A Mechanical Engineer's Perspective on Electrical System Commissioning

An unexpected power failure and the ensuing recovery can wreak havoc on a building and its systems, generating complaints, loss of environmental control, quality control problems, and occasionally, debris. But one often overlooked aspect of power systems failure is the effect on HVAC and building automation systems, and the problems that can ensue from loss of power.

05/01/2007


An unexpected power failure and the ensuing recovery can wreak havoc on a building and its systems, generating complaints, loss of environmental control, quality control problems, and occasionally, debris.

But one often overlooked aspect of power systems failure is the effect on HVAC and building automation systems, and the problems that can ensue from loss of power.

Here, I want to discuss the important HVAC and building system considerations that merit attention when assessing and testing the ability of a building and its system to recover from a loss of electrical power, as well as the loss of other types of utilities.

The bottom line is that power failures happen—they will happen irrespective of whether the design of a building and its systems anticipated them or not. Similarly, the building will recover when power is re-applied, be it via emergency generators or the restoration of normal power.

The only real question is, as Dr. Phil would say, “So tell me, how did that work for you?”

There are a number of important characteristics associated with a power outage that need to be considered. One is simply, what constitutes a power outage?

The answer, of course, depends somewhat on personal perspective. Let's say, for example, an individual is in a windowless office located in the core of a building. The outfall of the circuit that serves those occupants' lights and receptacles tripping off is indistinguishable from the outfall of the circuit breaker serving a panel feeding all of the lights and receptacles on the floor tripping off.

In contrast, nobody else on the floor may know of the localized outage until a co-worker stumbles out of his or her darkened office. If the panel serving the floor looses power, then everyone is impacted.

The implications of the outage also can vary. Our worker in the windowless office with the circuit breaker trip will experience a significant drop in productivity until the problem is resolved.

But, the productivity of other workers on the surrounding floor remains high unless the outage impacts the entire floor. If our worker gets promoted, and the windowless office becomes a broom closet, a power outage affecting only the broom closet may go undetected for weeks or months and have no impact.

If, however, the windowless space was an active operating room in a surgical suite, the loss of light and power could be life threatening, not just an impact on productivity.

Ripple effects

From the perspective of the load or occupants in the area served by an HVAC system, the ripple effects of the outage can be as significant as or more significant than the actual loss of power. Consider a 100% outdoor air surgical air-handling system serving a hospital in a hot and humid environment. The surgery may be operating at 65°F, 50% RH (Figure 1) due to the nature of the procedure being performed. Typically, this would require a discharge temperature in the low 50ing airflow in a matter of seconds; in most instances, code will require this.

However, if chilled water service is not restored at the same time, then the hot, humid air drawn in by the system will cause condensation on any of the surfaces that are at or below its dew point. In the case of our example, this would include the duct system and all of the surface in the operating room. This will lead to some serious consequences including:

  • Saturation of the HEPA filters in the diffusers serving the surgery

  • Water dripping from the diffusers into the sterile field and open wound

  • Condensation in the sterile supplies stored in the suite

  • Condensation inside tools and equipment in use in the surgery, including inactive electrical and electronic equipment

  • A slip hazard due to water accumulation on the floor.

In light of the preceding, it may be desirable not to restart the air-handling system when emergency power is restored, if chilled water is not available and the outdoor air dew point is above the temperatures typically found in the surgical suite and the systems serving it. Such an approach may be counter to common wisdom and, in some instances, counter to code or infection control requirements targeted at re-establishing air change rates designed to control infection and protect the patient.

It is interesting to note that in our example, the events described could be triggered by a power outage that was:

  • Area wide: a thunderstorm knocks out the local utility serving the entire district in which the hospital is located

  • Building wide: a fault in the transformer serving the hospital's central plant building could take the chilled water plant off line but not the hospital building

  • Localized: a controller fault could shut down the chilled water distribution pumps serving the surgery AHU with out impacting the hospital buildingor chillers.

Mass in motion = power

Most HVAC systems have energy place into them from an electrical source via a motor. At first blush, the concept of a power outage and the ensuing recovery from a power outage is associated with the loss and reapplication of electricity to the motor. But, the fact is that the energy input from the motor is conserved in the system as mass in motion; typically a fluid flowing in a duct or pipe (chilled water, air, refrigerant, steam, etc.). It is this mass in motion that actually provides the thermal phenomenon (heating, cooling, dehumidification, etc.) required to serve the load. Thus, anything that disrupts this mass in motion will disrupt or corrupt the thermal processes required to meet the load. Loss of electrical power is only one possibility. Others include:

  • Drive system failures: the failure of a coupling, belt or VFD eliminates the energy input to the system required to keep the mass in motion just as effectively as removal of electrical power to the motor.

  • Motor failures: a motor can fail for reasons other than loss of electrical power. Windings can burn up, bearings can seize, shafts can shear.

  • Controller failures: controllers can fail or cold-start, shutting down the equipment they serve, even though power is available at the starter or drive serving the machinery.

  • Operator error: it is alarmingly easy to throw the wrong selector switch or command the wrong point off; I know because I've done it. The result is indistinguishable from an electrical outage.

The preceding are but a few examples of how the integrity of a building's electrical system and the power it supplies are crucial to the integrity of HVAC systems. Power failures are a reality for virtually all operating buildings. By taking the time to consider the implications on all fronts, when inevitable occurs, you'll be able to look the Dr. Phil's of the world in the eye when they ask “So tell me, how did that work for you?” and respond “Pretty well, actually; we'd thought it through and we were ready.”

Buildings are becoming more technologically advanced. For this reason, commissioning of power systems must consider all types of systems. And systems are becoming much more complicated. New requirements in fire protection, building safety, energy performance and information technology are driving engineers to constantly learn complex systems.

Resources

There are a number of resources one can make use of when dealing with electrical systems and the related engineering issues. Of critical importance is a working relationship with knowledgeable electrical engineers. If you're as lucky, you'll meet a number of them as you work on various projects. Take the time to develop relationships. They understand the mysteries behind the “magic” in the wires that power the motors that make our systems work. They will become an invaluable resource, be it via a quick phone consult or as a co-consultant assisting you with a project. Other useful resources include:

InterNational Electrical Testing Association (NETA): NETA is an excellent resource for guidelines targeting the testing of electrical equipment, including emergency generators, uninterruptible power systems, and automatic transfer switches. Visit their website for additional information and to subscribe to their bi-monthly magazine at www.netaworld.org .

Single Phasing and Motor Protection Issues: Bussman's Overcurrent Protection and the 2002 National Electric Code provides valuable insights into motor protection topics, including single phasing and is available at www.bussmann.com .

The Functional Testing Guide: This free, downloadable resource, developed by STAC (State Technologies Advancement Collaborative) includes a chapter on Integrated Operation and Control. Contained with-in that chapter, under topic 2.2 %%MDASSML%% Test Guidance and Sample Test Forms is a test guidance document on the topic of System Recovery from Power Failure available at www.peci.org/ftguide .



The Building Commissioning Association - BCA

The Building Commissioning Assn. (BCA), headquartered in Portland, Ore., and on the web at

The BCA's goal is to achieve high professional standards, while allowing for the diverse and creative approaches to building commissioning that benefit our profession and its clients. For this reason, the BCA focuses on identifying critical commissioning attributes and elements, rather than attempting to dictate a rigid commissioning process.

BCA provides a number of commissioning resources to its members and to the public to increase awareness and promote building commissioning. For example, “The Building Commissioning Handbook, Second Edition,” by John A. Heinz and Rick Casault, has been revised by the original authors to include the most up-to-date information on all aspects of building commissioning.

As described on the BCA website, it is a guide to: staying on budget; improving the quality of buildings; meeting schedule; increasing energy efficiency. Chapters outline the commissioning process from pre-design to occupancy and explain the economics of commissioning and retrocommissioning.

BCA has more than more than 670 members, including individual commissioning professionals, member firms/organizations, and associate members (consulting engineers, property managers, building owners, etc.).

If you are looking for a commissioning provider, a searchable directory of BCA members is available to the public at the BCA website. If you are looking to become one, a Career Listings page with quite a few job postings is also at the BCA Website, as well as a calendar of events that include training programs and conferences.

Another valuable resource is BCA's quarterly electronic newsletter, “The Checklist,” designed to keep members informed of the happenings within the association. Other resources include commissioning process templates, webcasts and white papers.

The Critical Challenge—Reducing Downtime

In product literature describing its new Downtime Reduction System, Cooper Bussman, St. Louis, describes a comprehensive study of manufacturing facilities published in 2006 by the AMG, Advanced Technology Services, Inc., Meta Group. The study, which addresses the issue of downtime in the automotive, petroleum, chemical, steel and aluminum industries found that an open circuit event resulted in a average of 41 minutes of downtime—including 11 minutes on average to notify maintenance and 24 minutes on average to locate and trouble-shoot:

Average length of downtime per incident (time in minutes to identify and replace a blown fuse for the various industries was as follows: automotive industry, 15.8 min.; petroleum/chemical, 36.9 min., and steel & aluminum, 63.2 min.

It goes without saying that downtime is a continuing problem in many industries, according to Cooper Bussman. Downtime costs can range from $300,000 to the millions of dollars per site per hour, as shown by the following figures from the AMG study:

Automotive industry $1,320,000

Petroleum/Chemical 308,657

Steel & Aluminum $2,050,189

The literature also points out that downtime disrupts an integrated supply chain and idles the workforce. Even something as simple as a conveyor can stop production...and that's lost time, money and productivity.

The AMG study analyzed the average number of fuses blown per year (per site), and came up with the following figure for each of the profiled industries:

Automotive industry 456

Petroleum/Chemical 156

Steel & Aluminum 534

Many machines that control critical processes are fusible. Research has shown 90% of motors, 80% of heating and cooling equipment, and 60% of presses are fusible. But fuses and breakers aren't the only issue in maintaining reliable power.

The ultimate goal of a power-quality strategy is to provide all of a building's utilization equipment with power that is free from outages, voltage transients and other distortions. A power outage might be an overall system outage from the utility supply, or an isolated outage in the facility due to an unnecessary event. Transients are momentary disturbances where the system voltage is out of tolerance, either high (spikes) or low (notches). Voltage spikes can be caused by events such as lightning strikes or utility-line capacitor switching, and are generally a short burst of energy passing through the system. Voltage spikes can damage equipment by breaking down equipment insulation on wiring, especially on printed circuit boards where electrical tolerances are tight.

Studies indicate that approximately 90% of all power quality problems in a facility are generated within the facility. Harmonic voltage and current distortion is created by facility loads. Switch-mode power supplies used in electronic ballasts, computers and office equipment take power nonlinearly, which creates harmonics. Control motors in copiers and commutation contacts in motors create small voltage spikes and noise on the power system. In essence, the power system must be protected from itself.



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