From the fumes of a welding station to the dust in a woodshop, industrial environments are filled with invisible airborne hazards. How can you be sure your workspace is truly safe and healthy? The answer isn’t a feeling; it’s a number. This number is your Air Changes per Hour (ACH), and it’s the key to protecting your team and your assets. Air Changes per Hour is a fundamental metric for measuring air quality and ventilation efficiency in indoor environments. In this blog, we will demystify ACH, covering its calculation, its critical role in industrial health and safety, and practical ways to optimize it for a healthier and more productive workspace.
What exactly is Air Changes per Hour?
Air Changes per Hour, or ACH, is a measure of how many times the entire volume of air in a room or enclosed space is replaced with new, filtered, or outside air in one hour. A higher ACH indicates a greater rate of ventilation, which is crucial for maintaining good indoor air quality by reducing the concentration of airborne pollutants, odors, and contaminants. The formula to calculate ACH is
- ACH=(60×CFM)/(L×W×H)
- CFM: This is the volume of air that a ventilation system, such as an HVAC unit or an air purifier, moves per minute.
- 60: This converts the airflow rate from per minute to per hour
- L, W, H: Length, Width, Height of the space.
Example of ACH Formula
Let’s break it down using an example with a small warehouse. To calculate the air changes per hour (ACH) for a small manufacturing facility, you first determine the room’s total volume and then use that value to find the ACH. For a facility measuring 50 feet long, 30 feet wide, and 15 feet high, the volume is 22,500 cubic feet. If the space is equipped with a fan that has an airflow rate of 3,000 cubic feet per minute (CFM), you can find the ACH by multiplying the fan’s CFM by 60 (to convert it to cubic feet per hour) and then dividing by the facility’s volume. Using the formula, this results in an ACH of 8.0. This means the air inside the facility is completely replaced approximately 8.0 times every hour. This ACH is typical for industrial spaces to ensure the rapid removal of heat as well as contaminants like dust and fumes.
ACH also differentiates between other metrics, such as MERV ratings. While often discussed together, ACH (Air Changes Per Hour) and MERV (Minimum Efficiency Reporting Value) measure different aspects of indoor air quality. ACH focuses on the quantity and speed of air movement, telling you how many times a room’s air is replaced per hour. In contrast, a MERV rating assesses the quality of air filtration, indicating how effective a filter is at capturing airborne particles.
Why ACH is Critical for Industrial Spaces
ACH is a way for an industrial space to ensure that its ventilation system is working properly, as well as protecting its employees. There are several reasons why ACH i
s crucial for industrial processes.
- Health and Safety:
- Pollutant control: ACH helps with flushing out dust, VOCs, fumes, and chemicals from processes such as chemical mixing, painting, and welding.
- Pathogen Mitigation: Proper air changes and ventilation reduce the risk of bacteria and viruses from entering the space and protecting your employees.
- Odor and Toxin Removal: Different processes can cause unpleasant odors, which can result in the buildup of harmful gases.
- Equipment and Product Protection:
- Dust and Particulate Removal: It is easy for dust and particulates to settle on machines and products in a process. ACH helps remove the dust and particulates from potential damage.
- Humidity Control: Proper ventilation and air changes also reduce the amount of humidity in the facility. Too much humidity can cause rust, mold, and damage to moisture-sensitive equipment.
- Employee Comfort and Productivity:
- Temperature and Airflow: Good ACH contributes to a comfortable temperature and reduces stuffiness for your workers.
- Cognitive Function: Good indoor air quality boosts cognitive function and productivity. It prevents CO2 and pollutant buildup, thus reducing “brain fog” and improving focus.
Industrial processes, especially those dealing with sensitive products/machines, need effective ventilation. ACH can make all the difference between a comfortable and uncomfortable environment for your employees.
Factors That Influence ACH Requirements
Although Air Changes per Hour seems pretty straightforward, there are several factors that can influence its requirements. Some of these factors include,
- Type of Industrial Activity: Different types of industrial spaces need different ventilation. For example, a welding workshop needs a higher ACH than a storage warehouse because of the fumes.
- Occupancy Density: The more people there are in a facility, the more the air needs to be changed.
- Types of pollutants: Different types of pollutants, like chemical vapors and dust, each require a different ventilation strategy.
- Internal Conditions: Heat-generating equipment will require a higher ACH for employee comfort and productivity.
- Building Design: The age, insulation, and layout all play a role in the ventilation and ACH calculations.
These factors all have an impact on how an industrial ventilation engineer designs the system.
How to Improve Air Changes per Hour
It is not only about calculating the ACH; it is also about the different strategies that can improve the air quality.
- Mechanical Ventilation:
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- Industrial ventilation systems with fresh air intake.
- Exhaust fans and ducted systems.
- Spot ventilation for specific tasks. An example of this would be a fume hood over a welding area.
- Natural Ventilation:
- Leveraging windows, doors, and roof vents. These are your friends when it comes to natural ventilation! The more you use them, the less energy and power an industrial ventilation system has to use.
- The stack effect (hot air rising).
- Filtration and Purification:
- Air filters are categorized by their MERV (Minimum Efficiency Reporting Value) rating. A higher number indicates greater efficiency at capturing increasingly smaller airborne particles. Typically, they range from MERV 1 filters that capture large debris like dust and pollen, to MERV 13+ filters that can trap fine particles such as bacteria and viruses.
- HEPA (High-Efficiency Particulate Air) filters are the gold standard for high-purity environments, as they are specifically designed to capture at least 99.97% of airborne particles as small as 0.3 microns
- Maintenance:
- Changing industrial air filters and doing regular maintenance on your system can help improve how efficiently the air changes per hour.
As mentioned above, utilizing these strategies can create a great difference in the air quality in your industrial space.
Calculating ACH with an Industrial Ventilation Engineer
At the end of the day, understanding your facility’s ACH isn’t just about meeting a number on a checklist; it’s about making a strategic investment in the health of your employees, the longevity of your equipment, and the overall efficiency of your operations. It’s the metric that connects a healthier workspace to a more productive business.
By taking the time to measure your current ACH and implement a targeted ventilation strategy, you’re moving into a proactive approach to air quality management. Don’t wait for a problem to arise. Take control of your air and control of your environment. If you’re unsure where to start, let our professional industrial ventilation engineers work with you in designing your perfect system.