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An absorption chiller can turn an otherwise unused thermal stream into chilled water. That can be attractive where generation and cooling operate together, but a heat-driven chiller is not a source of free cooling. The temperature of the recovered heat, cooling-water conditions, operating schedule and auxiliary power determine whether the project makes sense.
Match the chiller to the available heat
DOE’s absorption-chiller fact sheet describes single-effect machines using lower-grade heat and multi-effect machines requiring higher-temperature sources. Its illustrative single-effect hot-water examples use inlet temperatures of 190°F and 208°F, with thermal coefficients of performance around 0.70–0.79. These are examples from a 2017 publication, not universal minimum temperatures or current equipment quotations. [1]
The practical question for a generator project is what arrives at the chiller after recovery and piping losses. Ask for heat-source inlet and outlet temperatures, flow, minimum duty, control limits and seasonal availability. A chiller selected from engine nameplate power alone may be seriously mismatched.
Keep thermal COP and electrical COP separate
Thermal COP compares cooling produced with heat supplied. An illustrative 1 MW of usable heat at a thermal COP of 0.70 yields 0.70 MW of cooling—about 199 refrigeration tons. The corresponding heat-rejection requirement is roughly 1.70 MW before small additional inputs. A cooling loop and heat sink must handle that rejected heat.
For a deliberately simplified comparison, assume an electric chiller would deliver the same 700 kW of cooling at electrical COP 5. It would use 140 kW of electricity. If the complete absorption alternative adds 25 kW of electrical auxiliaries, the illustrative avoided demand is 115 kW. The COP and auxiliary values here are assumptions, not a vendor guarantee. Include pumps and fans on the same system boundary for both alternatives.
The cooling tower can decide the project
DOE highlights heat-rejection and auxiliary considerations, and distinguishes lithium-bromide/water applications from ammonia/water systems used for colder duties. The appropriate working pair depends on the required temperature and engineered system. [1] The existence of a cooling tower does not prove it has sufficient spare summer capacity.
Our site review would request the design wet-bulb temperature, water availability and quality, tower duty, approach temperatures, water treatment, plume constraints and the consequences of a tower outage. It would also check whether the useful recovered heat has another higher-value purpose. Heat already sold to a process is not an unused resource.
Make cooling continuity explicit
For a critical cooling loop, determine what happens when generation is stopped for maintenance or loses fuel. Retaining an electric chiller, thermal storage or another engineered backup may be appropriate. The heat-driven system should be able to unload without upsetting generator cooling, while generation should retain its approved heat-rejection path.
We recommend quoting the recovery exchanger, chiller, cooling-water system, pumps, controls and integration as a defined system. For used equipment, request the actual model, working pair, rating conditions, maintenance history and available acceptance test. A generic surplus “chiller” listing does not establish that it is an absorption machine.
Use the operating overlap, not 8,760 assumed hours
Estimate annual savings from hours when heat and useful cooling are simultaneously available. Deduct added maintenance, water, chemicals, auxiliary power and any fuel needed to maintain heat input. Test a warm-weather case and a generator-outage case before deciding how much cooling capacity to buy.
Source review: 24 September 2026. DOE technical examples are dated 2017. Calculations use explicit illustrative inputs and do not establish project performance or savings.