This is the second half of a two-part article discussing principles and application of the AC induction motors that provide motive power for most of the equipment HVACR engineers specify.
So, you want to generate your own power, for emergencies and/or for everyday use. For the sake of your design/budget/schedule, learn what the utility might expect from you — and what you should expect from it.
In the first of a pair of articles on motor fundamentals for HVACR, the author gets into everything from industry standards and service conditions to changing speeds, enclosures, and the often misunderstood service factor. You’ll want to save this one for your team’s reference library.
Our objective in specifying motors for HVACR equipment is to start and run the driven equipment under all operating conditions reliably and with reasonable life expectancy.
These days, designs are favoring higher total system capacities, larger generators at higher output voltages integrated into “campus-type” power distribution systems, and security. Review design approaches, lessons learned, and relevant codes.
Consolidation within the healthcare industry and the rise of regional medical centers has led to larger facilities, often spread over a large area in a campus environment.
Different types of load, from uninterruptible power supplies to VFDs and beyond, make for different approaches to your specific backup power situation.
In my experience, one of the trouble spots in project specifications is coordinating the control panels furnished with mechanical equipment with the standards that apply to the balance of electrical equipment on the project. Regardless of what you may include about NEMA enclosure types, short-circuit ratings, and other features, manufacturers tend to supply their standard control panel. The result is often an installation that cannot be verified to meet code or project requirements.
Microprocessor-based systems greatly increased the power and flexibility of BMS while lowering the cost of sophisticated control. A similar evolu-tion in electrical metering and protection devices has increased the amount of power system information available to building operators.
For motors in certain applications, the boilerplate approach to specification and design will get the system stopped because the motor won't start. Consider voltage, speed, and torque for these special instances, and follow along with the Case Of The Not-So-Centrifugal Pump Curve and the Case Of The Frequent Motor Failure to do some real-life motor- starting sleuthing. By Tim Coyle, P.E.