Specifications

J) Damper Controlled Chilled Water Cooling with Electric Heat
Fan Operation
The supply fan shall run continuously in the occupied and tenant (unoccupied) override modes. The fan shall
cycle with calls for cooling or heating in the unoccupied mode.
Cooling Operation
When the space temperature exceeds the cooling setpoint, a proportional-integral control loop shall position
the face & bypass damper to maintain the space temperature. When the space temperature falls below the
cooling setpoint, the face & bypass damper shall close (bypass).
The face and bypass damper shall be driven closed (full bypass) if the discharge air temperature falls below
55°F OR the low limit thermostat closes. The damper shall remain closed until the discharge air temperature
exceeds 57°F AND the low limit thermostat opens.
Heating Operation
There is a fixed 15-second delay between the engagement of each electric heat stage. Each electric heat
stage must be engaged for 1 minute (minimum ON timer) and each stage cannot be re-engaged for 1 minute
after being switched OFF (minimum OFF timer). These delays are built into the unit controller.
When the space temperature falls below the heating setpoint, electric heating shall be staged on to maintain
the space temperature. The face & bypass damper shall fully open (face) when an electric heat stage is
engaged. A proportional-integral control loop and built-in digital sequencer shall be used to control up to 3
stages of electric heat. When the space temperature exceeds the heating setpoint, all electric heat stages
shall be staged OFF.
If the discharge air temperature falls below 52°F, all electric heat stages are immediately. All electric heat shall
remain ON until the discharge air temperature rises above 55°F.
If the discharge air temperature exceeds 130°F, all electric heat stages shall be immediately disengaged,
regardless of the space temperature or the minimum ON timer. Electric heating shall remain disengaged until
the discharge air temperature falls below 110°F.
End-of-Cycle Valve Operation (Optional)
A normally closed, 2-position valve with return on power failure is optionally used as a cooling end-of-cycle
(EOC) valve. This valve prevents radiant effects from overcooling the space when the face & bypass damper
is in the full bypass position. The EOC valve shall open when the face & bypass damper is commanded to
open.
The EOC valve shall be closed whenever the discharge air temperature falls below 55°F OR the coil low limit
thermostat closes. The valve shall remain closed until the discharge air temperature exceeds 57°F AND the
low limit thermostat opens.
Outdoor Air Damper Control
The outdoor air damper shall be closed in the unoccupied mode, regardless of the space temperature
conditions.
The outdoor air damper shall be closed in low limit conditions (See Safeties).
The outdoor air damper shall be closed if the space temperature falls more than 3°F below the heating
setpoint. The damper will not open until the space temperature rises within 2°F of the heating setpoint.
The outdoor air damper shall be closed if the space temperature rises more than 3°F above the cooling
setpoint. The damper will not open until the space temperature falls within 2°F of the cooling setpoint.
The outdoor air damper shall close to minimum position when the outdoor air temperature exceeds 68°F
The outdoor air damper shall be controlled with a proportional control loop based upon the deviation from
setpoint. The outdoor air damper shall begin to modulate open from minimum position when the space
temperature exceeds the (space setpoint - 0.5°F). The outdoor air damper shall be fully open when the space
temperature rises 1.5°F above the setpoint. Except as noted in the paragraphs above, the outdoor air damper
shall not close beyond minimum position during occupied operation.
Safeties - Low Limit Conditions
If the low limit thermostat trips OR the discharge air temperature falls below 55°F, the unit enters low limit
mode. This shall drive the outdoor air damper closed. In cooling mode, this shall force the face & bypass
damper into full bypass position and the optional EOC valve shall close. If the discharge air temperature falls
below 52°F, the all stages of electric heat shall be engaged.
Electric heat shall return to normal control when the discharge air temperature exceeds 55°F.Normal unit
operation shall resume when the discharge air temperature exceeds 57°F and the low limit thermostat opens.
7/1/03 Part Number 011-200001-003 Page 18