Measuring CFM (cubic feet per minute) of a compressor is an important step in evaluating the size of the compressor in an HVAC (heating, ventilation, and air conditioning) system. CFM is a measure of the volume of air that the compressor can move in a given time period, which is important for determining the efficiency and effectiveness of the compressor. In this article, we’re going to show you how to calculate the CFM of a compressor.
Basics of Compressor
A compressor is a device that compresses air to a specific temperature and pressure. The purpose of a compressor is to provide a constant supply of cool air. When the air is compressed, it becomes dense, so more of it can fit into a given space. This allows the air to be moved through the ducts of the HVAC system more efficiently.
Measuring CFM of Compressor
CFM is the abbreviation of cubic feet per minute. Here is a more detailed, step-by-step guide to measuring CFM of a compressor:
Step 1- Determine the Volume of the Tank
The first step in measuring CFM is to determine the volume of the tank. To do this, you need to know the tank capacity (in gallons). This should be clearly marked on the tank itself by the manufacturer. The volume of your air compressor tank in gallons should be clearly marked on the tank itself by the manufacturer.
If it is not marked by the manufacturer, you can calculate it using the dimensions of the tank. The formula for volume in gallons is:
Volume (in gallons) = Length (in inches) x Width (in inches) x Height (in inches) / 231
Step 2- Convert the Volume from Gallons to Cubic Feet
There is a 0.1333-cubic foot amount of fluid in one gallon of fluid. So in order to convert the volume of the tank from gallons to cubic feet, multiply the total gallons determined in the first step by 0.1336. For example, if the volume of the tank in gallons is 20 then in cubic feet it will be,
The volume of Tank: 20 gallons x 0.1336 = 2.67 cubic feet
Step 3- Empty the Tank
Empty the tank by releasing the air from the compressor. This will ensure that the compressor is starting with a full tank and will allow you to accurately measure the time it takes to refill the tank.
Step 4 – Refill the Compressor
Begin refilling the compressor with air. Record the amount of time that it takes to refill the tank while paying close attention to the compressor’s tank gauge. You will need to record the psig (pounds per square inch) at two separate times in the refill process: once at the moment the compressor kicks in and once at the moment the compressor kicks out.
Step 5 – Calculate the Difference Between Pressures
Calculate the difference between the two recorded psigs. Subtract the psig indicated when the compressor kicked in from the psig indicated when it kicked out. For example, if the compressor kicks in at 75 psig and kicks out at 100 psig, the difference would be 25 psig. This difference represents the pressure added to the tank during the filling cycle.
Step 6 – Convert the Pressure added to atm
Convert the pressure added to atm (atmospheric pressure). The standard atmospheric pressure at sea level is 14.7 psig, so you can use the following formula:
Pressure added (in atm) = Pressure added (in psig) / 14.7
For example, if the pressure added during the filling cycle is 25 psig, the pressure added in atm would be 25 / 14.7 = 1.70 atm.
Step 7 – Calculate the Volume of Air Pumped
Calculate the volume of air pumped during the filling cycle. Multiply the volume of the tank in cubic feet (calculated in Step 2) by the pressure added in atm (calculated in Step 6). This will give you the volume of air pumped during the filling cycle. The formula is:
Volume of air pumped (in cubic feet) = Volume of tank (in cubic feet) x Pressure added (in atm)
For example, if the volume of the tank is 2.67 cubic feet and the pressure added during the filling cycle is 1.70 atm, the volume of air pumped would be 2.67 x 1.70 = 4.54 cubic feet.
Step 8 – Convert the Volume of Air Pumped to CFM
Convert the volume of air pumped to CFM. Divide the volume of air pumped (calculated in Step 7) by the time it took to refill the tank, and then multiply the result by 60 to convert the volume to minutes. This will give you the CFM of the compressor. The formula is:
CFM = Volume of air pumped (in cubic feet) / Time to refill tank (in seconds) x 60
For example, if the volume of air pumped is 4.54 cubic feet and it took 60 seconds to refill the tank, the CFM of the compressor would be 4.54 / 60 x 60 = 7.57 CFM.
By following these steps, you can accurately achieve measuring CFM of your compressor and determine the size of the compressor needed for your HVAC system. This will help you ensure that the compressor is operating efficiently and effectively, and that it is able to provide a constant supply of cool air as needed.
