Tag Archives: Control system

VFD bypasses and backups: Which should you use?

VFD bypasses and backups: Which should you use?

Advanced motor protection and consistent energy savings are possible, with true redundancy.

By: Tommy Trullinger, Franklin Control Systems

Learning objectives

1. Learn the differences between traditional solutions to VFD failure and newer methodologies, and the pros and cons of each.

2. Describe a simple selection process to ensure the application is properly protected and backed up in the most economical way.

Originally introduced as an efficient and effective way to reduce energy consumption by allowing motors to be run at different speeds, variable frequency drives (VFDs) have become commonplace in the HVAC industry. While there is no question that VFD technology helps save energy, unfortunately it was somewhat unreliable in the early years. The VFD bypass was introduced to ease concerns around reliability, and it played a significant role in the rise of VFD usage.

A traditional mechanical bypass acts as a backup system to ensure equipment stays operational when or if a VFD fails. A bypass is essentially a motor starter that is built into (around) the VFD to maintain full voltage (across the line) control of the application. The backup allows the application to run at full speed until the problem with the VFD can be addressed.

The bypass, along with the VFD, have become staples of the typical HVAC configuration, and over the years have made their way into almost all consulting engineers’ specifications. The problem is that the majority of specifications today still hang on to the idea that bypasses are always needed. VFDs, like most electronics, have improved dramatically since they were first invented. They’re more reliable now and have extremely low failure rates. They’re also much more compact and economical than in years past.

Recently, VFD manufacturers have developed new and improved bypasses, as well as motor drive packages with full redundant capabilities. Opinions abound about which backup or bypass should be used for various HVAC applications, but there are few guides that provide a definitive answer. To better understand the selection process, it’s important to first look at the pros and cons of the various bypasses and backups available.

Traditional bypass

A traditional bypass consists of a separate motor starter, mechanically interlocked with its

3 Phase Power

3 Phase Power

companion VFD output contactor in a way that allows only the VFD or the bypass to operate the motor at any given time. Most traditional bypasses default to “manual” operation to engage the bypass. In other words, someone must manually turn on the bypass in the event that the VFD fails. A VFD fault relay can be used to start the bypass automatically based on a VFD fault, but only if the VFD is not damaged. Traditional bypasses are also available in 2- or 3-contactor variations. A 3-contactor bypass (Figure 1) introduces an additional contactor or a VFD isolation switch that disconnects the VFD from power supply. This enables an electrician to completely remove the VFD while the application is running in bypass mode. However, this is not recommended as it sets up the electrician to work in close proximity to high-voltage wiring. A 2-contactor bypass is sufficient for most applications requiring a bypass and does not provide a complete VFD isolation. Also keep in mind that local codes may restrict the actual configuration. Common features of a traditional bypass include:

  • Available in 2- or 3-contactor variations
  • Disconnect is typically integral
  • Hand, Off, Auto switch for VFD and bypass
  • VFD/Off/Bypass switch
  • Manual bypass standard (auto relay available)
  • Thermal overload protection.

The traditional bypass is readily available. Other advantages are that it is inexpensive in comparison to other backups, allows for building automation system (BAS) control, and is extremely reliable. On the downside, a traditional bypass offers no advanced motor protection, needs relays for automatic control, and has no soft start capability. Communication to BAS is limited, communicating status/fault only. All energy savings is lost and consumption is not monitored in bypass mode. Finally, the traditional bypass offers 60Hz operation only…

Electronic bypass (smart bypass)

3 Phase Power

3 Phase Power

The electronic bypass was recently introduced to address a number of concerns with built-in logic and advanced motor protection. This microprocessor-based bypass (Figure 2) offers advanced features such as protection from phase loss, ground fault, over/undervoltage, and over/under power. These protection features go far beyond what a traditional thermal overload provides. Electronic bypasses also typically include a provision for BAS to communicate directly to the bypass in the event of VFD failure. This should be coordinated with BAS software manufacturer. The electronic bypass allows users to select certain conditions in which they want the bypass to start automatically, and incorporates other features that traditionally would only be supported by the VFD (fault logging, delays, etc.). There are also electronic bypasses on the market that integrate full ANSI grade power metering, and BACnet or other communications interfaces to allow for seamless control and communications whether in VFD or bypass mode. Common features of an electronic bypass include:

  • Keypad with LED indication
  • Communication card
  • Advanced motor protection
  • Common start/stop terminals
  • Fireman’s override
  • Bypass fault logging
  • Selectable auto bypass
  • Power failure modes.

On the positive side, electronic bypasses offer features such as advanced motor protection, BAS communications, logic to assist with troubleshooting, flexible control features, and compact physical size. But these bypasses come at a higher cost. They also lack soft start capabilities and motor speed control in bypass (60Hz only).

Redundant drives

3 Phase Power

3 Phase Power

Redundant VFDs are the logical next step in control for critical applications (Figure 3). They work on the principle that if one VFD fails, full control and protection are maintained by a second VFD that automatically takes over. Redundant VFDs are not a new concept; the idea has been around for years, but only recently has this concept become cost-effective. With the VFD market becoming more and more competitive, it’s only a matter of time before bypasses fade away as a viable choice, and dual VFD systems become the standard for critical applications. Most VFD manufacturers offer some type of packaged redundant drive systems as part of their custom offering. This means they must be approached on a “job-by-job” basis.

It’s important to understand that these packages require a level of customization because they consist of more than just two VFDs. To maintain true redundancy, extra power and control circuitry must be added. The standby VFD must be isolated from power while the primary VFD is running to ensure both primary and backup VFDs aren’t damaged in the event of a power surge or spike. To isolate the VFDs, mechanically interlocked input contactors should be added. Provisions must also be made to ensure that the backup VFD doesn’t sit for extended periods without being periodically powered up. VFD DC bus capacitors have a shelf life and can degrade without periodic charge cycles. The control system should provide scheduled alternation or charge cycles for standby VFD. The downside of the added power and control components is unfortunately an additional cost.

Pros of redundant VFDs include full redundancy, full control with backup VFD, and advanced motor protection all the time. They provide consistent energy savings. (VFD operation is maintained even when one fails.) However, they are more expensive than traditional and electronic bypasses and have a larger footprint.

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Case Study: Buckley Air Force Base

Unique prolems to solve: An old World War II base, Buckley had 100-plus buildings in various

Rod White, Chief Mechanical

Rod White, Chief Mechanical

stages of disrepair. Often buildings had stand- alone systems; many had no building controls whatsoever.

There were at least eight different control systems in place, none of which could “talk” to one another. The Air Force’s goal was to tie everything to a single central control station to monitor the entire base.

System solution: After researching control systems at bases throughout the country, Buckley chose Delta Controls. Deciding factors included 3-D animated graphics, system reliability and ease of use. In Phase One of the base’s upgrade, Setpoint Systems installed Delta Controls in 14 buildings, including office spaces, hangars, HQ buildings, shops, work areas, fitness areas and the cafeteria.

ResultsAccording to Rod White, utilizing Delta Controls’ BACnet® system has balanced base performance for the first time. The Delta Controls’ system is much easier to understand, maintain and control. This means much less repair work for the staff. With HVAC working so well, the next step is to incorporate Access, Lighting and Irrigation. Rod calls the experience “one of the best projects I’ve ever been associated with.”

The former home of the Colorado Air National Guard, Buckley has been transformed into a fully operational Air Force base, home of the 460th Air Base Wing, as well as the 140th wing of the Colorado Air National Guard and 42 other units.

Maintaining High Performance Control Systems

Maintaining High Performance Control Systems By: Jim Sinopoli, PE, RCDD, LEED AP

“Another flaw in the human character is that everybody wants to build and nobody wants to do Maintenance.” Kurt Vonnegut, Jr.

We rely on control systems to monitor and manage our building systems. For the most part it’s been assumed that once the control system is installed and configured it will work for years with little attention and minimal maintenance. Some systems may be trouble-free, but the majority of them will need regular attention and maintenance. Over time hardware will fail, software parameters and versions change and slowly the control system will “drift” from its original configuration and performance.

The role of control systems is somewhat undervalued. When you examine the most complex system in most buildings, the HVAC infrastructure, you find that it’s the HVAC control system, not the HVAC equipment, which produces the most operational issues and is the leading cause of inefficient energy use. Lawrence Berkley National Laboratories examined 60 buildings and found the highest frequency of common problems with HVAC was in the control system. Texas A&M research determined that of the operational and maintenance measures that could produce significant energy savings, 77% of the savings were from correcting control problems.

Maintaining a high performing control system involves regular maintenance, software and data management and organizational policies. The issues that can cause problems with a building control system are the same challenges all of us have had at one time or another with our computer or smartphone: problems related to software, hardware, communications networking and “user” mistakes. What follows is an overview of some of the typical control system issues and recommendations as to how to keep it performing at a high level.

Software Issues
Software is probably the number one issue with control systems. Given that control systems are networks monitoring and managing data points and running control sequence programs, issues with software and the management of data is no big surprise. Problems can crop up with the initial configuration of the data points in a new or replacement BMS system. In existing buildings you may find multiple naming conventions, a lack of as-built control drawings and overall poor data management, thus making it difficult and time consuming to obtain accurate information on point configuration. Even if you get accurate information on the data points there may be human errors in configuring the points in the software.

Beyond the configuration of individual points is the organization of the control strategy software where both the control logic and appropriate parameters must be identified. If the control logic between different HVAC equipment is not sound, or parameters for set points or ranges for other data variables are not suitable, or if the space use has changed, you have a control system that is providing suboptimal performance for the underlying building system.

The BMS that manages and monitors controllers, data points, control sequences, etc. can also be a software issue. Many of the problems are related to the BMS really being an IT device; it has databases, operating systems, software applications, requirements for security and a need for IT support. With no underlying support from IT or a lack of IT expertise within Facility Management, you are bound to have software problems come up. In addition, a typical BMS system also has problems of “omission”. The BMS may not have graphics, analytic software or any application tools or displays to support technicians and engineers in quickly identifying problems and their likely remedy.

The BMS that manages and monitors controllers, data points, control sequences, etc. can also be a software issue. Many of the problems are related to the BMS really being an IT device; it has databases, operating systems, software applications, requirements for security and a need for IT support. With no underlying support from IT or a lack of IT expertise within Facility Management, you are bound to have software problems come up. In addition, a typical BMS system also has problems of “omission”. The BMS may not have graphics,analytic software or any application tools or displays to support technicians and engineers in quickly identifying problems and their likely remedy.

Communications Issues
Assuming that the software and hardware of a control system is properly working, network communication problems will usually involve cabling faults, improper cabling, excessive network traffic or the interface into IT network equipment. Cabling can get damaged and network connections can become loose resulting in a loss of signal across a communications span. If you’re using wireless technology you can possibly lose contact if you’re using an unlicensed frequency and other equipment using the same frequency is introduced into the space, causing interference.

The interface of a control system into the client’s IT network is another potential source of communication issues. It involves not only cabling into an IT network switch, but possibly additional equipment such as a gateway that may be need to translate the control systems protocol and data format into an acceptable format and protocol for the IT network.

With field controllers where the controller uses an analog signal to communicate with the field device such as temperature sensor the issue is calibration. A typical sensor may signal their output via a range over a DC current (4mA to 20mA is a common example, identifying zero level and maximum level of the output of the device). These analog communication links need to be calibrated, configured and validated to ensure the controller is getting accurate data.

Hardware Issues
At some point hardware devices fail, so every piece of hardware in a control system is a potential point of failure and possible hitch. At the lowest control system level we have devices that provide or facilitate communication of the monitoring data to the system, with
the data usually being a measurement or state of a device. These are the typical sensors, relays and transducers. In addition to complete failure of a device such as a sensor, you can have an operating sensor that’s just inaccurate. Sensors need to be recalibrated on a regular basis although many organizations never think to do so. The issue here being the control system may be receiving and acting on inaccurate or poor quality data.

At this same control system level are devices that the control system is managing and
controlling. These are devices such as valve or damper operators and variable speed drives.
Failure of the device, such as a leaking control valve, really negates the control request and
overall control strategy of the building system. The controller themselves may fail. This is typically related to controller’s circuit board, either the components on the circuit board or the board’s ability to bond different parts of the board.

Operator Issues
Operator issues are the human aspect of control systems. A typical example would be an engineer or a technician overriding a control parameter such as a set point, but not documenting the change. The override affects the control system, as well as other engineers or technicians that may be working on that portion of the system but not informed of the change. This human aspect of the control systems plays a part at the larger organizational level of a Facility Management department, where the operation that doesn’t emphasize preventative maintenance training for its staff or maintenance of the control systems.

Steps to Take

  1.  Inventory and document your control systems. Identify the location of all equipment and the version of the components and software.
  2.  Recalibrate your sensors as well as the analog signals to the field controllers.
  3. Gather and manage data related to the control systems such as as-built control drawings and points a list. Don’t wait for an emergency and then have to scramble to find everything.
  4.  Audit and evaluate the existing controllers for parts availability, service, and overall capability.
  5. Develop a step-by-step methodology for troubleshooting. For example, you may start with the information from the BMS, check the controllers and any IT network involved, which should help in localizing the problem. After that you may need some instrumentation to check cables, communications signals, and voltage or current between a field controller and a sensor or actuator.
  6. Assess the needs of the building owner and operators. If you are dealing with a portfolio of buildings, get a BMS system that can provide an enterprise-wide solution rather than managing buildings individually.
  7. Identify the software applications required. At a minimum you’ll need energy Management and an analytic application, such as fault detection and diagnostics.
  8. Evaluate whether an upgrade is justified. Take into account maintenance cost on the older control system and the energy savings and potential utility rebates and incentives on the new control system.

About the author: Jim Sinopoli, PE, RCDD, LEED AP – Managing Principal, Smart Buildings, LLC

Download the article here: http://www.smart-buildings.com/uploads/1/1/4/3/11439474/2012marmaintaining.pdf

Meet David Polsley – Apprentice Technician

Setpoint Systems Corporation is pleased to announce David Polsley, apprentice technician, to our growing Irvine, California Office.

While David is a native of Colorado, he moved to California 7 years ago. David brings a wealth of controls experience, specifically in residential automation hardware. David’s multifaceted background includes sales and project management on residential new construction and refit for low-voltage applications.

As an apprentice technician, David will be responsible for assisting in the development and maintenance of temperature control systems. Setpoint Systems Corporation apprentice technicians play a key role in assisting with project startup, planning, and scheduling.

Outside of work David is an accomplished marksman, and enjoys reading and staying current in the industry. David is also quite a fan of reptiles; he currently has four 9-foot Drumeril ground boa constrictors, 2 ball pythons, and a Guyana rainbow boa. Whoa!

Welcome, David!

Meet Jubal Smith – Service Technician

Setpoint Systems Corporation is pleased to announce Jubal Smith, Service Technician, to our Colorado corporate headquarters.

Jubal has six years of experience in the DDC industry, with a focus on service and installation. Jubal comes from a long line of family members devoted to the controls industry.

As a service technician Jubal will be responsible for developing, assisting and maintaining the design of temperature control systems. Setpoint Systems Corporation service technicians play a big role in project startup, planning, and scheduling.

Jubal is very athletic outside of the office, from running to martial arts. However, it’s also important to maintain a strong relationship with his family and friends.

The name Jubal comes from a book called “Jubal Sackett”, written by Louis L’amour.

Welcome, Jubal!