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EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER
74-2958—162
INDOOR AIR QUALITY (IAQ) OVERRIDE
The Excel 10 W7750 Controller supports an IAQ override
feature that upon detection of poor air
q
ualit
y
in the space,
allows the economizer dampers to be opened above the
standard minimum position settin
g
to a value set in
EconIAQPos. Two different methods of detectin
g
poor air
q
ualit
y
are supported, The first is b
y
usin
g
an IAQ switch
device connected to a di
g
ital input on the W7750 Controller,
where a contact closure indicates poor air
q
ualit
y
and initiates
the IAQ override mode. The second, which is onl
y
available
on the W7750B,C is throu
g
h an analo
g
input that connects to
a CO
2
Sensor
(
0 to 10V
)
. The measured value of CO
2
from
this sensor
(
0 to 2000 ppm
)
is compared to the setpoint
IAQSetpt. When the CO
2
level is hi
g
her than the setpoint
(
800
PPM
)
, the IAQ override is initiated. The IAQSetpt h
y
steresis is
50 PPM, IAQ override is deactivated at a CO
2
level less than
750 PPM.
When the W7750 Controller is in the COOL mode durin
g
an
IAQ override, it is possible for the
heating
outputs to be
activated. This can occur if the outdoor air temperature is cold
enou
g
h to cause the dischar
g
e air temperature to drop below
the DaTempLoLim setpoint when the dampers open to the
EconIAQPos position,
and
the Ia
q
UseHeat fla
g
is set. If this
situation occurs, the heatin
g
is controlled to maintain the
dischar
g
e air temperature at 1°F
(
0.65°C
)
above the
DaTempLoLim setpoint.
FREEZE STAT
Upon receivin
g
a contact closure, the W7750 control
al
g
orithm will close the outdoor air damper and open the hot
water and chilled water valves
(
if available
)
to the full open
position as a safet
y
precaution. If
manual-reset
operation is
desired, the Freeze Stat device must provide the ph
y
sical
pushbutton, which the operator presses, to reset the s
y
stem
after a
freeze
condition has occurred.
DISCHARGE AIR LOW LIMIT CONTROL
If the dischar
g
e air temperature falls below the user-settable
dischar
g
e air low limit setpoint
(
DaTempLoLim
)
, an alarm is
issued, and the outdoor air damper is driven below the
minimum position settin
g
until the dischar
g
e temperature is up
to the low limit. If necessar
y
, the damper can
g
o completel
y
closed even durin
g
Occupied mode operation. As the
dischar
g
e temperature warms up, the economizer modulates
open until the minimum position settin
g
is reached. At this
point, the low limit alarm is cleared.
ECONOMIZER ENABLE/DISABLE CONTROL
The W7750 Controller has inputs to determine if the outdoor
air is suitable to au
g
ment coolin
g
. The economizer dampers
can be enabled/disabled for usin
g
outdoor air as the first
sta
g
e of coolin
g
based on one of ten allowable strate
g
ies:
1. Digital Input Enable/Disable—
contact closure enables
economizer.
2. Outdoor Temperature—
when the outdoor temperature
is less than OaEconEnTemp, then the outdoor air is
suitable to au
g
ment coolin
g
.
3. Outdoor Enthalpy, Type A—
when the outdoor
enthalp
y
meets the H205 t
y
pe A re
q
uirements, the
outdoor air is suitable to au
g
ment coolin
g
.
4. Outdoor Enthalpy, Type B—
when the outdoor
enthalp
y
meets the H205 t
y
pe B re
q
uirements, the
outdoor air is suitable to au
g
ment coolin
g
.
5. Outdoor Enthalpy, Type C—
when the outdoor
enthalp
y
meets the H205 t
y
pe C re
q
uirements, the
outdoor air is suitable to au
g
ment coolin
g
.
6. Outdoor Enthalpy, Type D—
when the outdoor
enthalp
y
meets the H205 t
y
pe D re
q
uirements, the
outdoor air is suitable to au
g
ment coolin
g
.
7. Differential Temperature—
the difference between
outdoor temperature and return air temperature is
compared to DiffEconEnTemp to determine whether
outdoor air or return air is more suitable for use to
au
g
ment mechanical coolin
g
.
8. Single Calculated Enthalpy—
the calculated outdoor
enthalp
y
in btu/lb is compared to the enthalp
y
setpoint
(
OaEnthEn
)
in btu/lb, and the outdoor temperature is
compared to the outdoor temperature limit setpoint
(
OaEconEnTemp
)
for a hi
g
h limit. The compared
difference determines whether outdoor air is suitable for
use to au
g
ment mechanical coolin
g
.
9. Differential Enthalpy, Either Sensed or Calculated—
the difference between outdoor enthalp
y
and return air
enthalp
y
determines whether outdoor air or return air is
more suitable to au
g
ment mechanical coolin
g
. When
enthalp
y
sensors are confi
g
ured, the
y
are used for
comparin
g
enthalp
y
. If no enthalp
y
sensors are
available, then enthalp
y
is calculated usin
g
outdoor and
return air humidit
y
and temperature sensors. The
switchin
g
differential is fixed at 1.0 mA for enthalp
y
sensors, and 0.25 btu/lb for calculated enthalp
y
.
NOTE: If no return temperature sensor is confi
g
ured,
space temperature is used to calculate return
air enthalp
y
.
10. Network Enabled—
the network input
DestEconEnable
controls the enablin
g
and disablin
g
of the economizer.
When usin
g
the network input, select Econo Enable
T
y
pe:
No Economizer
in E-Vision. The network input
has priorit
y
over the other nine economizer control
selections.
Appendix C. Complete List of Excel 10
W7750 Controller User Addresses.
See Table 18 for W7750 Controller User Address table
numbers and point t
y
pes.
The
User Address Index
followin
g
Table 18 lists the User
Addresses alphabeticall
y
and
g
ives the pa
g
e number where
the Address is located in each Table Number/Point T
y
pe.
After Table 18 there is an alphabetical list of
Mappable User
Addresses and Table Numbers
. Followin
g
this is an
alphabetical list of
Failure Detect User Addresses and Table
Numbers
.
Table 18. Excel 10 W7750 Controller User
Address Point Types.
Table Number Point Types
Table 20 Input/Output
Table 21 Control Parameters
Table 22 Ener
gy
Mana
g
ement Points
Table 23 Status Points
Table 24 Calibration Points
Table 25 Confi
g
uration Parameters
Table 26 L
ON
M
ARK
/Open S
y
stem Points
Table 27 Direct Access and Special Manual Points
Table 28 Data Share Points