74 RT-SVD03G-EN
Operation with a Conventional Thermostat (Constant
Volume)
The ReliaTel module has conventional thermostat connections as well as Zone Sensor Module
connections. When a conventional thermostat is controlling the unit, operation differs as follows.
• Supply Air Tempering feature is not available. If outdoor air is being introduced through the
equipment, discharge air temperature may be cold when not actively heating.
• Proportional Integral (PI) control is not available.
• Zone Sensor Diagnostics are only available on the RTRM module on the J6 terminals, instead
of at the Zone Sensor in the space.
• Intelligent Fall-Back is not available. If a failure occurs in the device controlling the equipment,
operation will cease.
• Heat Pump Smart Recovery and Smart Staging is not available. Heat Pump operation becomes
more costly unless the generic control being applied can accomplish this.
• Remote Sensing Capabilities are not available on most mechanical thermostats.
• Space Temperature Averaging capabilities are not available on most mechanical thermostats
• Built in Night Set Back and Unoccupied Functions function differently with a conventional
mechanical thermostat.
• A built-in algorithm which allows for automatic reset of the discharge air temperature while
economizing is not available.
Note: 27½ to 50 VAV -Conventional thermostat input terminals are inactive.
The terminal strip for attaching the thermostat wires is located on the RTRM module in
the control compartment. The purpose of each terminal is discussed in the next section.
Customers occasionally require operation with a conventional thermostat rather than a
zone sensor. In some cases there is a preference for a specific thermostat model, and in
others there is reluctance to adopt newer technology that may not be as well understood
as conventional thermostats.
In addition, non-Trane Building Controllers typically provide an interface to HVAC
equipment based on a conventional thermostat interface. Units applied with this type of
controller need to accept conventional thermostat inputs.
Conventional thermostat signals represent direct calls for unit functions. In their
simplest applications, thermostat contacts directly control contactors or other load
switching devices. This function provides inputs for the thermostat signals and
processing to enhance reliability and performance. Compressor protection and reliability
enhancement functions (HPC, LPC, Minimum On/Off timers, etc.) all operate the same whether
applied with zone sensors or a conventional thermostat.
Logic is also provided to cause appropriate unit functions when inappropriate thermostat signals
are provided.
Simultaneous calls for heating and cooling will be ignored (the unit will not heat or cool). The
supply fan will be turned on with a call for heating or cooling even if the fan request is not detected.
If the thermostat is immediately changed from a heating to a cooling call, or vice versa, there will
be a five minute delay before the new call will initiate. For units with modulating gas heat, see p. 77
for a flow chart outlining operation with a conventional thermostat.
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