What Is a Chiller? How It Works, Main Parts, Layout and Types
founder and CEO of Cold Energy (NCT)
A chiller is a refrigeration machine that cools water or glycol, and the chilled fluid carries cooling through pipes to machine tools, reactors, fan coils and servers. Inside are four main components: evaporator, compressor, condenser and expansion valve. The typical duty is water entering at 12 °C and leaving at 7 °C; for every 1 kW of electricity the machine delivers 2.4 to 6.9 kW of cooling, depending on the type.
I run Cold Energy: we manufacture NCT chillers, cooling towers, pump skids and controls. This article is for the chief engineer and process engineer choosing cooling for a plant or building for the first time. How to avoid mistakes in selection is covered in How to choose an industrial chiller; other material is in the Chillers section.
What is a chiller, and how is it different from other refrigeration machines?
A chiller (from the verb "to chill") is a vapor-compression refrigeration machine with the compressor, evaporator, condenser and expansion valve mounted on one frame. An NCT chiller leaves the factory assembled, with its control panel: on site you only run the cable and connect the pipes.
The main difference between a chiller and a cold room or an air conditioner is that it cools a liquid, not air. At the outlet of an NCT machine the coolant can be anywhere from −15 to +20 °C; below +6 °C only with glycol. The liquid can then be piped hundreds of meters through a building or shop, whereas refrigerant lines in practice rarely run longer than 30–50 m.
Our reference list includes 42 plants in Russia and Kazakhstan where NCT chillers cool a printing press, a welding gantry at Severstal Metiz, sunflower oil, a furnace, chemical reactors and the air in shopping malls.
You do not need a chiller if the process is fine with +25 to +30 °C water: a cooling tower will deliver that by evaporation. For central Russia the rule from our catalog is: if you need water colder than 23 °C, you need a chiller. Another neighbor is the absorption chiller: it makes cooling from heat and uses 5–10 kW of electricity per 1 MW of cooling, against 200–300 kW for a compressor chiller.
How is a chiller built: what are its main parts?
A chiller consists of the four components of the refrigerant circuit plus a control panel and a frame. The refrigerant circulates in a closed circuit, the consumer's water passes only through the evaporator, and the cooling air or water passes only through the condenser.
| Component | What it does | How it is made in NCT chillers |
|---|---|---|
| Evaporator | Refrigerant boils and takes heat from the water or glycol | Refrigerant-to-water heat exchanger; flooded shell-and-tube in NWCV and NARV screw units |
| Compressor | Compresses refrigerant vapor; the main power consumer | Scroll, screw or oil-free centrifugal; 1 to 6 per unit |
| Condenser | Rejects heat to air or water, refrigerant turns back into liquid | Air-cooled microchannel with axial fans, remote, brazed-plate or shell-and-tube water-cooled |
| Expansion valve | Drops the pressure and meters refrigerant into the evaporator to match the load | Electronic expansion valve (EEV) is an option in the quote |
| Control panel | Starts compressors to match the load, holds temperature, runs protections | Controller on the unit, link to the building management system |
A machine has one or two independent refrigerant circuits; two give partial redundancy. On request the frame carries a pump module, a filter, a winter kit and anti-vibration mounts.
How does a chiller work: what refrigeration cycle runs inside?
A chiller works by having the refrigerant boil, get compressed, condense and expand in a loop, carrying heat from the consumer's water to outdoor air or to cooling tower water. Scroll and screw machines change capacity in steps, switching compressors on and off; the centrifugal NWCV does it smoothly with a variable-speed drive.
1. Evaporator. Warm water from the consumer, say 12 °C, passes through the evaporator. On the other side of the wall the refrigerant boils at low pressure: in the worked example in our design guide for an R410A circuit, at 3 °C. The boiling refrigerant takes heat, and the water leaves for the consumer chilled to 7 °C.
2. Compressor. The compressor draws refrigerant vapor from the evaporator and compresses it. Superheated high-pressure gas goes down the discharge line to the condenser. This step takes most of the electrical power: the NASA91 packaged unit at 12/7 °C and +35 °C outdoors delivers 309 kW of cooling and uses 101 kW for the compressors.
3. Condenser. The hot gas gives up heat to outdoor air or water and turns into liquid. In the same example, at +35 °C air the condensing temperature is 50 °C; with cooling tower water, about 35 °C. More heat comes out here than cooling went in, because the compressor work adds to it: at a coefficient of performance of 5, the condenser rejects 1.2 kW of heat per 1 kW of cooling.
4. Receiver and expansion valve. Liquid refrigerant flows through the receiver to the expansion valve; to make sure it arrives without vapor bubbles, it is subcooled, by 4 K in the example. The valve drops the pressure to the boiling pressure and feeds the evaporator as much refrigerant as the load needs. The cold mix of liquid and vapor enters the evaporator again, and the cycle repeats.
A refrigeration machine is rated by its coefficient of performance (COP or EER: kilowatts of cooling per kilowatt of electricity). Every degree of condensing temperature costs money: according to manufacturers, compressor power rises by 1.8–4.0% per 1 K.
What does a chiller system layout look like?
A chiller on site has three circuits: the refrigerant circuit inside the machine, the chilled-fluid loop to the consumers, and the heat rejection loop to the outside. The factory builds the refrigerant circuit; the other two are designed for the site.
The chilled-fluid loop exists with any chiller. Water or glycol flows from the evaporator to the consumers and back through a pump, an expansion tank, a filter and a flow switch (a sensor that lets the machine run only while water flows through the evaporator). The return enters the evaporator at the bottom and the supply leaves at the top, so the vessel purges air on its own.
The heat rejection loop of a packaged air-cooled unit is hidden inside the machine. On a water-cooled machine it is a water or glycol loop to a cooling tower or a dry cooler (a dry fluid cooler); on a machine with a remote condenser it is a copper refrigerant line to the roof.
In our experience, three quarters of chiller start-up problems come from water flow and water quality, one quarter from electrics. So loop flushing, the filter and the flow switch are discussed before the contract: the cause is in the piping, but the complaint goes to the manufacturer.
What types of chillers are there?
Chillers are classified by two features: how the condenser is cooled (packaged air-cooled, remote condenser, water-cooled condenser) and which compressor is installed: scroll up to hundreds of kilowatts, screw for medium and large capacities, centrifugal for large central chiller plants.
In NCT model codes this reads letter by letter. The first N stands for NCT; the second letter is condenser cooling: A for air-cooled on the unit, C for remote air-cooled, W for water-cooled. The third is the compressor: S for scroll, R for screw, C for centrifugal.
| Series | Condenser cooling | Compressor | Refrigerant | Cooling per 2026 catalog | Where installed |
|---|---|---|---|---|---|
| NASA | Air-cooled on the unit | Scroll, 2–6 | R410A | 69–621 kW | Outdoors, roof |
| NARA | Air-cooled on the unit | Screw | R404A, R134a | Per selection | Outdoors, large capacities |
| NCSA | Remote air-cooled | Scroll, 2–6 | R410A | 69–621 kW | Unit indoors, condenser on the roof |
| NCRA | Remote air-cooled | Screw | Per selection | Per selection | Same, larger |
| NWSA | Water-cooled, brazed-plate | Scroll, 2–6 | R410A | 69–621 kW | Plant room |
| NWRA | Water-cooled, shell-and-tube | Screw, 2 | R134a | 436–1,412 kW | Plant room |
| NWCV | Water-cooled, shell-and-tube | Oil-free centrifugal, 1–4 | Per selection | 229–7,033 kW | Large central chiller plants |
The NWCV centrifugal compressor runs on gas bearings without oil, so the heat exchangers stay clean longer. There are also versions with adiabatic air pre-cooling, with a heat pump function, and explosion-proof versions.
How does an air-cooled chiller differ from a water-cooled one?
The refrigeration cycle is the same in both; the difference is where the condenser rejects heat. An air-cooled chiller rejects it to outdoor air and condenses 10–15 K above the air temperature. A water-cooled chiller rejects heat to cooling tower water and condenses at about 35 °C, so it uses noticeably less electricity.
A packaged air-cooled unit stands outdoors or on the roof, everything in one casing. At +30 °C outdoors, a NASA unit condenses at 46 °C. The operating range per the catalog is +10 to +35 °C, and down to −30 °C with the full winter kit. It is not installed in a room without powerful ventilation: it would blow hot air back into itself.
A chiller with a water-cooled condenser stands in a plant room, and its heat leaves with water to a cooling tower or with glycol to a dry cooler. An open cooling tower gives the coldest water to the condenser, about 27 °C in our designs; a dry cooler cools only to the dry-bulb air temperature, and in summer the glycol arrives warmer, with 40/45 °C as the typical regime.
Per NCT catalogs, the NASA packaged unit at 12/7 °C and +35 °C delivers 2.38–2.68 kW of cooling per 1 kW of electricity; the NWCV centrifugal on 30 °C cooling tower water, 6.01–6.85. By our calculation for 1,000 kW of cooling and 3,000 operating hours, the water-cooled system saves about 198,000 kWh per year, roughly RUB 2 million at RUB 10 per kWh, minus water, water treatment, and the cooling tower's pumps and fans.
A chiller with a remote condenser is the middle option: the compressor-evaporator unit stands indoors, the air-cooled condenser on the roof, with a refrigerant line between them. How to save in winter with any of these systems is covered in Chiller free cooling.
How do a chiller and fan coils work together?
In a chiller–fan coil system, the chiller produces chilled water, usually 7 °C with a 12 °C return, and pumps carry it through the building to fan coils (terminal units with a coil and a fan in the room) and air handling units. Water brings the cooling into the room; the refrigerant stays in the machine.
In our reference list, a NASA chiller serves ventilation and air conditioning at the Iskra shopping mall in Perm, and at the Fakel sanatorium in Krasnodar Krai the dining hall is cooled by a NASA chiller and an NCSA chiller with a heat pump function. For scale: a 10,000 m² office building needs about 1 MW of cooling, and a conventional chiller draws about 333 kW of electricity continuously to provide it.
Branch lines to fan coils are up to DN50, in steel or polypropylene pipe. The key condition is that the fan coils are selected for the same temperature regime as the plant. If they are designed for a 5 K difference and the plant for 7 K, you get low delta-T syndrome: water returns colder than designed, the machines run underloaded, and the pumps move excess flow.
Key takeaways
1. A chiller is a refrigeration machine that cools water or glycol, not air; NCT machines deliver −15 to +20 °C at the outlet.
2. The chiller's refrigeration cycle has four steps: refrigerant boils in the evaporator, the compressor compresses the vapor, the condenser turns it into liquid, the expansion valve drops the pressure and returns the refrigerant to the evaporator.
3. The condenser rejects more heat than the machine delivers as cooling: at a coefficient of performance of 5 that is 1.2 kW of heat per 1 kW of cooling, and the cooling tower or dry cooler is sized for that heat.
4. A packaged air-cooled unit condenses 10–15 K above the air temperature, a water-cooled machine on a cooling tower at about 35 °C; for 1,000 kW of cooling and 3,000 hours the difference is about 198,000 kWh per year.
FAQ
What is the difference between a chiller and a cooling tower?
A cooling tower cools water by evaporation, without a compressor, and cannot go below the design wet bulb per SP 131.13330 (Russian building climatology code) plus 3–4 K. A chiller cools with a compressor cycle and delivers 7 °C water or colder in any weather. Many plants run both: in summer the cooling tower cools the chiller's condenser, in winter it supplies cold water on its own.
How much electricity does a chiller use?
Per NCT catalogs, for 1,000 kW of cooling a packaged air-cooled unit at 12/7 °C and +35 °C draws about 370–420 kW; a centrifugal machine on 30 °C cooling tower water, about 145–165 kW. What this adds up to over 15 years is in Chiller total cost of ownership.
Why does a chiller not deliver its rated capacity?
Nine times out of ten water quality is to blame, not the manufacturer and not the installers. One millimeter of scale on a heat exchanger takes away about 30% of capacity. In a glycol loop, too low a glycol concentration is dangerous: corrosion rises sharply.
What does "tons" mean in a chiller model name?
A refrigeration ton is a unit of cooling, 1 ton ≈ 3.52 kW. In the NWCV model name the digits are tons and the number after the hyphen is compressors: NWCV 300-1 means 300 tons, about 1,055 kW of cooling, one compressor.
Sources
-
SP 131.13330 (Russian building climatology code).
-
NCT chiller catalogs 2026: NASA, NARA, NCSA, NCRA, NWSA, NWRA, NWCV series.
-
Experience and calculations of Cold Energy; NCT chiller reference list, January 2026.
Need a cooling solution for your site? Get a consultation