In industrial sectors, CFM is often used as an indicator of airflow. You may have noticed this unit in many electronic appliances like the chimney, AC pr cooler etc. So, what does CFM stand for? And how does it denote the affines of a machine or a room? Let’s check it out!
Definition of CFM
CFM, or you can say, cubic feet per minute, is a unit that measures the amount of airflow or gaseous matter flow inside a space or area.
The amount of air moving in each cubic foot area of a room or space can vary with temperature. It happens because the gaseous matters expand with heat and shrink as the temperature decreases.
On top of that, if there are two outlets in a particular area and the gas temperature is more in one outlet, the volume of the gasket increases in one direction, but that does not mean the mass will also flow at the same rate.
Hence, it may not have the standard value for all situations and may change with time, area, temperature fluctuation etc.
Why is the CFM Important?
CFM is used to measure the capacities of applicants like kitchen chimney hoods, kitchen fans, air conditioners, HVAC systems etc. In the case of all these appliances, the airflow matters a lot. The room may get stuffy and uncomfortable if there is minimal airflow. Similarly, too much airflow can also cause problems.
The higher CFM indicates that the machine you use has better ventilation capacity. But that does not mean you need an appliance with a higher CFM.
Similarly, higher CFM may offer better air conditioning through the HVAC duct if the room is large.
Steps to Calculate the Volume of a Room
To calculate the CFM of a room, you first need to calculate the room’s or space’s volume. Most rooms are rectangular or square, and you can easily imagine the room as a rectangular prism.
Now, take the formula of area of a rectangular prism = length x width x height.
For example [le consider a room that is 10 ft tall, 12 feet wide and 15 ft long.
Then the area of the room = 15 x 12 x 10 = 1800 feet3
Suppose the room is not an even shape or has uneven walls or ceilings. In that case, you need to divide the room into different cuboids or rectangular prisms and then calculate the area separately of each imagined prism. Add the digits, and you will get the room’s total area.
How to Calculate the CFM?
In general, 1 CFM is equal to 28.3 litres per minute. Here is the mathematical formula to calculate CFM-
Q= V x A
Where,
Q= Airflow in CFM
V= Air or gas Flow velocity in feet/ minute
A= cross-sectional area of the duct/ room/space
If a room is 1800 cubic feet, then iot will need an 1800 CFM system for proper airflow/
How Often Do We Need to Exchange Air?
Airflow does change with the room condition and the setup, footfall etc. The higher temperature generated inside the room, the higher CFM rated machine or system required to channel fresh air inside it. Here are some details-
1. Kitchen, Cafeteria, Bakery, Bar : The kitchens, cafes, bakeries or cafeterias need moderate to high air circulation per 2-5 minutes. In a 2000 cubic feet room, a system must offer 400-1000 CFM airflow.
For kitchens, especially where Asian cooking is done or cooking with high heat is commonly performed, a kitchen chimney with higher CFM may be best.
2. Laboratory : In the case of labs, also moderate to high airflow is needed. For 1000 cubic feet of lab room, 400-600 CFM airflow is required per 3-5 minutes.
3. Industrial Area : Industrial areas like warehouses, machine shops, factories or warehouses need minimum to moderate airflow. For a 200 cubic feet area, a system should be able to produce an airflow of 250-700 CFM per 3-7 minutes.
4. Classroom, Gymnasium, Stores, Auditoriums : Even though the footfall is high in these areas, the airflow circulation is low, i.e. roughly 200-500 CFM in a 200 cubic feet room per five to ten minutes.
Conclusion
CFM, or cubic feet per minute, is a unit of measuring airflow inside a particular space. It doesn’t have a proper standard valve, and the value changes with temperature, space etc. If you are planning to buy a kitchen hood, an HVAC system, or an air filtration system, you should check the CFM rating of the appliance to determine whether it serves your purpose.
