Scroll Screw and Reciprocating Compressors in Chiller Systems
The compressor type influences a chiller’s energy consumption, sound levels, maintenance requirements and response to changing cooling demand. However, no single technology is ideal for every application. Selection should consider cooling capacity, required fluid temperature, annual operating hours and the system’s load profile.
Scroll compressors
Scroll compressors compress refrigerant between two interleaved spiral elements. Their compact construction and low vibration make them a common choice for comfort cooling and various process cooling applications.
In chillers with multiple scroll compressors, capacity can be adjusted by staging individual compressors. Variable-speed models can adjust compressor speed to follow demand more closely.
Hermetic scroll compressors generally offer limited access to internal components for field repairs. An internal mechanical failure may require compressor replacement, making service availability and spare parts support relevant selection factors.
Screw compressors
Screw compressors use rotating rotors to compress refrigerant. They are a strong option for medium- and high-capacity chillers, central air conditioning systems and industrial process cooling.
Depending on the model, capacity can be regulated mechanically or through variable-speed control. Part-load efficiency depends on the control method, compressor selection and operating conditions. A screw compressor should therefore not be assumed to deliver the highest efficiency at every operating point.
Oil management, filters and manufacturer-specified maintenance should be included in the operating plan.
Reciprocating compressors
Reciprocating compressors compress refrigerant using pistons moving inside cylinders. Appropriate models can serve a range of operating conditions, including process cooling and low-temperature applications.
Semi-hermetic and open-drive designs may allow access to internal components for servicing, depending on their construction. This can be a significant maintenance advantage. Piston, valve and other moving-component condition remains important, while vibration isolation and installation quality also require attention.
Key differences
| Criterion | Scroll | Screw | Reciprocating |
|---|---|---|---|
| General selection tendency | Small to medium capacities; scalable through multiple compressors | Medium to high capacities | Broad capacity and temperature coverage, depending on model |
| Capacity control | Compressor staging; variable speed on suitable models | Mechanical control or variable speed on suitable models | Cylinder unloading, staging or speed control on suitable models |
| Sound and vibration | Generally low vibration | Depends on installation and operating conditions | Isolation is important because of reciprocating motion |
| Service approach | Limited internal repair access on hermetic models | Specialist servicing and oil management are important | Internal servicing possible on suitable semi-hermetic and open-drive designs |
| Typical applications | Comfort cooling, modular systems and process cooling | Central systems and high-capacity process cooling | Process cooling and low-temperature duties with suitable models |
Capacity categories are general tendencies, not fixed limits. Product families and multiple-compressor arrangements overlap considerably.
How should energy consumption be compared
Comparing compressor types or rated motor power alone is insufficient. Chiller proposals should be assessed at the same cooling capacity, leaving-fluid temperature and ambient-air or condenser-water conditions.
Alongside full-load efficiency, consider part-load performance, minimum stable capacity, annual operating hours and fan and pump energy consumption. Refrigerant compatibility, service support and maintenance costs complete the total cost of ownership assessment.
The right compressor is the one that reliably and economically meets the facility’s actual cooling requirements throughout its operating life.
This article provides general information. Product selection and operating limits must be based on the relevant model’s technical documentation and project-specific calculations.
