STULZ E
2
SERIES CONTROLLER FOR PERIMETER SYSTEMS OPERATION MANUAL
13
Cool Only- No
Humidifi cation
Needed
Actual
Temp/RH
(Dewpoint)
Setpoint
Psychrometric Chart
On dual compressor systems, equipped with a remote
condenser and enabled for hybrid control, the second stage of
cooling (compressor 2) is turned on when the measured
dewpoint is above the dewpoint cut-in setpoint for the second
stage. When the dewpoint drops below the cut-out setpoint
for the second stage, the second stage of cooling is turned off.
4.5 Operating Confi gurations
The operating confi guration for the controller depends on what
type of air conditioner is being controlled (i.e. AR, AHU, CW, W/G)
and what features are selected. The operating confi guration is
preset by the factory according to the application. If certain
features discussed in this manual are not factory enabled, no
screens for that feature will be shown.
4.5.1 Cooling
4.5.1.1 Chilled Water/AWS/FC
Upon a call for cooling, the controller activates a chilled
water control valve with a 010 VDC signal. The valve
opens proportionally to the demand for cooling based on
air temperature. The control settings consist of the return
temperature setpoint (in the Control>Set>Temperature
menu), the integration time (in Factory>Cool>Energy Savings
menu), and the CW Cut-in/Out offset and cooling band (in the
Service>COOL>CW1, AWS, FC menu). The chilled water
valve closes to the minimum position and remains at that
position when the return air temperature is less than the return
temperature setpoint plus the CW Cut-in/Out offset.
When the actual return air temperature rises above the return
air temperature setpoint plus the CW control cut-in value, the
CW valve position begins to increase proportionally from the
minimum position to the maximum, fully open position at the
return air temperature setpoint plus the cooling band. The
integration time allows the rate the valve position changes to
increase over a period of time as long as the difference between
the actual return air temperature is higher than the sum of the
return temperature setpoint plus the CW control cut-in and
cut-out offset (see Figure 6).
The starting voltage for the valve to be 0% open and ending
voltage for the valve to be 100% open varies, and is set in the
Confi guration level. For a valve that is fully closed at 2.5V and
fully open at 10V, the controller sends 2.5V to the valve when
0% opening is called for and ramps to 10V when the demand
increases to 100%.
For AWS and FC units the entering water temperature must
be colder than 55 °F (default value) for the unit to enter the
cooling mode and below 45 °F (default value) to enter the
dehumidifi cation mode. (This does not apply to CW systems.)
4.5.1.2 Compressor Based Direct Expansion (DX)
The controller cycles compressor(s) on and off for capacity
control when it is determined that a stage of cooling is called
for. A stage of cooling is turned on based upon the controller's
cooling response to temperature and humidity inputs from the
air sensors.
For systems with dual compressors, each cooling stage will turn
on following a time delay, once the programmed “Cooling Stage
Enable” setpoint value for that stage has been reached (see
Figure 6). When a compressor is turned on, it remains on until
the "minimum on" time has expired regardless of temperature
or humidity conditions. When a compressor is turned off, it
remains off until the "minimum off" time has expired regardless
of temperature or humidity conditions.
Figure 5. Dewpoint Control
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