Building Air Quality

Indoor Air Quality versus Energy Use

Discussing IAQ vs. energy use would take more words than this column offers. But consider this situation which our staff recently found in a 5 year old building.

The building, an 8 story commercial office building is occupied by a single tenant. This building houses the employees of a major oil company, and is owned by a division of the company. It is a state-of-the art high-tech facility. In an effort to ensure that their employees are not put at undue risk, the building owner contracts for a proactive IAQ survey each year. That's why we were there.

As part of the proactive program, we routinely sample carbon dioxide (CO2) levels in the space. This helps us to determine whether the indoor enviroment is kept consistent. It also allows us to approximate the amount of outside air being delivered to the building.

The building has two air handler units (AHUs) designed to pre-condition outside air, and both units were running on the day of our visit. Consequently, the morning readings for carbon dioxide were low (from 400-500 parts per million) as they were expected to be. Afternoon readings for carbon dioxide fell into the 600-650 ppm range which is not unusual for a heavily occupied building receiving large quantities of outside air.

After a late lunch break, our staff proceeded to re-inspect the mechanical rooms located on each floor, and noticed something strange. The outside air supply louvers leading to each mechanical room were closed, where they had been fully open during previous portions of the day. On further inspection we found that the outside air units had stopped running. The building automation system had turned them off. Although the remainder of our samples, running until 6:30 p.m., did not show any unusual readings we did perform an additional check. We found that the toilet exhaust fans for the building continued to run.

During normal operating conditions the building's toilet exhaust fans draw approximately 2,000 CFM of air out of the building. This exhausted air is made up by the outside air handler units. When the outside air handler units were turned off however, outside air needed to find other ways into the building.

Although not an issue on the day of our visit, as summer progresses, this process of exhausting air without the delivery of makeup air, can cause warm and humid air to be drawn in through doors, around window seals, and through wall penetrations. When unfiltered and unconditioned air is brought in through this method, condensation can occur, and indoor air quality problems begin.

Our suggestion to property management was that when outside air units are turned off, the exhaust systems for the building should be as well, to ensure that the building is not placed under a negative pressure. At the very least, 2,000 cubic feet of conditioned air should be delivered to make-up for that which is being exhausted.