we are well within our controlled environment,” said Walker.
To improve efficiency, the store uses dew point demand to float suction temperature “instead of just driving HVAC out,” Walker said. He added that the store could also play with the temperature difference between the flash tank and the DX (direct expansion) coil by using “sophisticated” controls to narrow the difference to 7°F (4°C).
From March 1 to October 31, 2022, the total HVAC compressor run time was just over 3,000 hours, which was less than anticipated, according to Walker, who noted that “the improved sensible heat ratio of the DX coil reduced the time to satisfy demand.” Additional smart controls also improved energy efficiency, he added.
Data for the HVAC discharge and flash tank operation show the flash tank pressure staying steady – within 30psi (2.1bar) – of 600psi (41.4bar) at all ambient temperatures while the gas cooler pressure jumped from roughly 600psi at 44°F to 1,200psi (82.7bar) at 90°F (32.2°C).
The group gathered bin data for the HVAC system, tying the energy efficiency ratio (EER) to outdoor temperature. In transcritical mode, the system operated for 31.42 hours last year with a 9.17 EER. In the transition zone between subcritical and transcritical, the EER was 8.35 due to the cycling of the compressors, Walker said.
But the system spent most of the time in subcritical conditions to meet the dehumidification demand, Walker noted. The EER ranged from 20 to 13 in the 64–80°F (17.8–26.8°C) outside temperature range.
Headquartered in Italy, Arneg is a global manufacturer with 21 manufacturing facilities worldwide, with four facilities dedicated to compressor racks, Walker said.
TechnoRef4 is a group of four contractors specializing in commercial and industrial refrigeration. “We do blast freezers, multisystem flashbacks, and more,” said Vanelslande.
Frigo-Zone completed its first CO2 system in 2009. “Since that time, we’ve done over 30 transcritical systems in the Quebec, Canada, area in almost every aspect of CO2,” said Bruneau, including grocery stores and HVAC boosters
“We’ve heard a lot of people in the industry say that HVAC CO2 doesn’t exist, but we are doing it.”Phillip Walker, Director of Refrigeration Solutions at Arneg Canada