Refrigerant regulations are becoming more stringent, particularly in states such as California, where starting next year, there is a 150-GWP limit for new or fully remodeled facilities that utilize commercial refrigeration equipment containing more than 50 pounds of refrigerant. The federal government has not yet adopted this low GWP limit, but it could be on the table. Right now, the Environmental Protection Agency (EPA) is in the process of figuring out how it will administer the phasedown of HFC production and consumption in the U.S., and the final regulation should be finished by October.

Many food retailers have been considering their refrigerant options for several years, and when looking for alternatives under 150 GWP, CO₂ is usually a top contender. With a GWP of 1, it is environmentally friendly and will likely not be phased out in the future; however, CO₂ does operate at a much higher pressure than traditional HFC refrigerants, which may cause concern for both contractors and end users. For contractors who have worked with CO₂ for years, proper preparation and working closely with the OEMs go a long way to alleviating the fear factor.

Getting Started

CoolSys, which is headquartered in Brea, California, and is the parent company of refrigeration and HVAC services companies nationwide, is involved with the design, installation, and/or service of CO₂ systems on a daily basis, said Bryan Beitler, vice president and chief engineer at CoolSys.

The company designed and installed its first CO₂ system in 2010 in a supermarket in Southern California. The design was a subcritical system with an R-134a top cycle over CO₂, and the system combined a scroll parallel low-temperature rack and a pumped CO₂ supply for low- and medium-temperature fixtures. CoolSys was the Engineer of Record for the refrigeration and mechanical plans for the project but also worked very closely with the rack OEM, as it was their rack design that was incorporated into the project plans.

Since this was their first CO₂ installation, CoolSys personnel traveled to the OEM’s facility with their mutual customer to review design details. The OEM was also on-site during installation and start-up and was critical in making sure CoolSys was aware of any nuances that were new or foreign to the field technicians, said Beitler.

“We tried to surround ourselves with as many supporting entities as possible to make sure we were prepared in advance and that there were few surprises,” he said. “The first experience is always an exciting one, but it did take an investment in time to thoroughly understand those first projects. It is still ‘just refrigeration’; however, the cycle looks a little different. It is important to visit operating systems, take advantage of what is on the internet for supporting documents, talk to those who have had experience, and rely on the component manufacturers to support their products. Repetition goes hand-in-hand with comfort levels, so the more you install and the more technicians that are involved, the greater the comfort level.”

The first transcritical CO₂ system that South-Town Refrigeration & Mechanical (STRM), Brooklyn Park, Minnesota, installed was in 2017, and it was an application for a meat processing facility that had 10,000 square feet of processing with two coolers and one freezer. The system was set up to used chilled water through a city water loop, which made it the perfect application for efficiency, said Ryan Welty, vice president of STRM.

To prepare for this first installation, STRM had the OEM help design and engineer the system, as well as train their technicians. The company also hired the OEM to come in for startup in order to assist as needed.

“Overall, we were prepared and ready to address any issues as they came,” said Welty. “We are now designing and/or installing CO₂ systems monthly across our entire footprint. We have installed six systems over the past couple of years and expect to install three or more in 2021.”

At Omni Mechanical Solutions in Livermore, California, the OEMs primarily design the CO₂ systems that the company installs. Most of these are loop systems, said Joe Tenca, president and CEO of Omni Mechanical Solutions, and his company usually installs an average of one system a year. In order to prepare for the first installation, he and his staff took a training course provided by an OEM.

“CO₂ systems aren’t that much different than HFC systems,” he said. “They run at a higher pressure but are similar in design to a lot of the old two-stage systems that used to be common in the marketplace. In addition, there are safety and relief valves all over the system to prevent a mishap from happening. They also are 100% controlled by control systems that monitor all of the systems activity from the rack to the cases and coils.”

What To Know

Welty agrees that while there are not too many differences between CO₂ and HFC systems, there are a few that need to be considered.

“A CO₂ system will force the end user to their maximize control strategy through the use of electronic valves,” he said. “It will also be a loop piping system with small diameter piping, which means that on an installation, the electrical contractor needs to work with us more closely to ensure everything is set up correctly from a controls standpoint. Installing the pipe for the project should go a bit faster, though, as it is smaller pipe and there is less of it due to it being a loop system.”

Beitler added that while the heat transfer process is still quite similar between CO₂ and HFC systems, there are some unique items related to safety, system pressures, and the refrigeration cycle that are worth noting.

“As CO₂ is a higher pressure refrigerant, it is important for the designer and installer to select and install the correct pressure rated components to match the system design,” he said. “Tubing, valves, and all components must be rated for use in a higher pressure application. The designer must understand the proper components to specify and also provide clear design details to ensure that there is an uninterrupted path to the safety relief valve for the refrigerant to follow in the event of a pressure excursion. Finally, electronic expansion valves (EEVs) are used exclusively in DX applications, so a controls plan must be incorporated that provides an emphasis on fixture controls for each evaporator.”

Indeed, CO₂ systems use a great deal more electronic controls than HFC systems, as EEVs are used at all of the fixtures. For that reason, Tenca said that contractors should make sure their technicians are comfortable and proficient in working on control systems.

Many of the same installation techniques that are used for traditional HFC refrigerants apply to CO₂ as well, but according to Beitler, the following tips will help ensure a smooth installation:

• A clean system is paramount, so always purge with nitrogen in the right proportion;
• If high-pressure iron copper piping is used, ensure that all fittings and tubing are of a high-pressure rating. When pressure testing, test pressures must align with the ratings of the system;
• Have a helium leak detection system available prior to evacuation in order to locate hard-to-find leaks;
• Charging methods are somewhat different than chemical refrigerants, so make sure that there is adequate vapor pressure in the system prior to introducing liquid, or the resulting dry ice formation inside the system may ruin your day;
• Make sure the correct grade of CO₂ is used. Most manufacturers recommend Coleman grade, which has a purity level similar to beverage-grade CO₂. The supply chain may not always have backup Coleman-grade CO₂ available, so it is important to talk with customers about establishing a backup charge; and
• To maximize evaporator efficiency, ensure that the case controllers are performing correctly upon start-up, as this sets the tone for good product temperatures and efficient operation. Depending on the case controller manufacturer, each valve may have a transducer, suction temperature sensor, and coil inlet and outlet temperature sensors to calibrate and check.

If all this sounds too complicated or confusing, rest assured that it really isn’t, said Welty. Especially if contractors and technicians take advantage of the training programs offered by most OEMs.

“At first, our technicians were intimidated by CO₂ systems, but once they got it running, they realized it isn’t any different and that they have the skills and abilities to work on these systems,” he said. “If you’re new to CO₂ systems, take your time and think about everything you are doing. Use the method of ‘measure twice and cut once,’ and do not be scared to call for help or ask questions of others.”

Contractors should also not let fear of new technology dissuade them from learning about CO₂ systems, because they will be a big part of the future in both commercial and industrial refrigeration, said Beitler. He added that the keys to mitigating any fears or nervousness include having the proper training, tools, and equipment; making sure that technicians have a lifeline to reach out to when they get into a jam; providing basic safety and system operation instruction in advance; and finally, repetition.

“These systems are safe, the installation techniques are similar to chemical refrigerants, and the systems control and operate quite well,” he said. “All aspects of working with CO₂ systems have been rewarding and challenging, but our company has been fortunate enough to operate along the leading edge and gain experience and knowledge of these systems as they evolved.”