What are Air Changes per Hour (ACH) and Why Do They Matter

air changes per hour

We take a lot of things for granted, such as the air we breathe every day. Whether we’re relaxing at home or working onsite in an office building or attending classes at school, we breathe in air that contains pollutants. This could include contaminants such as chemicals but also dust, mold, viruses, and other pathogens. We rely on the HVAC system to provide fresh outside air, but that system needs to be properly maintained to deliver the right number of air changes per hour (ACH). If you are unfamiliar with indoor air quality and what are air changes per hour, read on.

What is Indoor Air Quality?

The HVAC system works hard to heat and cool buildings, but it also helps maintain healthy indoor air. This is referred to as indoor air quality or IAQ. Proper IAQ creates a healthier indoor environment. Conversely, poor IAQ leads to health problems. Short-term issues include the triggering of asthma and allergies. Over the long term, a risk of serious respiratory problems exists. Studies show that poor air quality impairs cognitive functioning as well. Students in school buildings with poor IAQ test lower. Workers in office buildings with poor IAQ produce less. In short, maintaining proper IAQ is important. Therefore, the HVAC system’s ability to remove pollutants from the air is important. This is why air changes per hour are critical to our health indoors. 

What Are Air Changes per Hour (ACH)

The air exchange rate is the process of bringing outside air into buildings. Air changes per hour (ACH) is the amount of air brought in. Pollutants exist in the air we breathe every day. Outside, however, their presence is diluted by the sheer volume of air. Inside, it’s a different story. In fact, the inside air is more polluted than the air outside. Pollutants include dust, pollen, soot, bacteria, mold, even viruses. Bringing more outside air into the building lowers the levels of these pollutants. It also helps reduce odors and maintain proper temperature and humidity levels. 

Air Changes per Hour and IAQ

Certain factors affect how much fresh outside air a building needs to maintain healthy IAQ. The occupancy of the building is important as well as activity levels. For instance, the recommended number of ACHs for a commercial building is four, while between six and 20 ACHs is the recommendation for classrooms. For warehouses, it’s between six and 30. This is a general rule, of course, because each building is different. Depending on the activity of the building, other contaminants may be a part of the daily operation of a business. Chemicals or dust and gasses from manufacturing would need special consideration in the design and efficiency of mechanical systems. More extensive exhaust ventilation would work to keep these pollutants out of the building’s air stream.

How to Measure ACH

HVAC technicians use tools to measure ACH, but it’s also possible to calculate air changes per hour yourself. This requires measuring the air volume of the room which is the length of a room multiplied by the width and the height: Volume = L x W x H. To determine the ACH, take the cubic feet per minute (cfm) of your air filtration device multiplied by 60 minutes then divided by the volume of air in the room ( L x W x H).

Dyson TP04 Tower Pure Cool digital display
What are Air Changes per Hour?

How to Improve IAQ

Keeping IAQ at healthy levels in the home or office requires regular HVAC maintenance. However, you don’t need to rely solely on your HVAC system to supply clean air. Air cleaning technologies, such as air purifiers, trap pollutants in HEPA filters thus preventing them from entering the air. HEPA filters remove a minimum of 99.97% of all particles 0.3 microns in diameter. 

Air cleaning devices designed with smart technology sense the number of people in a room and adjust performance accordingly. The placement of these devices in the room is important as well as is the size of the device. For example, the design of the AeraMax Professional 2 works well for commercial use in rooms up to 300 square feet while a home model like the Dyson TP04 Pure Cool Link Tower uses Air Multiplier technology to provide over 77 gallons per second of airflow. 

Improve Air Changers Per Hour

We hope this answers your questions about what are air changes per hour and why it’s important for your health and well-being. To learn more about how to improve the indoor air quality of your home, office, or commercial business, give us a call at 727-572-4550.