DCN: 141-00940-09 11/02/07
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TXB16 HVAC Control Unit
The TXB16 HVAC Control Unit works in conjunction with the Wall Display Unit to provide thermostatic
control of the HVAC system. In addition, the Control Unit can receive X10 commands for remote control of
the setpoints, temperatures and modes of the thermostat. The TXB16 X10 bi-directional protocol also
allows the unit to transmit information via the pre-set dim commands.
The TXB16 Control Unit connects to the HVAC system the same as, and in place of, a standard
thermostat. It is usually mounted near the HVAC system, although it can be mounted anywhere
convenient. It is connected to the WDU by a 4 wire cable, either standard thermostat wiring or typically Cat
3/5 in new construction.
Actual thermostatic control of the HVAC system is provided by the Control Unit. Changes in the current
temperature, setpoint, system or fan modes are sent to the Control Unit either from the WDU or via X10
commands. The Control Unit monitors this information and operates the HVAC system accordingly.
HVAC System Compatibility
The TXB16 works with almost all heating and cooling systems, including standard Gas/Electric, Heat
Pump, Radiant, or Hydronic systems and with single or multi-stage systems. Compatible with single or
separate transformer heating/cooling systems.
System Type
Heating Stages
Cooling Stages
Notes
Gas
2
2
Single or split transformer
Electric
2
2
Selectable Fan with Heat
Heat Pump
3
2
Selectable Changeover with Heat or Cool
Radiant
2
2
Hydronic
2
2
Pump output
STANDARD GAS/ELECTRIC HVAC SYSTEMS OPERATION
The TXB16 has Standard HVAC system operating modes of Heating, Cooling and Auto changeover.
In the
HEAT
mode, the stage 1 heating will be turned on at one degree below the heating setpoint and will
turn off
at
the setpoint. In the
COOL
mode, the stage 1 cooling will be turned on at one degree above the
cooling setpoint and will turn off
at
the setpoint. This is referred to as the setpoint Delta T (temp) mode of
operation.
Second stage heating/cooling deltas are factory set at 3 degrees. This means that second stage will come
on when the delta from setpoint reaches 3 degrees. Second stage heating/cooling calls will stay on until
the first stage setpoint is satisfied.
In the
AUTO
mode, the system will maintain the heating or cooling setpoints and switch automatically from
heating mode to cooling mode as needed. There is a
deadband
between heating and cooling setpoints
that keeps the two setpoints from overlapping. This is set to 4 degrees.
Setpoint Push.
If you adjust the heating setpoint to be less than 4 degrees from the cooling setpoint, the
cooling setpoint will be
pushed
to maintain the 4 degree deadband separation. Same for adjusting the
cooling setpoint, if you get within the deadband separation, the heating setpoint will be pushed.
Minimum run time (MRT)
. The HVAC Control Unit has a minimum run time set to 6 minutes. Whenever
a heating or cooling call turns on, the system will run a minimum of 6 minutes even if the call is satisfied
before then.
If the system is set to Off mode, the MRT will be canceled and all operation stopped.
Minimum Off Time (MOT)
. The HVAC Control Unit has a short cycle protection (SCP) delay of 6 minutes
after any compressor operation. This delay prevents a subsequent compressor call until the delay times
