Climate change is arguably the defining crisis of our time. As such, forward-thinking industries are seeking sustainable refrigeration solutions that not only meet regulatory requirements but also offer superior performance. One such solution that has gained significant attention is the use of R744 (CO2) as a natural refrigerant for certain applications.
Advances in technology have made leveraging high-pressure and high-temperature CO2 a viable alternative to synthetic refrigerants such as hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs). “People are focusing on trying to use natural refrigerants, or low global warming potential refrigerants, to reduce their environmental impact,” explains Parham Eslami Nejad, Vitalis’ R744 Program Manager.
R744 (CO2) has an ozone depletion potential (ODP) of zero, and a global warming potential (GWP) of one (CO2 is the baseline against which other compounds are measured for their GWP), making it among the most environmentally friendly natural refrigerants. For comparison, some of the most common HFCs’ GWP can range from 323 to 12,000 over 20 years according to the U.S. Environmental Protection Agency.
“Hydrocarbons like propane or butane have lower, based on values reported recently by the Intergovernmental Panel on Climate Change (IPCC), GWPs than CO2,” Eslami Nejad says. “So they are environmentally friendly, but the flammability is an issue,” which can create additional building rating expenses.
With its remarkable efficiency, lower operational costs, and unique suitability for industries with both heating and cooling needs, R744 (CO2) presents itself as a better refrigeration solution—in the right application.
R744 Efficiency
Eslami Nejad notes that when it comes to refrigeration or heat pump systems, energy efficiency is a paramount concern. In this regard, R744 as a refrigerant stands out as a highly efficient option for certain applications.
“The thermophysical properties and the thermodynamic characteristics of R744 are pretty different from any other refrigerant,” he explains. Unlike some synthetic refrigerants, R744 operates at higher pressures and can achieve lower temperatures efficiently, making it particularly well-suited for applications in low-temperature environments.
“For example, if you are trying to heat water or any other fluid from pretty low temperatures to relatively high temperatures, R744 definitely is the best,” Eslami Nejad says. When operating under transcritical conditions, R744 systems can simultaneously chill and heat. Vitalis’ Coolshift R744 chiller package can produce up to 702,000 BTUs/hour of cooling capacity and more than 532,000 BTUs/hour of heat reclaim, all while using less than 150 kW of power.
“When you are using a high-efficiency heat pump, for each unit of electricity that you consume you produce seven to eight units of heat and cool combined. We are talking about 700% or 800% efficiency compared to gas boilers, which is 80%,” Eslami Nejad says.
What’s more, synthetic refrigerant heat pumps cannot necessarily reuse that heat. When compressing synthetics to try to increase heat reclaim, synthetic compounds become unstable. In its transcritical format, R744 can be continually compressed, expanding its heat retention ability and allowing it to be used in other operations (or for general heating).
Even accounting for pressure drop—the fluctuations in pressure as the coolant circulates throughout the system—R744 (CO2) refrigeration units remain extremely efficient compared to other refrigerants. “Higher pressure drop doesn't mean higher energy consumption for CO2 circulation. Because of CO2’s very unique thermophysical properties, even if you have the same or even higher pressure drop in the pipe, you consume up to 10 times less energy to circulate liquid CO2,” Eslami Nejad says. “That's why it makes it the best for when you have long pipes or when you have different branches” as the coolant will be evenly distributed.
Costs of R744 Refrigeration
Reducing operational costs is a top priority for any business. Life cycle analyses that consider capital expenditures and all costs associated with refrigerant leakage, natural gas consumption, and metric tons of CO2 equivalent reductions show that R744 refrigeration systems have competitive ROIs.
While the initial cost of an R744 unit might be more expensive because of the need to operate at higher pressures, “R744 systems are four to five times more compact than other refrigerants,” Eslami Nejad says, meaning that freed space can be converted into a productive area rather than remain a cost-driver. Smaller pipes also are less expensive and improve efficiency by reducing the exposed surface area from which heat can dissipate.
Businesses converting to an R744 system might also be able to save on installation by keeping certain components of their existing refrigeration systems and adapting them for R744.
Additionally, unlike many synthetic refrigerants, R744 is widely available and low-cost, and inexpensive CO2 sensors can eliminate accidental poisoning risks. “If you have a refrigerant leak, replacing synthetic refrigerants is more costly compared to recharging your system with R744,” Eslami Nejad says. “There definitely are some cost advantages.”
Potential Applications
R744 performance is unmatched in industries where demand for simultaneous heating and cooling is required. Examples include breweries, supermarkets, and the dairy industry. R744's versatility as a refrigerant offers a unique solution to meet this specific requirement. By using R744, businesses can harness the heat generated during the refrigeration process and repurpose it for heating applications, thereby achieving a dual benefit.
Breweries can utilize this heat for mashing and brewing operations while using refrigeration capacity of the unit to chill finished products. Supermarkets can employ it for space heating during the colder months while keeping freezers operating efficiently. The dairy industry can leverage R744's capability to simultaneously cool milk and produce hot water for cleaning processes.
In the right conditions, R744’s versatility is unmatched. Its inherent ability to provide both heating and cooling within the same system brings operational efficiency, reduced energy consumption, and cost-effectiveness to industries that rely on such capabilities.
It’s Inevitable
As sustainability and energy efficiency become central considerations in refrigeration systems, regulators have already enacted standards that render legacy technology obsolete. The adoption of R744 systems offers a myriad of benefits. Its efficiency, lower operational costs, and suitability for industries requiring simultaneous heating and cooling make it an ideal choice for businesses looking to embrace environmentally friendly solutions and future-proof their operation without compromising performance.