22 Pub. No. OM-A-10E — April 2004
DEWPOINT DEMAND CONTROL “DPD”
The Dewpoint Demand control is an energy saver that can
extend the drying cycle without purging, during periods of
lower moisture loads. The Dewpoint Demand system
offers, in one compact package, the utmost in flexibility
and accuracy sensing the actual dewpoint of the outlet air.
The hygrometer senses the dewpoint at the outlet of the
dryer at the end of the drying cycle, and extends the
drying cycle until the preset adjustable dewpoint setpoint
is reached. During this extended drying cycle, the purge
valves are closed and the opposite tower is pressurized
and prepared for the drying cycle. The dewpoint demand
option reduces purge loss and extends valve life. This
option consists of the following:
• Digital Dewpoint Display
• Adjustable Setpoints
• Demand Cycle Light
• High Humidity Alarm Light with Dry Contact
• 4-20mA Output
Calibration: To maintain accuracy, the probe should be
recalibrated annually. Recalibrated probes are
available through your local distributor.
Probe Replacement: Isolate and depressurize the
probe chamber. Disconnect the sensor cable from the
sensor. Remove, and replace the probe. Pressurize the
probe chamber and connect the sensor cable. A small
amount of sample air (approximately 2-10 SCFH) should
expel out the chamber needle valve.
PULSE PURGE REGENERATION (PPR) WITH
DEWPOINT DEMAND (DPD)
(PE & EE Series only)
Pulse Purge Regeneration systems use the same NEMA
cycle of 8 hours as PE & EE Series dryers except during
the regeneration cycle, instead of continuously flowing 7%
of the purge air and blowing it out into the atmosphere,
the purge air is cycled at 30 minute intervals during the 4
hour regeneration period. It is observed that this method
of purging and holding greatly enhances the regeneration
process and considerably reduces the period the heater is
energized, and also cuts down the purge flow by
approximately 50%, since purging and holding during the
regeneration cycle is equal.
Pulse Purge Regeneration (PPR) with Dewpoint Demand is
designed to achieve the maximum energy savings benefits
of Pulse Purge at loaded conditions. At low load
conditions, Dewpoint Demand takes over for added
energy savings. The amount of time that the unit is in
demand is proportional to the moisture load. This cycle is
only recommended for continuous operation.
This system is controlled by a PLC which has a nonvolatile
memory. The program is stored in the E-PRom memory.
A dewpoint monitor with High Humidity Alarm and three
hour meters are provided to monitor the system and show
savings. The hour meters display “Heater Run Time”,
“Dryer Run Time” and “Demand Time”.
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