4 Steps to Reduce Your HVAC Energy Costs with a Quick Payback

In an ever increasingly expensive business environment, saving money is important now more than ever. Many companies don’t realize their building systems contribute to a huge part of their economic health. Taking simple preventative measures will save time and money in the long run. Today’s post discusses 4 easy steps to reducing your HVAC energy costs, and with a quick payback!

The Challenge

Despite the economic advantages and significant energy savings available by using AC Variable Frequency Drives (VFDs) in HVAC applications, many building operators do not repair or replace drives when they fail. This is due to the fact that VFD motors can easily continue to run through a bypass contactor after failure. While this is a great solution for short-term outages, continued operation in this mode quickly becomes a very expensive way to operate a fan.

Budget cuts and competitive pressures have reduced building maintenance staffs in many public and private enterprises. This frequency results in a reprioritization of activities, forcing concentration on addressing issues which are required to be fixes at the moment. Repair items such as a HVAC drive system operating in bypass mode may be considered only a nuisance to be dealt with as time permits, and of course, time seldom does permit.


Historical Perspective

By reducing the speed of a motor, the variable speed drive ensures no more energy than necessary is used to achieve the required system flow. In theory, a fan running at half speed consumes only 1/8th of the energy compared to one running at full speed. Field experience has shown that when the effect of static back pressures is factored in, the relationship is somewhere between ¼th and 1/8th of the energy consumed at full speed depending on the applications mechanical application.

Bypass Failures

The intent of a bypass contactor is for use in case of a drive failure for short-term emergency service. It was never intended to be a long-term solution to a drive malfunction. While the misapplication of long-term use is understandable due to increased pressures on typically under-manned building maintenance organizations, there are proven approaches to solving this pressing problem. Energy costs continue to soar. When VFDs were purchased for the application, the additional costs were justified based on saving money and improving profitability by using less energy for HVAC in the building. As an example of how long-term use of bypass contactors effects energy costs, if 10% of the drives are in bypass mode, up to 56% more energy can be consumed by the HVAC system. This is based on the assumption of all motors being the same size, average at 50% flow.


A number of significant improvements have been made to present-day VFD systems compared to what was available ten years ago. Drive size and parts count have been reduced along with cost, while increasing performance, quality and warranty periods. VFD systems installed in the facility have a proven track record of reducing energy costs and improving client comfort. The ability to keep drives running as designed will assure continued savings and comfortable clients.

Retrofitting ABB VFD

Next Steps

The path forward presents two clear choices. First, do nothing and continue to lose increasing amounts of money every day as additional VFD systems periodically fail and go into bypass operation. Second, develop a program which will change the way drives are proactively maintained.

A typical Preventative Maintenance Program is centered on the following activities:

1. Review your situation. Inventory the drives in the building or complex to gather the following information:

  • Make and model of each unit.
  • Age of the drives and how long they actually have been in service.
  • The Horsepower (HP) of each drive.
  • The number of drives operating in the bypass mode.

2. Replace or repair all of the drives operating in the bypass mode. It is important to work with a supplier that demonstrates the capability to easily replace or repair drives. Select one that will              assist in the maintenance and support on an ongoing basis.

VFD Preventative Maintenance

3. Create or contact a supplier to help you with a Preventative Maintenance Program which focuses on the specific issues of drives and how to keep them up and running. These activities typically        include, but are not limited to:

With the VFD deenergized

  • Inspection of the environmental conditions on each drive.
  • Inspection of power components and circuit boards for deterioration.
  • Inspection for loose connections.
  • Cleaning interior components of the drives.

With the VFD reenergized

  • Simulation or variation of signals from the control system to verify that the VFD is responding properly.
  • Calibration of the drive to original factory settings.
  • Review of the drive application for possible upgrades and operation enhancements.
ABB drive change out

4. Replace older and highly critical drives before they fail. When a drive is over ten years old and/or in a demanding and highly critical application consideration should be given to replacing it              before failure.

If you are interested in the four steps above, but need some guidance on where to start, a complementary facilities audit will help you map out the process and define where you can lower your energy costs.

For additional resource information regarding VFD preventative maintenance and VFD technical data, please contact us, or visit our website! Feel free to share with your colleagues and friends, and don’t forget to follow us on Twitter and connect with us on LinkedIn.

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