Issue
This is a guideline to do air balance settings (airflow calibration) on a VAV ASC using a I/STAT or M/STAT.
Product Line
TAC INET
Environment
- MR-VAV-AX
- MR-VAV-X1
- MR-VAV-X2
Cause
The air balance company needs a procedure to properly set up the MR-VAV-AX products for the air balance settings.
Resolution
- Understand the cooling setpoint is 75°F, and the heating setpoint is 70°F. This information is important in knowing which state the system is trying to control.
While in the PP mode of the I/STAT, it is important to verify the setpoint is 75°F. This allows Test & Balance to set the temperature to:- 77°F for maximum cooling
- 72°F for minimum cooling with no fan
- 68°F for heating mode - minimum primary airflow with fan
- To verify the current setpoint, use the Select key and scroll up to Set Temp. The I/STAT will display the current setpoint. For testing purposes as described in Step 1, if the temperature setpoint is not 75°F, press the + or - key to raise or lower the setpoint to 75°F.
- In order to enter the Service Mode, press the Service key. Enter the I/STAT password 183. Press the + or - key to see the left most digit change accordingly.
- Press the + key to scroll to 1 and press Enter. The cursor on the I/STAT will move to the center digit.
- Press the - key to 8 and press Enter. Now the cursor will move to the right most digit.
- Press the + key to 3 and press Enter. You are now in the Service Mode. While in the Service Mode, the Service key is the escape key and the Enter key will allow the controller to accept your desired changes.
- The first step in the calibration process is to make sure the controller is at the Factory Calibration Setting (FCS). Press the Select keys to scroll to Airflow Parameters (AP) and press Enter. CLF is displayed on the I/STAT. Press the Select keys to scroll to FCS, press Enter. The I/STAT will display NO. Press the + key to change the display to YES and press Enter.
- Press the Service key to back up one screen.
- To verify duct diameter (dd) press the Select key and scroll to Unit Parameters (UP). The I/STAT will display the current duct diameter as 10.0 (default of 10 inches) unless the value has already been changed. Press the + or - key to raise or lower the value, and the Select keys to move between the right most and center digit. Sample: 8 inch box is displayed as "08.0" Press the Enter key to allow the changes to take place.
- Press the Service key to back up one screen.
- To verify Cooling Low Flow (CLF) and Cooling High Flow (CHF) setpoints, press the Select keys to scroll to Airflow Parameters (AP) and press Enter.
- CLF is displayed on the I/STAT. Press Enter, the I/STAT will display the current value. Note that CFM is displayed as KCFM, for example 0.50 = 500 CFM. If the values are correct, press Enter. If the values need to be changed, use the + and - keys to change the values and the Select keys to move the cursor from the left most digit to the right most digit. Once you have the desired value displayed, press Enter.
- The I/STAT is now displaying CLF. Press the Select keys to scroll to CHF and press Enter. If the values are correct, press Enter. If the values need to be changed, use the +, -, and Select keys to change the CHF to the desired value then press Enter.
- CHF is displayed on the I/STAT. Press the Select keys to scroll down to Calibrate Primary Low (CPL), press Enter. The VAV controller will modulate the damper to maintain its design CLF. The I/STAT is currently displaying the CFM the controller is reading. Note that during this process, the CFM value may go to -0.1, 0.0, etc.; the controller is calibrating itself to the 100% actual closed position. Once the CFM comes within 10% of the CLF setpoint, the ON/OFF LED will turn on. While the LED is on, the controller is not modulating the damper and the controller has the damper in a fixed position for approximately 60 to 90 seconds.
(Do not attempt to enter any values at this point. When the LED goes off, the controller takes back control of the damper and will modulate it to maintain CLF.) - Once the airflow has stabilized and the I/STAT is displaying the CLF CFM, measure the airflow and input the actual value (do this as soon as possible because once the + or - key has been pressed, it freezes the damper into a fixed position to allow enough time to enter the actual value and to minimize chances of the actual CFM changing), into the I/STAT using the +, -, Select and finally the Enter key as described in Step 8.
Important: Even if the current reading is correct, press Enter. - The I/STAT will display Calibrate Primary High (CPH), press Enter. The VAV controller will modulate the damper to maintain its design CHF. Again, once the CFM comes within 10% of the CHF setpoint the controller's ON/OFF LED will come on and the controller will perform as described in Step 9. When the LED goes off, the controller takes back control of the damper and will modulate it to maintain CHF.
- Once the airflow has stabilized and the I/STAT is displaying the CHF CFM, measure the airflow and input the actual value (again, do this as soon as possible) into the I/STAT using the +, -, and Select and finally the Enter key as described in Step 8.
Important: Even if the current reading is correct, press Enter. The I/STAT should be displaying CLF. - Once the low and highs have been calibrated, press the Service key.
- Press the Select key to scroll to Operational Parameters (oP), press Enter. Press the Select key again to scroll to Prove Performance (PP). This mode will place the program's Room Temperature in a test state. The I/STAT display will toggle between the current CFM and the room temperature. This step will allow the balance engineer to verify proper operation of the VAV controller to maintain the design maximum and minimum airflow.
- Press the + and - keys to increase or decrease the room temperature in order to manipulate the system to control between cooling and heating as described in Step 1.
- Once the VAV has controlled the damper to design minimum CFM, the balance engineer can adjust the fan (if applicable) to design airflow.
- Important: If at any time during the calibration process, (not during Prove Performance (PP)) a mistake is made, make sure that the controller is reset back to the Factory Calibrated Settings (FCS), (see Step 4) and restart the calibration process. Also, if the VAV box does not control the CFM within the maximum allowable percentage, normally within 10%, go back to Step 4 and restart the calibration process.
For further information see the following:
- TCON126 (Micro Regulator Controllers and I/STAT)
- TCON147 (ASC MR-VAV-AX)
- TCON155 (ASC MR-VAV-X1)
- TCON165 (ASC MR-VAV-X2)
Go to TCON Number and Title Cross Reference (with links) and download the TCONS above.
