An indirect fired chiller uses a separate heat source, such as steam or hot water from an external boiler or district heating system, to power the absorption cooling cycle. This configuration provides flexibility in heat source selection and allows operators to switch between multiple fuel types or utilize waste heat from industrial processes. Indirect fired chillers range from 100 to 10,000 tons capacity with thermal COP values of 0.65-0.85.
Technical Details
Indirect fired systems connect to external hot water supplies at 200-350°F or low-pressure steam at 5-15 psi through dedicated heat exchanger circuits. The approach enables operators to implement high-efficiency boilers separately, optimizing equipment selection for specific facility conditions. Heat input requirements of 10,000-13,000 BTU per ton of cooling support chilled water delivery at 40-45°F. Modulation capabilities allow heat input variation from 10-100% capacity.
Applications and Practical Significance
Facilities with existing boiler infrastructure, combined heat and power (CHP) systems, or access to renewable thermal sources prioritize indirect fired chillers for operational flexibility. Universities, hospitals, and industrial facilities leverage waste heat recovery integration to maximize energy efficiency. These systems support demand response programs and thermal storage applications, reducing peak electrical demand charges. Multi-chiller arrangements utilizing indirect fired units facilitate load shifting and equipment redundancy for mission-critical cooling requirements.