Compressed-air cooling applications

Why compressed-air cooling costs more than it looks

An air jet, vortex tube or cabinet cooler has no motor of its own, so it can look free. It is not. The compressor station uses a significant amount of electrical power to make each cubic metre of air, and nearly all of that ends up as heat at the compressor, not as cooling at the point of use. Each additional bar of generation pressure needs about 7% more compressor power, and air treatment, maintenance and leaks add to the cost.

For this reason, compressed-air cooling should be a deliberate choice for duties that suit it, not a default. Typical good uses are spot cooling of a cutting tool or weld, cooling a small electrical enclosure in a dusty or wet area, and cooling where electrical equipment is not permitted. Typical poor uses are cooling large rooms, people or whole machines continuously.

Define the temperature problem and the boundary

Start by writing down what must be held at what temperature, and why:

• a control panel whose drives trip above their rated ambient;
• a tool or part that must not exceed a temperature during machining or forming;
• a product that must be cooled before packing or the next step;
• a sensor, camera or lens that overheats near a furnace.

Draw a boundary around what is being cooled and list every heat flow across it: heat generated inside, heat from sunlight or nearby furnaces, heat through the walls from hot surroundings, and heat carried in by product. In Telangana and Andhra Pradesh, summer ambient temperatures of 40–45 °C, and above 45 °C on open sites, dust and direct sun on outdoor panels are common reasons that cooling which worked in winter fails in May.

Sensible cooling, evaporation and drying are different

Most compressed-air cooling is sensible cooling: cold or cool air absorbs heat and rises in temperature. The heat removed equals the mass flow of air times its specific heat times its temperature rise. Because air has low specific heat, large flows or large temperature differences are needed for meaningful cooling. Evaporative cooling, where water evaporates from a surface, removes far more heat per kilogram but needs a wet surface. Drying air does not cool a product by itself. Keep these effects separate when you read claims about a cooling device.

Calculate a first heat balance

1. Estimate heat generated inside the boundary, in watts (for example, drive losses in a panel from the drive maker’s data).
2. Estimate heat gained through walls from the surroundings, which rises as ambient approaches or exceeds the target temperature.
3. Add solar gain for outdoor equipment, or radiant heat from nearby hot plant.
4. For product cooling, use mass flow, specific heat and the required temperature drop.
5. Separate steady duty from transient peaks, such as a start-up or a batch of hot parts.

The total is the cooling duty in watts. Only with this number can you compare options fairly. Our compressed-air cooling load worksheet sets out the method.

What jets, vortex tubes and cabinet coolers can do

A simple air jet cools by blowing room-temperature or slightly cooler air at a surface. It increases convection and works best on small, hot areas such as a tool tip. It cannot cool below the temperature of the air it supplies.

A vortex tube splits compressed air into a cold stream and a hot stream with no moving parts. Adjusting the hot-end valve changes the cold fraction, the share of air leaving as the cold stream. A small cold fraction gives the lowest temperature but little flow; a larger cold fraction gives more flow at a less low temperature. Useful cooling depends on both, so the coldest setting is often not the most cooling. The hot stream must be vented safely.

Cabinet coolers use vortex tubes to cool sealed electrical enclosures in harsh areas. They keep the panel slightly pressurised and clean, which is useful in dusty plants. They do, however, use compressed air continuously unless a thermostat controls them.

Budget the compressed-air supply

Vortex tubes and cabinet coolers are rated at a stated inlet pressure and consumption. Check that the plant can supply that flow at that pressure without dropping other users, and that the branch pipe and filter can carry it. Their performance falls if inlet pressure falls, so measure at the device while it runs.

Air quality matters. Vortex tubes and cabinet coolers need filtered, dry air; water and oil in the supply can enter electrical enclosures and block the vortex generator inside the tube. A refrigerated dryer with a typical pressure dew point around +3 °C is generally adequate; colder outputs may justify a desiccant dryer. Fit a filter with automatic drain close to the device.

Condensation and product effects

Cooling a surface below the dew point of the surrounding air causes condensation, even when the cooling air itself is dry. This is a particular risk for enclosures that are cooled hard and then opened in humid monsoon air, and for chilled products. Keep enclosures sealed, avoid over-cooling and use a thermostat so the panel is held at a sensible temperature rather than as cold as possible.

For products and tooling, rapid local cooling can cause distortion, stress or uneven properties. Agree acceptable cooling rates with the process owner before increasing flow.

Compare energy on a common basis

To compare options, use the same cooling duty and the same running hours:

• for compressed-air devices, work out the air consumed, then the compressor power attributable to it from the station’s specific power (kW per m³/min) and how its controls respond;
• for fans and blowers, use motor input power;
• for refrigeration, use the unit’s electrical input at the expected ambient;
• include running hours and whether each option is switched by a thermostat.

In most continuous duties the electrically driven alternatives use much less energy than compressed air for the same heat removed. The comparison narrows for short, intermittent duties where a compressed-air device is switched on only when needed. Measure the change in compressor power before and after, under comparable conditions, rather than assuming that air saved equals energy saved. Our specific power page explains the station measurement.

Control cooling to the process need

A device that runs all the time costs far more than one that runs when the heat is there. Practical controls include:

• thermostats on cabinet coolers, opening a solenoid only when the panel warms;
• interlocking spot-cooling jets with the machine cycle or spindle;
• regulators set to the lowest pressure that keeps the process in limits;
• replacing permanently open cooling pipes with engineered nozzles and timers.

Noise from vortex tubes and jets can be significant; fit silencers on hot and cold outlets where practical and check exposure at the operator position.

Diagnose cooling problems

After any change, commission the arrangement by checking the actual process or panel temperature over a hot day and a full production cycle, not just the outlet temperature of the device.

How Reddy Compressors helps

Reddy Compressors has worked with industrial compressed-air systems since 2002, from our office at Tarnaka, Secunderabad. Our service teams cover all of Telangana and Andhra Pradesh, and we supply compressors, blowers, dryers, rentals and spares across India. For cooling applications we:

• log station flow and power to show what compressed-air cooling is really costing;
• survey cooling devices and open jets, with pressure checks at each point;
• supply and service dryers and filters so cabinet coolers and vortex tubes receive clean, dry air;
• sell, rent and service blowers and compressors, new and used, where a different supply suits the duty better;
• help you keep compressors running well in high summer ambient through an annual maintenance contract (AMC) and compressor-room ventilation advice.

We are independent and multi-brand (ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and others), not an authorised dealer. We have tie-ups with all major and reputed brands. Call +91 99590 60718 or +91 92468 88812.

What to send us

• What is being cooled and the temperature limit
• Heat source details: drive losses, product rate or nearby hot plant
• Location, ambient conditions and whether it is outdoors
• Existing cooling devices, their inlet pressure and how they are switched
• Compressor make, model, pressure setting and running hours
• Any condensation, trips or energy concerns

Frequently asked questions

Is compressed-air cooling expensive to run?

Usually, yes. Most of the electrical energy used to compress air is turned into heat at the compressor, so very little of it becomes useful cooling at the point of use. For continuous duties, fans, heat exchangers, liquid cooling or panel air-conditioners normally remove the same heat with much less energy. Compressed air remains useful for small, spot, intermittent or hazardous-area duties where other options do not fit.

How does a vortex tube produce cold air?

Compressed air enters a vortex tube tangentially and spins at high speed. The tube separates it into a hot outer stream, which leaves through a control valve at one end, and a cold inner stream, which leaves at the other. Adjusting the valve changes the share of air leaving cold. There are no moving parts, but the device needs clean, dry air at its rated pressure.

Does the coldest vortex tube setting give the most cooling?

Not necessarily. The coldest setting sends only a small share of the air out of the cold end, so although the temperature is very low, the flow is small. Useful cooling depends on cold-stream flow and how much it warms while absorbing heat. A setting with more cold flow at a slightly higher temperature often removes more heat. Follow the maker’s performance data for the duty.

Can a fan replace a cabinet cooler on a control panel?

A filtered fan can work when the surrounding air is well below the panel’s maximum internal temperature and dust can be managed. It cannot cool below ambient, so in Indian summer heat it may fail where a cabinet cooler or panel air-conditioner succeeds. An air-to-air heat exchanger keeps the panel sealed. Compare options using the same heat load and the hottest expected ambient.

Why is there water inside my cooled control panel?

Either the supply air is wet, or the panel is being cooled below the dew point of humid surrounding air, which condenses when doors are opened or seals leak. Fit a dryer and a filter with automatic drain, keep the enclosure sealed, and use a thermostat so the panel is held at a sensible temperature rather than as cold as possible.

How do I reduce the cost of compressed-air cooling?

Fit thermostats or interlocks so devices run only when needed, replace open cooling pipes with engineered nozzles, set the lowest pressure that keeps the process in limits, and fix leaks on cooling branches. For continuous duties, consider fans, blowers, heat exchangers or refrigeration instead. Confirm the saving by measuring compressor power before and after under comparable production and ambient conditions.

Related pages

• Compressed air cooling load worksheet
• Air jets and blow-off alternatives
• Specific power and station performance
• Compressed-air energy and efficiency
• Compressor room ventilation worksheet
• Pneumatic applications hub