42
AC-SVX002C-EN
The Tracer
®
TU Service Tool must be used to set the
input signal type from the factory default of 2-10 VDC
to that of 420 mA current. Tracer TU must also be used
to install or remove the External Demand Limit
Setpoint Option for field installation, or can be used to
enable or disable the feature (if installed).
Figure 19.
Demand limit setpoint via 2–10 VDC signal
0
1
2
3
4
0
10
20
30
40
50
60
70
80
90
100
Active Demand Limit Setpoint (%)
N
u
m
b
e
r
o
f
a
ll
o
w
e
d
c
o
m
p
r
e
s
s
o
r
s
(
4
c
o
m
p
r
e
s
s
o
r
s
u
n
it
)
Figure 20.
Demand limit setpoint via 4–20 mA signal
0
1
2
3
4
5
6
0
10
20
30
40
50
60
70
80
90
100
Active Demand Limit Setpoint (%)
N
u
m
b
e
r
o
f
a
ll
o
w
e
d
c
o
m
p
r
e
s
s
o
r
s
(
6
c
o
m
p
r
e
s
s
o
r
s
u
n
it
)
EDLS and ECHWS Analog Input Signal
Wiring
Both the ECHWS and EDLS can be connected and setup
as either a 2–10 VDC (factory default), 4-20 mA, or
resistance input (also a form of 4–20mA) as indicated
below. Depending on the type to be used, the Tracer
®
TU Service Tool must be used to configure the LLID
and the unit controller for the proper input type that is
being used. This is accomplished by a setting change
on the Custom Tab of the Configuration View within
Tracer
®
TU.
IIm
mp
po
orrtta
an
ntt:: For proper unit operation, BOTH the EDLS
and ECHWS settings MUST be the same (2-
10 VDC or 4-20mA), even if only one input
is to be used.
When not Installed, external chilled hot water setpoint
analog input, external demand limit setpoint analog
input and auxiliary binary input setpoint enable will not
be used (Front panel or BAS sources used, depending
which one is valid).
Setpoint Source selections are: BAS/Ext/FP, Ext/FP, or
Front Panel
When Installed, both analog I/O and binary will be
used, with respect of following status:
•
E
Ex
xtte
errn
na
all cch
hiilllle
ed
d h
ho
ott w
wa
atte
err sse
ettp
po
oiin
ntt:: IF it is the
highest priority and it is a valid source THEN use
this external setpoint for active chilled water
setpoint.
•
E
Ex
xtte
errn
na
all d
de
em
ma
an
nd
d lliim
miitt sse
ettp
po
oiin
ntt:: IF it is the highest
priority and it is a valid source THEN use this
external setpoint for active demand limit setpoint.
•
E
Ex
xtte
errn
na
all a
au
ux
xiilliia
arry
y cch
hiilllle
ed
d h
ho
ott w
wa
atte
err sse
ettp
po
oiin
ntt
e
en
na
ab
blle
e iin
np
pu
utt:: IF setpoint source is set to external/
Front Panel or Front Panel THEN:
–
IF input open, use the next highest priority
setpoint source (see priority list below)
–
IF input closed, use the auxiliary chilled water
setpoint
Priority (from highest to lowest):
•
BAS communication (BACnet
®
, LonTalk
®
or
Modbus
™
)
•
Ice Building
•
External setpoints
•
Front Panel setpoints
Chilled Water Reset (CWR)
UC800 resets the chilled water temperature setpoint
based on either return water temperature, or outdoor
air temperature. Return Reset is standard, Outdoor
Reset is optional.
The following shall be selectable:
•
One of three Reset types: None, Return Water
Temperature Reset, Outdoor Air Temperature
Reset, or Constant Return Water Temperature
Reset.
•
Reset Ratio setpoints: For outdoor air temperature
reset there shall be both positive and negative reset
ratios.
•
Start Reset Setpoints.
•
Maximum Reset setpints.
V
Va
arriia
ab
blle
e D
De
effiin
niittiio
on
nss
•
CWS is the arbitrated chilled water setpoint before
any reset has occurred
•
CWS' is the active chilled water setpoint, includes
the effect of chilled water reset
•
CWR is the amount of chilled water reset (also
called Degrees of Reset)
The above values are related by the equations:
CWS’ = CWS + CWR
O
OR
R
CWR = CWS’ — CWS
With the chiller running and any type pf chilled water
reset enabled, CWR is allowed to change at a
