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The thermostat has an economizer feature that allows the use of outside
air to cool the controlled space when outside air is at an appropriate
temperature with respect to Room Temperature and Temperature Set
Point (SP). This section also outlines logic to be used with RH sensor
enabled units (-002 Models) to address potential increases to indoor
humidity caused by humid outside air during Economizer operation.
The OA output is disabled anytime the thermostat is operating in the
OFF or SETBACK modes, or when the Setback input is closed. If you
are installing a TH170-001 (no onboard RH sensor), selections 4 and 5
are disabled. An OA Sensor is required for OA3-5.
The Outside Air Economizer user selection configurations are:
1.
outside air damper (Default): Any time the thermostat is out
of OFF mode or not operating in Setback, the Outside Air output
is enabled (damper open). This feature can be used to provide
minimum ventilation.
2.
outside air damper Cycle: This feature enables OA output with
an active heating or cooling demand.
3.
outside air economizer: In this setting, the OA damper
operates only during active Cooling demand and is based on
OA temperature. If the sensed OA Temperature is ≤ the room
temperature minus the OA Economizer Offset, then the OA output
is enabled. The OA output is disabled when the OA Temperature
> the Room Temperature minus the OA Economizer Offset. OA
Economizer Offset range is user selectable from 0 - 15°F in the
Service Menu, with a default of 10°F. The Outside Air Econo-
mizer conditions are continuously checked.
4.
oa and relative Humidity economizer: Like option 3, the
OA damper operates only during active Cooling demand, but its
operation is based on both OA temperature and %RH values.
The OA economizer follows the logic of option 3, unless excess
humidity is created and/or the conditions in configuration 3 are no
longer met.
5.
oa and relative Humidity economizer with Humidity abate-
ment: Like option 3 and 4, the OA damper operates only during
active Cooling demand. Like option 4, operating logic is based
on both OA and % RH values. The OA economizer uses OA
to provide economizer operation and will OVERCOOL to abate
excess humidity.
Mode
Conditions
1
Any Temperature
2
Room Temp = 76
Temp SP = 72
Cool or Auto Mode
3
OA = 60
Temp = 72
Offset = 10
Cool or Auto Mode
4
OA = 60
Temp = 72
Offset = 10
Current RH = 72%
New RH = 80%
RH SP = 77%
Cool or Auto Mode
5
OA = 60
Temp = 72
Offset = 10
Current RH = 72%
New RH = 80%
RH SP = 77%
Cool or Auto Mode
© COPYRIGHT 2008 PECO, INC. ALL RIGHTS RESERVED.
operation (i.e. example)
OA damper is always enabled (damper open). OA closed in OFF or Setback modes.
76 > 72 = Active Cooling demand and OA Damper is enabled. OA damper is enabled (damper open) whenever there is active
heating or cooling demand.
60 ≤ 72 – 10 = OA Economizer Enabled (Open) if an active cooling demand exists.
OA Economizer offset is user adjustable in the service menu.
60 ≤ 72 – 10 = OA Economizer Enabled and Timer Set
RH also checked : 72%RH (value is stored)
5 minutes pass with Damper enabled
Thermostat checks for 2 conditions. If either is TRUE, the OA is disabled.
1.
New RH - Stored RH > 10%
2.
New RH > RH SP
1 hour timer begins. After 1 hour, OA & RH are checked again.
60 ≤ 72 – 10 = OA Economizer Enabled and Timer Set
RH also checked : 72%RH (value is stored)
5 minutes pass with Damper enabled
If New RH > RH SP, the OA is disabled
Overcooling operation begins, allowing the Temp. to drop up to 3°F below the Temp SP to satisfy the dehumidification demand.
1 hour timer begins
After 1 hour OA & RH are checked again
oCCuPanCy oPeration
If the TH170 is installed with occupancy sensors, operation is as follows:
In an occupied state the thermostat operates normally and looks for an
open door.
•
On a Door Open signal the thermostat begins to control the
ambient temperature to the programmed Set Point and waits for a
door close. If door is open for more than 2-minutes the thermo-
stat outputs are disabled. If a button is pressed on the keypad
before the two minute timer expires, the time delay is extended
to 10 minutes. The time delay can only be extended once. If the
thermostat is powered up in the Occupied State and the door is
open, after 10 minutes the thermostat will disable its outputs. The
Reversing value may remain enabled depending on the demand
and configuration. Once the thermostat outputs are disabled, a
door closure is required to re-enable the outputs.
•
On a Door Closed signal the thermostat starts a 2-minute timer in
which to look for occupancy. If the occupancy sensor transitions
to unoccupied and the timer expires, the thermostat enters into
the Unoccupied State. If the occupancy sensor transitions from
unoccupied to occupied while the timer is running the thermostat
will remain in Occupied State. If the occupancy sensor transitions
from unoccupied to occupied after the 2-minute timer expires, the
thermostat will remain in the Occupied State.
In an unoccupied state the thermostat sets Heating and Cooling Set
Points to Setback values, as determined by factory or user settings. In
this mode the fan is automatically set to cycle with demand. The ther-
mostat will continue to monitor the occupancy sensor and will go to the
Occupied State if it sees occupancy.
If the only a Door / Window Switch is installed, the thermostat will dis-
able the thermostat outputs when the input is open for longer than 2
minutes.
80 - 72 > 8%
FALSE
80 > 77
TRUE
OA is disabled
80 > 77
OA is disabled
requirements
None
None
OA Sensor
TH170-002 Model
+ OA Sensor
TH170-002 Model
+ OA Sensor
P/N 69290 3220-2088 REV 0 PAGE 5
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