Specifications

K) Valve 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 control valve to maintain the space temperature. When the space temperature falls below the cooling
setpoint, the control valve shall be closed.
The chilled water valve shall be driven closed when 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 coil 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. 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.
All electric heat stages shall be immediately engaged when the discharge air temperature falls below 52°F.
Electric heat shall remain engaged 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.
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 cooling valve
closed. If the discharge air temperature falls below 52°F, 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 19