DriSteem HUMIDI-TECH DI Installation Guide download pdf (Page 9)

DRI-STEEM Vapor-logic

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TP modulation (electric humidifiers)

The standard form of modulation with an electric humidifier is time

proportioning (TP) modulation. With TP modulation, the outputs

cycle on and off at a certain rate to approximate humidifier demand

as the example below illustrates. To calculate the example, imagine

that each contactor represents 25% of the output of the humidifier.

With a 55% system demand, you need two full contactors plus 5/25

of a third contactor. Therefore, two contactors are full on and a

third contactor is on for 5/25 of 60 seconds, or 12 seconds.

Example

If a Vaporstream humidifier has four heat output stages (four

contactors) and a demand of 55%, two of the contactors are

energized all of the time; one contactor cycles on and off at a certain

rate, and one contactor is off. The rate at which the third contactor

cycles is determined by the demand and the heater cycle time.

Continuing with the example, if you have a heater cycle time of 60

seconds and a demand of 55%, the third contactor cycles at a rate of

12 seconds on and 48 seconds off.

To minimize wear on cycling contactors, Vapor-logic

keeps track

of the number of cycles on all contactors, and rotates the TP cycling

contactor to ensure that all contactors get equal wear. In addition,

to prevent short cycling, no contactor has a cycle time less than two

seconds or greater than the heater cycle time minus two seconds.

If system demand dictates that a contactor is on for less than a

second, the contactor does not energize. If the contactor is on

for between one and two seconds, the contactor energizes for the

minimum two-second period. Also, if a contactor is de-energized

for less than one second, it stays on. If a contactor is de-energized

for between one and two seconds, the contactor de-energizes for the

minimum two-second period.

These measures prevent short cycling of the contactors and extend

their life. On a TP system with contactors, the heater cycle time

is user adjustable and can be set from 30 seconds to 99 seconds

(default is 60 seconds) via the Vapor-logic

keypad/display.

TP modulation (gas humidifiers)

GTS burners provide TP modulation control when system

demand is low. See Page 7 for more information about gas burner

modulation.

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