HVAC Systems: Saving energy at the zone level

HVAC systems are complex, but there are a variety of ways to improve system performance. One option is to start at the zone level or conditioned space and work your way back to major system components. Addressing energy efficiency in this order allows you to take advantage of downstream savings before tackling more complicated (and costly) opportunities.

As an example of this approach, repairing corroded dampers that aren’t opening and closing properly will increase occupant comfort while reducing energy waste. Fixing the dampers may also reveal additional energy- saving opportunities, such as resetting controls or rightsizing equipment.

Optimizing Zone-Level Performance

Zone-level equipment includes mixing dampers, reheat coils and thermostats that control the conditioned space. As facilities age, this equipment can fall into disrepair or out of calibration, reducing overall system performance. Fixing zone-level problems can save energy and increase occupant comfort. Common energy- saving opportunities at the zone level include the following.

Inspect dampers. Without regular maintenance, dampers often become frozen in position, rendering them ineffective at regulating air flow and saving energy. Locating and repairing non-functioning dampers can be time-consuming and expensive, but it can pay dividends in increased system efficiency and enhanced comfort.

Recalibrate thermostats. In systems with pneumatic controls, recalibrate thermostats every six to 12 months to make sure the temperature is regulated accurately and efficiently. Although calibration should be checked in response to a problem or complaint, proactive maintenance can optimize system efficiency and energy savings.

Maintain reheat coils. Inspect reheat valves and coils to ensure they respond appropriately to control system commands. Verify the capacity of the reheat coil by measuring its power input with an amp probe and comparing it to the nameplate value. If the measured value is significantly lower than the nameplate value, the coil may need to be replaced.

Shut off reheat systems in summer. If your facility includes a constant-volume reheat system, consider disabling it during the cooling season. With electric reheat systems, it’s possible to power off reheat coils at the breaker, saving energy. In certain situations, it may be necessary to leave some reheat coil breakers active to maintain comfort.

Control static pressure. Dual-duct systems typically include static-balance dampers to regulate static pressure in hot and cold ducts in response to zone demands. Over time, these dampers can fall into disrepair and fail, resulting in wasted energy and reduced comfort. Regular inspection and repair will help optimize system performance.

Looking for more ways to save? Work upstream by inspecting ducts for leaks, verifying operation of economizers and maintaining or replacing fans, compressors, evaporators and condensers. If your business or facility needs to replace a heating or cooling system, your local electric cooperative offers Power Moves® rebates for qualifying energy efficiency upgrades. Contact your co-op’s energy advisor for details.