Indoor Air Quality Case Study: Office Air Reaches Hazardous Particulate Levels

Background

• Building: 3-story - 1st story retail, 2nd & 3rd story offices
• Building Completed: 2021
• Windows: Sealed, Inoperable
• HVAC: Rooftop units - provide both heating and cooling with economizer control
• Indoor Air Quality Monitor: Kaiterra Sensedge Mini

The focus of this case study is one 24 hour period for a 100 sq ft office equipped with an air quality monitor.

The office is conditioned with supply air from the HVAC system. For this 24 hour period the outside air temperature varied between 65°F in the morning to 80°F in the afternoon. For most of the day the office was supplied with cool air.

Outside air on the day being analyzed was significantly affected by smoke from a wildfire 30 miles from the metropolitan area where the building is located. Wind direction caused the smoke to settle over the city.

Indoor Air Quality Data

The indoor air quality monitor located in the office, the Kaiterra Sensedge Mini, measures CO2, VOCs, Large Particulates (10µg) and Small Particulates (2.5µg and smaller). The monitor feeds real time data to a dashboard that can viewed on a computer screen or mobile device.

This image shows an initial rapid rise in PM2.5µg/m³ particulates at the beginning of the 24 period. PM2.5 is a group of very small particles capable of penetrating deep into lungs causing potentially serious health issues. Particles of this size can come from vehicle exhaust, wildfires, power plant emissions or other combustion sources. In this example, the source was a wildfire.

By the time the occupant arrived at the office, the PM2.5µg/m³ reading was already in the bright red zone indicating "unhealthy" air. The PM2.5 µg/m³ reading was in excess of 120µg/m³ by 10:30am. At this level the air is considered "hazardous".

This image shows the entire 24 hour period. The PM2.5µg/m³ level peaked at over 250 µg/m³ around 12:30pm and then progressively declined to the green zone, below 12µg/m³ at 11pm. The entire work day from 8am to 5pm was in the red "unhealthy air", or, dark red "hazardous air" range.

Discussion

A combination of witnessing the PM2.5 levels rise from the air quality monitor dashboard and from hearing occupant complaints, prompted the building manager to inspect the HVAC settings and the rooftop unit itself. The unit was designed to deliver cool or heated air in combination with code required (ASHRAE Standard 62.1) outside air.

This diagram shows the basic operation of the rooftop unit equipped with an economizer to save energy by providing optimum outside air when the air outside is cool enough. Three sets of dampers control the flow and volume (CFM) of the three air streams: Outside Air / Economizer, Return Air and Exhaust Air.

The building manager discovered the economizer control was not working properly. Even though the outside air temperature was not cool enough to condition the inside space, the outside air dampers were wide open allowing a significant amount of smoke laden outside air into the supply air ducts. The air did pass through filters before getting into the building, but the installed filters were not rated for 2.5µg or smaller particulates. The result was a rapid rise of PM2.5µg/m³ in the offices.

Once the economizer control was fixed the air quality in the offices returned to "good" even though smoke still dominated the outside air.

While the hazardous indoor air issue in this case was resolved within a day, the situation demonstrates the value of installed indoor air quality sensors providing real time data that can be monitored. By sensing and displaying levels of CO2, VOCs and particulates (by size), building managers can focus on appropriate mitigation strategies.