Chiller Systems (Commercial) Reference

Why this matters

Commercial chillers are central air conditioning's bigger sibling - instead of cooling air directly, they cool water (chilled water at 42-45 °F supply) that's then circulated to air handlers throughout the building. They scale from 10 tons (small office) to 1000+ tons (high-rise). The diagnostic approach differs from split residential systems - chillers have more sub-systems (chilled water loop, condenser water loop, refrigerant circuit, controls, often multiple compressors), and a chiller failure can shut down an entire building's cooling.

Chiller architecture

Refrigerant circuit:

• Compressor (centrifugal / screw / scroll / reciprocating, varies by tonnage)
• Condenser (water-cooled or air-cooled)
• Expansion valve (TXV or EEV)
• Evaporator (cools the chilled water loop)

Chilled water loop:

• Pumps circulate water through evaporator (where it's cooled)
• Distributed to AHUs (air handler units) throughout the building
• Returns warm to the chiller for re-cooling

Condenser water loop (water-cooled chillers only):

• Pumps circulate water through condenser (where it picks up heat)
• Routed to cooling tower (rejects heat to atmosphere via evaporation)
• Returns to condenser

Air-cooled chillers skip the water condenser; instead, large condenser coils with fans reject heat directly to outdoor air. Simpler but less efficient and noisier.

Compressor types by tonnage

Key performance metrics

• Tonnage: 1 ton of cooling = 12,000 BTU/hr (the energy to melt 1 ton of ice in 24 hours)
• kW/ton: electrical input per ton of cooling. Lower is better. Modern chillers: 0.45-0.55 kW/ton at full load; 0.35-0.50 at part-load IPLV.
• IPLV (Integrated Part-Load Value): weighted-average efficiency across load profile; meaningful for buildings that run mostly part-load.
• COP (Coefficient of Performance): cooling out / electricity in. Modern chillers: 5-7+ at full load.
• ΔT chilled water: typical 10-12 °F (55 °F return - 44 °F supply, for example)
• ΔT condenser water: typical 10 °F (85 °F supply - 95 °F return, for example)

Refrigerants in chillers

• R-134a: common in centrifugal chillers; being phased down under HFC regulations
• R-1234ze, R-513A: low-GWP replacements becoming common
• R-410A: scroll chillers, packaged units
• R-32: newer scroll units
• Ammonia (R-717): industrial / very large; not residential
• Always check the refrigerant type before service; EPA Section 608 cert required

Common failure modes

Chiller won't start / locks out on safety:

• Low chilled-water flow → flow switch open
• High discharge pressure (condenser water issue, cooling tower problem, refrigerant overcharge)
• Low suction pressure (refrigerant undercharge, low chilled-water temperature)
• Compressor overload
• Microprocessor fault (read fault codes)

Chiller runs but doesn't cool to setpoint:

• Refrigerant low → recover, leak-check, recharge
• Condenser tubes scaled / dirty → reduced heat rejection → high discharge
• Evaporator tubes scaled / dirty → reduced heat absorption → low chilled-water capacity
• Compressor mechanical degradation → low compression ratio
• Excess load → building demand exceeds chiller capacity

Chiller cycles rapidly:

• Chilled water flow inadequate (short cycling on flow switch)
• Setpoint too tight
• Pump issues

Cooling tower issues (water-cooled):

• Fan failure → no heat rejection
• Spray nozzles plugged → low water flow over fill
• Bleed-off valve clogged → high TDS in water → scale formation
• Belt drive worn → fan slow

Maintenance schedules (industry-standard)

Daily / weekly:

• Read pressures, temperatures, water flows
• Log chiller status
• Check cooling tower water quality (TDS, pH)
• Verify normal operation

Monthly:

• Clean cooling tower strainer
• Check chilled water and condenser water pH, biocide levels
• Inspect for visible leaks
• Verify control sequence

Quarterly:

• Check refrigerant charge (subcool / superheat) - see Superheat Subcooling Method Reference
• Test safety controls (high-pressure cutout, low-pressure cutout, freeze stat)
• Inspect electrical connections in starter

Annually:

• Eddy-current testing of chiller tubes (every 3-5 years)
• Condenser water chemistry full analysis
• Refrigerant leak test (per EPA 608)
• Compressor oil analysis
• Bearing lubrication / replacement per manufacturer

Water quality (water-cooled chillers)

Cooling tower water is exposed to air and concentrates impurities as water evaporates. Without treatment:

• Scale formation: calcium carbonate deposits on condenser tubes; thermal resistance climbs; chiller efficiency drops
• Biological growth: algae, bacteria (including Legionella) thrive in warm, oxygenated water
• Corrosion: dissolved oxygen + dissolved minerals attack metal components

Treatment program:

• Conductivity-based bleed-off (controls TDS / cycles of concentration; typical 3-5 cycles)
• Corrosion inhibitor
• Scale inhibitor / dispersant
• Biocide (oxidizing + non-oxidizing rotation)
• Routine testing (weekly or biweekly)
• Annual Legionella testing per ASHRAE 188 in some applications

Brand-specific notes

• Trane CenTraVac (centrifugal): premium, common large commercial; Magnetic Bearing chillers (no oil) on newer Series E units
• Carrier 19XR / 23XR (centrifugal): premium large
• York Millennium / OptiView (screw): common
• Daikin McQuay: screw and scroll across range
• Tecnoclima / specialty European: premium efficiency, limited US distribution

Common service mistakes

References

• ASHRAE Handbook - HVAC Systems and Equipment (chillers chapter)
• ASHRAE 90.1 (energy standard for buildings; chiller efficiency requirements)
• ASHRAE 188 (Legionellosis: Risk Management for Building Water Systems)
• AHRI 550/590 (chiller performance ratings)
• EPA Section 608 (refrigerant handling)
• Manufacturer service manuals (Trane, Carrier, York, Daikin McQuay)