Correct CFM (if needed):
Chart B – Correction Multipliers
Explanation of charts
Chart A is the nominal dry coil
1 ½ TON SYSTEM ( 18,000 Btu)
Operating on high speed @ 230 volts with dry coil
measured external static pressure .10
Air Flow = 450 CFM
In the same SYSTEM used in the previous example but having a WET coil you must use a correction factor of
.95 (i.e. 450 x .95=428 CFM) to allow for the resistance (internal) of the condensate on the coil.
It is important to use the proper procedure to check external Static Pressure and determine actual airflow. Since in the case of the
It is also important to remember that when dealing with
Indoor Airflow Data
The
The
For thermostats with
Ductwork Preparation
If flex duct is used, be sure all the slack is pulled out of the flex duct. Flex duct ESP can increase considerably when not fully extended. DO NOT EXCEED a total of .30 ESP, as this is the MAXIMUM design limit for the
IMPORTANT: FLEX DUCT CAN COLLAPSE AND CAUSE AIRFLOW RESTRICTIONS. DO NOT USE FLEX DUCT FOR: 90 DEGREE BENDS, OR UNSUPPORTED RUNS OF 5 FT. OR MORE.
Fresh Air Door
The Fresh Air Door is an “intake” system. The fresh air door opened via a slide on the front of the chassis located just above the indoor coil. Move the slide left to open and right to close the fresh air door. The system is capable of up to 60 CFM of fresh air @ ~.3” H20 internal static pressure.
Checking Approximate Airflow
If an inclined manometer or Magnehelic gauge is not available to check the External Static Pressure, or the blower performance data is unavailable for your unit, approximate air flow call be calculated by measuring the temperature rise, then using tile following criteria.
KILOWATTS x 3413
= CFM
Temp Rise x 1.08
Electric Heat Strips
The approximate CFM actually being delivered can be calculated by using the following formula:
DO NOT simply use the Kilowatt Rating of the heater (i.e. 2.5, 3.4, 5.0) as this will result in a
EXAMPLE: Measured voltage to unit (heaters) is 230 volts. Measured Current Draw of strip heaters is 11.0 amps.
230 x 11.0 = 2530 2530/1000 = 2.53 Kilowatts 2.53 x 3413 = 8635
Supply Air |
| 95°F |
Return Air |
| 75°F |
| ||
Temperature Rise | 20° |
20 x 1.08 = 21.6
8635
= 400 CFM
21.6
22