EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER
74-2958—152
Occasionall
, the PID parameters re
uire tunin
to optimize
comfort and smooth e
uipment operation. This applies to the
W7750A,B,C Controllers.
CVAHU Controllers are confi
ured b
E-Vision with default
values of PID parameters as shown in Appendix C Table 21. If
different values for these parameters are desired, Table 13
lists some recommended values to use as a startin
point.
These recommended values are based on past experience
with the applications and in most cases do not re
uire further
ad
ustment.
Table 13. Recommended Values For PID Parameters.
If the PID parameters re
uire ad
ustment awa
from these
values,
use caution
to ensure that e
uipment problems do not
arise
see CAUTION below
. If an
chan
e to PID control
parameters is made, the ad
ustments should be
radual. After
each chan
e, the s
stem should be allowed to stabilize so the
effects of the chan
e can be accuratel
observed. Then
further refinements can made, as needed, until the s
stem is
operatin
as desired.
CAUTION
If lar
e or fre
uent chan
es to PID control parameters
are made, it is possible to cause e
uipment problems
such as short c
clin
compressors
if the sta
e
minimum run times were disabled in User Addresses
DisMinClTime or DisMinHtTime
. Other problems that
can occur include wide swin
s in space temperature
and excessive overdrivin
of modulatin
outputs.
If ad
ustment of PID parameters is re
uired, use the followin
.
In the items that follow, the term, error, refers to the difference
between the measured space temperature and the current
actual space temperature setpoint.
— The
Proportional Gain
also called Throttlin
Ran
e
determines how much impact the error has on the output
si
nal. Decreasin
the Proportional Gain amplifies the
effect of the error; that is, for a
iven error, a small
Proportional Gain causes a hi
her output si
nal value.
— The
Integral Gain
also called Inte
ral Time
determines
how much impact the error-over-time has on the output
si
nal. Error-over-time has two components makin
up its
value: the amount of time the error exists; and the size of
the error. The hi
her the Inte
ral Gain, the slower the
control response. In other words, a decrease in Inte
ral
Gain causes a more rapid response in the output si
nal.
— The
Derivative Gain
also called Derivative Time
determines how much impact the error rate has on the
output si
nal. The error rate is how fast the error value is
chan
in
. It can also be the direction the space
temperature is
oin
, either toward or awa
from the
setpoint, and its speed—
uickl
or slowl
. A decrease in
Derivative Gain causes a
iven error rate to have a lar
er
effect on the output si
nal.
— The
Control Band
is used onl
for dischar
e temperature
control of modulatin
outputs, which includes controllin
the economizer dampers, and heatin
and coolin
valves
usin
Cascade Control. The Control Band dictates the
span throu
h which the dischar
e temperature must travel
to cause the output si
nal to
o from full
closed to full
open. Also, 10 percent of the Control Band value is the size
of the
deadband
around the setpoint where no actuator
motion occurs. For example, if controllin
a coolin
valve
with Cascade Control enabled and with the dischar
e
temperature within 0.1 X DaTempClCtrlBd of the dischar
e
setpoint, there is no chan
e in the current valve position.
The smaller the Control Band, the more responsive the
control output. A lar
er Control Band causes more slu
ish
control. Be careful not to set the Control Band too low and
cause lar
e over or under shoots
huntin
. This can
happen if the space or dischar
e sensors or wirin
are in
nois
environments and the value reported to the controller
is not stable
such that it bounces
. The Control Band is
used onl
in modulatin
control, and has no purpose when
sta
ed control is confi
ured.
Appendix B. Sequences of Operation.
This Appendix provides the control se
uences of operation for
the models of the Excel 10 W7750 CVAHU Controller. The
W7750A,B,C Controllers can be confi
ured to control a wide
variet
of possible e
uipment arran
ements. Table 14 and 15
copied from Tables 3 and 4
summarize the available options.
This Appendix provides a more detailed discussion of these
options.
Equipment Configuration
Heat
Prop.
Gain
Heat
Integ.
Gain
Heat
Deriv.
Gain
Heat
Control
Band
Cool
Prop.
Gain
Cool
Integ.
Gain
Cool
Deriv.
Gain
Cool
Control
Band
Econ
Control
Band
Single Stage
2 3000 0 10 2 3000 0 10 10
Two Stages
3 2000 0 10 3 2000 0 10 10
Three Stages
4.5 1500 0 10 4.5 1500 0 10 10
Four Stages
6 1000 0 10 6 1000 0 10 10
Series 60 Modulating (Floating)
2 750 0 10 2 750 0 10 10
PWM Modulating
2 900 0 10 2 900 0 10 10
