How does a water-cooled screw compressor reject heat?
Almost all the electrical energy a compressor absorbs ends up as heat. In an oil-injected screw compressor most of that heat is carried by the injected oil, and the rest leaves with the compressed air. An air-cooled package blows room air across finned oil and air coolers. A water-cooled package replaces those with shell-and-tube or plate heat exchangers:
- Oil cooler: hot oil from the separator passes through a water-cooled exchanger before it returns to the airend.
- Aftercooler: compressed air leaving the separator is cooled by water, condensing much of its moisture before it reaches the dryer.
- Thermostatic or mixing valve: keeps oil at the correct injection temperature, so the machine does not run too cold and condense water in the oil.
- Water regulating valve: on many packages, adjusts water flow to the heat load.
The water then carries the heat to a cooling tower, a dry cooler, a chiller or a process stream. The compressor room stays cooler, but the heat has simply moved to another part of the site.
Water-cooled or air-cooled: which suits your site?
| Factor | Air-cooled | Water-cooled |
|---|---|---|
| Heat path | Into room air, then ducted out | Into a water circuit, then to a tower, cooler or process |
| Room ventilation | Large air volume needed; ducting critical | Much less ventilation; motor and radiant heat only |
| Infrastructure | Fans, ducts, louvres | Pumps, piping, tower or cooler, water treatment |
| Hot ambient behaviour | Discharge temperature rises with room temperature | Depends on water temperature, which depends on the tower and wet-bulb |
| Main maintenance risk | Dust-blocked coolers | Scale, fouling, corrosion, biological growth |
| Heat recovery | Warm air for space heating or drying | Hot water, easier to use for process or boiler feed |
| Typical use | Small and medium machines, well-ventilated rooms | Large machines, enclosed rooms, sites with existing cooling water |
For many Indian plants the honest answer is that a well-ventilated air-cooled installation is simpler. Water cooling earns its place where the machine is large, the room cannot be ventilated properly, cooling water already exists and is well managed, or heat recovery into hot water is planned.
Start with the air requirement, not the cooling type
Cooling type does not set compressor capacity. Before discussing water cooling, define:
- Required free air delivery (FAD) and working pressure at the point of use.
- Minimum, average and peak demand, and running hours per year.
- Required air quality, by ISO 8573-1 class where relevant.
- Criticality and whether a standby machine is needed.
- Control strategy: fixed speed, VSD, or a mix sequenced together.
Only then decide how the heat will leave the building. Compare machines on specific power, kW per m³/min at the stated pressure, at the cooling-water temperature you can actually supply.
What the cooling-water circuit must provide
Each manufacturer states the water flow, maximum inlet temperature, allowable pressure and water-quality limits for its model. The site must meet them all year, not just on commissioning day. The items to engineer are:
- Heat load: roughly the compressor shaft power, plus a margin. Ask the supplier for the heat rejected to water at full load.
- Flow: enough to carry that heat with the stated temperature rise. Too little flow means high outlet temperature and faster scaling.
- Inlet temperature: a cooling tower cannot cool below the wet-bulb temperature. In humid coastal Andhra Pradesh or during Hyderabad’s pre-monsoon heat, tower water can run warm, so check the worst month.
- Pressure: within the exchanger’s rating, with isolation and drain valves for service.
- Water quality: hardness, chlorides, pH, suspended solids and biological control within the manufacturer’s limits.
- Strainers and bypass: a strainer upstream of the exchangers and valves that allow cleaning without stopping the whole circuit where possible.
- Protection: a low-flow or high-temperature alarm, so a pump trip does not become an airend failure.
Open tower, closed loop or once-through?
| Arrangement | How it works | Points to watch |
|---|---|---|
| Open cooling tower | Water circulates through the compressor and an evaporative tower | Concentration of salts, scale, airborne dust and algae; needs a treatment programme and blow-down |
| Closed loop with dry cooler | Treated water or glycol in a sealed circuit, cooled by air fans | Clean exchangers, but water temperature rises with ambient; size for summer peaks |
| Closed loop with tower and plate exchanger | Sealed compressor circuit, separated from tower water by a plate exchanger | Protects the compressor; plate exchanger itself must be cleaned |
| Once-through supply or borewell water | Water passes once and is discharged | Wasteful, often hard and scaling; generally a poor choice |
Where borewell water is the make-up supply, as on many Telangana and Andhra Pradesh sites, hardness is often high. Untreated hard water can scale an oil cooler quickly, so a sealed loop or proper treatment is strongly preferred.
Symptoms of a cooling-water problem
| Symptom | Likely cause | What to check |
|---|---|---|
| Discharge temperature rising over weeks | Scale or fouling in the oil cooler | Water temperature difference across the cooler, cooler cleanliness |
| High-temperature trips on hot afternoons | Tower water too warm, tower fans or fill in poor condition | Tower approach, fan operation, water inlet temperature |
| Sudden high-temperature shutdown | Pump trip, closed valve, blocked strainer | Flow, strainer, valve positions, alarms |
| Water in the oil, milky oil | Leaking exchanger, or oil running too cold | Exchanger leak test, thermostatic valve |
| Excess condensate load at the dryer | Aftercooler fouled or water too warm | Air temperature after the aftercooler |
A normal oil-injected screw discharge temperature is about 75–95 °C. A steady upward drift is an early warning. Our pages on thermal performance and overheating and cooler service and fouling control go deeper.
Maintenance for water-cooled packages
- Record water inlet and outlet temperatures and compressor discharge temperature at each service visit, so trends show up early.
- Clean strainers regularly and inspect exchangers at intervals set by water quality and manufacturer guidance.
- Descale or mechanically clean exchangers with methods approved for their materials.
- Keep the water-treatment programme and blow-down working; check tower fill and drift eliminators.
- Test low-flow and high-temperature protection.
- Carry out the usual oil, filter and separator service; see our rotary screw service page.
Heat recovery: making use of the moved heat
Because a water-cooled machine already delivers its heat into water, recovering it is often straightforward. Hot water from the oil cooler can preheat boiler feed water, wash water or process water. The value depends on whether the site has a steady heat demand at the right temperature when the compressor runs. See heat-recovery rotary screw systems.
Installation checklist for a new water-cooled compressor
- Confirm the heat rejected to water at full load and the required flow and maximum inlet temperature from the supplier.
- Check that the cooling tower or dry cooler has spare capacity in the hottest, most humid month, not just on average.
- Fit isolation valves, a strainer, thermometers and pressure gauges on both water connections so performance can be checked.
- Provide a flow switch or temperature alarm interlocked with the compressor.
- Plan drains and access so exchangers can be cleaned without dismantling pipework.
- Agree who owns the water-treatment programme: the utilities team, a treatment contractor or the compressor service provider.
- Still ventilate the room for motor and radiant heat, and keep the air intake cool and clean.
How Reddy Compressors helps
From our office at Tarnaka, Secunderabad, we have served industry since 2002 as an independent multi-brand specialist, not an authorised dealer. We have tie-ups with all major and reputed brands. We sell new and used/refurbished water-cooled and air-cooled screw compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makers.
- Advice on whether water cooling suits your room, water supply and duty.
- Service, AMC and cooler cleaning for water-cooled packages, by more than 20 service engineers and technicians covering Telangana and Andhra Pradesh.
- Diagnosis of overheating, water-in-oil and cooler fouling problems.
- Spare parts identified from the nameplate, serial number or old part, with fit confirmed before quoting, supplied across India.
- Rental compressors from our own fleet if a cooling-water outage or cooler repair would stop production.
What to send us
- Compressor make, model, serial number and nameplate photo.
- Cooling arrangement: open tower, closed loop, dry cooler or other.
- Water inlet and outlet temperatures and discharge temperature readings, if you have them.
- Water source and any treatment in use.
- Fault history, trip messages and running hours.
Frequently asked questions
Is a water-cooled compressor more efficient than an air-cooled one?
Not automatically. The compressor’s specific power depends mainly on the airend, motor and control. Water cooling can keep inlet and discharge temperatures lower in a hot room, which helps, but pumps and tower fans add their own power. Compare the whole system’s energy, including cooling equipment, at the water temperature your site can really supply in summer.
Why is my water-cooled compressor overheating?
The usual causes are scaled or fouled oil coolers, warm tower water, low water flow from a blocked strainer or failing pump, and closed or partly open valves. Check water temperatures in and out of the cooler and compare them with the compressor discharge temperature. A slow upward trend suggests fouling, while a sudden trip usually points to a flow problem.
Can I use borewell water to cool a screw compressor?
It is generally not recommended. Borewell water in much of Telangana and Andhra Pradesh is hard and can scale exchangers quickly, and once-through use wastes water. A sealed closed loop with treated water, cooled by a tower through a plate exchanger or by a dry cooler, protects the compressor far better.
What causes water in the compressor oil?
Either a leak inside the oil cooler lets water into the oil circuit, or the oil runs too cold so moisture from the intake air condenses and stays in the oil. A failed thermostatic valve or excessive cooling-water flow can cause the second problem. Milky oil needs prompt attention, because it damages bearings and the airend.
How often should water-cooled compressor coolers be cleaned?
It depends on water quality, treatment and running hours, and the manufacturer’s guidance comes first. The practical method is to record water and discharge temperatures at every service and clean when the temperature difference shows the exchanger is losing performance. Poorly treated tower water may need cleaning far more often than a well-managed closed loop.
When should I choose water cooling for a new compressor?
Consider it for larger machines, enclosed or hot rooms that cannot be ventilated well, sites with an existing and well-maintained cooling-water system, or where you plan to recover heat into hot water. For small and medium machines in rooms that can be ventilated properly, air cooling is usually simpler and cheaper to maintain.
Related pages
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.