Changing seasons have a habit of bringing system issues to the surface. For many parts of the U.S., HVAC systems have been running constantly to cool structures with very few opportunities to economize. At this time, chillers are loaded, and boilers are not a large focus. Now is the time to preemptively investigate customers’ buildings. This is also the last opportunity to fix or troubleshoot certain building issues concerning cooling efficiency or humidity control as the fall, for many places will bring drier air. Let us take a look at some things to consider as we move into our next season, but, first, make sure the equipment is being trended. There is nothing worse than trying to investigate a new issue only to learn there is no baseline to previously compare to.
System control is only as reliable as its sensors. Now is a great time to test outside air dampers and confirm temp and humidity sensors are reading accurately. If unable to physically be at the units, a simple mixed-air equation can help this process. Mixed-air percentage can be calculated as:
(((Return Temp - Mixed Temp) / Return Temp - Outside Temp) x 100)
Modulating outside air dampers while reviewing this equation can help determine if a unit is operating effectively. After testing, be sure to validate the outside air humidity sensor as well if the unit is going to be economizing based on enthalpy.
Temperature resets can often be looked over or ignored, thinking a customer already has it set the way he or she wants. Discharge air resets are important factors in maintaining energy efficiency and comfort during shoulder seasons. Investigate and determine whether these resets are functioning or recommend programming a reset to take advantage of savings. The weather will bring times when full heating is not a necessity, but bringing up the discharge temp and not cooling the air quite as much will help maintain occupancy comfort. While checking for these resets, be sure to also pay close attention to lockouts — whether that be compressor cooling lockouts or boiler outside air lockouts.
Pay attention to preheat set points. Countless times, I have seen preheat set points set too high in large buildings only to find multiple chillers running in very cold temperatures. The best way to pick a set point is to properly calibrate temp sensors and set them to what they were designed for in the original sequence. If they’re set too low, the coil is put at risk. If they’re set too high, excessive energy costs could occur. This is best left to the original design and not personal opinion. If a unit is tripping off in cold weather, it's best to investigate the unit and not just keep raising the preheat set point and masking whatever the real issue is. More than likely, the fix is simpler and much cheaper than avoiding the investigation and overriding the preheats wide open. The worst I have seen was an entire hospital with preheats wide open. The temp was in the 30s outside, and every preheat temp was in the 90s. Essentially, the building was simulating a summer day in the dead of winter. The boiler plant was doing all it could, and six large centrifugal chillers were running wide open.
Freeze protection is there for a reason. It’s important to properly validate freeze protection based on the system being tested. In the past, I have seen a technician quickly trip the freeze protection and only validate the unit turned off. If a unit has a preheating coil, it's critical to verify the valve opens 100% and the outside air dampers close. It’s also important to review the control sequence as, many times, freeze protection will want the return fan to continue to run to push warmer air over the coils.
Morning warm-up can be a blessing and a burden to a control system. If the warming process within a building is started too late, occupants will lack good control and comfort, but if the process is started too early, excessive energy is wasted on heating for no reason. It's also important that morning warmup runs long enough to not only heat the air but the objects in the space as well. Blasting a space with hot air quickly and then turning it off soon after can cause excessive reheat costs, especially in buildings with electric reheat in the zones. Checking trends for reheat usage during the day can help fine-tune an appropriate equipment startup time.
Lastly, documentation proves we did our job. Documenting calibration is the most important thing I can stress. In complicated systems, it’s incredibly easy to forget to test a particular item. Documentation helps maintain the firm’s commitment to customers and avoids finger-pointing when a customer's system is not working as expected and tensions are high. Documentation also helps with having a unified service offering among all technicians.
These are just a few simple reminders as we approach colder weather. There are energy savings to be found and problems to be repaired. I hope this quick review gets everyone thinking about the changing seasons ahead and reiterates the importance of being proactive rather than reactive.
James Regan has been working in the building automation industry since 2013. He started as a controls technician for Johnson Controls, working primarily in critical hospital environments. He moved on to an energy engineering role optimizing the automation systems of hospitals with a major focus on maintaining proper air quality settings as efficiently as possible. In 2018, he accepted a role as building systems analyst with Piedmont Service Group. In this role, he supported efforts to increase efficiency through identifying poor sequences, faulty field devices, or failing mechanical equipment. He currently is the analytics manager overseeing the building analytics platform where he supports Piedmont Service Group and CMS Controls with optimizing or continuous commissioning through analytics.