- A chilled-water plant moves heat with water instead of refrigerant lines running through the building. It pairs one or more chillers with pumps, piping, air handlers or fan coils, and (for water-cooled plants) cooling towers.
- Air-cooled chillers are simpler and dominate mid-size buildings in Orange County; water-cooled chillers are more efficient at scale but require tower water treatment and Legionella controls.
- Most plant failures come from ignored basics: water quality, flow, strainers, and control calibration, not from the chiller compressor itself.
- Trend data (approach temperatures, amp draw, pressure differentials) shows decline long before failure.
- A plant replacement is a multi-month project; planning for lead times and phased cutovers protects occupants.
How a chilled-water plant works
A chiller makes cold water (typically around 44°F supply). Pumps circulate that water through coils in air handlers, fan coils, or process equipment. Air passes over the coils, warms the water by a few degrees (about 10°F is a common design rise), and the warmed return goes back to the chiller. The heat the chiller removes is rejected either directly to outdoor air (air-cooled) or to a second water loop that goes to a cooling tower (water-cooled).
| Plant element | Role | Common issues |
|---|---|---|
| Chiller | Removes heat from chilled water | Low refrigerant, tube fouling, compressor or oil issues, control faults |
| Chilled-water pumps and VFDs | Circulate water | Seal leaks, bearing wear, VFD faults, loss of differential-pressure control |
| Air handlers / fan coils | Transfer cold to air | Dirty coils, valve failures, actuators, strainers |
| Cooling tower (water-cooled) | Rejects heat to atmosphere via evaporation | Scale, biological growth, fan/gear failures, drift eliminators |
| Condenser water pumps | Circulate tower water | Same as above plus strainer plugging |
| Controls / BAS | Stage equipment, reset temperatures, alarm | Sensor drift, bad setpoints, overridden equipment |
Chiller types and where they fit
- Air-cooled scroll or screw chillers: The workhorse for buildings up to a few hundred tons. No tower, no condenser water treatment, but higher energy use in peak heat and roof or pad space required.
- Water-cooled screw and centrifugal chillers: More efficient, long-lived, and standard for large campuses and high-rises. Need a tower, water treatment, and more operator attention.
- Modular and heat-recovery chillers: Multiple smaller modules provide redundancy and part-load efficiency; heat-recovery versions can supply simultaneous heating.
- Absorption chillers: Use heat rather than electricity as the driver; niche, with specialized service needs.
Refrigerant choice is changing the market. Chillers built around older high-GWP refrigerants face phase-down pressure under federal and California rules. See our refrigerant compliance guide.
Water treatment and Legionella controls
Water-cooled plants are open to the atmosphere at the tower. Dissolved minerals concentrate as water evaporates; without treatment they scale condenser tubes (cutting efficiency) and corrode steel. Warm, nutrient-rich tower water also supports biological growth, including Legionella bacteria.
- Contract a qualified water treatment provider for chemical feed, blowdown control, and regular testing.
- Maintain a written water management plan for towers, consistent with industry guidance such as ASHRAE Standard 188; many jurisdictions and insurers expect one.
- Inspect and clean towers on a regular schedule, including basins, fill, and drift eliminators.
- Closed hydronic loops (chilled water, hot water) also need treatment: inhibitor, pH, and periodic testing.
Maintenance that protects the plant
| Interval | Typical tasks |
|---|---|
| Monthly / operator rounds | Log temperatures, pressures, amp draw, oil levels; check for leaks, noise, vibration; verify alarms are clear |
| Quarterly | Inspect strainers, check VFDs, verify control sensors, review trends against baseline |
| Annual | Chiller service per manufacturer (oil and filter-drier checks where applicable, electrical inspection, safety testing), tube-fouling evaluation, tower inspection and cleaning, pump alignment and seal checks |
| Periodic (multi-year) | Condenser tube cleaning and eddy-current testing, oil analysis, major overhaul planning, control system updates |
Our maintenance plans cover chillers within the broader equipment mix; see commercial HVAC preventive maintenance programs for how to structure scope across equipment types.
What operators should watch
- Rising approach temperature (difference between leaving condenser water and refrigerant saturation temperature): tube fouling or low flow.
- Falling delta-T (small difference between supply and return chilled water): flow being overpumped, valves stuck open, or coils not transferring heat. A common hidden energy waste.
- Increasing amp draw at the same load: fouling, mechanical wear, or control drift.
- Frequent low-pressure or freeze trips: low flow, low charge, or control issues.
- Short cycling at part load: staging problems or an oversized unit.
Planning a chiller replacement
- Evaluate actual load. Buildings often use less cooling than they did when the plant was built; right-sizing saves capital and energy.
- Choose type and refrigerant with regulations in mind.
- Check structural, electrical, and rigging constraints. Crane picks, rooftop or mechanical room access, and power capacity drive schedule and cost.
- Plan for temporary cooling if the building cannot tolerate downtime. Rental chillers and temporary piping connections are common.
- Phase cutover to minimize disruption and commission the controls sequence thoroughly.
- Capture baseline data at startup so future trends have a reference.
Large projects usually follow a formal procurement path. See commercial HVAC project delivery and bidding for how bid-build, design-build, and negotiated work differ.
Frequently asked questions
How long does a commercial chiller last?
Air-cooled chillers commonly 15–25 years; water-cooled centrifugal chillers 25+ years with proper maintenance and water treatment.
Do I need a cooling tower?
Only for water-cooled plants. Air-cooled chillers reject heat directly to outdoor air and need no tower or condenser water treatment.
What is a low delta-T problem?
It means chilled water returns too cool, so the chiller works harder moving more water for the same cooling. Causes include stuck valves, coil fouling, and control problems.
Do you handle chiller and boiler projects?
Yes, we pursue commercial mechanical projects including central plant work, as part of our service and bid work. Send plans or scope for review.
Have a site this applies to?
Davinci Mechanical is the commercial and union division of Scottish Tom's Heating & Air. Send us the equipment list or the problem and we'll tell you what we'd check first.