Commissioning: For Indoor Air Quality
After a number of bad situations involving IAQ problems in new and existing K-12 school buildings, the state of Minnesota has legislated commissioning for all major K-12 HVAC projects. The primary focus of the commissioning process, as defined by Minnesota, is on confirming that ASHRAE 62 ventilation rates are achieved in all occupied spaces and that the ongoing operation can maintain and document those levels throughout the life of the system.
On a more global basis, the IAQ issue is what is driving commercial office building owners and developers to consider commissioning. They are beginning to feel pressure from their tenants to provide healthy buildings and are starting to realize that there can be a desirable bottom line impact associated with being able to market and deliver "healthy buildings."
Commissioning can help building owners realize their IAQ goals. The process can also provide meaningful documentation of system operation and ventilation rates in case the IAQ of a facility is ever questioned.
The designs used to achieve IAQ goals, while maintaining affordable energy consumption rates, often involve new, more complex, and interrelated systems - configurations to which most installation and controls contractors have not been exposed in the past. Our experience in commissioning these systems has been that the contractors are not necessarily "getting it right" the first time. The following are some examples of findings we've uncovered during functional performance testing on just two schools:
- The AHU did not have a programmed minimum outside air position. During testing, the outside air dampers fully closed when the mixed air temperature setpoint was reset to 70 degrees F. The sequence as designed and submitted requires a minimum position during occupied mode.
- The specified alarm point for high return air CO2 was not programmed. This point is required by both the designers' specification and the legislated requirement for CO2 monitoring.
- The outdoor air dampers did not go to the specified 50% position of primary design flow setpoint when the conditions were set up.
- Mixed air temperature sensor was not reading correctly and needs to be calibrated or replaced.
- Specified CO2 sensor was not installed
- There was no "real" outdoor air makeup to this unit. The outdoor air ductwork was connected to another unit's return air duct near where the other unit's outdoor air duct ties in. It is doubtful if any outdoor air was reaching this unit. If it were, it would be dependent upon the other unit's damper being open and set for a minimum position sufficient to provide design outdoor air quantities to both units.
- CO2 sensor was bad (failed open).
- There were no access panels for inspection and repair of the outside air damper. Without access panels, we cannot verify that the dampers are working as designed. In addition, no maintenance can be performed in the future.
- Testing verified that the minimum outside air damper position was not set properly.
The value of commissioning for this school system far outweighed the cost to add the process and its associated rigorous testing to its capital improvement program. ES