Water-Cooled Screw Chiller Systems
A water-cooled screw chiller removes heat from a chilled-water or process-fluid circuit and rejects it through a separate condenser-water system. It is suited to industrial processes and central cooling plants where the design load, operating hours and heat-rejection infrastructure justify a screw-compressor configuration.
GESON selects each system from the required cooling duty, chilled-fluid temperatures and flow, condenser-water conditions, fluid type, load profile, electrical supply, installation environment and destination requirements. A proposal must state cooling capacity, input power and efficiency at defined rating conditions; nominal tonnage alone is not a valid equipment selection.
Where a Water-Cooled Screw Chiller Fits
A screw chiller is not selected simply because the project is described as “large.” The choice depends on the operating point, minimum load, required temperature, redundancy, service access and lifecycle cost of the complete plant.
- Central HVAC plants serving commercial or institutional buildings
- Plastics, chemical, food, beverage and other process-cooling systems
- Facilities with long annual operating hours or a broad load profile
- Projects that already include—or can support—a condenser-water loop
- Plants requiring staged compressors, multiple chillers or planned redundancy
Applications with a small load, limited water-treatment capability, restricted mechanical-room access or no practical heat-rejection system may be better served by another chiller configuration.
How a Water-Cooled Screw Chiller Works
The evaporator transfers heat from the chilled-water or process-fluid loop to the refrigerant. The screw compressor raises the refrigerant pressure and temperature. In the condenser, heat passes into the condenser-water loop. A cooling tower, dry cooler, heat-recovery circuit or another approved heat-rejection system then releases or uses that heat.
Rotary screw compressors are positive-displacement machines. Capacity control may use compressor staging, internal slide-valve or control-piston arrangements, or speed control, depending on the selected compressor and package. Effective capacity steps and efficiency vary with operating conditions, so a generic percentage table should not be copied into a project specification.
Water-Cooled Screw Chiller System Scope
| System element | Engineering function | Information to confirm |
|---|---|---|
| Chiller package | Contains the compressor, evaporator, condenser, refrigerant circuit, controls and protection devices defined in the equipment schedule | Selected model, rated capacity, input power, refrigerant, sound data, dimensions and shipping sections |
| Chilled-water circuit | Transfers heat from the process or building to the evaporator | Entering/leaving temperatures, flow, pressure drop, fluid, glycol concentration and minimum system volume |
| Condenser-water circuit | Transfers rejected heat from the condenser to the external heat-rejection equipment | Entering/leaving temperatures, flow, water quality, fouling allowance and pump arrangement |
| Heat rejection | Rejects or recovers condenser heat | Cooling-tower selection, outdoor wet-bulb, approach, heat-recovery duty or alternative heat sink |
| Plant controls | Coordinates flow proof, pumps, tower fans, valves, chiller enable and alarms | Sequence of operation, BMS points, protocol, staging, reset strategy and current limit |
Rated Capacity, COP and Part-Load Performance
AHRI 550/590 and 551/591 standardize how vapor-compression water-chilling packages are rated. Published values are meaningful only with the corresponding rating conditions. For water-cooled equipment, the selection schedule should identify at least:
- chilled-fluid entering and leaving temperatures;
- chilled-fluid flow, fluid type and glycol concentration where applicable;
- condenser-water entering and leaving temperatures and flow;
- evaporator and condenser pressure drops;
- fouling assumptions;
- net cooling capacity and total chiller input power; and
- full-load COP or kW/ton and the stated part-load metric.
COP is cooling capacity divided by power input at the same operating condition. A higher cooling COP indicates less chiller input per unit of cooling at that condition. The complete plant must also account for chilled-water pumps, condenser-water pumps, cooling-tower fans and other auxiliaries.
IPLV is a standardized part-load comparison metric. NPLV or project-specific performance may better represent a plant operating outside standard conditions, but neither replaces an hourly load and climate analysis when energy cost is a major buying criterion.
Screw Chiller vs Scroll Chiller
| Selection factor | Screw-compressor chiller | Scroll-compressor chiller |
|---|---|---|
| Capacity arrangement | One or more screw compressors with model-specific unloading or speed control | Multiple scroll compressors commonly provide capacity stages |
| Best comparison method | Compare certified or manufacturer-selected performance at the same chilled-water, condenser-water and load conditions | |
| Minimum operating load | Depends on compressor unloading, oil management, lift and package controls | Depends on compressor quantity, staging and circuit arrangement |
| Service strategy | Requires technicians familiar with screw compressors, oil system and package controls | Individual compressors may be replaced as modules, subject to circuit design |
| Decision | Use the load profile, redundancy, efficiency, first cost, maintenance capability and available model selections—not compressor type alone | |
Water-Cooled vs Air-Cooled Screw Chiller
| Factor | Water-cooled screw chiller | Air-cooled screw chiller |
|---|---|---|
| Heat-rejection medium | Condenser-water loop connected to external heat rejection | Outdoor air moved across condenser coils |
| Site equipment | Normally requires condenser pumps, tower or another heat sink, water treatment and added piping | Avoids the condenser-water loop and tower but requires outdoor airflow and service clearance |
| Design weather input | Outdoor wet-bulb and the selected tower approach affect condenser-water temperature | Outdoor dry-bulb directly affects air-cooled condenser performance |
| Maintenance focus | Condenser tubes, water treatment, tower, pumps and strainers | Condenser coils, fans, airflow, corrosion exposure and defrost where applicable |
| Energy comparison | Compare total plant input at the same load and design conditions; do not compare chiller COP while ignoring pumps or tower fans | |
Condenser Water, Cooling Tower and Water Quality
The condenser-water system has a direct effect on capacity, compressor lift and power. The project team should define the tower design point, condenser entering-water temperature, water flow, pipe pressure loss, pump duty and minimum permitted chiller flow. Flow switches or sensors must prove chilled-water and condenser-water flow before compressor operation.
Open cooling towers concentrate dissolved solids and can introduce airborne contamination. A site-specific water-management and treatment program should address scale, corrosion, biological control, blowdown, filtration and tube inspection. Universal pH, conductivity or chemical-treatment targets should not be copied from another site.
Fluid Temperature and Low-Temperature Process Cooling
Low leaving-fluid temperature changes evaporating pressure, compressor operating limits, capacity, power, refrigerant selection and freeze risk. If glycol or another secondary fluid is required, provide the exact fluid and concentration; viscosity and heat-transfer properties affect evaporator pressure drop and pump power.
Do not assume that every water-cooled screw chiller can operate at a stated sub-zero temperature. The written selection must confirm the compressor application envelope, evaporator design, freeze protection, controls and performance at the requested entering/leaving-fluid and condenser-water conditions.
Refrigerant and Legacy GESON Support
- New R454B chillers: GESON can provide new chiller selections using R454B. Suitability for a water-cooled screw project depends on the selected model, rated conditions, safety design, destination regulations and written technical confirmation.
- New R513A chillers: GESON can provide new chiller selections using R513A, subject to model, operating conditions, destination requirements and written confirmation.
- Legacy GESON R22 equipment: spare-parts and refrigerant-related service support is available, subject to the original model, equipment condition, local refrigerant rules, qualified-technician scope and written confirmation.
The quotation must identify the exact refrigerant. Terms such as “environmentally friendly refrigerant” do not define safety classification, regulatory suitability, service availability or lifecycle requirements.
Controls, Electrical and Installation Requirements
Before ordering, confirm voltage, frequency, phase, starting method, maximum running current, short-circuit requirements, control power and field wiring scope. Define the required BMS points and protocol rather than assuming every controller includes every interface.
The mechanical-room review should cover equipment dimensions and weight, shipping splits, lifting route, service clearance, foundation, vibration isolation, ventilation, refrigerant safety requirements, drainage, tube-pull space and access for compressor or heat-exchanger service.
Information Required for Selection and Quotation
| Required input | Why it changes the selection |
|---|---|
| Application and heat-load calculation | Defines the design duty and whether load is continuous, cyclic or seasonal |
| Required cooling capacity | Must be tied to the stated design operating point |
| Chilled-fluid entering/leaving temperatures | Sets evaporator duty and compressor operating condition |
| Chilled-fluid flow | Determines heat-exchanger pressure drop and flow protection |
| Fluid and glycol concentration | Affects freeze protection, heat transfer, viscosity and pump power |
| Condenser-water temperatures and flow | Defines heat rejection, condensing condition and condenser pressure drop |
| Outdoor wet-bulb and tower data | Supports cooling-tower and condenser-water design |
| Minimum and typical load | Supports compressor quantity, unloading and staging decisions |
| Operating hours and redundancy | Influences equipment quantity, lifecycle evaluation and maintenance availability |
| Voltage, frequency and phase | Defines motor, starter and electrical configuration |
| Destination country and required documents | Supports refrigerant, electrical, code and documentation review |
| Plant-room dimensions and scope | Confirms access, service clearances and factory/site-supplied equipment |
Water-Cooled Screw Chiller FAQ
What is a water-cooled screw chiller?
It is a vapor-compression chiller that uses a rotary screw compressor, cools a water or process-fluid circuit at the evaporator, and rejects heat through a water-cooled condenser connected to an external heat-rejection system.
Does every water-cooled screw chiller need a cooling tower?
No. An evaporative cooling tower is common, but an approved dry cooler, closed-circuit cooler, heat-recovery load or other heat sink may be used when engineered for the required condenser-water conditions and heat-rejection duty.
Is a screw chiller more efficient than a scroll chiller?
Not under every condition. Compare capacity, full-load input, part-load performance and auxiliary power at the same chilled-water, condenser-water and load conditions. Compressor type alone does not prove lower operating cost.
What conditions are needed to compare screw chiller COP?
Use the same chilled-fluid entering/leaving temperatures and flow, condenser-water temperatures and flow, fluid properties, fouling assumptions and load point. Include pumps and tower fans for a whole-plant comparison.
Can GESON provide an R454B or R513A water-cooled screw chiller?
GESON can provide new chiller selections using R454B and R513A. Application to a specific water-cooled screw model requires confirmation of capacity, operating conditions, safety design, destination requirements and the final written proposal.
What should I send for a screw chiller quotation?
Send the application, design load, chilled-fluid entering/leaving temperatures, flow, glycol type and concentration, condenser-water conditions, ambient wet-bulb, operating profile, power supply, installation constraints and destination country.
Request a Water-Cooled Screw Chiller Selection
Send your project data to GESON. The engineering proposal will define the selected model, rated capacity and power, refrigerant, water flows, pressure drops, controls, supply scope and site requirements.
Engineering References
- AHRI 550/590 and 551/591: Water-Chilling Package Ratings
- AHRI Water-Cooled Chiller Certification Program Scope
- BITZER: Screw-Compressor Capacity Control
- Johnson Controls: Chilled- and Condenser-Water Monitoring Points
Related resources: water-cooled chiller systems, air-cooled chillers, screw vs centrifugal chillers, and the industrial chiller maintenance checklist.