How to Specify a Chiller: Procurement Cheat Sheet with 12 Key Parameters

Cooling capacity at the design condition

The most-quoted parameter and the most-manipulated. State the required capacity in kW cooling at the design ambient temperature, the design chilled water supply temperature, and the design chilled water flow rate. Do not accept nominal capacity at 35°C ambient if your design ambient is 46°C for a Gulf project.

For air-cooled chillers, capacity falls with rising ambient. A 500 kW nominal chiller can deliver 350 to 400 kW at 46°C ambient depending on the model. Ask vendors to submit performance data at the design condition, not the nominal.

For water-cooled chillers, capacity is more consistent because condensing conditions are controlled by the cooling tower. But specify the entering condenser water temperature (typically 32°C in the GCC) and the design cooling-tower approach so the capacity is comparable across bids.

Efficiency at full and part load

Specify both the full-load efficiency (kW/kW or IPLV in cooling capacity per kW input) and the integrated part-load value (IPLV) or non-standard part-load value (NPLV). Chillers spend most of their operating hours at 40 to 70% load, so the part-load value matters more than the full-load number.

For a commercial air-cooled screw chiller in 2026, expect COP around 2.7 to 3.2 full load and IPLV 3.8 to 4.4. For a water-cooled centrifugal chiller, expect COP 5.5 to 6.5 full load and IPLV 8 to 10.

Watch for vendors quoting IPLV at 27°C entering condenser water when your design is 32°C. IPLV assumes fixed condenser conditions per AHRI 550/590; if the vendor deviates, the number is not comparable.

Refrigerant choice

R-134a is being phased out in most jurisdictions. Current-generation chillers use R-1234ze, R-513A, R-32, R-454B, or ammonia depending on size and application. Confirm compliance with the applicable F-gas regulation and the project sustainability target.

GCC projects increasingly require GWP below 750 for new installations. GCC-EU and international finance-institution funded projects require low-GWP by default. Specify the maximum allowable GWP in the tender.

For district cooling and large industrial applications, ammonia (R-717) is increasingly cost-competitive but requires special code compliance for occupied buildings.

Compressor type

Small (below 250 kW): scroll compressors. Mid-range (250 to 1000 kW): screw compressors. Large (above 1000 kW): centrifugal compressors, often with magnetic bearings (Turbocor, DanFoss Turbocor).

Magnetic-bearing centrifugals dominate the premium segment for their oil-free operation, high part-load efficiency, and low vibration. They cost 20 to 40% more than conventional centrifugals but pay back within 3 to 5 years on high-runtime installations.

For district cooling plants above 5000 kW, screw and centrifugal are both common. Specify N+1 redundancy and diverse compressor manufacturers if resilience is a priority.

Chilled water temperature range and flow

Standard design: 6°C supply, 12°C return, delta-T 6°C. Some projects use delta-T 8°C to reduce pump energy. Low-temperature systems (ice storage, dedicated dehumidification) go down to 2°C supply.

State the flow rate in L/s or m³/h at the design delta-T. Confirm the chiller's minimum flow rate and maximum flow rate; running below minimum causes freezing on the evaporator, running above maximum causes tube erosion.

Variable primary flow systems need chillers with wide flow-range capability and fast recovery on load changes. Confirm the model supports variable primary flow if that is the design.

Sound rating

Chiller noise matters for rooftop and courtyard installations. Specify sound power (dBA at each octave band) or sound pressure at a defined distance. Air-cooled chillers on rooftops in occupied buildings typically require sub-85 dBA at 10 m.

Standard chillers offer optional low-noise or extra-low-noise configurations that add 5 to 15% to cost but drop the noise level by 5 to 8 dBA. For sensitive locations (hospitals, hotels), specify the low-noise variant.

Isolation mounts and flexible pipe connections at the chiller are always required regardless of noise class; do not price these separately.

Water quality and materials

Standard shell-and-tube evaporators and condensers are copper on the water side. For aggressive water chemistry (high chlorides, high total dissolved solids), specify cupronickel or titanium tubes.

For open cooling-tower water on water-cooled chillers, specify cupronickel condenser tubes as standard. The upcharge is 10 to 20% but avoids tube failure within the first 3 to 5 years.

Chilled water side is generally closed loop with chemical treatment. Confirm the water treatment specification is called for as part of the chiller commissioning package.

Checklist

1. Cooling capacity stated at design ambient and design flow
2. Full-load and part-load efficiency both specified
3. IPLV rating conditions confirmed per AHRI 550/590
4. Refrigerant GWP compliance with jurisdiction and sustainability target
5. Compressor type appropriate to size and duty
6. Chilled water design delta-T and flow range stated
7. Sound rating specified in dBA at defined distance or dBA sound power
8. Tube material for water-side conditions
9. Approved manufacturer list attached
10. Warranty period stated (typically 12 months on chiller, 5 years on compressor)
11. Spare parts kit included in tender
12. Commissioning agent and factory witness test included

Common mistakes

• Specifying nominal capacity instead of capacity at design ambient
• Comparing IPLV at different rating conditions across bids
• Ignoring refrigerant regulatory changes over the equipment life
• Missing low-noise specification for sensitive locations
• Accepting standard copper tubes on aggressive cooling-tower water
• No factory witness test on chillers above 1000 kW

Frequently asked questions

Air-cooled or water-cooled?

Water-cooled is more efficient (COP 5.5-6.5 vs 2.7-3.2) but needs cooling towers, water treatment, and higher maintenance. Air-cooled is simpler and cheaper below 500 kW; water-cooled dominates above 1000 kW.

How much capacity to order?

N+1 redundancy for critical loads, N for non-critical. Do not oversize on top of N+1; oversized chillers run at very poor part-load efficiency in the first years of operation.

Factory witness test required?

Recommended for chillers above 750 kW. It typically costs 1 to 2% of the equipment value and catches serious problems before shipping to site.

Related calculators on this site

• Cooling Load Estimator
• Chilled Water Pipe Sizing
• TR To CFM Calculator

About this reference

Umar Dar is an MEP engineer with more than 15 years of experience in mechanical, electrical, and plumbing design and procurement across the Middle East and South Asia. He founded I Love MEP as a free resource for engineers, estimators, and procurement professionals.