Create Date: July 9, 2024
Last Modified Date: January 23, 2025
A few variables are required for calculating air changes per hour. They are:
Air changes per hour will tell you how many times the air will be replaced with fresh new air per hour. If you get an answer of 7 that means each hour there will be new air cycled into the room 7 times. Certain establishments require a minimum value for this to ensure the safety of those who are in the building, such as hospitals.
Our air changes per hour tool is very easy and simple to use. You can get an answer in under a minute by following these steps:
Let's say we have a room we need to make sure is properly ventilated. We want to check if the current air changes per hour is acceptable. We can use this tool to help us with that. We get the area of the room, which is 300 square feet, the height of the room is 10 feet and the airflow is about 215 feet cubed per minute.
After we enter these values into the fields and select the proper units we can hit calculate to get an answer of 4.3 air changes per hour.
Despite seeming like a term that is only relevant when discussing modern day, air ventilation was a concept that goes back to ancient civilizations like the Romans who built ventilation shafts in homes to improve airflow. During this time they were not able to measure and quantify proper air ventilation requirements and values.
Moving into the medieval and renaissance era, windows, chimneys, and other natural drafts became more important. Architects would begin to incorporate those types of structures knowing that they would have to design living spaces with good air flow.
Air flow and quality became critical when the industrial revolution hit. Factories where there were chemicals in the air and other harmful things made it impossible to ignore. Ventilation systems began to be implemented which even included fans at this time. It wasn't until the late 19th century when engineers and scientists began to calculate the rate of air exchange, and thus ACH-like concepts were born.
Air Changes Per Hour (ACH) refers to the number of times the air within a specific space is replaced with fresh air in one hour. It is a key indicator used to assess the effectiveness of ventilation systems in maintaining indoor air quality.
Calculating ACH is crucial for ensuring that a space has adequate ventilation to maintain air quality and comfort. It is particularly important in settings like hospitals, laboratories, and residential homes to prevent the buildup of pollutants, moisture, and odors.
The correct airflow rate depends on the specific requirements of the space, including its size, the number of occupants, and its use. Generally, guidelines or standards provided by local building codes or by organizations such as ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) can offer specific recommendations for minimum ventilation requirements.
Yes, changes in room layout, such as the addition of partitions, furniture, or equipment, can affect the distribution of air and potentially block airflow pathways, thereby affecting the calculated ACH. It's important to consider these factors when assessing ventilation effectiveness.
Understanding air changes can be difficult if some of the terms and keywords used are not ones you understand. Here we shed some more light on some of these terms.
| Term | Definition |
|---|---|
| Airflow | Airflow is the flow of air through a structure or outside. |
There are many interesting things that can be shared about ACH. Here are some of our favorites.
Operating rooms in hospitals typically have 15–25 ACH, meaning the air is replaced up to 25 times per hour to keep it free from contaminants
Even a sealed room has natural air leakage, so it’s virtually impossible to have zero ACH, as small cracks and materials allow air to seep in and out.
When you use "recirculate" mode in your car, you’re effectively reducing ACH to nearly zero, while "fresh air" mode can create a high ACH of 20+ as outside air flows in.
