Commissioning for Indoor Air Quality

There are a lot of reasons why facility owners believe commissioning is important. Different owners have different reasons, but near the top of many lists has been the need for positive verification and documentation of the proper startup and operation of indoor air quality control features for their buildings.

After a number of bad situations involving indoor air quality 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 on-going operation can maintain and document those levels throughout the life of the system.

On a more global basis, the indoor air quality 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 indoor air quality goals. The process can also provide meaningful documentation of system operation and ventilation rates in case the indoor air quality of a facility is ever questioned.

The designs used to achieve indoor air quality goals, while maintaining affordable energy consumption rates, often involve new, more complex, and inter-related 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:

1. Air handler 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^oF. The sequence as designed and submitted requires a minimum position during occupied mode.
2. The specified alarm point for high return air Carbon Dioxide (CO2) was not programmed. This point is required by both the designers’ specification and the legislated requirement for CO₂ monitoring.
3. The outdoor air dampers did not go to the specified 50% position of primary design flow setpoint when the conditions were setup.
4. Mixed air temperature sensor is not reading correctly, needs to be calibrated or replaced.
5. Specified CO2 sensor was not installed
6. There is no “real” outdoor air make up to this unit. The outdoor air duct work is 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 is 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.
7. CO2 sensor is bad (failed open).
8. There are no access panels for inspection and repair of the outside air damper. Without access panels we can not verify that the dampers are working as designed. In addition no maintenance can be performed in the future.
9. 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 their capital improvement program.

 

COMMISSIONING: GETTING IT RIGHT

Engineered Systems, April, 2003

Rebecca Ellis, PE, LEED AP, CCP, CxA
President
Questions & Solutions Engineering
1079 Falls Curve
Chaska, MN  55318
rteesmag@QSEng.com