Some troubleshooting tips on VariTrac CCP II and Voyager: calibration, reference, daughterboards and more!!!!

Issue:

Some troubleshooting tips on VariTrac CCP and Voyager: calibration, reference, daughterboards and more!!!!

Resolution:

Problem:

Some troubleshooting tips on VariTrac CCP and Voyager: calibration, reference, daughter boards and more!!!!

Solution:

This is a brief summary of CCPs most troublesome and confusing aspects. 

Helpful Random facts:

1. Voyager decides what it is going to do when in Tracer (Summit, Tracer 100, or Tracker) control--we can manipulate setpoints, override etc. but Voyager takes the input and makes its own decisions.

2. When hooked up to CCP, voyager goes into Slave State and CCP is directly in charge of what Voyager does. When comm is lost to the CCP, 15 minutes later the Voyager goes into standalone mode and if it has a zone temperature it will try to control the space temperature. Voyager operation at this point is random and unpredictable, and this is why zone sensor modules should not be used on CCP jobs that use Voyager Units.

3. CCP will only work with constant volume air handlers, generic AHUs can also be controlled (with the aux relay board). Some Voyagers have VAV configuration (without inlet guide vanes) and THEY WILL NEVER WORK WITH A CCP!! When this happens it is a disaster, they need a Summit system or they need extensive re-work to the Voyager--see Brian for damage control.

4. CCP runs the bypass damper in these constant volume systems. This damper is run directly by CCP and has no UCM.

5. Varitrac systems need AT LEAST TWO VAVs to work and three or more to work well.

6. Standalone Voyager MUST have a zone temp to work.

7. CCP will do a calibration:

• When power is cycled or
• When the CCP is unoccupied (this can fool people because the building goes unoccupied and then a few minutes later the Voyager starts up and runs for a few minutes).

If none of the above happens, CCP will calibrate randomly once a week.

Calibration finds the worst case scenario for the system, ie. with all the VAVs at their maximum flow positions, how much static pressure can be maintained? This value is "reference". The static setpoint is 140% of reference (by default, this can be specified), and now the CCP will try to maintain this pressure. When CCP starts the calibration, it looks at the sensor when the fan is off and then compares this with the value after the fan is on. The CCP must see .25 to .33 volts dc with the fan off or it will consider the sensor failed. Some small increase (.1 vdc) must occur in the reading from this sensor or the calibration is considered to have failed and the default value is used. NOTE: Simply cycling power to the CCP will not do a calibration--if you do this an error message showing sensor failure will be displayed--you must unoccupy the area to do a proper calibration.

8. There are two ways the CCP regulates the bypass damper; static pressure (a much simpler system used in 90% of applications) and velocity pressure (a notoriously unreliable system). As of now, the CCP is shipped with the dipswitch set for velocity measurements. Double check that this dipswitch is in the correct position.

9. Another problem with "Out of the Box" units. The Voyager TCI is shipped with the daughter board in the Comm 3 position. CCP will only talk to Comm 4 equipment. The daughter board must be removed and rotated to the Comm 4 position.

COOL TROUBLESHOOTING STUFF TO TRY:

Use hyper terminal and an RS232 cable to hook up to CCP. There are three screens that will usually find the trouble.

Screen # 6, Service Summary. This screen displays comm status to the VAV UCMs. If these are not communicating, the Voyager will shut down to safeguard the ductwork. One very common cause of this is loss of 24 volt power to the UCMs. If the VAVs are. communicating they should show current status, temps and deviation from setpoint. Remember, AT LEAST ONE VAV MUST BE COMMUNICATING, OR VOYAGER WILL SHUT DOWN. Tracer Summit has the equivalent to this screen, Go to the UCM editor for Varitrac, choose the status Tab and then Push the Service Summary button.

Screen #5 Varitrac Central Control Panel Control Inputs. This screen shows ICS comm status.

NOTE: A lot of comm problems arise because there are actually TWO buses on Tracker/VariTtrac systems, the ICS bus, and the UCM bus. This can be very confusing because there may be Voyagers hooked up to either or both of them (stand alone, co-ordinated by the Tracker and the one controlled by the VariTrac zoning system). Having the VariTrac Voyager hooked up to the ICS bus is a VERY common problem.

Screen #3 AHU status. There is a line that shows Static Pressure XX.X Setpoint 1.40 Reference XX.XX. The "Reference" is a value obtained during calibration. IF THIS VALUE IS 1.00, THEN CALIBRATION HAS FAILED!! When this happens, the default of 1.00 is very high, and will most commonly cause a dramatic increase in the noise level of the HVAC system. If calibration has failed, look at the wiring/sensors and the dipswitch that specifies static or velocity type measurements (see 8 above). If the problem is not in wiring/sensors/dipswitches check these two very common problems:

• The bypass damper is mis-wired backwards, so that it is driven open, not closed, during the calibration time.
• Grossly oversized duct work. This can happen because residential HVAC contractors are accustomed to sizing ductwork for 600 CFM flow, whereas commercial ductwork is sized for 1200 CFM flow.

Another critical thing to see in AHU status is whether the values are generic, with few values. If this is the case then comm to the Voyager is down. This may be the only clue to comm failure with the Voyager. So look for a lot of values in this area including Economizer, Unit Type, Enthalpy, etc. These things show communication with Voyager is working.

MORE ON CALIBRATION FAILURES: 

FIRST AND FOREMOST-- Put the CCP into test mode and close the bypass dampers. GO UP ON THE LADDER AND VISUALLY VERIFY THE DAMPER POSITION. Now drive them open and verify again. This is very frequently the source of calibration failure, the dampers are not closing. When looking at the end of the shaft of the damper blade, how can you tell the position of the damper? The cotter pin in the end of the shaft is Perpendicular to the blade of the damper--this is counter-intuitive but it's true, the blade is NOT parallel to the cotter key as you would think. Because the wiring diagram given to the field for the bypass dampers is very confusing the dampers are frequently mis-wired. If there is more than one damper the likelyhood of miswiring is greatly increased to near 100% levels. ALWAYS CHECK THIS FIRST for calibration failures.

SECOND big problem: The CCP uses either velocity pressure or static pressure for calibration. The velocity pressure is very rarely used but it is the default on the CCP and the sensor so almost all the time BOTH the CCP and the Sensor must be reconfigured for static pressure. Reset the dipswitch on the CCP. On the Sensor, mount the sensor so that the flow arrow is perpendicular to the airflow--That's right--for static pressure the sensor is set crossways from what it looks like it should be. There are two tubes hooked up inside the sensor, disconnect the one marked LO. DON'T plug it up, just unhook it and let it dangle. It might be wise to write a note in the box at this point to indicate that this is unhooked intentionally so that some future technician will not hook it back up. Remember Bryan's motto "the LO has got to go!"

Note: Varitrac III is coming soon and it will only use static pressure, preventing many problems.

UCM HEAT/COOL MODE:

This is a source of many phone calls, it can be difficult to understand. The Control Action for a UCM is determined by two things: The Supply Air Temperature, and the Zone Temperature.

• If the SA temperature is below the zone temperature the UCM Control Action is cool.
• If the SA temp is ten degrees or more above the zone temp the Control Action is heat.

NOTE: This mode simply states WHAT WILL HAPPEN IF THE VALVE OPENS, NOT WHAT IS DESIRED. If the air in the duct is cooler than the zone, and the valve is opened it will cool the space; therefore it is in Cool mode. If the SA temp is ten degrees more than the zone, and the valve is opened, it will heat the space; it is in Heat mode. In the ten degree deadband the air is no good for cooling and no good for heating and the UCM is in whatever state is required to get the valve closed to its minimum flow position.

Control Action can be very confusing. Consider this possibility: The Compressors on the AHU are down and the SA temp is 89 degrees. The building setpoint is 74 degree and the zone temp is 78. The building manager is frantic, the tenants are all complaining, it's really getting hot, and when he looks at CCP all of the UCMs are in HEAT MODE! He will naturally think that the problem is with the CCP when it's actually the compressors.

REMEMBER: THE CONTROL ACTION OF THE UCMS IS WHAT YOU GOT, NOT WHAT YOU WANT!

VOTING IN CCP:

The CCP system is a changeover system, that is, it changes from cool to heat. This changeover is determined by voting.

There are five types of voters:

• Strong Heat caller
• Heat caller
• No call
• Cool call
• Strong Cool caller

A strong caller is more than two degrees above or below the active setpoint. A normal caller is between one and two degrees from setpoint. A UCM is considered opposite if the system is giving it heat when it is callin.g for cool or cool when it is calling for heat.

THE RULES OF CHANGEOVER:

1. There is a minimum changeover timer which has a default value of 15 minutes (this can be changed). For this example we will assume the default value. The system cannot change more often than every 15 minutes, no matter what the votes. Even if every UCM in the system is screaming for a changeover, it will not occur until the changeover timer has reached 15 minutes.

2. Normal Changeover: If there are no strong callers, that is, all callers are less that two degrees off of setpoint, the changeover will not take place until all the UCMs that are calling for the current state are satisfied. When these UCMs have been satisfied AND the clock has reached 15 minutes, the change will occur.

3. Strong Caller's changeover: When Strong Callers want a changeover, it will occur when the time clock reaches 15 minutes, whether the normal callers are satisfied or not.

Using CCP we can manipulate the number of Opposite callers or opposite strong callers required for a changeover.

CCP will not go to the second stage of heat or cool without a strong call.

This system is often plagued by thumbwheel abuse problems: Imagine a building with big south-facing windows on a cold winter day with brisk Northwest winds. The people on the South side have cranked the thumbwheels to 45 degrees. The people on the North side have their thumbwheels at 85 degrees. The Voyager is cycling from two stages of heat to two stages of cool every fifteen minutes and the owner of the building is beside himself. Setting fairly tight high and low limits on thumbwheel control can save much energy and grief and most people will not be able to even perceive that the limits have been imposed.

NOTE: The CCP can handle 16 zones. Some jobs will be set up specifically to have more zones (like 24) so that Trane equipment will not compete. A careful look at these jobs will usually reveal that some of the zones are extraneous, and have been specified only to preclude the Trane CCP from bidding. Most of the time these jobs will work perfectly well with fewer zones, or some zones can be slaved to others (CCP permits this).

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Notes:

Changes:

Other Question/Problem/Cause Statements:

• Some troubleshooting tips on VariTrac CCP and Voyager: calibration, reference, daughter boards and more!!!!

Facts:

• Tracer Summit (Windows)
• VariTrac III Central Control Panel (CCP)

Original wave: case1535