Air-Cooled vs Water-Cooled Air Compressor Cooling Systems

Air-cooled or water-cooled, the choice is simple.

Does your plant have a cooling water system? Yes, connect to it, use water-cooled. No, use air-cooled.

For the vast majority of small and medium power applications, this one rule is enough. Construction cost of cooling water systems is severely underestimated. Ingersoll Rand sales people know this better than anyone. They push air-cooled very firmly in the North American small and medium customer market. Machines under 100 hp, basically don't proactively offer water-cooled option. Customer insists on water-cooled? Quote a long lead time, wait for customer to give up. Not that Ingersoll Rand water-cooled version isn't good. They've done the math, know these types of customers will have more problems later with water-cooled, higher after-sales costs.

Atlas Copco's GA series has very high market share in this power range. Air-cooled version shipments ten times or more than water-cooled. Kaeser's situation similar. These manufacturers' stocking strategies speak volumes. Air-cooled models complete lineup, always in stock, ship within a week. Water-cooled often needs to be made to order, eight to ten weeks is normal. Market demand determines inventory strategy, inventory strategy in turn reinforces market pattern.

Same 60 hp screw machine, water-cooled version might be $1,000-2,000 cheaper than air-cooled. This price difference makes some purchasing folks think they got a bargain. Nobody helps them calculate what comes after. Cooling tower needs to be bought, smallest ones still cost $2,000-3,000. Circulation pump needs to be bought, piping needs installing, valves and instruments need configuring, construction costs need paying. Freeze protection needs insulation and heat tracing, another expense. Water treatment chemicals several hundred dollars a year unavoidable. Heat exchanger needs cleaning every three to five years, if cleaning doesn't work needs replacing. Atlas Copco plate heat exchangers $3,000-4,000 each. Calculate ten years out, savings on bare machine price difference already repaid many times over.

Large power centralized deployment situations really are different.

Five or six 250+ hp machines placed together, air-cooled heat dissipation too much, machine room ventilation very hard to do. Sullair does a lot of these projects, their water-cooled big machines have good reputation among heavy industry customers. CompAir similar positioning. These customers usually already have cooling water systems, connecting compressors has low marginal cost. Only then does water-cooled economic math work out.

Problem is many people wrongly apply large power centralized application experience to small and medium power distributed applications. One or two 100 hp machines, plant doesn't have existing cooling water, insisting on water-cooled is purely creating trouble for yourself.

Water treatment needs someone monitoring. Regular testing, regular chemical dosing, regular blowdown. Many plants don't have this awareness, don't have the manpower either. Water quality management completely left alone. Problems arise then finding people to fix it, treatment costs several times higher than proper regular management.

Winter is nightmare for northern plants. After shutdown, water in pipes and heat exchangers not drained, nighttime temperature drops, freeze expansion directly cracks equipment. Every year before heating season ends, Atlas Copco and Ingersoll Rand parts departments get more heat exchanger orders. Most are freeze damage. Doing insulation and heat tracing properly can avoid this problem, but that's another investment, requires someone checking and maintaining.

High ambient temperature situations really do require serious consideration of water-cooled.

Kaeser marks design ambient temperature upper limit at 115°F. Atlas Copco most models mark 104-113°F. Running near upper limits, machine condition noticeably worsens, discharge temperature runs high, lubricating oil life shortens, various small problems emerge. Next to heat treatment workshops, next to forging shops, tin roof buildings, summer easily hits 113°F. That kind of environment, air-cooled machines really can't handle it. These situations, choosing water-cooled is right, no hesitation.

Gardner Denver these years pushing large power air-cooled machines, 300 hp and up they have. Targeting customers who hate cooling water systems but need large power. Whether it works well depends entirely on machine room ventilation design. Ventilation done right, large power air-cooled completely viable. Some factories willing to spend money on machine room ventilation, large power air-cooled also runs stable.

Mixed configuration approach seen in some big factories. Main units water-cooled, backup units air-cooled. Cooling water system has problems, air-cooled machines can cover.