A secondary refrigerant is a heat transfer fluid that carries thermal energy between a primary refrigeration circuit and the load, without undergoing phase change itself. Common secondary refrigerants include water, glycol solutions, and specialized brines that circulate through piping to cooling coils or direct-contact applications. This approach separates the volatile refrigerant system from end-use locations, improving safety and system flexibility.
Technical Details
Secondary refrigerants typically operate in liquid form within temperature ranges of -30°C to +15°C, depending on formulation. Water-glycol mixtures provide freeze protection down to -25°C with specific heat values of 3.2-3.5 kJ/kg·K. Propylene glycol solutions prevent bacterial growth and corrosion better than ethylene glycol alternatives. System pressure drops to 2-5 bar, enabling lighter piping and simpler component requirements compared to direct refrigerant circuits.
Applications
Secondary refrigerants suit retail food display cases, warehouse cooling, and applications requiring long distribution distances. They eliminate refrigerant charge in occupied spaces, reducing EPA regulatory compliance burden. Circulation pump power requirements add 5-10% to system energy consumption, but safety and installation advantages often justify this penalty in commercial facilities.