The Millig Difference:

The root of the problem was traced back to the VAV box, which was failing to properly control airflow into the zone. Given that VAVs control both ventilation and temperature, any malfunction in airflow control inevitably results in inconsistent heating and cooling cycles. This specific airflow control issue stemmed from the VAV's airflow damper being perpetually forced open, thus preventing proper modulation. 

Consequently, the system continuously delivered a high volume of cold air. During the morning warmup phase, the VAV box initiates reheat to assist the zone in reaching the desired temperature. However, the required reheat was excessive, needing to counteract the constant influx of cold air, far exceeding the space's typical heating demands. This likely explains the "too hot" complaints. As the day progressed, solar gain and occupancy increased the building's temperature, reducing or eliminating the need for reheat and potentially requiring cooling. Nevertheless, due to the damper being fixed in the open position, the room continued to receive maximum airflow regardless of the actual needs. This resulted in the overcooling complaints. In essence, when a VAV is unable to effectively control airflow, its ability to regulate zone temperature is compromised.

Initial Key Findings

• The RTU trends indicate that it follows the control temperature setpoint, meaning it does what it should be doing and the issue probably lies within the VAVs

• The trends for a single VAV in the system shows temperature swings, but not any damper response, implying “non-functional” controls which could be due to a number of reasons.

Millig’s Immediate Action Plan
To quickly address these issues and prevent ongoing occupant complaints, Millig recommended the following corrective actions:

• Restore airflow control and verify full damper movement (0%-100%) by physically inspecting it

• Using the BAS, ensure that each VAV box is properly controlling airflow

• Expand the verification process to all VAVs in the middle school and other facilities within the District

Long-Term Best Practices Recommended by Millig
Additionally, Millig advised the client to implement the following long-term best practices:

• Regularly review system graphics to quickly detect problematic zones

• Document any manual overrides with timestamps and explanations for future troubleshooting

• Ensure clear labeling of system trends for better data interpretation

• Confirm that all airflow setpoints align with design specifications and/or ASHRAE ventilation standards.

• Consider investing in client-owned airflow measurement equipment or hiring a Test and Balance (TAB) contractor to verify airflow accuracy throughout the district buildings.

• Monitor existing sequences to verify they work properly, i.e. monitoring based commissioning

By applying these recommendations, the school will be empowered to address these airflow issues as they happen again in the future, reinforcing the importance of knowledge and proactive maintenance.