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Component Operation and Maintenance, Checks and Adjustments
59
7.5.2 Steam Generating Humidifier
The humidifier drains and refills to maintain a current setpoint and alert the operator when the
humidifier canister needs to be replaced. The humidifier is located in the lower section of upflow
units, and in the middle section of downflow units.
Figure 10 Steam generating humidifier
Operation
1. During start-up, when the humidity control calls for humidification, the fill valve opens and allows
water to enter the canister. When the water level reaches the electrodes, current flows and the
water begins to warm. The canister fills until the amperage reaches the setpoint and the fill valve
closes. As the water warms, its conductivity increases and the current flow, in turn, rises. If the
current reaches 115% of the normal operating current, the drain valve opens and drains some of
the water out of the canister. This reduces electrode contact with the water and lowers the current
flow to the amperage setpoint. Boiling soon commences, and the canister operates normally.
2. If the conductivity of the water is low, the canister fills and the water level reaches the canister
full electrode before the current setpoint is reached. The humidifier stops filling to prevent
overflow. Boiling should commence in time. As water is boiled off, the mineral concentration in
the canister increases and current flow also increases. The canister eventually reaches full output
and goes to normal operation. No drain is permitted until then.
3. When full output is reached the circuit board starts a time cycle which is factory set at 60 (84)
seconds. During this repeating time cycle, the fill valve will open periodically to replenish the
water being boiled off and maintain a “steady state” output at the set point.
4. After many cycles, the mineral concentration in the canister becomes too high. When this occurs,
the water boils too quickly. As the water quickly boils off and less of the electrode is exposed, the
current flow decreases. When the current crosses the low threshold point before the end of the
time cycle, the drain valve opens, draining the mineral-laden water out and replacing it with
fresh water. This lowers the mineral concentration and returns the canister to “steady state”
operation and prolongs canister life. The frequency of drains depends on water conductivity.
5. Over a period of time (usually between 500 and 1500 hours depending on water quality), the
electrode surface will become coated with a layer of insulating material, which causes a drop in
current flow. As this happens, the water level in the canister will slowly rise exposing new
electrode surface to the water to maintain normal output. Eventually, the steady state water level
will reach the canister full electrode and indicate so by activating the canister full alarm and
opening the humidifier contactor. At this point, all of the electrode surface has been used up and
the canister must be replaced.
6. After the entire electrode surface has been coated, the output will slowly begin to fall off. This
usually occurs in the last several hours of electrode life and should allow enough time to schedule
maintenance. During these last hours, the mineral concentration can increase. If the mineral
concentration is too high, arcing can occur. If the electrodes start to arc, turn off the humidifier
immediately and replace the canister with the identical part.