Evaluating the Efficiency of Thermal Energy Utilization
On August 27, 2018, four large air handling units (AHUs) were in operation at GBP, a commercial building. However, it was discovered that AHU-1A and AHU-1D were not operating efficiently in terms of heat recovery, as indicated by higher heat recovery return water temperatures compared to the other units.
Fortunately, the AHUs were able to maintain discharge temperature utilizing the preheat coils, preventing low temperature alarms. The issue with the heat recovery system in the AHUs was not detected onsite due to partial heat recovery from the exhaust side.
Cimetrics, a building analytics and heat recovery diagnostics company, was brought in to address the issue. They identified the root cause as the heat recovery valves not opening completely, causing water to bypass the coils.
Incomplete opening of heat recovery valves in air handling units is generally caused by mechanical issues, control signal errors, or system fouling. Troubleshooting involves inspecting mechanical components, checking control signals, and ensuring the heat exchanger and valves are clean and functional.
To resolve the issue at GBP, several steps were taken:
- A mechanical inspection was performed on the valves and actuators for damage, wear, or blockage.
- The control system and wiring were checked for fault codes, communication failures, or sensor errors, with faulty components replaced as necessary.
- The heat exchanger surfaces were cleaned to remove fouling that impeded flow and pressure equalization.
- Airflow distribution across the unit was verified to ensure consistent demand signals and avoid improper valve modulation.
- The valve operation was tested manually if possible to confirm full stroke capability.
- Control parameters in the AHU’s control system were reviewed and calibrated to ensure correct valve positioning commands.
These steps, along with regular preventive maintenance, have helped ensure efficient heat recovery performance at GBP.
As a result of Cimetrics' solution, GBP achieved an annual carbon emissions reduction of 605 metric tons and annual energy savings of $34,852. The heat recovery system operates when the outside air temperature decreases below 54°F and is disabled when the temperature rises above 55°F. The exhaust side of the heat recovery system consists of nine coils in the fume exhaust system.
Cimetrics worked closely with GBP staff and the controls vendor to fix the valves that were not opening, maximizing heat recovery for all four AHUs. This case study demonstrates the importance of regular maintenance and expert diagnostics in maintaining energy-efficient and environmentally friendly building operations.
- The efficiency of the heat recovery system in the air handling units (AHUs) at GBP was improved through the application of environmental science and technology, as detected issues were addressed by implementing solutions in the fields of mechanical engineering and control systems.
- The improvement in the heat recovery system enabled GBP to save a significant amount of both energy and finance, as it achieved an annual energy savings of $34,852 and reduced carbon emissions by 605 metric tons.
- By maximizing heat recovery for all four AHUs, GBP not only improved its energy efficiency and reduced its environmental footprint, but also demonstrated the importance of collaborative efforts between building industry professionals, controls vendors, and experts in the field of environmental science for successful climate-change mitigation strategies.
