McQuay OAC User Manual

Motor Control Options for Vision™Indoor & Skyline

™

Outdoor Air Handlers

What fan motor control options does McQuay offer to reduce energy costs, meet code requirements and protect against overloads on its air handling equipment?

A wide variety of motor control options are available for both Vision indoor and Skyline outdoor air handlers. These include three types of disconnect switches, two types of motor starters, and three brands of variable frequency drives (VFDs). Complementary options such as 120V or 24V transformers, line reactors, bypass and HOA switches are also available.

All motor control options are factory-mounted and sealed with a professional fit and finish to maintain our low,

0.5 cfm/ft

cabinet leakage rate. This also reduces field labor and installation costs. All options are ETL/c-ETL listed for proof of safety compliance and minimized risk when installing, maintaining and using these products.

Factory-Mounted VFDs

McQuay factory-mounted VFDs provide local or remote speed control of a single-fan motor with minimal field labor costs. Three brands are offered: McQuay, ABB and Danfoss. The McQuay VFD is application-specific and optimized for variable-torque applications (fans and pumps). It’s also smaller in size, costs less and provides reliable, quiet operation. See McQuay brochure A/SP 31-213 for details.

The McQuay VFD provides easy integration with building automation systems. Available communication options include Modbus, L

ONWORKS,

BACnet,®Johnson

Metasys

and Siemens Apogee.

A factory-mounted VFD with a disconnect switch and a bypass switch offers added motor control at the unit for mission critical air handler applications. With bypass control, power to the VFD can be switched to allow full operation of the fan motor in case of VFD failure. McQuay has standardized on a simple, two-contactor bypass in all of its Applied Air Handling products as this provides the best value for our customers.

Note: Caution should be taken when using a bypass switch with a VFD: When in bypass mode, the fan motor operates constantly at full speed. This can cause the HVAC system to shut down on a duct highstatic-pressure trip or, worse yet, cause damage to the ductwork. In addition, operating in bypass mode for long periods of time can increase energy costs by 50% or more.

Considering the reliability of the modern VFD— with an average service life of more than 20 years—the need for a bypass switch may be questioned. The switch consumes space, increases control complexity and adds cost. For mission-critical applications, a reasonable alternative might be to keep a replacement VFD in inventory. In the unlikely event of failure, most VFDs are relatively easy to remove and replace.

System Solutions From McQuay

Engineered for flexibility and performance.

Non-fused disconnect switch and McQuay VFD

Vision indoor air handler with factory-mounted VFD and disconnect switch

Factory-Mounted Disconnect Switches

McQuay unit-mounted disconnect switches provide the means to disconnect power in sight of the fan motor as required by the National Electric Code (NEC). All are housed in a NEMA 1 enclosure for Vision indoor air handlers and a NEMA 3R enclosure for Skyline outdoor air handlers. These switches are available in combination with any starter or VFD for a quick, easy field connection. Three heavy-duty types are available:

• Non-fused disconnect switch. This is a simple on-off switch with no over-current protection.

• Fused disconnect switch. This is an on-off switch with fused over-current protection. The fuse type varies by application. For constant-speed applications, Class RK5 fuses are employed. For VFD applications, Class J time-delay fuses are employed.

• Circuit breaker disconnect switch. This offers the same over-current protection as a fused switch, but allows the user to reset the breaker after an over-current

trip event without having to replace a blown fuse.

Factory-Mounted Starters

McQuay factory-mounted starters provide remote startstop operation and overload protection of an individual fan motor. Minimal field labor is required to wire the line and control circuit power. A Hand-Off-Auto (HOA) switch can also be selected for field connection to the building’s control system. A 120V transformer is also provided. Two types are available:

• NEMA (National Electrical Manufacturers Association) starters.

• IEC (International Electrotechnical Commission) starters.

NEMA contactors and starters are designed in standardized sizes from 00 to 9. Each size has a defined

current and a resultant voltage and frequency which are dependent on the horsepower rating. No matter who manufactures the component, the current and horsepower rating will be identical for a given size.

IEC contactors and starters are typically smaller and less costly than NEMA types. They are not designed to a standardized size. Instead, the manufacturer designs them to meet defined applications which are referred to as utilization categories. For our application—starting a motor for a fan—we use an AC-3.

Mounting Specifics

Vision indoor air handlers are typically furnished with motor control components mounted on the outside of the fan cabinet. For smaller air handlers, an optional section is needed to provide good service access to the fan. In these cases, the VFD is mounted in the air stream with the VFD keypad display mounted on the unit exterior. This allows for complete control with all access doors closed.

Skyline outdoor air handlers are always furnished with an exterior-mounted keypad display for easy control access. Complementary control components, including a disconnect switch, transformer and bypass switch are also available. All components are mounted on the exterior in a NEMA 3R enclosure. When ordered, the VFD is mounted inside the fan compartment. For smaller Skyline air handlers an optional section is needed to provide good fit and service accessibility.

Digital Ready™Controls

In addition to these cost-saving motor control options, McQuay offers Vision air handlers equipped with factoryinstalled Digital Ready control components, including limit switches, pressure transducers, actuators and sensors. Each component is optimally located, factory-mounted and factory-wired to junction boxes on the outside of each shipping section of the unit. This allows you to optimize air handler performance while minimizing the cost and potential problems associated with field installation of control devices. See our brochure A/SP 31-205 for more information.

For more information on factory mounted motor control options and Digital Ready control components, contact your local McQuay representative. To locate your representative, visit www.mcquay.com or call (800) 432-1342.

Motor Control Options for Vision and Skyline Air Handlers

A/SP 31-240 (04/08)