Installation and Maintenance
EHU-600 Series Humidifiers
15
Principle of
Operation
Figure 15-1: 100% demand. Filling with
water low, increasing steam output.
Figure 15-2: 100% demand. Fill valve
cycling to maintain output. High water
level. High, constant steam output.
Figure 15-3: No demand. Contactor opens.
No steam output.
1.
Operation
The Armstrong EHU-600 Series electronic steam humidifier
converts ordinary tap water to steam and distributes it within
the air being humidified to bring the relative humidity up to the
desired level. It is the ideal solution for providing humidifi-
cation where no steam is available or where a steam source is
too remote for easy or economical piping. The Armstrong
EHU-600 Series consists of three models: The EHU-600, 601
and 602. The maximum capacity of the series is 192 lb/hr.
The humidity demand, sensed by the humidistat, is indicated
by the EHU demand meter. The microprocessor converts this
demand signal into an amperage requirement. The power
contactor closes, applying voltage to the electrodes, and the
fill valve begins to fill the tank.
Water enters the bottom of the steam generator tank and rises
until it reaches the electrodes. Upon contact, electrical current
flows through the water, causing it to boil and produce steam
(Fig. 15-1).
When the water level rises, as shown in Fig. 15-2, increased
electrical current flows through the water, producing more
steam. This increase will continue until the required output
of steam (i.e. amperage requirement) is reached.
At this point, the fill valve will cycle off and on to maintain the
required amperage. When the humidistat senses the added
moisture in the air, the demand for humidity begins to drop. As
the demand drops, the output of the unit is modulated down by
boiling away water and not filling, allowing amperage to
decrease, thereby reducing the steam flow. The fill valve can
then cycle at the lower steam output (amperage) requirement.
Fig. 15-3 shows what happens when the humidistat demand
signal drops below a minimum demand: The contactor is
de-energized, and steam output stops.
Steam output may also be stopped by a duct high-limit
humidistat or a fan interlock switch. These devices prevent
excess moisture and condensation in the duct. If these devices
open, the Tank Off light will illuminate and the fill will turn off.
A high-water float switch prevents water carryover into the duct
due to too high a water level in the tank. When the high water
level is reached the TANK FULL light comes on and the fill
valve is blocked until some water is boiled away and the
water level drops. This is not uncommon on startup. If the
TANK FULL light is on continuously during normal service
then the tank probably needs cleaning.
