The Commercial Chiller Guide: How Chilled-Water Cooling Works

The compressor drives the refrigeration cycle, and the type generally scales with plant size. Scroll compressors serve smaller chillers; screw compressors cover the broad mid-range with strong part-load performance; and centrifugal compressors handle the largest tonnages found in big towers, hospitals, and district plants. Compressor type strongly influences both efficiency and capital cost, and many modern chillers add variable-speed drives so the compressor can throttle down to match part-load demand — where chillers actually spend most of their operating hours.

The evaporator is the heat exchanger where refrigerant absorbs heat from the building's water, producing the chilled water that gets pumped out to the building. This is the 'product' side of the chiller — the chilled-water supply that air handlers and fan coils use to cool the space. Maintaining proper water flow, water quality, and a clean evaporator is essential; fouling or low flow here directly cuts capacity and efficiency.

The condenser is where the refrigerant gives up the heat it collected. On an air-cooled chiller the condenser is a finned coil with fans, rejecting heat to outdoor air. On a water-cooled chiller the condenser is a shell-and-tube heat exchanger that transfers heat into the condenser-water loop headed for the cooling tower. The condenser's effectiveness sets the condensing temperature, which is precisely why the water-cooled approach — rejecting at a lower temperature — is more efficient than air-cooled.

A water-cooled chiller doesn't reject heat by itself — it sends warm condenser water to a cooling tower, which evaporates a portion of that water to shed heat to the atmosphere, then returns cooler water to the chiller. Condenser-water pumps move the loop, and water treatment controls scale, corrosion, and biological growth, including Legionella risk management. This whole subsystem is the price of water-cooled efficiency: more components, makeup-water and sewer cost, and more maintenance — but a lower condensing temperature and a better kW/ton.

The chilled water the evaporator produces is circulated by chilled-water pumps through insulated piping to air-handling units (AHUs) and fan coils throughout the building. Air blown across those chilled-water coils is cooled and dehumidified and delivered to the space; the now-warmer water returns to the chiller to be re-cooled. This loop is what lets one central machine cool an entire high-rise — and its pumps, valves, and coil cleanliness are part of the plant's overall efficiency, not separate from it.

An expansion valve meters refrigerant into the evaporator and drops its pressure so it can absorb heat, completing the cycle. The refrigerant itself is undergoing an industry transition toward lower-GWP options, which matters for any long-horizon plant decision. Chiller controls — and integration with the building-automation system (BAS) — stage capacity, manage chilled-water and condenser-water reset, sequence multiple chillers, and trend performance, which is where a surprising amount of real-world efficiency is won or lost.

• •No cooling tower, condenser pumps, or condenser-water piping
• •Zero process water and sewer consumption
• •Outdoor packaged install — no indoor machine room needed
• •Requires freeze protection (glycol or drain-down) in the Northeast

• •Lowest full- and part-load kW/ton, advantage grows with tonnage
• •Indoor machine-room install generally yields longer equipment life
• •Requires cooling tower, condenser-water pumps, piping, and treatment
• •Best fit for office towers, hospitals, data centers, and campuses

• •Stages capacity to demand for better part-load efficiency
• •Built-in redundancy — one chiller can be serviced online
• •Supports phased capacity growth as load changes
• •Pairs with sequencing controls and BAS integration

Full Central-Plant Capability

Com+ Mechanical works the whole plant — chillers, cooling towers, condenser-water and chilled-water pumps, piping, controls, and BAS integration — across the NYC metro. Whether the issue is one machine or the whole loop, one contractor owns the diagnosis, the service, and the result.

Vendor-Neutral, Lifecycle-Aware

We service and install both air-cooled and water-cooled plants, so our recommendation follows your building's load, site, and total cost of ownership — energy, water, maintenance, and equipment life — rather than a single product line. The goal is the right plant, not the easy sale.

Engineering-First Sizing

We size to a real block-and-zone load calculation and compare options on full- and part-load efficiency, not nameplate alone, so the plant holds up over a 20-plus-year service life instead of just on day-one price.

Compliance & 24/7 Metro Coverage

We factor Local Law 97, ASHRAE 15 machine-room requirements, refrigerant transition, and NYC permitting into chiller decisions, and back the installed plant with response across the five boroughs and surrounding metro.

Assessment & Diagnosis

Plant survey, performance review, and — when selecting equipment — a load calculation and lifecycle comparison ending in a documented recommendation.

Preventive Maintenance

Maintenance scoped to the plant you run, protecting efficiency, equipment life, and warranty across the cooling season.

Installation / Replacement

Turnkey design-build of the selected plant — chiller, tower and pumps where applicable, piping, electrical, controls, and commissioning.

Own a Commercial Property?

Business+ plans start at $499/year — includes 2 rtu tune-ups, 10% off all services, and priority scheduling.

How does a commercial chiller actually cool a building?

A chiller uses a refrigeration cycle to remove heat from water, producing chilled water — typically around 42°F to 55°F — which is pumped through insulated piping to air-handling units and fan coils throughout the building. Air blown across those chilled-water coils is cooled and dehumidified, then delivered to the space; the now-warmer water returns to the chiller to be re-cooled, and the cycle repeats. This chilled-water approach lets one central machine cool an entire high-rise or campus, because circulating cold water across many floors is far more practical than running refrigerant everywhere.

What's the difference between an air-cooled and a water-cooled chiller?

Both make chilled water the same way; they differ in how they reject the heat they collect. An air-cooled chiller blows outdoor air across refrigerant condenser coils and dumps heat straight to the atmosphere, so it's a self-contained package that lives outdoors with no cooling tower. A water-cooled chiller rejects heat into a condenser-water loop served by a cooling tower; because water rejects heat at a lower temperature than air, the compressor works less and the plant runs more efficiently — but it adds a tower, condenser-water pumps, piping, and water treatment. Air-cooled is simpler and water-free; water-cooled is more efficient at scale. Our air-cooled vs. water-cooled chillers guide works through which fits a given building.

What are the main components of a chiller?

Every chiller has four core refrigeration components: a compressor (which drives the cycle), an evaporator (where refrigerant absorbs heat from the building's water to make chilled water), a condenser (where that heat is rejected — to air or to a condenser-water loop), and an expansion device (which meters refrigerant into the evaporator). Around those sit the refrigerant charge, controls and BAS integration, and — on a water-cooled plant — the cooling tower, condenser-water pumps, piping, and water treatment that make up the heat-rejection subsystem.

How is chiller capacity sized, and what is a 'ton'?

Chiller capacity is measured in tons of refrigeration, where one ton equals 12,000 BTU per hour of cooling. Commercial chillers range from a few tons to thousands of tons in the largest plants. Correct sizing comes from a building cooling-load calculation that accounts for occupancy, internal heat gains, glazing, and ventilation — not a rule of thumb. Oversizing wastes capital and runs inefficiently at low load; undersizing can't hold the building on design days. Larger buildings often use multiple chillers that stage to demand and provide redundancy. See our commercial HVAC system sizing guide for the method.

What do kW/ton and IPLV mean for chiller efficiency?

kW/ton is the headline efficiency metric — the kilowatts of electricity used per ton of cooling, where lower is better. Water-cooled chillers typically run well under 1.0 kW/ton (high-efficiency machines can approach or beat 0.5 kW/ton at favorable conditions); air-cooled chillers run higher because they reject heat to warmer air. But chillers rarely run at full load, so part-load efficiency matters more, and that's captured by IPLV (Integrated Part-Load Value), a weighted blend of efficiency at 100%, 75%, 50%, and 25% load. Two chillers with identical full-load ratings can have very different IPLVs, so comparing IPLV is essential. Minimum efficiencies are set by ASHRAE Standard 90.1.

What types of compressors do chillers use?

Compressor type generally scales with plant size. Scroll compressors serve smaller chillers; screw compressors cover the broad mid-range and offer strong part-load performance; and centrifugal compressors handle the largest tonnages in big towers, hospitals, and district plants. Many modern chillers add variable-speed drives so the compressor can throttle to part-load demand, which is where the plant spends most of its operating hours and where much of the real-world energy savings live. Compressor type affects both efficiency and capital cost.

How long does a commercial chiller last?

Chillers are long-lived assets. Water-cooled chillers, living indoors in a controlled machine room, commonly last about 20 to 30 years, and ASHRAE lists a median of roughly 23 years for centrifugal packaged chillers. Air-cooled chillers, exposed outdoors to sun, rain, and freeze-thaw, typically last about 15 to 20 years. Maintenance, water treatment, run hours, and refrigerant management strongly influence where a given machine lands. For the replace decision, see our commercial HVAC lifespan and when-to-replace guide.

What maintenance does a chiller need?

Core chiller maintenance includes scheduled inspections and operating-log trending to catch efficiency drift, condenser-tube cleaning (water-cooled) or coil cleaning (air-cooled), refrigerant and oil checks, controls verification, and — on water-cooled plants — cooling-tower cleaning and condenser-water treatment to manage scale, corrosion, and biological growth including Legionella risk. Because the chiller is usually the building's biggest electrical load, neglected maintenance shows up directly as higher energy bills. Com+ Mechanical's commercial chiller maintenance and cooling tower service cover this scope across the NYC metro.