types of water cooled chillers

What Are Water Cooled Chillers?​
Before exploring types, it’s essential to define water cooled chillers. Unlike air cooled chillers (which use ambient air to release heat), water cooled chillers transfer heat from the process coolant (e.g., water-glycol mixture) to a separate “cooling water” loop. This cooling water then flows to an external component (typically a cooling tower) where heat is dissipated into the atmosphere (via evaporation or convection). Once cooled, the water returns to the chiller to repeat the cycle.​

Water cooled chillers are valued for higher efficiency (especially in warm climates, where air cooled units struggle with high ambient temperatures) and quieter operation (since heat rejection components are external). They are widely used in commercial buildings, industrial facilities, and data centers—but their reliance on a cooling water system means they require more installation space and additional components (towers, pumps, piping) compared to air cooled alternatives.​
The Four Main Types of Water Cooled Chillers​
Water cooled chillers are categorized by their compressor type—the core component that circulates and compresses the refrigerant, driving the refrigeration cycle. Below are the four primary types, each suited to specific cooling needs.​
1. Reciprocating Water Cooled Chillers​
Working Principle​
Reciprocating chillers use a reciprocating compressor—a piston-driven device that moves up and down within a cylinder to compress refrigerant vapor. The cycle works as follows:​
Low-pressure refrigerant vapor is drawn into the cylinder (suction stroke).​
The piston compresses the vapor, increasing its pressure and temperature (compression stroke).​
High-pressure vapor is pushed into the condenser (discharge stroke), where it releases heat to the cooling water loop.​
The condensed liquid refrigerant flows through an expansion valve, reducing pressure and temperature, before entering the evaporator to absorb heat from the process coolant.​
Key Specifications​
Cooling Capacity: Typically 10–500 kW, making them ideal for small to medium cooling loads.​
COP Range: 3.0–4.5 (moderate efficiency, lower at partial loads due to on/off cycling of the compressor).​
Compressor Design: Single or multi-cylinder (multi-cylinder models can adjust capacity by deactivating cylinders, improving partial-load efficiency).​
Ideal Applications​

Small industrial processes (e.g., plastic injection molding, small-scale metal finishing).​
Commercial spaces with moderate loads (e.g., restaurants, small hotels, retail stores).​
Laboratory cooling (e.g., cooling small batches of samples or compact equipment).​
Pros & Cons​
Pros: Low initial cost, simple design (easy to maintain), compact size (fits in tight spaces), compatible with low-temperature applications (down to -10°C with modifications).​
Cons: Noisy operation (due to piston movement), limited capacity (not suitable for large loads), lower efficiency at partial loads (on/off cycling wastes energy), higher wear on components (pistons and valves may require frequent replacement in high-use scenarios).​
2. Scroll Water Cooled Chillers​
Working Principle​
Scroll chillers use a scroll compressor, which consists of two interleaved spiral “scrolls”—one fixed, one orbiting (rotating in a circular motion without spinning on its axis). The cycle operates as follows:​
Refrigerant vapor is drawn into the outer edges of the scrolls.​
The orbiting scroll pushes the vapor toward the center of the spiral, gradually reducing the volume and increasing pressure (compression).​
High-pressure vapor is discharged from the center into the condenser, where it transfers heat to the cooling water.​
Liquid refrigerant expands through a valve and enters the evaporator to cool the process coolant.​
Key Specifications​
Cooling Capacity: 20–350 kW, suited for small to medium loads (slightly higher than reciprocating models for similar sizes).​
COP Range: 3.5–5.0 (higher efficiency than reciprocating chillers, especially at partial loads).​
Compressor Design: Hermetic (sealed) or semi-hermetic; no valves or pistons (fewer moving parts).​
Ideal Applications​
Commercial HVAC (e.g., office buildings, schools, hospitals with moderate cooling needs).​
Food and beverage production (e.g., cooling dairy processing lines, small breweries).​
Data centers with distributed cooling (cooling individual server racks or small server rooms).​
Pros & Cons​
Pros: Quiet operation (no piston noise), fewer moving parts (reduced maintenance and wear), higher efficiency (especially at 50–75% load), compact design, good temperature stability (smooth capacity control).​
Cons: Higher initial cost than reciprocating chillers, limited capacity (not for large industrial loads), sensitive to liquid refrigerant (can damage the scrolls if liquid enters the compressor), not ideal for very low temperatures (typically limited to 0°C and above).​

3. Screw Water Cooled Chillers​
Working Principle​
Screw chillers use a screw compressor—two intermeshing helical rotors (male and female) that rotate in opposite directions. The compression process is:​
Refrigerant vapor enters the gap between the rotors at the suction end.​
As the rotors rotate, the vapor is trapped in the spaces between the rotor threads and pushed toward the discharge end, where the volume decreases and pressure increases.​
High-pressure vapor is discharged into the condenser, transferring heat to the cooling water.​
Liquid refrigerant expands and flows to the evaporator, absorbing heat from the process coolant.​
Key Specifications​
Cooling Capacity: 100–2,000 kW, designed for medium to large cooling loads.​
COP Range: 4.0–5.5 (high efficiency, especially at full load; variable-speed models can reach COP >6.0 at partial loads).​
Compressor Design: Semi-hermetic or open (open models allow for easier compressor maintenance); variable-speed options available (adjust rotor speed to match load).​
Ideal Applications​
Large commercial buildings (e.g., shopping malls, high-rise offices, convention centers).​
Industrial processes (e.g., large-scale plastic extrusion, metalworking, chemical processing).​
Data centers with centralized cooling (cooling entire server floors or large IT rooms).​
District cooling systems (supplying chilled water to multiple buildings in a complex).​
Pros & Cons​
Pros: High capacity (handles large loads efficiently), low noise (smoother rotation than reciprocating compressors), excellent partial-load efficiency (variable-speed models), durable (fewer moving parts than reciprocating units), suitable for high-temperature lifts (e.g., cooling from 35°C to 5°C).​
Cons: Higher initial cost than reciprocating/scroll models, larger footprint (requires more installation space), sensitive to refrigerant contamination (debris can damage rotor threads), requires professional maintenance (complex rotor alignment).​
4. Centrifugal Water Cooled Chillers​
Working Principle​
Centrifugal chillers use a centrifugal compressor—a rotating impeller that uses centrifugal force to accelerate refrigerant vapor, increasing its pressure. The cycle steps are:​
Refrigerant vapor is drawn into the center of the impeller (eye).​
The rotating impeller flings the vapor outward at high speed, converting kinetic energy into pressure (compression).​
A diffuser (stationary component surrounding the impeller) slows the vapor, further increasing pressure before it enters the condenser.​
Heat is transferred to the cooling water in the condenser; liquid refrigerant expands through a valve and cools the process coolant in the evaporator.​
Key Specifications​
Cooling Capacity: 500–18,000+ kW, the largest capacity option for water cooled chillers.​
COP Range: 4.5–6.5 (high efficiency at full load; magnetic bearing compressors can reach COP >7.0).​
Compressor Design: Typically open (driven by an external motor) or semi-hermetic; advanced models use magnetic bearings (no physical contact, reducing friction and wear).​
Ideal Applications​
Mega-commercial projects (e.g., airports, stadiums, large hospitals with 24/7 cooling needs).​
Heavy industry (e.g., petrochemical plants, steel mills, large manufacturing facilities).​
Data centers with high-density cooling (e.g., cloud computing facilities, supercomputer centers).​
District cooling for urban areas (supplying chilled water to entire neighborhoods or business districts).​
Pros & Cons​
Pros: Extremely high capacity (handles the largest cooling loads), excellent full-load efficiency (lowest energy consumption per kW of cooling), quiet operation (magnetic bearing models are nearly silent), long lifespan (20–30 years with proper maintenance).​
Cons: Very high initial cost (prohibitive for small applications), large footprint (requires dedicated mechanical rooms), sensitive to part-load operation (traditional models have low efficiency below 50% load—though variable-speed and magnetic bearing models mitigate this), complex design (requires specialized technicians for maintenance and repairs).​
Auxiliary Components for Water Cooled Chillers​
All water cooled chillers rely on additional components to function—these are not part of the chiller itself but are critical to the system’s performance. Understanding them helps in evaluating the overall setup.​
1. Cooling Tower​
The cooling tower dissipates heat from the chiller’s cooling water loop. It works by spraying warm cooling water into the tower, where it comes into contact with ambient air (natural draft) or forced air (mechanical draft, using fans). Heat is removed via evaporation (most common) or convection, and the cooled water returns to the chiller’s condenser.​
Types of Cooling Towers: Cross-flow (air flows horizontally, water vertically) and counter-flow (air and water flow in opposite directions). Counter-flow towers are more efficient but require more height; cross-flow towers are shorter but larger in footprint.​
2. Water Pumps​
Two types of pumps are required:​
Condenser Water Pump: Circulates cooling water between the chiller’s condenser and the cooling tower.​
Chilled Water Pump: Circulates the cooled process coolant (chilled water) between the chiller’s evaporator and the application (e.g., building HVAC coils, industrial equipment).​
Pumps are sized based on flow rate (LPM) and pressure (kPa) to ensure adequate water circulation. Variable-speed pumps are recommended for energy efficiency, as they adjust speed to match cooling demand.​
3. Piping and Valves​
Piping connects the chiller, cooling tower, pumps, and application. It must be sized for the water flow rate and made of corrosion-resistant materials (e.g., copper, steel, or PVC for non-industrial applications). Valves (e.g., control valves, isolation valves) regulate water flow, allowing for temperature control and system maintenance.​
4. Water Treatment Systems​
Cooling water is prone to scaling (mineral deposits), corrosion, and biological growth (algae, bacteria). Water treatment systems (e.g., chemical injectors, filters, UV sterilizers) prevent these issues, which can reduce chiller efficiency, damage components, and shorten lifespan. Common treatments include:​
Scale Inhibitors: Prevent mineral buildup in the condenser.​
Corrosion Inhibitors: Protect metal components (pipes, condenser coils) from rust.​
Biocides: Kill bacteria (e.g., Legionella, which can cause illness if aerosolized).​
Factors to Consider When Selecting a Water Cooled Chiller Type​
Choosing the right type of water cooled chiller depends on your application’s specific needs. Below are the key factors to evaluate:​
1. Cooling Load (kW)​
The most critical factor—match the chiller’s capacity to your peak cooling load:​
Small Loads (<500 kW): Reciprocating or scroll chillers (cost-effective and compact).​
Medium Loads (500–2,000 kW): Screw chillers (balance of capacity and efficiency).​
Large Loads (>2,000 kW): Centrifugal chillers (only option for ultra-high loads).​
Always include a 10–15% capacity buffer to account for unexpected heat spikes (e.g., hot weather, equipment upgrades).​
2. Energy Efficiency​
Prioritize efficiency to reduce long-term operational costs:​
Full-Load vs. Partial-Load Use: If the chiller operates at partial load most of the time (e.g., office buildings with variable occupancy), choose scroll or variable-speed screw/centrifugal models (better partial-load efficiency).​
COP Rating: Higher COP means lower energy use. For example, a chiller with a COP of 5.0 uses 200 W of electricity to produce 1 kW of cooling, while a COP of 4.0 uses 250 W for the same cooling output.​
Magnetic Bearings: For centrifugal chillers, magnetic bearing compressors eliminate friction, boosting efficiency and reducing maintenance.​
3. Installation Space​
Consider the physical size of the chiller and its auxiliary components:​
Reciprocating/Scroll: Compact, suitable for small mechanical rooms or tight spaces.​
Screw: Larger than scroll/reciprocating, requires dedicated space for the chiller and cooling tower.​
Centrifugal: Largest footprint, needs a large mechanical room and tall cooling tower (for counter-flow designs).​
Also, account for clearance around the chiller (0.5–1 meter) for maintenance and airflow.​
4. Temperature Requirements​
Different chillers handle temperature ranges differently:​
Low Temperatures (<0°C): Reciprocating chillers (modified with glycol coolant) or specialized screw chillers. Scroll and centrifugal chillers are not ideal for sub-zero process temperatures.​
Standard Temperatures (5–15°C): All four types work, but choose based on load and efficiency.​
5. Maintenance Access and Cost​
Reciprocating/Scroll: Simple design, low maintenance cost (easily serviced by local technicians).​
Screw: Moderate maintenance cost (requires periodic rotor inspection and oil changes).​
Centrifugal: High maintenance cost (needs specialized technicians for impeller alignment, magnetic bearing servicing, and refrigerant handling).​
Factor in long-term maintenance costs when comparing initial prices— a cheaper reciprocating chiller may have higher maintenance costs over 10 years than a more expensive but durable screw chiller.​
Maintenance Practices for Water Cooled Chillers​
Proper maintenance ensures optimal performance, extends lifespan, and reduces energy costs. Below is a type-agnostic maintenance schedule (adjust based on manufacturer recommendations):​
Weekly Checks​
Temperature Monitoring: Verify that the chilled water supply/return temperatures and condenser water temperatures are within the recommended range (e.g., chilled water supply: 6–12°C; condenser water return: 30–35°C).​
Pressure Checks: Monitor refrigerant pressure (high and low sides) and water pressure in the chilled water and condenser water loops. Abnormal pressures may indicate leaks or blockages.​
Cooling Tower Inspection: Check the tower’s water level, fan operation, and spray nozzles (ensure no clogs). Remove debris from the tower basin.​
Monthly Maintenance​
Filter Cleaning/Replacement: Clean or replace air filters (if the chiller has an air-cooled condenser for auxiliary components) and water filters in the chilled water/condenser water loops. Clogged filters reduce flow and efficiency.​
Water Treatment Testing: Test the cooling water’s pH (ideal range: 7.5–8.5), mineral content, and biocide levels. Adjust chemicals as needed to prevent scaling, corrosion, or bacterial growth.​
Oil Level Check: For reciprocating, scroll, and screw chillers, check the compressor oil level and quality. Replace oil if it appears discolored or contaminated.​
Quarterly Maintenance​
Coil Cleaning: Clean the chiller’s evaporator and condenser coils. For water cooled coils, use a low-pressure water jet or chemical cleaner to remove scale or debris (scale buildup reduces heat transfer efficiency by up to 30%).​
Valve and Pump Inspection: Check all valves for leaks and proper operation. Inspect pump motors for unusual noise or vibration (indicates bearing wear). Lubricate pump bearings if needed.​
Annual Maintenance​
Compressor Service: For reciprocating chillers, inspect pistons, valves, and gaskets (replace worn parts). For scroll/screw chillers, check scrolls/rotors for damage. For centrifugal chillers, inspect the impeller for erosion or imbalance (requires specialized equipment).​
Refrigerant Leak Test: Use a leak detector to check for refrigerant leaks. Even small leaks (e.g., 10% annual loss) reduce capacity and efficiency, and contribute to environmental harm (most refrigerants are greenhouse gases).​
Electrical System Check: Inspect electrical connections, wiring, and controls (thermostats, pressure switches). Tighten loose connections and replace faulty components. Test the chiller’s safety controls (e.g., high-pressure cutoffs, low-temperature freezestats) to ensure they function properly.