Dry coolers: questions and answers
founder and CEO of Cold Energy (NCT) · Updated October 30, 2026
This page is for engineers who choose, design or run a dry cooler, the air-cooled fluid cooler. These are the questions customers, design engineers and plant operators ask us in projects, on site and by email. The figures come from our articles, guide and design guide for engineers; the exact figure for your site comes from a selection run.
Questions on this page (20)
- What is a dry cooler, and how is it different from a cooling tower?
- What temperature will a dry cooler deliver in summer? Can I get 27 °C when it is 30 °C outside?
- Can I run a dry cooler on plain water instead of glycol?
- What glycol concentration does a dry cooler need?
- How does an adiabatic dry cooler work, and what systems are there?
- Up to what outdoor temperature does an adiabatic dry cooler hold the design glycol temperature?
- How much water does an adiabatic dry cooler use?
- What happens to the adiabatic system in winter, and how should it drain?
- Can I use a vertical dry cooler instead of a V-type?
- How much air does a dry cooler need, and can it go in a shaft or inside a building?
- What outdoor design temperature should I use for a dry cooler?
- Can a dry cooler cool water in winter without the chiller (free cooling)?
- Can I split the capacity across several dry coolers for redundancy?
- How do I add capacity to rooftop dry coolers: adiabatic pre-cooling or one more unit?
- Can I drain the glycol for the summer and run the dry coolers on water?
- How should dry coolers be placed on a high, windy roof?
- Can you calculate the dry cooler noise at a given distance?
- The dry coolers cannot cope in summer and we have to unload the equipment. What should we do?
- Can a dry cooler serve an absorption chiller?
- Can an evaporative condenser run in winter without water?
What is a dry cooler, and how is it different from a cooling tower?
A dry cooler is a finned heat exchanger with fans. The fluid, usually a glycol solution, flows through the tubes, air blows across the fins, and heat leaves only by warming the air. There is no water outside: no make-up, no blowdown, no water treatment. A cooling tower cools by evaporation and works from the wet-bulb temperature; a dry cooler works only from the dry-bulb. On a hot day in central Russia the gap between them is 7–10 °C. More in "Cooling tower vs dry cooler"
What temperature will a dry cooler deliver in summer? Can I get 27 °C when it is 30 °C outside?
No. A dry cooler cannot cool fluid below the outdoor air temperature: that is its physical limit. The closer you want the fluid to the air, the faster the coil grows: take a 10 °C approach as the baseline, and 6 °C needs twice the surface, 4 °C four times. A selection for your flow, fluid and climate gives the exact outlet temperature. If summer fails, look at adiabatic pre-cooling, a closed-circuit cooling tower or a trim chiller. More in "Dry cooler, cooling tower or chiller"
Can I run a dry cooler on plain water instead of glycol?
In practice, no. If circulation stops or power fails during frost, a water-filled coil can freeze and burst within hours. Water is acceptable only with automatic draining, backup power for the pump and heating, and the design engineer has to justify it. If the process cannot take glycol, keep glycol in the outdoor loop and send water to the equipment through a plate heat exchanger. It costs 2–4 °C of approach, and the dry cooler is sized for that. More in "Cooling tower vs dry cooler"
What glycol concentration does a dry cooler need?
The minimum that is enough for the coldest temperature the loop will see: the site's design winter low plus a 3–5 °C margin. According to manufacturers, 40% ethylene glycol freezes at about −23 °C, 40% propylene glycol at about −22 °C. Every extra percent costs coil capacity and pump energy all year round. Use only inhibited glycol rated for heat exchangers, never automotive antifreeze. Check the concentration with a refractometer at start-up and every autumn, and top up only with premixed solution. More in "Cooling tower vs dry cooler"
How does an adiabatic dry cooler work, and what systems are there?
It is a standard dry cooler with inlet air humidification. In hot weather water sprayed in front of the coil evaporates and cools the air: by 5–15 °C depending on climate, according to NCT data; for Moscow about 5 °C is realistic. Humidification uses wetted pads or nozzles; NCT dry coolers use high-pressure nozzles that make a fine mist, which evaporates before it reaches the fins. Water runs only above a set outdoor temperature; otherwise the unit runs dry. More in "How to cut industrial cooling costs"
Up to what outdoor temperature does an adiabatic dry cooler hold the design glycol temperature?
Up to the selection's design point; above it the glycol warms with the air. Adiabatic cooling cannot take air below the wet-bulb. Moscow example: dry coil sized for 26 °C; at the 29.9 °C design hour the air must drop 3.9 °C against a 7.8 °C potential, so there is margin. At the 38 °C record high it must drop 12 °C, and the wet-bulb in that hour decides. For continuous processes it is a reserve, not the basis of selection. More in our design guides for engineers
How much water does an adiabatic dry cooler use?
Only for evaporation and only in hot hours, far less than an evaporative tower of equal capacity. In our Moscow calculation a 1300 kW unit needs about 1.2 m³/h in the peak hour. The dry-bulb exceeds 28 °C for about 88 hours a year, so the annual total is no more than 106 m³. A cooling tower of the same capacity evaporates up to 2.0 m³/h and runs on water for thousands of hours. The selection gives the figure for your climate. More in "Cooling tower vs dry cooler"
What happens to the adiabatic system in winter, and how should it drain?
The water line to the nozzles is emptied: adiabatic cooling does not run in winter, and standing water in the pipe will freeze. The design includes a motorized shut-off valve in a heated room, an outdoor section sloped to a drain, a drain valve at the low point and an air vent at the high point. Where water can stay, add heat tracing under insulation. Filters and the high-pressure pump stay indoors. The dry-mode setpoint and draining sequence go into the controls specification. More in our design guides for engineers
Can I use a vertical dry cooler instead of a V-type?
Yes. NCT DC dry coolers come in three layouts. Horizontal: the coil lies flat, the fans are on top; it goes on the ground or a roof. Vertical: the coil stands upright and air moves horizontally, which suits narrow service passages and gaps between buildings. V-type: two coils at an angle, more surface per metre of length. The layout is chosen for the site; the selection gives the capacity and dimensions of each option. More in our design guides for engineers
How much air does a dry cooler need, and can it go in a shaft or inside a building?
A lot: a 1300 kW dry cooler with an 8 °C air temperature rise needs about 500,000 m³/h. That air must reach the unit freely and leave without coming back to the inlet, otherwise capacity drops in hot weather. Manufacturers recommend at least 1.2 m to a wall and to the next unit, with the fan tops no lower than surrounding walls. In a shaft or a room, this is the first check. The selection sheet gives dimensions and weight. More in "Cooling tower vs dry cooler"
What outdoor design temperature should I use for a dry cooler?
The summer dry-bulb, and its design frequency matters more than for a tower. For Moscow, the Russian climate code (SP 131) gives 26 °C, the ASHRAE 0.4% dry-bulb is 29.9 °C, and the record high is 38 °C. The step from 26 to 30 °C is a third of the coil surface. Comfort cooling usually works with the code value. For a process that must never stop, the process engineer sets it, often the record high. Glycol also needs the winter low. More in our design guides for engineers
Can a dry cooler cool water in winter without the chiller (free cooling)?
Yes, that is free cooling: when it is colder outside than the water, a glycol dry cooler cools without a compressor. For 1000 kW its fans draw about 30 kW against 300 kW for compressors. It goes in series ahead of the chiller evaporators, or the condenser dry cooler switches to a chilled-water heat exchanger. With a 7 °C combined approach and 7/12 °C water, partial free cooling starts below +5 °C and full below 0 °C; with 12/18 °C, below +11 and +5 °C. More in "Chiller free cooling"
Can I split the capacity across several dry coolers for redundancy?
Yes. NCT DC dry coolers start at 300 kW, and system capacity is built up in modules. To take one unit out for service without stopping the rest, fit isolation valves on each coil, an option in the inquiry form. For future growth, plan headers with blanked-off branches and space on site from the start: a new block then connects without shutting down the running ones. More in "Cooling tower vs dry cooler"
How do I add capacity to rooftop dry coolers: adiabatic pre-cooling or one more unit?
First calculate the actual heat load: it tells you how much is missing. Adiabatic cooling adds margin in hot hours, but it needs treated water and a drained line in winter, and it is never the basis of a selection. An extra dry cooler in parallel adds surface all year, but it changes the hydraulics, so the pumps are rechecked. Either way, give the structural engineer the operating weight with fluid: the unit sits on load-bearing structures, not on the roof membrane. More in our design guides for engineers
Can I drain the glycol for the summer and run the dry coolers on water?
Technically yes: water transfers heat better, while glycol needs 11% more flow for the same heat and makes the pump work harder. But it is a seasonal job with risks. Glycol is drained into containers, not the sewer, and has to be stored. An empty, damp steel pipe rusts from the inside faster than a full one. Before frost the loop is refilled with premixed solution; leftover water in low spots will dilute it, so check the concentration with a refractometer. More in "Cooling tower vs dry cooler"
How should dry coolers be placed on a high, windy roof?
The main rooftop threat is hot discharge returning to the inlet. Place a group in a row, discharging at one level above the parapet, fan tops no lower than nearby walls. Orient units so the prevailing summer wind carries discharge away from intakes. Keep the discharge of an adiabatic dry cooler at least 7.5 m from ventilation intakes. Set support height for snow depth, or the unit gets buried. Wind and snow loads go to the structural engineer with the operating weight. More in our design guides for engineers
Can you calculate the dry cooler noise at a given distance?
Yes, the sound level is calculated during selection. In the inquiry form, state the permitted level in dBA and the distance at which it must be met; octave-band data are available on request. A unit that runs around the clock near housing is checked against the night limit, 45 dBA under Russian sanitary rules. Noise is reduced with variable-speed fan control and a perimeter acoustic screen. Attenuation added after installation is almost impossible, so set the requirement before selection. More in our design guides for engineers
The dry coolers cannot cope in summer and we have to unload the equipment. What should we do?
Find the cause first. Common ones: the heat wave is hotter than the design temperature, so the fluid warms with the air; on a roof the unit breathes its own discharge; the load has grown. Collect equipment and dry cooler data and measure temperatures in a hot hour. Then recalculate for the real site temperature: add modules, adiabatic cooling as a peak reserve, or a trim chiller. For hot fluids, check outlet air: above +55 °C the fans fail. More in "Cooling tower vs dry cooler"
Can a dry cooler serve an absorption chiller?
Only with a Thermax selection for warmer cooling water and reduced capacity. An absorption chiller is rated for 29.4 °C cooling water at the inlet, and a dry cooler cannot deliver that in hot weather. For absorption chillers we recommend a closed-circuit cooling tower: it works from the wet-bulb and keeps the loop clean. More in "Cooling tower vs dry cooler"
Can an evaporative condenser run in winter without water?
Yes. NCT evaporative condensers run in dry mode, with the spray off. Models with a finned coil (e-series) run without spray from 0 °C; bare-tube models need the optional dry-section coil. Dry mode is seasonal only and must be agreed with the factory, and the basin is always drained: water in it would freeze even with heaters. In the project example from our design guide, water is shut off below −5 °C. More in our design guides for engineers