Temperature Control - General Overview; Discharge Temperature Calculation; Sensors And Set-Points; The Master Set-Points - EngA C-TRAC2 Installation, Operation And Maintenance Manual

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XIII. TEMPERATURE CONTROL – GENERAL OVERVIEW

Discharge Temperature Calculation

NOTE:
If any resets are not connected but the switch is on, the discharge temperature will
be affected. This is especially true of BMS systems that have not been wired in but
the control was specified for it.
The C-TRAC2.1 is designed primarily as a discharge air control. However, the discharge temperature can
be reset up or down if a reset control is connected to the system. The C-TRAC2.1 has the ability to modify
the discharge temperature by any of the following:

The temperature at the optional room sensor.

The temperature at the optional return air sensor.

The temperature at the optional outside air sensor.

The position of an optional VAV damper sensor.

An input signal from a Building Management System (BMS).
If any optional reset controls are used, a calculation is done by the C-TRAC2.1 to select the corrected
discharge temperature to satisfy the conditions of all the sensors and set points.
NOTE:
The reset can drive discharge temperatures up more then down in all applications
(e.g. up 20 or down 7) except BMS (which will reset equally up 20, down 20).
Example:
In all applications there is a discharge sensor and a discharge set point. We will assume a 55ºF
discharge set point. If no other control were activated on the C-TRAC2.1 it would maintain a 55º
discharge. If, however, there were an optional room sensor at 69º and a remote room set point at
72º, then the space needs less cooling. The calculated discharge temperature would be adjusted
up to a higher temperature to conserve energy and avoid overcooling the space.
If the room sensor temperature rose to 75º and the remote room set point is at 72º then the C-
TRAC2.1 will bring on more cooling to cool the space.
If the C-TRAC has any reset option enabled, the discharge set point should not be set below 60ºF
as the reset could drive the discharge temperature very low.
The amount and rate of the reset depends on the authority given to the room control by the room
reset factor pot (pot 5) and how far the room and discharge temperatures are from their respective
set-points.
XIV. SENSORS AND SET-POINTS
The C-TRAC2.1 is designed to operate with JOHNSON CONTROLS TE 6000-960 sensors and TE 6100-
960 sensor/set-point dial or equivalent. This is nearly linear from 40 to +140ºF. Following is a resistance
temperature graph (Page 15).
If a JOHNSON CONTROLS TE 6100-960 combination sensor set point is used, it is not necessary to use
both functions at the same time. In fact many applications use only the sensor or the set-point function in a
"remote" application.

The Master Set-Points

The master discharge air set point is the same for both the economizer and the mechanical cooling. The
heating set point is offset below the cooling set point. (This is similar to the offset between the levers on a T874
thermostat, which allows a deadband between the two set points. The deadband will not allow the control to cycle
between the heating and cooling.) This procedure is covered in the HEAT OUTPUT section.
As a MASTER SET POINT, the C-TRAC2.1 is designed to use either:

The set point mounted on the face of the C-TRAC2.1 (range of 10-35ºC or 52-95ºF). If the C-TRAC2.1
face mounted set-point is used, terminals "SP and S" must be jumped, or;

The Johnson TE 6100-960 set point (range of 50-85ºF and usually remote mounted). If the TE 6100-960 is
used as a set-point, "S to SP" are not jumpered and the TE 6100 must be wired to U, S and M:
IOM-12
C-TRAC2.1 MANUAL
Page 9 March 1999 R1