Compressor Selection in Water-Cooled Chillers
Water-cooled chillers, considered the heart of HVAC systems, play a critical role in providing reliable cooling for comfort conditioning in large-volume buildings and industrial processes. The performance, energy consumption, initial investment cost, and service life of these systems largely depend on the engineering precision applied in compressor selection.
Compressors used in chiller systems directly affect system efficiency, operating range, response to load variations, and maintenance requirements. Therefore, selecting the correct compressor type, capacity, and control strategy is not only a technical but also an economic and environmental engineering decision.
1. The Role of the Compressor in Water-Cooled Chillers
The compressor is the key component circulating the refrigerant within the chiller system. Its functions include:
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Compressing the refrigerant vapor from low pressure to high pressure
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Enabling the refrigerant to pass through the condenser for condensation
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Directly affecting the system efficiency expressed by the COP (Coefficient of Performance)
Compressor selection requires a multidimensional evaluation covering thermal load profiles, operating time, climate conditions, energy costs, and automation scenarios.
2. Compressor Types: Advantages and Applications
The main types of compressors commonly used in water-cooled chillers are summarized as follows:
a) Screw Compressor
Advantages:
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Ideal for medium to large capacity systems
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High reliability and long service life
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Quieter operation
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Good performance at staged or variable loads
Disadvantages: -
Efficiency loss at partial loads
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Higher initial investment cost
Applications:
Hotels, shopping malls, large office buildings, industrial processes
b) Centrifugal Compressor
Advantages:
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High efficiency at very large capacities (above 1000 kW)
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Oil-free operation possible
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Compact design
Disadvantages: -
Efficiency drops at low loads
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High-speed design requires careful maintenance
Applications:
Industrial plants, airports, large data centers
c) Scroll Compressor
Advantages:
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High efficiency at low capacities
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Quiet operation
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Low failure risk
Disadvantages: -
Not preferred for large capacities
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May require redundancy
Applications:
Small commercial buildings, independent zones in hotels
d) Reciprocating (Piston) Compressor
Advantages:
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Low initial cost
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Easy maintenance
Disadvantages: -
High noise level
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Low efficiency
Applications:
Older systems, small process cooling applications
3. Technical Parameters Affecting Compressor Selection
a) Cooling Capacity (kW / RT)
The required cooling capacity directly determines the compressor type. For example:
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< 200 kW → Scroll / Reciprocating
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200 – 1000 kW → Screw
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1000 kW → Centrifugal
b) Load Profile (Partial Load Operation)
In places where load varies during the day, such as hotels and offices, inverter-driven or multi-compressor systems with modulation capability are preferred.
c) Ambient Conditions
To maintain efficiency at high ambient temperatures:
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Water-cooled condenser systems
-
Advanced motor protection and cooling solutions
are preferred.
d) Energy Efficiency and COP / IPLV Values
Compressor efficiency should be evaluated not only at full load but especially at partial load (IPLV). Screw and inverter systems can provide 20–40% energy savings.
4. Compressor Control Strategies
To increase energy efficiency, compressor control can be performed by:
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Inverter (VFD) application: motor speed adjustment for capacity modulation
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Step-controlled multi-compressor systems: staging compressors on/off based on load
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Automation integration: communication with Building Management Systems (BMS)
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Load sharing algorithms: optimization in multi-chiller systems
These controls help reduce carbon footprint and operating costs.
5. Oil Management and Refrigerant Compatibility
Other important considerations in compressor selection include:
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Oil type and return system
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Centrifugal compressors often operate oil-free
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Screw compressors require oil separators
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Compatibility with refrigerants such as R-134a, R-1234ze, R-410A
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Preference for low GWP options compliant with F-Gas regulations
6. Maintenance and Service Accessibility
For long life and uninterrupted operation:
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Availability of spare parts
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Local service network
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Remote monitoring and fault diagnosis support
are important.
Manufacturer support and maintenance contracts are critical, especially for screw and centrifugal compressors.
7. Initial Investment Cost – Life Cycle Cost (LCC)
When selecting a compressor, consider not only the initial investment but also operational costs over 10–15 years.
LCC = Initial Investment + Energy Consumption + Maintenance Cost + Failure Risks
For example, although an inverter-driven screw compressor may cost 15% more initially, it becomes more economical within 5 years due to energy savings.
Compressor Selection Is Not Just a Technical but a Strategic Decision
Choosing the right compressor in water-cooled chillers is fundamental to system performance and operational success. Selections based on appropriate technology, correct capacity, high efficiency, and sustainability principles provide both technical and economic return on investment.
“The compressor is like the heart in a human — if it is healthy, the whole system works well.”
Compressors selected with the right engineering approach positively shape not only today’s operation but also future operating costs and environmental impacts.
İlker KURAN
Alperen Mühendislik Ltd. Şti.