CEMP-E
TI 810-11
30 November 1998
(g) Return fan volume control.
(h) Hydronic heating supply temperature control.
(i) Hydronic-heating space-temperature control.
(10) If integral and derivative control modes are not appropriate for an application, the controller is
manually tuned for proportional mode control, and the integral and derivative mode constants are set to
zero. Applications where manual tuning is used are as follows:
(a) Relative humidity high limit control.
(b) Outdoor air scheduling of hydronic heating supply temperatures or hot deck/ heating coil
discharge air temperatures.
(c) Space temperature control of single-zone HVAC units and heating and ventilating units.
(11)When the single-loop digital controller is manually tuned to operate as a temperature controller
in the proportional mode, the proportional band setting is determined by the use of equation 2-
1.
( TR x 100 )
(eq. 2-1)
PB =
Ts
Where:
PB =
Proportional band constant (percent).
TR =
Throttling range or the portion of the transmitter span required for full-scale controller output
change (deg. C (deg. F)).
Ts =
The temperature span of the transmitter (degrees C (degrees F)).
(12) If the controller output is to change from 4 to 20 milliamperes over the range of minus 18 to
plus 16 degrees C (0 to 60 degrees F) and the transmitter range is in the range of minus 35 to plus 55
degrees C (minus 30 to plus 130 degrees F) (a span of 90 degrees C (160 degrees F)), the use of equation
2-1 would result in: PB = 37.5 percent.
(13) When a single-loop controller is configured for proportional control mode only, the output of
the controller must be set to match the value required for the application when the PV input value coincides
with the controller setpoint. This is accomplished by configuring the manual reset setting as a percent of
controller output. The effect of this configuration parameter is to shift the controller output throttling range
with respect to the controller setpoint. As an example, refer to figure 2-6 which shows the setpoint relative
to the controller throttling range for manual reset settings of 25, 50 and 75 percent for a direct-acting
controller.
Figure 2-6. Manual reset feature.
(14) When used as an economizer switching controller, the functions of the controller inputs and
outputs will be as follows:
(a) A return air temperature transmitter connected to the PV input.
(b) An outside air temperature transmitter connected to the CPA input.
2-11
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