Daikin Europe, a division of Japanese manufacturer Daikin Industries, in observing the operation of its CO2 (R744) Conveni-Pack integrated HVAC&R condensing unit system at retail demonstration sites in Europe, found that user/staff behavior can have a “large impact” on energy consumption and that adhering to manufacturer installation guidelines in regard to system location “significantly” influences performance.
Nishant Karve, Environmental Research Engineer, Environmental Research Centre for Daikin Europe, presented the “lessons learned” from the Conveni-Pack demonstration sites and compared the lifecycle climate performance (LCCP) of the CO2 packs to the previous pack containing HFC (410A) refrigerant at the November 2022 ATMOsphere (ATMO) Europe Summit in Brussels. ATMO Europe was organized by ATMOsphere, publisher of R744.com.
Designed for convenience stores or small supermarkets, Daikin’s CO2 Conveni-Pack is an integrated refrigeration/air-conditioning/heating system using CO2 refrigerant. A prototype was first installed at a Belgium convenience store in January 2020. Traditionally, stores have two independent systems: One provides food refrigeration, and the other meets indoor heating/cooling demand. “The Conveni-Pack, on the other hand, is a combined unit satisfying all three of these functions with one outdoor unit,” Karve said.
“The heat taken from the refrigeration cabinets need not be wasted outside, but rather can be directed towards the indoor units as recovery heat,” said Karve. “If there is additional heating demand, the unit can also work as a heat pump and take the heat from the outdoors.”
In 2022, Daikin Europe installed the Conveni-Pack in 13 stores with locations in Belgium, the Czech Republic, France, Germany, Spain and the U.K. as demonstration sites to observe mainly energy efficiency and safety performance as part of Natural HVACR 4 LIFE, a sustainability-focused research project co-funded by the EU. This project is expected to run for three years and include 20 demonstration projects with two more sites currently planned.
Lessons from the field
Karve’s first Conveni-Pack example focused on the year-round energy consumption of a 600m2 (6,458ft2) supermarket in southeast Germany. Though the ambient temperature dipped to 11°C (51.8°F) in October and 7°C (44.6°F) in November, the store used little to no heating in those months because of the user behavior, Karve said. “We noticed the user set the indoor unit to cooling mode rather than the heating mode in these two months, which was surprising to us. By setting the units in cooling mode, they negated the need for heating in the supermarket, [which] caused energy savings.” The store wasn’t warm enough to trigger comfort cooling either.
He surmised that “possible internal loads [such as store occupants and equipment can] prevent indoor air temperature from dropping to unacceptable levels.”
Dakin looked at the distribution of energy consumption based on the indoor setting (heating and cooling). During the year, the control was set to heat mode 56% of the time, yet this accounts for 75% of the overall energy consumption. Indoor units can be controlled manually or by a building management system. In this case, the indoor temperature was set manually.
Karve noted that at 7°C ambient temperature, there were as many hours of cooling as heating. “This gives rise to questions about the perception of air temperature by the staff and over-dimensioning units for heating,” he said.
The refrigerant load in this example was 12.2kW (3.47TR), with a heating load of 23kW (6.5TR) and a cooling load of 20.4kW (5.8TR). The refrigeration load remained constant throughout the year, while the heating/cooling load varied with the ambient temperature.
The second example investigated the influence of installation location on the performance of the Conveni-Pack. An installation of an outdoor unit in an enclosed space with downward-facing louvers reduced performance by 20–25% compared to an open outdoor installation. Higher performance differences were observed with ambient temperatures above 30°C (86°F).
In the enclosed installation, the outtake air, instead of being released straight up, is directed downward above the intake, causing the air to circulate back to the intake. This makes the intake air at least 5°C (9°F) hotter than in an open installation, said Karve, causing operating pressures to rise above 10MPa (1,450psi) at higher ambient temperatures. At an ambient temperature of 30°C (86°F), the open installation operating pressure was 8MPa (1,160psi) compared to 9.2MPa (1,334psi) in the enclosed installation.
CO2 Improves LCCP
Karve compared the Conveni-Pack’s LCCP based on using CO2 or R410A and said that “the CO2 unit outperforms the HFC [one] with 21% lower life emissions over a lifetime of 10 years.” GWP was the major differentiator, and with electricity emissions heading towards decarbonization by 2050, “the CO2 unit becomes even more favorable.”
In January 2022, Daikin launched the ceiling-mounted Round Flow CO2 Cassette for its CO2 Conveni-Pack to support store air-conditioning/space heating. The Cassette features “intelligent sensors and 360 [degree] airflow,” with large flaps and a unique swing pattern, [which] ensure equal air distribution for maximum comfort,” Daikin said in a Linkedin post. “The CO2 Cassette has been successfully commercialized as a result of the observation of the demonstration sites,” Karve said.
To explore further optimization of the energy efficiency of the Conveni-Pack, Daikin integrated a thermal storage and adiabatic cooling system with a unit in Valencia, Spain. Testing during last summer’s heat wave demonstrated that “the system was technically feasible but not cost-effective,” he said.
“By setting the units in cooling mode, they negated the need for heating in the supermarket, [which] caused energy savings.”Nishant Karve, Environmental Research Engineer, Environmental Research Centre for Daikin Europe