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
ualit
in the space,
allows the economizer dampers to be opened above the
standard minimum position settin
to a value set in
EconIAQPos. Two different methods of detectin
poor air
ualit
are supported, The first is b
usin
an IAQ switch
device connected to a di
ital input on the W7750 Controller,
where a contact closure indicates poor air
ualit
and initiates
the IAQ override mode. The second, which is onl
available
on the W7750B,C is throu
h an analo
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
her than the setpoint
800
PPM
, the IAQ override is initiated. The IAQSetpt h
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
an
IAQ override, it is possible for the
heating
outputs to be
activated. This can occur if the outdoor air temperature is cold
enou
h to cause the dischar
e air temperature to drop below
the DaTempLoLim setpoint when the dampers open to the
EconIAQPos position,
and
the Ia
UseHeat fla
is set. If this
situation occurs, the heatin
is controlled to maintain the
dischar
e air temperature at 1°F
0.65°C
above the
DaTempLoLim setpoint.
FREEZE STAT
Upon receivin
a contact closure, the W7750 control
al
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
precaution. If
manual-reset
operation is
desired, the Freeze Stat device must provide the ph
sical
pushbutton, which the operator presses, to reset the s
stem
after a
freeze
condition has occurred.
DISCHARGE AIR LOW LIMIT CONTROL
If the dischar
e air temperature falls below the user-settable
dischar
e air low limit setpoint
DaTempLoLim
, an alarm is
issued, and the outdoor air damper is driven below the
minimum position settin
until the dischar
e temperature is up
to the low limit. If necessar
, the damper can
o completel
closed even durin
Occupied mode operation. As the
dischar
e temperature warms up, the economizer modulates
open until the minimum position settin
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
ment coolin
. The economizer dampers
can be enabled/disabled for usin
outdoor air as the first
sta
e of coolin
based on one of ten allowable strate
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
ment coolin
.
3. Outdoor Enthalpy, Type A—
when the outdoor
enthalp
meets the H205 t
pe A re
uirements, the
outdoor air is suitable to au
ment coolin
.
4. Outdoor Enthalpy, Type B—
when the outdoor
enthalp
meets the H205 t
pe B re
uirements, the
outdoor air is suitable to au
ment coolin
.
5. Outdoor Enthalpy, Type C—
when the outdoor
enthalp
meets the H205 t
pe C re
uirements, the
outdoor air is suitable to au
ment coolin
.
6. Outdoor Enthalpy, Type D—
when the outdoor
enthalp
meets the H205 t
pe D re
uirements, the
outdoor air is suitable to au
ment coolin
.
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
ment mechanical coolin
.
8. Single Calculated Enthalpy—
the calculated outdoor
enthalp
in btu/lb is compared to the enthalp
setpoint
OaEnthEn
in btu/lb, and the outdoor temperature is
compared to the outdoor temperature limit setpoint
OaEconEnTemp
for a hi
h limit. The compared
difference determines whether outdoor air is suitable for
use to au
ment mechanical coolin
.
9. Differential Enthalpy, Either Sensed or Calculated—
the difference between outdoor enthalp
and return air
enthalp
determines whether outdoor air or return air is
more suitable to au
ment mechanical coolin
. When
enthalp
sensors are confi
ured, the
are used for
comparin
enthalp
. If no enthalp
sensors are
available, then enthalp
is calculated usin
outdoor and
return air humidit
and temperature sensors. The
switchin
differential is fixed at 1.0 mA for enthalp
sensors, and 0.25 btu/lb for calculated enthalp
.
NOTE: If no return temperature sensor is confi
ured,
space temperature is used to calculate return
air enthalp
.
10. Network Enabled—
the network input
DestEconEnable
controls the enablin
and disablin
of the economizer.
When usin
the network input, select Econo Enable
T
pe:
No Economizer
in E-Vision. The network input
has priorit
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
pes.
The
User Address Index
followin
Table 18 lists the User
Addresses alphabeticall
and
ives the pa
e number where
the Address is located in each Table Number/Point T
pe.
After Table 18 there is an alphabetical list of
Mappable User
Addresses and Table Numbers
. Followin
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
Mana
ement Points
Table 23 Status Points
Table 24 Calibration Points
Table 25 Confi
uration Parameters
Table 26 L
ON
M
ARK
/Open S
stem Points
Table 27 Direct Access and Special Manual Points
Table 28 Data Share Points
