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Air Changes Per Hour: Complete ACH Guide

Globally, air pollution is responsible for almost seven million deaths every year. It’s the third most common health risk factor after high blood pressure and smoking. Indoor air pollution causes over two million of these deaths.

Two major factors affect indoor air quality. They are pollutant sources and inadequate ventilation. This should be a cause for concern for US businesses as employees spend at least eight hours a day.

Employers must ensure their buildings are properly ventilated. They can do this by measuring the air changes per hour.

This article delves further into this metric. It will answer questions such as, What does air changes per hour (ACH) refer to? and How many changes of air are required per hour? Read on to find out.


What Does Air Changes Per Hour (ACH) Refer To?

ACH measures the number of times the air in a room gets replaced within one hour. This is also known as the air change rate or the air exchange rate.

This is important when determining indoor air quality (IAQ). Often there are specific ACH rates. Facilities must meet these to satisfy the requirements of various regulatory bodies.


How Do You Calculate Ventilation Air Changes Per Hour?

Wondering how to calculate ventilation? The formula for ACH is ACH=60(Q)/V.

V is the air volume, while Q is the cubic feet per minute (cfm) of your air purifier or filtration device.

You can determine the air volume in a room by multiplying the room’s length by width and height. The cfm determines how fast air flows through your filtration device or purifier.

Better devices have a higher cfm. This means the air changes more times every hour. There are also ACH calculator tools you can use to determine this.


How Many Changes of Air Are Required Per Hour?

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends specific ACH levels. These rates depend on room usage, the size of the room, and the number of people in the room.

Rates for some more familiar areas include:

  • Office buildings and rooms  – 0.5 – 1.5
  • Meeting rooms – 4 – 6
  • Educational institutions – 4 – 6
  • Chemical stores – 10 – 15

When it comes to ACH and HVAC systems, most don’t have adequate filtration capabilities. ACH rates for the average system are between 1 – 3.

It can be even lower if the system is older. You may have to look at other air purifier options to compensate for this deficiency.

How Many Air Changes Per Hour Should a Warehouse Have?

The recommended ACH for a warehouse is 6 – 30. Warehouse environments have many potential pollutants. These include carbon monoxide from the equipment used in material handling such as forklifts.


Getting the Air Right for Your Employees

Your employees spend more time at your facility than they do at home. OSHA sets out specific guidelines businesses must adhere to. This helps keep employees healthy and safe.

This should also extend to the air they breathe. Getting your ACH at the recommended rate is crucial to ensuring optimal IAQ. Does it help to know the answer to What air changes per hour (ACH) refer to? You’ve also learned how many changes of air are required per hour.

Still in doubt? Get assistance from an IAQ expert such as Atlantic Environmental. We can inspect your HVAC system to ensure you’re maintaining air quality. Contact us today to learn more!

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