What are secondary refrigerants?
Secondary refrigerants are fluids that carry heat from the point of use to a primary refrigeration system. Common types include water and glycol mixtures, salt brines, and CO₂ used as a volatile secondary fluid. The primary system, often using ammonia, propane, CO₂, or an HFC, cools the secondary fluid in a heat exchanger, and the secondary fluid is pumped to display cases, cold rooms, process equipment, or air handlers. Because the secondary fluid circulates in a closed loop, it can be monitored and maintained much more easily than refrigerant spread through an entire building.

Why are secondary-loop systems growing?
HFC phase-down rules limit the amount of high-GWP refrigerant available and favor systems with small charges. Secondary loops allow supermarkets and industrial users to keep the primary refrigerant in a machine room, using natural refrigerants safely, while the secondary fluid distributes cooling throughout the facility. This reduces leak risk, simplifies maintenance, and helps meet safety standards for flammable and toxic refrigerants. This approach has been widely adopted in European supermarkets and is spreading in North America and Asia.

How are glycols used?
Ethylene glycol is widely used in industrial cooling and HVAC systems because of its low cost and good heat transfer, while propylene glycol is preferred in food, beverage, and pharmaceutical applications because of its low toxicity. Glycol mixtures protect against freezing and include corrosion inhibitors. They are used in supermarket loops, chillers, heat pumps, ice rinks, and data center cooling. Concentration is chosen based on the lowest expected temperature, with stronger mixtures giving more freeze protection but higher viscosity.

What role do salt brines play?
Calcium chloride and sodium chloride brines are traditional secondary refrigerants for ice rinks, cold stores, and industrial process cooling, offering low freezing points at low cost but requiring careful corrosion control. Potassium formate and potassium acetate brines offer lower viscosity at low temperatures and are used in supermarket low-temperature loops and some industrial applications. Formate brines are often marketed under trade names by suppliers such as Temper Technology and Kilfrost.

How is CO₂ used as a secondary refrigerant?
In some systems, CO₂ is pumped as a volatile secondary fluid that evaporates in display cases or air coolers and is condensed by a primary ammonia or propane system. Because CO₂ changes phase, it carries more heat per kilogram than glycols, reducing pipe sizes and pumping energy. CO₂ secondary systems are used in supermarkets, cold stores, and ice rinks. This approach combines the benefits of natural refrigerants with very efficient heat distribution.

Why is data center cooling important?
AI and high-performance computing are driving adoption of direct-to-chip and other liquid cooling technologies, which use water and glycol-based coolants to remove heat from processors. In May 2026, Dow launched the Dow Coolant Care Network to support data center operators with fluid testing, analysis, and field services for its DOWFROST LC and HD heat transfer fluids. Clariant offers Antifrogen PG 25, a propylene glycol-based fluid for direct-to-chip cooling. Data center operators require fluids with low electrical conductivity, strong corrosion protection, and resistance to microbial growth.

How do heat pumps use secondary refrigerants?
Ground-source and water-source heat pumps use glycol or brine loops to collect heat from the ground or water. Monoblock air-to-water heat pumps with propane keep the refrigerant outdoors and use water or glycol to carry heat into buildings. Industrial heat pumps also use secondary loops to deliver process heat safely. Ground-source heat pump loops can contain large volumes of fluid that must last for decades.

What are the main challenges?
Secondary loops add pumps, heat exchangers, and fluid, which increase energy use and capital costs compared with direct systems. Fluid maintenance, including monitoring of corrosion inhibitors and pH, is essential to prevent equipment damage. Viscosity at low temperatures can limit efficiency, which drives development of new fluids. Suppliers are developing low-viscosity fluids and better inhibitor packages to address these issues.

How is the market distributed?
Large users and system builders buy directly from producers, while distributors, HVAC&R equipment suppliers, and specialty fluid suppliers serve contractors and smaller users. Online sales channels serve smaller buyers. Service providers offer fluid testing and maintenance, adding recurring revenue. Fluid testing and replenishment services are an important way for suppliers to build long-term customer relationships.

Which secondary refrigerants market segments are growing fastest?
Propylene glycol fluids; data center cooling; heat pumps across residential, commercial, and industrial uses; supermarket and convenience store secondary loops; and specialty fluid suppliers offering testing and maintenance services are the fastest-growing segments. Data center cooling fluids are expected to show the highest growth rate, as liquid cooling becomes standard for high-density AI computing.