Set up a MR-VAV-AX (ASC) as Standalone

[Product_Support]

Issue

Set up a MR-VAV-AX (ASC) as Standalone

Product Line

TAC INET

Environment

MR-VAV-AX

Cause

Air balance must be done to calibrate the airflow sensor on the MR-VAV-AX.

Resolution

Download Tech Tip 072

Equipment:

Air Balancing Hood or Manometer and Digital Thermometer.

Assumptions:

• The MR is powered up.
• An I/STAT, or an M/STAT is plugged into the service port of a S/STAT or W/STAT, which is plugged into the MR-VAV-AX.
• The AHU is running.
• The Space sensor is installed.
• The Duct static pressure is constant.
• The dip switches are set properly for the desired VAV configuration. (See TCON 147)
• You have a Pocket Reference Card (TCON 149).
• You are familiar with the use and operation of the I/STAT / M/STAT with respect to navigating the Service mode to various mnemonics’ menus. (See TCON 147)

Initial Setup

You should notice that two things have already happened:

1. The MR is in the unoccupied mode.
2. The setpoint adjust has defaulted to "-5", making the setpoint display appear low.

For the MR to work in a Standalone mode the use of an off-board time clock for the occupied and unoccupied times is recommended. It should be connected to the "Local Occ" point(TB5 input #2 to TB5 ground.) The "Occ" mnemonic under Unit Parameters must be set to ONE for the "Local Occ" point to be used. If the MRs are to be left in the occupied mode indefinitely, install a jumper across the "Local Occ" point instead of using the time clock contacts. Connect the jumper to (TB5 input #2 to TB5 ground.) Using the I/STAT or M/STAT go to Set Temp and increase the value by 5°. This will get the Setpoint Adj. back to zero.

"Cooling Low Flow" (CLF - min. CFM) and "Cooling High Flow" (CHF - max. CFM) Setup

1. Put the I/STAT or M/STAT into the Service Mode.
2. Go to "AP", select "CLF", (the value displayed is "multiplied by" 1000 so 0.24 is 240). Enter the minimum CFM by using the arrow keys to position the LED for the digit to be changed and enter the value by using the "+" and "-" keys. Notice the decimal position will not move. You are entering the value "multiplied by" 1000. Refer to the Pocket Reference Card (TCON 149), paragraph 5.
3. Usually the minimum air flow value can be found on the Mechanical box schedule drawings. The lowest reading that the ASC’s sensor can sense is about .03" to .05" of Water Column(W.C.) Therefore, the "CLF" must be set above this level. If the ASC is required to control in that range, it will tend to oscillate.
4. Select "CHF" and enter the maximum CFM for this box at 1" W.C., this can be found on the DeltaP to CFM graph that is associated with this VAV box’s pickup device, or the box schedule may also provide the maximum cfm value.

Central Plant Heat "Heating Low Flow" (HLF) and "Heating High Flow" (HHF) Setup

• Use only if Central Plant Heat is required and setup Unit Parameter’s(UP) CPH set to "1".
• An open contact at Input 3 will indicate that the Central Plant Heat mode is on. A closed contact indicates CPH is off.
• Using the procedure described above for "CLF" and "CHF" instead select "HLF" and "HHF" and enter the desired Low and High Flow CFM values for the Heating Mode. Otherwise go to the next section.
• NOTE: If you have a auxiliary stage of heat, it will not be energized unless the CFM input is reading at least 80% of the "HLF" setting.

Calibrate the flow pickup:

1. Go to Unit Parameter "UP", select "dd" (duct diameter).
2. Enter the duct diameter this will enable the MR to calculate the Pickup Factor "PF" for us.
   NOTE: It is recommended that you begin with the value provided by the VAV Manufacturer for the pickup factor. Then calibrate if necessary using the following procedure.
3. Go to "AP", select "PPF" (pickup factor calibration).
4. The MR will drive the box open and modulate the damper to maintain the "CHF" level. This may take 5 - 10 minutes.
   NOTE: The stroke time is defined using the Damper Stroke (ds) parameter. The ASC provides several means of synchronizing the point with the physical damper position.
   1. 1. When this point is controlled to a value of 0, the decrease pulse will be on for 125% of the damper stroke.
   2. 2. When this point is controlled to a value of 100, the increase pulse will be on for 125% of the damper stroke.
   3. 3. When the damper stroke duration is modified, the decrease pulse will be on for 125% of the damper stroke.
   4. 4. When the power is cycled on the ASC, the decrease pulse will be on for 125% of the damper stroke.
   5. 5. Any time the ASC is the target of an Update_ASC or a Copy_Parms, the decrease pulse will be on for 125% of the damper stroke.
5. After the reading has settled out, take a reading with a Hood or Manometer, which has been setup, and measure the actual CFM and enter that value now into the I/STAT-M/STAT using the Select and change buttons.
6. The software has entered a unique Pick-up Factor "PF" in the MR for this box.

Calibrate space temperature (if necessary):

1. To calibrate the Space Sensor while in the Service Mode, go to "oP" Operational Parameters.
2. Select "CSS" (calibrate space sensor).
3. Measure the actual temperature with a digital thermometer and enter the value.
4. If your box has no heat or has a fan with electric heat. You’re finished. Go to the next box.

Hot water coil:

1. If you have a hot water valve on your box and the stroke time is not 600 seconds:
2. Go to "UP" (Unit Parameters) and select "Ho", Heating Output. Select1 for 1-OutPWM, 2 for 2 Out-PWM(Floating), or 3 for Duty Cycle 1 output.
3. Go to "UP" Unit Parameters and select "HS" (heating stroke) and enter the actual stroke time in seconds.

Air Balance:

If you require closely calibrated CFM readings proceed with the following steps:

1. Go to "AP" (Airflow Parameters)
2. Select "CPL" (calibrate low flow) and the damper will begin to close.
3. Remember, the damper motor may take 3 minutes to get to the Cooling Low Flow setpoint.
4. With a Hood, measure the total air flow and enter the measured CFM value.
5. Select "CPH" (calibrate high flow).
6. The damper will drive open to the Cooling High Flow setpoint. (remember the damper motor has a 185 sec stroke).
7. When the reading stabilizes, take your measured CFM reading and enter it now. This procedure will de-calibrate the CFM input from the 0-1"readings to compensate for box, pickup, or hood irregularities/errors.

Caution: When the decision is made to connect the MR-VAV-AX to a MRI or MCI please note the following: Avoid updating the MCI or ASC after initial setup as this will delete any MCI resident calculations, ATS, etc. that you may have added off-line that are residing at the same point addresses that the MR-VAV-AX is using. There are a variety of box types and a variety of other things that can be change if your application requires it. (Refer to TCON147)