Liebert CHALLENGER 3000 - Manual (Page 37)

System Performance with Advanced Microprocessor Controls
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4.0 S
YSTEM
P
ERFORMANCE WITH
A
DVANCED
M
ICROPROCESSOR
C
ONTROLS
This section provides details on how your Challenger 3000 unit responds to user inputs and room con-
ditions. Refer to this section when you need specific information. This section includes details on con-
trol.
4.1 Temperature Control
4.1.1 Cooling/Heating Required, in Percent (%)
The temperature control program for the advanced microprocessor is based on a calculated % require-
ment for cooling/ heating.
4.1.2 Response to Control Types
Proportional Control
The % requirement is determined by the difference between the return air temperature and the tem-
perature setpoint. As the return air temperature rises above the temperature setpoint, the % cooling
required increases proportionally (from 0 to 100%) over a temperature band equal to the temperature
sensitivity plus 1°F. The % heating requirement is determined the same way as the temperature
decreases below the setpoint. With this type of control the temperature at which the room is con-
trolled increases as the room cooling load increases. At full cooling load the room would be controlled
at a temperature equal to the setpoint plus the sensitivity.
For systems with SCR Reheats, the % requirement is determined only by the difference between the
return air temperature and the temperature setpoint. This permits tighter temperature control. The
SCR Reheats are controlled in a proportional manner inversely as described above for cooling. When
the return air temperature is at the temperature setpoint, the SCR Reheats will be on 100%. As the
temperature increased to the temperature setpoint plus the temperature sensitivity, the SCR Reheats
will be pulsed proportionally from full on to full off (0% to 100%) until the return air temperature
reaches the temperature setpoint plus the temperature sensitivity.
PID Control (Chilled Water or SCR Reheats only)
If PID control is selected, the return air temperature is controlled at or near the temperature setpoint
independent of the room load. The % cooling/heating requirement is calculated by adding together
three individual terms - proportional, integral, and derivative.
The proportional term is figured in a manner similar to the previously described proportional control.
The integral term (sometimes called “reset action”) is figured by measuring how much and for how
long the temperature has been above or below the setpoint. If the temperature is above the setpoint,
the % cooling requirement is slowly but continuously increased until the total is sufficient to bring the
temperature back to the setpoint. The derivative term provides an anticipation control for rapid
changes in temperature. If the temperature is rising, the % cooling is increased temporarily until the
temperature begins to stabilize. The % heating requirement is increased if temperature is falling.
The proportional, integral, and derivative terms are all adjustable through the control selection menu
and should be set or “tuned” to the characteristics of the room being controlled (see 4.3 - Control
Types).
Intelligent Control (Chilled Water only)
If intelligent control is selected, the return air temperature is controlled at or near the temperature
setpoint. The % cooling/heating required is calculated based on a set of logical “rules” that are pro-
grammed into the control. These “rules” simulate the actions that an expert human operator would
take if manually controlling the system (see 4.3 - Control Types).