HVAC Control Systems

When you’re in the market for HVAC motor speed controls, you want an experienced provider that delivers comprehensive solutions. Since pioneering the use of electronic servo drives in industry back in 1967, UNICO has been innovating answers to some of the world’s toughest motion-control challenges. From designing and manufacturing our own drives and control products to engineering thousands of systems in wide-ranging applications, we’ve built our experience and reputation one system at a time. Our approach to heating, ventilating, and cooling systems is a unique one that leverages upon our broad experience. We’re more than just drive suppliers. We provide complete, individualized solutions that economically address all of today’s HVAC issues—energy savings, environmental flexibility, power quality, integration, and aftermarket support. As a result, you get the best system at the best value from a single source. That’s the UNICO advantage.

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Variable-speed drives provide significant energy savings with centrifugal applications such as fans, pumps, and compressors. The amount of power drawn by these loads varies with the cube of motor speed. With traditional mechanical controls such as dampers, inlet vanes, or throttling valves, motors wastefully operate at full speed regardless of demand. By regulating motor speed to match actual need, energy usage is optimized. A 20% reduction in motor speed, for example, will cut power consumption in half. Precise speed control also yields smoother operation and extends equipment life. • Precise variable-speed control • Internal PI or PID • Plain-language interface • Integral communications • 11/2 to 1,200 hp


UNICO engineers have proven solutions for every environmental situation. From unattended sites in the frozen provinces of Canada to the steamy climate of Venezuela—from oily, contaminated factory air to the rooftops of office buildings, UNICO drives thrive in the harshest extremes. Our packaging know-how frees you to locate your equipment wherever you deem it most convenient and economical with the assurance of reliable, uninterrupted performance. • Standard NEMA 4 indoor and outdoor packages • High temperature and elevation solutions • Integral option panels in enhanced enclosures • NEMA 4X available

Power Quality

With the proliferation of sophisticated electronic equipment in most buildings today, power quality has become a genuine concern. Getting installations to meet IEEE standards while satisfying utility restrictions can be challenging. Harmonic distortion, power factors, and other concepts can seem complex and confusing. We understand harmonics and have developed a complete arsenal of harmonic reducing designs. Give us your system data, identify the point of common coupling, and we’ll select the appropriate solution to help you meet requirements in the most cost-effective way. We guarantee compliance to the most stringent standards. • Facility harmonic analyses • Line reactors • Built-in DC link chokes • 12-pulse input • 18-pulse input or equivalent • Passive filtration • High total power factor


We integrate solutions that are as simple or sophisticated as your application requires. From basic air handlers to complex field-engineered systems, our coordinated approach provides superior performance, efficiency, reliability, and safety. Our preengineered packages save time and money with typical applications, or we can custom engineer a solution. An extensive array of design templates accommodates the unique requirements that individual building systems may have. Drive systems can easily be integrated with a building automation system using popular communication protocols. • Pre-engineered and custom systems • Small footprint packages • Single- and multimotor coordination • Bypass flexibility • Short circuit and overload protection • Contactor motor selection • BAS logic and communications interface • Custom application software


Our commitment to you does not end with installation. We offer a full complement of products and services to help keep your equipment running reliably and efficiently. From service and training to customized diagnostic tools and technical aids, our support products, like our systems, are highly flexible to adapt to the needs of your staff. • Factory and on-site training • Custom classes • Global service and start-up assistance • 24/7 technical support • Spare parts and repair service • Support CD-ROMs • DriveLink™ drive monitoring software • Custom diagnostic hardware • Internet support

HVAC Fan/Pump Control

Variable-Speed Control

Motor speed is adjustable either locally from the keypad or a potentiometer or remotely from a building automation system (BAS). The drive will follow a 0 to 20 mA or 0 to 10 V DC analog speed reference and can switch between them based upon a digital input or serial command. The speed setpoint can also be programmed serially. In addition, seven input-selectable preset speeds, each with its own acceleration and deceleration settings, are provided for use with a BAS. Controlled S-curve acceleration and deceleration smoothes speed transitions and prolongs equipment life by minimizing shock. Customizable units adapt all speed references to application engineering units.

Keypad or Remote Control

The drive can be started and stopped manually from the keypad or automatically via a building automation system using digital inputs or serial commands. Keypad controls can be locked out for safe remote operation.

Process Control (PID)

Optional closed-loop PID control eliminates the need for an external process controller. Using temperature, pressure, or flow feedback from an appropriate sensor, the program regulates motor speed to maintain the requested process setpoint. Overpressure and no-flow protection for pumping systems shut the drive down in the event of a burst pipe, clogged pump, or other abnormal condition.

Automatic Restart

The drive can automatically restart following a fault trip. The number of restart attempts and the interval between them are selectable.

Spinning Restart

A spinning restart feature allows the drive to start smoothly into a rotating load, then accelerate or decelerate to speed without tripping.

Critical Frequency Avoidance

Three skip frequencies with adjustable windows enable the drive to avoid operating at speeds that resonate with the driven equipment. This is particularly important for stable operation with cooling towers.

Stopping Methods

Selectable stopping methods include decelerate-to-stop, coast-to-stop, DC injection braking, and DC hold braking.

Multimotor Capability

Variable-frequency software allows multiple motors to be operated in parallel from a single drive for installation cost and energy savings.

Power Loss Ride-Through

Extended power-loss ride-through helps avoid nuisance trips during brownouts or other outages. The 16 MHz variable-frequency control option additionally provides an adjustable deceleration time during ride-through.

Programmable I/O

Depending upon the software version, the user can specify the functionality of certain inputs and outputs to suit the requirements of the application, including using an analog signal to specify the value of selected parameters.


All popular industry-standard serial protocols are available for communicating with a building automation system, including Modbus RTU, ANSI, N2, LonWorks, BACnet, DF1, and Profibus. This allows the BAS to remotely monitor and control the drive as well as modify parameters.

Inputs & Outputs

The following inputs and outputs are typically provided for interfacing the controller with the system:


  • start
  • run enable
  • jog
  • reverse
  • fault reset
  • remote
  • programmable
  • no external trip
  • preset speed BCD 1
  • preset speed BCD 2
  • preset speed BCD 4

Analog Inputs

  • speed or torque reference
  • remote speed or torque reference
  • programmable


  • ready relay
  • programmable relay
  • programmable open collector

Analog Outputs

  • speed or torque
  • programmable

HVAC Fan/Pump Control Systems

Variable-Speed Drive

UNICO’s 1100 family of AC drives provides flux vector or variable-frequency (V/Hz) motor control from a single- or three-phase 230 or 460 V AC or three-phase 575 V AC input. Drives are available from 11/2 to 500 hp and are UL and C-UL listed.

Standard Packages

There are two basic option configurations. The Disconnect Package provides an AC input circuit breaker and operator, 115 V control transformer, and Hand/Off/Auto selector switch. The Bypass Package provides an AC input circuit breaker and operator, 115 V control transformer, Hand/Off/Auto selector switch, drive input and output contactors, bypass contactor, Drive/Off/Bypass selector, motor overload protector, keyed drive Test/Off selector, and bypass mode pilot light. Each of these components is described below.

Control Transformer

A step-down transformer converts the high-voltage line supply to 115 V AC for supplying the control circuits. Both the primary and secondary sides are fused.

Circuit Breaker/Disconnect

An input circuit breaker or fused disconnect interrupts the power to both the drive and bypass circuit. The breaker provides short-circuit protection when the motor is running across the line.

Hand/Off/Auto Selector

A three-position switch selects either local or remote operation. When set to hand, the user can start, stop, and adjust the speed of the motor from the drive’s keypad. In auto, the drive is controlled externally through contacts and gets its speed reference from a remote source or through the keypad. When set to off, the drive will not run.

Drive/Off/Bypass Selector

A three-position selector switch controls a bypass contactor and drive input and output contactors. When set to drive, the input and output contactors are closed and the bypass contactor opened for normal operation. When bypass is selected, the motor is connected directly to line power and runs at full speed. The input and output contactors are opened to electrically isolated the drive so that it can be serviced without interrupting operation. A pilot light indicates when the system is in bypass mode.

Test/Off Switch

A keyed switch permits testing of the drive while the motor is in bypass mode. The switch closes the drive input contactor to provide power to the drive while it is disconnected from the motor.

Motor Overload Protector

A thermal motor overload relay protects the motor while in bypass mode.


Systems can be packaged in NEMA 1, 4, 3R, or 12 enclosures to accommodate any indoor or outdoor application. NEMA 4 packages can be placed in wash-down areas or on rooftops. NEMA 12 packages can be placed in mechanical rooms that serve as the plenum. Customization is available for special environmental requirements. All work is done in a UL-certified panel shop.Enclosures for systems with bypass control feature mechanical isolation between the drive and the bypass to ensure electrical safety.

Other Options

Safety Terminals

A terminal block provides easy connection for freeze, fire, smoke, start/stop, and other external safety interlocks. This allows a building automation system to shut the motor down at any time by opening the 115 V circuit.

Motor Selection Contactors

Using motor selection contactors, two motors can be interchangeably operated by the same drive, such as for switching between primary and backup pumps. A Local/Off/Remote selector switch specifies whether the motor is selected locally using the Motor 1/Off/Motor 2 selector switch or remotely using contacts from a building automation system. Timers prevent a newly selected motor from being connected to the output of the drive until the drive has come to a stop. Pilot lights indicate the selected motor.

Automatic Bypass

The system can automatically enter bypass mode in the event of a drive failure.

Remote Bypass

A Remote/Off/Local Run selector switch selects the mode of bypass operation when the Drive/Off/Bypass selector is set to bypass. When set to remote, a contact must be closed to start the drive remotely in bypass. When local run is selected, the motor runs in bypass. If set to off, the drive will not run.

Power Conditioning

Various options are available for conditioning the incoming line, including an AC line reactors, isolation transformers, twelve-pulse transformers, or harmonic filters.