What is a chiller? A chiller is a refrigeration machine that removes heat from water (or a water and glycol mix) and supplies that cold water to air handling units, fan coil units or process equipment. It works on the vapour compression or absorption cycle and rejects the heat it collects to outdoor air or to a cooling tower.
Chillers drive central air conditioning in offices, hospitals, malls, data centres and pharma plants, and cool process equipment in factories. This guide covers the chiller working principle, types, plant layout, normal temperatures, and what Indian buyers should check on efficiency and refrigerants. If you are new to central systems, start with our explainer on what an HVAC system is.
Table of Contents
- Key Highlights
- How Does a Chiller Work? (Working Principle)
- Chiller Plant Diagram and Main Components
- Types of Chiller
- Air-Cooled vs Water-Cooled Chiller
- What Is the Normal Chiller Temperature?
- Chiller Capacity and Efficiency: TR, kW/TR, COP and IPLV
- Chillers in India: BEE, ECBC and Refrigerant Rules
- How to Select a Chiller
- Chiller Maintenance Checklist
- Frequently Asked Questions
- Sources and Further Reading
- Conclusion
Key Highlights
- A chiller produces chilled water; the air handling units and fan coil units use that water to cool the air.
- Most chillers use the vapour compression cycle: evaporator, compressor, condenser and expansion valve.
- Chillers are grouped by heat rejection (air-cooled or water-cooled) and by compressor (scroll, screw, centrifugal, reciprocating), plus absorption chillers that run on heat.
- Comfort plants commonly run chilled water at about 7°C supply and 12°C return.
- Capacity is quoted in TR (1 TR = about 3.517 kW); efficiency in kW/TR, COP and IPLV.
- In India, BEE runs a chiller star labelling programme, ECBC 2017 sets minimum chiller efficiency, and the Kigali Amendment drives a move to lower-GWP refrigerants.
How Does a Chiller Work? (Working Principle)
The chiller working principle is the same refrigeration cycle that runs a household refrigerator, scaled up. The chiller makes its refrigerant colder than the water, lets it absorb the water’s heat, then makes it hotter than the outdoor air or condenser water so it can reject that heat.
The four stages of the vapour compression cycle
- Evaporation: Low-pressure liquid refrigerant enters the evaporator, a heat exchanger with chilled water on the other side. The refrigerant boils at a low temperature and absorbs heat, so the water leaving the evaporator is cold.
- Compression: The compressor draws in the low-pressure refrigerant vapour and compresses it. Its pressure and temperature rise well above the temperature of the cooling medium.
- Condensation: In the condenser, the hot vapour gives up its heat to outdoor air (air-cooled) or to condenser water (water-cooled) and condenses back into a high-pressure liquid.
- Expansion: The liquid passes through an expansion device, such as a thermostatic or electronic expansion valve, which drops its pressure and temperature. The cold, low-pressure mixture returns to the evaporator and the cycle repeats.
How a vapour absorption chiller is different
A vapour absorption machine (VAM) replaces the mechanical compressor with a heat-driven process. Most commercial units use water as the refrigerant and lithium bromide solution as the absorbent. Heat from steam, hot water, engine exhaust or a direct-fired burner separates the water vapour from the solution, and the cycle produces chilled water with very little electricity. They make sense where waste heat or low-cost steam is available.
Chiller Plant Diagram and Main Components
A chiller does not work alone. A complete chiller plant connects three loops: the refrigerant loop inside the chiller, the chilled water loop that runs to the building, and (for water-cooled plants) the condenser water loop that runs to a cooling tower. The diagram below shows a typical water-cooled arrangement.
| Component | What it does | What to watch |
|---|---|---|
| Compressor | Raises refrigerant pressure and temperature; the main energy user | Current draw, oil pressure and temperature, vibration |
| Evaporator | Transfers heat from chilled water to boiling refrigerant | Approach temperature, water flow, tube fouling |
| Condenser | Rejects heat to air or condenser water | Condensing pressure, fin or tube cleanliness |
| Expansion valve | Meters refrigerant into the evaporator and drops its pressure | Superheat, hunting, blockage |
| Control panel | Runs capacity control, safeties and the BMS interface | Alarms, set points, sensor calibration |
| Chilled water pumps | Circulate chilled water to AHUs and FCUs | Flow rate, differential pressure, VFD speed |
| Condenser water pumps | Circulate water between condenser and cooling tower | Flow, strainer condition |
| Cooling tower | Cools condenser water by evaporation | Water quality, fan, fill condition |
| Expansion tank, strainers, valves | Absorb water expansion, protect heat exchangers, balance flow | Pre-charge pressure, strainer pressure drop |
On the air side, chilled water passes through the cooling coil of each air handling unit. Our guide to AHU parts and their functions explains how the coil, fan, filters and control valve use that water to cool and dehumidify the air.
Types of Chiller
Chillers are classified in two main ways: by how they reject heat, and by the type of compressor or cycle they use. The table compares the common types of chiller used in India.
| Type | Typical capacity range | Where it fits | Notes |
|---|---|---|---|
| Scroll chiller (air or water-cooled) | Small to medium, often in modules | Small offices, clinics, labs, process cooling | Simple, few moving parts; capacity stepped by multiple compressors |
| Screw chiller | Medium to large | Commercial buildings, hospitals, industry | Good part-load control, especially with VFD screw compressors |
| Centrifugal chiller | Large | Big campuses, malls, data centres, district cooling | Highest full-load efficiency in water-cooled plants; magnetic-bearing models are oil-free |
| Reciprocating chiller | Small to medium | Older installations, some process duties | Largely replaced by scroll and screw in new projects |
| Vapour absorption machine (VAM) | Medium to large | Sites with steam, hot water or exhaust heat | Low electricity use; needs a heat source and usually a larger cooling tower |
| Glycol / low-temperature process chiller | Small to large | Pharma, dairy, plastics, chemical processes | Runs below 5°C leaving fluid with glycol for freeze protection |
Capacity ranges overlap and vary by manufacturer, so treat the table as a guide. For a wider view of central plant options, see our article on the different types of HVAC systems.
Air-Cooled vs Water-Cooled Chiller
This is usually the first decision in a chiller project. Both produce the same chilled water; the difference is where the heat goes.
| Factor | Air-cooled chiller | Water-cooled chiller |
|---|---|---|
| Heat rejection | Directly to outdoor air via condenser fans | To condenser water, cooled in a cooling tower |
| Energy efficiency | Lower; condensing temperature follows dry-bulb air temperature | Higher; condensing temperature follows the lower wet-bulb temperature |
| Water use | No make-up water for heat rejection | Continuous make-up water for evaporation and blowdown |
| Plant room | Usually on the roof or at grade outdoors | Chiller indoors, cooling tower outdoors, plus condenser pumps |
| Maintenance | Coil cleaning, fan upkeep | Tube cleaning, water treatment, tower upkeep |
| Typical fit | Small and mid-sized buildings, water-scarce sites | Large buildings and campuses with reliable water |
In hot Indian summers, air-cooled chillers lose capacity as outdoor temperature climbs, so select them for the site’s peak dry-bulb temperature. Water-cooled plants are less affected, but water supply and treatment must be planned from day one. Read more about the tower side in our guide to cooling tower working principle and types.
What Is the Normal Chiller Temperature?
Chiller temperature usually refers to the chilled water leaving and returning to the chiller. The values below are common design points, not fixed limits; the actual set points come from coil selection, humidity targets and pump energy.
| Application | Chilled water supply | Chilled water return | Comment |
|---|---|---|---|
| Comfort cooling (offices, malls, hotels) | About 6 to 7°C | About 12 to 13°C | Most common design in India |
| Low-humidity areas (pharma, OT, labs) | About 5 to 6°C | About 10 to 12°C | Colder water helps the coil remove more moisture |
| Data centres | Often 10 to 18°C | Often 16 to 24°C | Warmer water raises chiller efficiency; check equipment limits |
| Process cooling with glycol | Below 5°C, down to sub-zero | Depends on process | Glycol prevents freezing |
On the condenser side of a water-cooled chiller, condenser water commonly enters at around 29 to 32°C and leaves about 5°C warmer, depending on the local wet-bulb temperature and cooling tower selection.
Chiller Capacity and Efficiency: TR, kW/TR, COP and IPLV
- TR (tonne of refrigeration): 1 TR = 12,000 BTU/h = about 3.517 kW of cooling. Indian projects usually specify chillers in TR.
- kW/TR: electrical input per tonne of cooling. Lower is better. Compare chillers at the same chilled and condenser water conditions.
- COP (coefficient of performance): cooling output divided by power input, both in kW. Higher is better. COP = 3.517 / (kW/TR).
- IPLV / NPLV: integrated part-load value, a weighted average of efficiency at 100, 75, 50 and 25 percent load. It is often a better guide to annual energy than full-load COP.
- Plant efficiency: pumps and cooling tower fans add to chiller power, so good plants are judged on whole-plant kW/TR.
Efficiency is rated under standard conditions such as AHRI 550/590; ask suppliers for full and part-load efficiency at your own design temperatures. Accurate load and energy measurement also helps; a BTU meter on the chilled water header shows how much cooling the plant actually delivers.
Planning a chiller plant or upgrading an old one?
Envigaurd designs, supplies, installs and commissions complete HVAC systems in Bangalore and across India, including chilled water piping, AHUs, ducting and controls, and provides AMC support. Share your building type, cooling load and site details for a technical recommendation. Call +91-8147606843 or email contact@envigaurd.com.
Chillers in India: BEE, ECBC and Refrigerant Rules
BEE chiller star labelling
The Bureau of Energy Efficiency (BEE), under the Ministry of Power, launched a star labelling programme for chillers on 16 September 2018 (World Ozone Day). It started on a voluntary basis and rates chillers from 1 to 5 stars on tested energy performance. Check the BEE Standards and Labelling portal for the current schedule and listed models before you specify a star rating.
Energy Conservation Building Code (ECBC 2017)
ECBC 2017 sets minimum full-load COP and part-load IPLV for chillers, by type and capacity, at three levels: ECBC, ECBC+ and SuperECBC. Commercial buildings above the connected-load threshold notified by each state must comply. The National Building Code of India 2016, Part 8 (Building Services), also covers air conditioning, heating and mechanical ventilation design.
Refrigerants: HCFC phase-out and HFC phase-down
Older chillers often use HCFC-22 (R-22), which India is phasing out under the Montreal Protocol through its HCFC Phase-out Management Plan, with a 97.5 percent reduction due by 2030 and complete phase-out by 2040. Most new chillers use HFCs such as R-134a and R-410A, or lower-GWP options such as R-513A, R-1234ze and R-1233zd. India ratified the Kigali Amendment in September 2021 and will freeze HFC consumption in 2028, then reduce it by 10 percent by 2032, 20 percent by 2037, 30 percent by 2042 and 85 percent by 2047 against its 2024 to 2026 baseline. The India Cooling Action Plan (2019) also targets lower cooling demand, refrigerant demand and cooling energy by 2037-38. For a chiller that will run for 20 years, refrigerant choice now affects future service cost and availability.
How to Select a Chiller
- Calculate the cooling load hour by hour, not from a thumb rule. ISHRAE weather data gives design conditions for Indian cities.
- Decide air-cooled or water-cooled based on capacity, water availability, plant room space and energy cost.
- Choose the compressor type (scroll, screw, centrifugal) or absorption, based on size and the available energy source.
- Plan redundancy: N+1 chillers for hospitals, data centres and pharma plants where cooling cannot stop.
- Compare life-cycle cost: energy, maintenance, water and refrigerant over the chiller’s life, not only price.
- Design the whole plant: pumps, piping, valves, cooling tower and controls together.
Good chiller selection is part of good HVAC design. Envigaurd’s HVAC contracting team can support load calculation, equipment selection and installation.
Chiller Maintenance Checklist
| Frequency | Task |
|---|---|
| Daily / every shift | Log chilled and condenser water temperatures, pressures, current, alarms; check for leaks and unusual noise |
| Monthly | Check refrigerant charge indicators, oil level, approach temperatures; clean strainers; review water treatment readings |
| Quarterly | Inspect electrical connections, starter and VFD; clean air-cooled condenser coils; calibrate key sensors |
| Yearly | Clean condenser and evaporator tubes (water-cooled); oil analysis; leak test; safety device testing; eddy current test as recommended by the manufacturer |
Rising approach temperature (leaving water minus refrigerant saturation temperature) is usually the first sign of fouled tubes or low refrigerant.
Frequently Asked Questions
What is a chiller in simple words?
A chiller is a machine that makes cold water (or a water-glycol mix) and pumps it to the places that need cooling. In a building, the cold water goes to air handling units and fan coil units, which cool the air. In a factory, it cools moulds, machines or process liquids. The heat it removes is rejected to outdoor air or to a cooling tower.
What is the working principle of a chiller?
Most chillers work on the vapour compression refrigeration cycle. A refrigerant evaporates in the evaporator and absorbs heat from the water, the compressor raises its pressure and temperature, the condenser rejects that heat to air or condenser water, and the expansion valve drops the pressure so the cycle can repeat. Absorption chillers use heat and a lithium bromide and water solution instead of a mechanical compressor.
What is the normal chilled water temperature?
Comfort cooling plants are commonly designed for chilled water leaving the chiller at about 6 to 7°C and returning at about 12 to 13°C, a difference of roughly 5 to 6°C. Process plants, low-humidity pharma areas and ice-storage systems may run colder, often with glycol. The right set point comes from the coil and load design, not a fixed rule.
What does TR mean in a chiller?
TR stands for tonne of refrigeration, the usual unit of chiller capacity in India. One TR equals 12,000 BTU per hour, or about 3.517 kW of cooling. A 300 TR chiller therefore removes about 1,055 kW of heat from the chilled water.
Do chillers need BEE star labelling in India?
The Bureau of Energy Efficiency launched a star labelling programme for chillers in September 2018 on a voluntary basis, with ratings from 1 to 5 stars based on tested energy performance. Separately, the Energy Conservation Building Code (ECBC) sets minimum chiller efficiency for buildings that fall under it. Always check BEE’s current listing and your state’s ECBC notification for the latest status.
How long does a chiller last?
A well-maintained chiller commonly gives 15 to 25 years of service, depending on type, operating hours, water quality and maintenance. Regular tube cleaning, refrigerant leak checks, oil analysis and correct water treatment have the biggest effect on life and efficiency.
Sources and Further Reading
- Bureau of Energy Efficiency (BEE): Standards and Labelling programme for chillers and the Energy Conservation Building Code 2017
- Ozone Cell, Ministry of Environment, Forest and Climate Change: HCFC Phase-out Management Plan, Kigali Amendment and India Cooling Action Plan (2019)
- ASHRAE: ASHRAE Handbook (HVAC Systems and Equipment) on chillers and chilled water systems
- AHRI: Standard 550/590 for rating water-chilling packages (COP and IPLV)
- ISHRAE: Indian weather data and HVAC design resources
- Bureau of Indian Standards: National Building Code of India 2016, Part 8 Building Services
Conclusion
A chiller turns electricity or heat into chilled water, and that water does the cooling across the building or process. Knowing how it works helps you ask the right questions: air-cooled or water-cooled, which compressor, what water temperatures, what part-load efficiency and which refrigerant will still be serviceable in 2040.
If you are planning a new chilled water plant, replacing an R-22 chiller or improving plant efficiency, talk to Envigaurd’s HVAC team for design, supply, installation, commissioning and AMC support.
