Armstrong World Industries EHU-703 Troubleshooting Guide, Principle Of Operation - An Overview

TROUBLESHOOTING GUIDE

CAUTION!: Disconnect the electric power supply at the circuit breaker or switch whenever the unit is to be inspected or serviced. DO NOT USE THE TANK ON/OFF SWITCH ON THE HUMIDI-

FIER BECAUSE THIS SWITCH DISCONNECTS THE STEAM GENERATOR TANK ONLY.

PRINCIPLE OF OPERATION - AN OVERVIEW

The Armstrong Series EHU-700 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.

The humidity demand is sensed by the humidistat. A micro- controller converts this demand signal into an amperage requirement. If humidistat demand is above 35%, the internal power contactor closes, applying voltage to the electrodes, and the fill valve opens to begin filling 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 (Figure 17-1).

As the water level rises (Figure 17-2) increased electrical current flows through the water, producing more steam. This increase will continue until the desired current level (i.e. required steam output) is reached. At this point, the fill valves will cycle off and on to maintain the desired amperage ±5%. The desired current level is a function of the nominal current rating, humidistat demand, and the automatic capacity adjust- ment feature.

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. This allows the amperage to decrease, thereby reducing the steam flow. The fill valve can then cycle at the lower steam output (current) requirement. When the humidistat demand signal drops below a minimum 25% demand, the contactor is de-energized, and steam out- put stops (Figure 17-3).

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 by opening the tank contactor if there is too much humidity or insufficient air- flow within the duct.

Figure 17-1
External	Internal
	Power
Disconnect	Contactor
Current Sensor
Line
Fill Valve	Distribution
	Tube
Controlling	Fill Cup
Humidistat
High-Limit
Humidistat
Fan Interlock	High-Water
Controller	Float Switch
	Drain Valve
	Overflow
	Line
Figure 17-2

	Internal
External	Power
Disconnect	Contactor
Current Sensor
Line
Fill Valve	Distribution
	Tube
Controlling	Fill Cup
Humidistat
High-Limit
Humidistat
Fan Interlock	High-Water
Controller	Float Switch
	Drain Valve
	Overflow
	Line
Figure 17-3

	Internal
External	Power
Disconnect	Contactor
Current Sensor
Line
Fill Valve	Distribution
	Tube
Controlling	Fill Cup
Humidistat
High-Limit
Humidistat
Fan Interlock	High-Water
Controller	Float Switch
	Drain Valve
	Overflow
	Line

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