Heat Reclaim CO2 Refrigeration
Left to right: Andy Baker, Your Clean Energy; Scott Martin, Hillphoenix; and Peter Reist, Flō Energy Solutions presenting at ATMO America 2024.

ATMO America: Optimized Heat Reclaim from CO2 Refrigeration System Cuts Natural Gas Use by 84% in Pennsylvania Store

Flō Energy Solutions’ optimized coil leverages heat reclaim to enhance payback for CO2 refrigeration systems, says Hillphoenix.

A small-format store in Pennsylvania with a Hillphoenix Flex CO2 refrigeration system cut its natural gas use for comfort heating during winter by 84% after replacing its passive reclaim coil with a Flō Energy Solutions’ optimized direct CO2 (R744) heat reclaim coil.

With a slight increase in CO2 rack pressure head, a direct CO2 heat reclaim coil inside a DOAS+ HVAC unit using Adaptive Multi-Path Technology boosts reclaimed heat by roughly three times that obtained from passive CO2 heat reclaim, according to Peter Reist, Director of Product and Sales Strategy at Flō Energy Solutions.

“We effectively use the compressors on the rack to heat the store, with the U.S. Department of Energy classifying it as a heat pump,” Reist said.

“This is an exciting time for retailers,” said Scott Martin, Senior Director of Industry Relations and Compliance at Hillphoenix. “We can heat a store with its CO2 refrigeration system to enhance the payback of that system.”

In a heat pump case studies presentation at the ATMOsphere (ATMO) America Summit 2024, Reist and Martin outlined the technology, the associated COPs and the data obtained from the Pennsylvania store. ATMOsphere is the publisher of NaturalRefrigerants.com, and the ATMO America Summit 2024 was held in Washington, D.C., June 10‒11.

“We can heat a store with its CO2 refrigeration system to enhance the payback of that system.”

Scott Martin, Senior Director of Industry Relations and Compliance at Hillphoenix

Free heat versus boosted

According to Martin, the Pennsylvania store, operating with a backup natural gas heater, had a passive CO2 coil for heat recovery, allowing a direct before-and-after energy-data comparison between the two coils.

Using data collected from January to March with ambient temperatures ranging from 30 to 50°F (−1 to 10°C), Reist showed the store used 58.6MBH of natural gas for comfort heating with the passive heat reclaim coil. However, with the optimized coil providing boosted heat reclaim, it only used 9.3MHB of natural gas.

Reist also used the data to compare the heating efficiencies of a boosted direct CO2 heat recovery system to an electric resistance heater and an air-source heat pump (ASHP), with the “incremental COP” accounting for the extra energy used to increase the discharge pressure.

An electric resistance heater operates with a COP of 1 regardless of the outside temperature. A synthetic HVAC refrigerant ASHP operates more efficiently at higher ambient temperatures, with COPs ranging from 2.5 at 20°F (−6.7°C) to 3.5 at 50°F. The boosted CO2 heat recovery system operates better at lower ambient temperatures, with an incremental COP of 6.0 at 20°F and 5.3 50°F, making it roughly six times more efficient than electric heat and twice as efficient as synthetic ASHPs.

Another advantage of the boosted CO2 HVAC system that Reist outlined comes from its ability to maintain comfort heat output at extremely low ambient temperatures, with a COP of 6.7 at −20°F (−28.9°C). ASHPs, on the other hand, only work down to certain outdoor temperatures, he explained.

Moving forward

According to Reist, Flō Energy Solutions will soon install its 1,000th direct CO2 heat reclaim system, collecting free heat from CO2 racks running at minimum nominal pressures. “However, with passive reclaim, heat is still discharged to the atmosphere through a gas cooler.”

Martin confirmed that statement. “I’ve stood on the roof of a supermarket many times in the winter, even in the snow, and seen the condenser fans or the gas cooler fans slowly turning,” he said, adding that almost every CO2 system built by Hillphoenix includes passive heat reclaim.

“With a slightly higher operating CO2 pressure head, we can support decarbonization by capturing all the heat produced by a CO2 refrigeration system with active heat recovery using an ‘incremental’ amount of additional electricity,” Reist explained.

Reist feels that with some adjustments, they can eliminate the need for natural gas heating in the Pennsylvania store by capturing the heat lost in the field piping between the rack and the HVAC unit. “In the past, we wanted to move the heat from the compressors into the atmosphere, but, now that we can put it to useful work, we want to collect it,” he said.

To better capture the heat, Reist suggested insulating the field piping and running the piping under the roof deck instead of over the top.

Regarding the scalability of the technology, Martin indicated that it works well for larger stores with additional heat recovery potential from more equipment.

“In many cases, we can heat the entire store or at least provide all the heating that a single HVAC unit needs with the waste heat stream,” Reist said, noting that the density of refrigeration in a store roughly balances its space heating demand.

Another use for the optimized coil outlined by Reist includes summertime store dehumidification. This is accomplished by using either a reheat coil to temper the air for dehumidification or by adding field piping to a reclaim coil on the CO2 refrigeration unit. “From an HVAC standpoint, it’s almost price parity,” Resit noted.

According to Martin, the boosted CO2 heat reclaim coil adds minimum cost to a CO2 refrigeration system since Hillphoenix’s systems already incorporate a free heat reclaim coil.

When asked about adding comfort cooling to the CO2 refrigeration system, Martin invited the industry to stay tuned. “It’s possible,” he said. “We are doing other things and hope to have more case studies to share next year.”

“We can support decarbonization by capturing all the heat produced by a CO2 refrigeration system with active heat recovery using an ‘incremental’ amount of additional electricity.”

Peter Reist, Director of Product and Sales Strategy at Flō Energy Solutions

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