Chiller (Chilled Water Unit)

Technical term

Chiller (Chilled Water Unit)

A chiller is a vapor-compression refrigeration system that cools water or a water-glycol mixture to a defined temperature level. It serves as a central source of cooling for industrial processes, technical equipment, or HVAC (Heating, Ventilation and Air Conditioning) systems. The generated cooling capacity is supplied to consumers such as production lines, reactors, or air-handling units via a closed chilled-water circuit.

In industrial energy systems, the waste heat generated during the refrigeration process at the condenser can be purposefully recovered, for example as a heat source for downstream heat pump systems or for direct heat recovery.

Operation in combination with high-temperature heat pumps

In integrated energy and process systems, chillers and high-temperature heat pumps can operate in a complementary manner. The chiller provides the required process cooling on the cold side. Depending on the temperature level, the resulting condensation heat can be used as a heat source for a high-temperature heat pump, which upgrades this heat to a higher temperature suitable for process use or heating applications. Alternatively, a two-stage or cascaded system can supply cooling and heating demand simultaneously and, as an integrated solution, achieves higher overall efficiency than two separately configured systems.

This approach allows two demands to be met at the same time:

defined and stable chilled-water temperatures for production or cooling processes,
usable heat for heating applications or industrial process heat.

Through this energetic coupling, electrical input energy can be utilized more efficiently at the system level, while the demand for external heat generation – such as from fossil fuel sources – can be significantly reduced.

Technical background

A chiller operates according to the conventional refrigeration cycle. The refrigerant evaporates in the evaporator, absorbing heat from the chilled-water circuit, and is then compressed to a higher pressure and temperature level in the compressor. In the condenser, the absorbed heat is released to a cooling medium, a heat rejection system, or – within an integrated plant concept – to a downstream heat circuit. In practice, this heat transfer is typically implemented via hydraulically decoupled circuits or heat exchangers.

The energy efficiency of a chiller is influenced, among other factors, by:

the temperature lift between the evaporation and condensation levels,
the stability of flow rates and load profiles,
the type and efficiency of heat rejection at the condenser,
the refrigerant, compressor technology, and control strategy, particularly under part-load operation.

Benefits of integration into industrial heat pump systems:

Improved overall system efficiency: Heat generated during the cooling process is not rejected unused but is recovered and utilized energetically.
Simultaneous provision of cooling and heating: One kilowatt of electrical input power delivers cooling while simultaneously providing heat for additional applications.
Flexible system operation: Coordinated control strategies allow prioritization of cooling or heating demand as well as load shifting.
Reduced heat rejection demand: Cooling towers or dry coolers are relieved, which can lower operating costs and reduce water and energy consumption.

System design and limitations

Combining a chiller with a high-temperature heat pump requires careful system design. Key factors include suitable temperature levels on both the cooling and heating sides, coordinated hydraulic layouts, and an appropriate control strategy. The energetic benefit of coupling strongly depends on sufficient temporal and capacity-related overlap between cooling and heating demand. In cases of highly fluctuating loads or excessively low condensation temperatures, the efficiency advantage can be significantly reduced.

Overall assessment

When combined with a high-temperature heat pump, a chiller can form a highly efficient integrated energy and process system. If the available waste heat is deliberately recovered and utilized, both the economic performance and sustainability of industrial cooling and heating supply can be substantially improved.