In commercial office buildings, ventilation is often an invisible system. We only notice it when it fails to do its job, which is immediately made evident by excess humidity, odors or dust.
Other indicators are less obvious. An entire group of employees might catch the same bug or one stuffy conference room might consistently leave its visitors sleepy. (Yes, there might be more to blame than PowerPoint slide 41.) And with extreme heat or-as we just experienced-cold, a massive spike in utility costs can signal over ventilation.
More than just comfort, understanding the important link between building ventilation and indoor air quality can lead to significant dollar savings and improvements in comfort and productivity.
Ventilation includes the exchange of indoor and outdoor air as well as circulation of air within the building. Because dozens of common organic pollutants have concentrations two to five times higher inside than outside, it is one of the most important tools for maintaining acceptable indoor air quality.
Not surprisingly, one of those pollutants most important to address is what we exhale: CO2. The ambient CO2 level in Middle Tennessee is roughly 300 parts per million (ppm). Inside a typical commercial office building, those levels range between 500 and 1,100 ppm.
CO2 levels in office buildings are lowest in the early morning before the building is occupied and highest when meetings and other gatherings occur. Prolonged levels of 1,000 ppm or higher may indicate poor ventilation and lead to complaints of drowsiness and poor air.
Outdoor air introduction helps dilute the air stream until CO2, or any other pollutant, levels subside. However, when outdoor air temperatures reach extremes, considerable energy is expended to pre-heat or -cool that fresh air before it reaches occupied space. This leads to unwelcome utility cost spikes if left unmanaged.
The key to maximizing energy cost savings is minimizing outdoor introduction without compromising air quality during occupied hours. While HVAC systems, the following are general tips for reducing energy costs:
1. Provide only the minimum outdoor airflow rates to each space.
Consider installing CO2 monitors that adjust outdoor air intake to maintain CO2 levels at less than 700 ppm above the outdoor levels.
2. Ensure that outdoor air dampers are closed completely during unoccupied hours.
Closing outdoor air dampers when buildings are unoccupied can save significant money on heating and cooling costs. Have a technician confirm dampers are operational and are responding properly to control signals.
3. Implement an HVAC system night temperature setback schedule.
With exception of spaces designed for 24/7 operation, identify hours during which the building will be unoccupied and temperature settings can be relaxed. Office buildings can be unoccupied for a majority of a day, so avoiding unnecessary heating and cooling is a painless change.
4. Ensure exhaust fans shut down on a similar schedule.
If exhaust fans continue to operate when HVAC system operation is reduced during unoccupied times, unconditioned outdoor air will be drawn in by the negative pressure, increasing energy costs.
Fortunately, fresh air intake systems don't require constant oversight. With periodic checks of settings and overall functionality, significant gains in energy and comfort will carry on with little additional effort.