McQuay Chiller Selection: A Practical Checklist for Facility Managers and Contractors

When This Checklist Saves You Time (And Money)

If you're a facility manager or a contractor replacing an existing McQuay chiller—or speccing one for a new build—you've probably found the range of models a bit overwhelming. Centrifugal, screw, water-cooled, air-cooled, with or without heat recovery. You're not alone. I review equipment specifications for a living, and even I need a reference list when jumping between product lines.

This checklist cuts through the noise. It's built around the three things I check every single time before an order goes out: model match, spec conformance, and site feasibility. There are five steps. Don't skip step four—it's the one most people miss, and it's often the reason a delivery gets rejected at the receiving bay.

Step 1: Lock Down the Application Type

This sounds obvious, but I've seen more than a few orders placed for a water-cooled chiller when the site only had cooling towers for a condenser loop. Start with the basics:

• Is it a replacement? Get the existing model number and serial plate data. You need to know refrigerant type (R-22, R-134a, R-410A, R-1233zd(E)), voltage, and tonnage.
• New construction? What's the primary loop? Chilled water only, or is there a heat pump system in the mix? McQuay's WDA and WDC series (water-cooled centrifugal) are common for large commercial, but the RTAE (air-cooled screw) often gets specified for retrofits where indoor space is tight.
• Heat pump application? If you need simultaneous heating and cooling, a water-to-water heat pump like the McQuay WHS series might be a better fit than a chiller with a boiler.

Checkpoint: Write down the required leaving water temperature (LWT) and entering water temperature (EWT) for both chilled and condenser sides. If you don't have these numbers, you'll overshoot the selection every time.

Step 2: Match the Compressor Type to the Load Profile

McQuay uses two main compressor types in its chillers: centrifugal and screw. They don't behave the same way under part-load conditions.

• Centrifugal compressors (in the WDC, WDA, and some WSC models) are efficient at full load but can surge at very low loads if not managed by a VFD. They're a good pick if your building load is fairly steady (e.g., hospitals, data centers).
• Screw compressors (in the RTAE, RTHD, and some AGZ models) have a better part-load efficiency curve. They're more forgiving if the building load varies through the day—think office buildings, schools, or retail spaces.

I'm not a compressor engineer, so I can't speak to the minute details of rotor profiles. What I can tell you from a specification review perspective is this: if the spec sheet shows less than 30% load for more than 20% of operating hours, don't spec a fixed-speed centrifugal. You'll waste energy and shorten the compressor life.

Checkpoint: Look at the IPLV (Integrated Part Load Value). A higher IPLV isn't always better—it depends on your climate. In a hot climate (Houston, Phoenix), the full-load efficiency (EER or kW/ton) matters more. In a moderate climate (Seattle, Chicago), the IPLV is a better indicator of real-world performance.

Step 3: Verify the Evaporator and Condenser Approach Temperatures

This gets a bit technical, but stay with me. The approach temperature—the difference between leaving water temperature and saturated refrigerant temperature—tells you how well the heat exchanger is performing. For a new chiller, McQuay typically specs:

• Evaporator approach: 2°F to 4°F (shell-and-tube, with 0.7-1.5 fouling factor)
• Condenser approach: 5°F to 10°F (depending on water quality and tube material)

If the proposed chiller shows an evaporator approach of 6°F or higher, something's off. Either the selection is marginal, or the manufacturer is pushing the envelope on tube surface area. I rejected a batch of six chillers in Q1 2023 because the evaporator approach was 7.2°F against our spec of 3.5°F max. The supplier claimed it was 'within industry standard'—and technically, it was. But it wasn't within our standard. They re-selected the heat exchanger at their cost.

Checkpoint: Ask for the selection report. Don't accept a 'budgetary selection' that skips the approach temperatures. You'll pay for that missing margin in higher fouling and reduced efficiency in year two.

Step 4: Verify the Chiller's Physical Fit and Service Clearance (This Is the One Everyone Forgets)

This step isn't about performance—it's about the real-world act of getting the chiller into the building and keeping it running. I've seen a 30-ton air-cooled chiller delivered to a roof that had no crane access except from an active street. The install crew had to disassemble the unit and bring it up in parts. That added $4,200 to the project cost.

What I check, in order:

1. Rigging path: Doors, hallways, elevators, roof hatches—measure everything. The chiller's shipping dimensions are rarely the final dimensions. Add 12 inches for packing and lifting spreaders.
2. Service clearance: The manual will specify minimum clearance for tube removal (usually 1.5x the tube length on the waterbox end). If you're pushing the chiller against a wall to save floor space, you'll pay for it when a tube leaks.
3. Weight distribution: A McQuay WDC 180 (200 tons) weighs about 18,500 lbs. The weight isn't evenly distributed—the compressor end is heavier. Check the structural load on the roof or floor slab, not the average weight.
4. Airflow clearance (air-cooled models): McQuay's RTAE units need at least 6 feet of clearance on the condenser face. Less than that causes recirculation and short cycling. I ran a test on a site where they squeezed an RTAE 300 into a 4-foot clearance—the discharge temperature was 12°F higher than spec. The unit tripped on high head pressure within a month.

Checkpoint: Walk the installation site yourself. Don't rely on a floor plan from the architect. Architects rarely account for subsections and coil pullers.

Step 5: Confirm the Controls and Interface Compatibility

McQuay chillers ship with either the MicroTech II or MicroTech III controller, depending on the model year. If you're integrating this into an existing BAS (Building Automation System), the communication protocol matters.

• MicroTech III supports BACnet MS/TP, BACnet/IP, Modbus RTU, and LonWorks. It's the easiest to integrate with modern systems.
• MicroTech II is older but still common on legacy units. It supports BACnet and Modbus, but the data points are different. If you're replacing a chiller and keeping the old panel, you might need a gateway.

I'm not a controls specialist, so I can't walk you through the wiring diagrams. What I can say: specify the protocol in your RFQ. If you say 'BACnet compatible,' and the supplier sends a LonWorks-only chiller, you're stuck with an integration cost that could be $1,500–$3,000 for a simple gateway. I've seen this happen three times in the last two years.

Checkpoint: Get the exact part number for the control board in writing. Cross-reference it with McQuay's compatibility list for your BAS vendor.

Common Mistakes That Slip Through the Cracks

I've rejected about 12% of first-run chiller selections in 2024—not because the equipment was defective, but because the documentation didn't match the site conditions. Here are the ones I catch regularly:

• Ignoring the project-specific submittal: A standard 'McQuay Chiller' submittal is not enough. You need a project-specific selection with site-verified EWT/LWT and 0.0% glycol unless specified.
• Assuming factory charge covers the system: A McQuay chiller ships with a dry nitrogen holding charge. The refrigerant charge is separate—and the amount of R-134a or R-1233zd(E) is based on the chiller alone, not the system. If you have long piping runs, you need extra refrigerant.
• Ordering the wrong fan coil or AHU to match: If you're pairing a McQuay WSC chiller with McQuay fan coil units (like the SG Series), make sure the entering water temperature at the coil matches the chiller's leaving water temperature. A mismatch of 2°F can cause the coil to undersize or overshoot. I see this about once a quarter.

Final thought: Don't hesitate to ask McQuay's application engineering team to re-run the selection if anything feels off. I've called them with a 'just-checking' question more than a few times. It's better to spend 30 minutes on the phone than to explain to a building owner why their chiller isn't hitting setpoint in July.