Parameter Generation and Control 9354-4250, Installation And Operation Manual

Page: 12 / 90

PGC Inc. Horizontal 500-1000 CFM June 2006
Parameter Generation and Control, Inc. 12
Control Modes
The PGC conditioning system offers four modes of temperature and humidity control.
1. Cascade Temperature Mode
This is the most commonly used mode because the user specifies only the desired
air temperature and relative humidity (Rh) level in the chamber. The temperature
of the water spray controls the dew point of the discharge air and the water
temperature is adjusted in order to achieve desired humidity level. The air is then
re-heated to the desired temperature before returning to the test chamber. This
allows the system to respond to load variations while retaining the basic stability
of a spray system.
2. Two-Temperature Mode
In this mode, the user establishes the desired air and water temperatures that are
required to produce the desired relative humidity level, as determined by a
psychometric chart. The Two-Temperature mode can be used when operating the
very edges of the system capabilities.
3. Slow Damper Mode
This mode is similar to Cascade mode with the difference being that the air
bypass damper control loop and the air heater control loop have been separated.
In this mode the damper is moved slowly and its final position is when the desired
percentage of air heat output is achieved. The desired percentage of air heat is
determined by the user in the tuning parameters (Manual Adjust) section of the
controller. In some situations, slow damper mode can be applied to improve
energy efficiency or extend the operating range of the system. Typically, slow
damper mode is most effective when the system is operated at a single condition
as it will often require manual tuning adjustments for proper operation at multiple
set points.
4. Dry Mode
This mode is required to control dew points below 4°C. In this mode, all water is
removed from the spray chamber and an optional desiccant dryer is used to
control humidity. Although this mode is accessible in SmartPad, it is non-
functional unless the system is equipped with a desiccant dryer.