DriSteem Vaporstream Specifikace stáhnout pdf (Strana 58)

P a g e 5 4 • D R I - S T E E M D e s i g n G u i d e

D R I - S T E E M D e s i g n G u i d e • P a g e 5 5

and dilutes the mineral concentration in the tank water while

causing a minimal reduction in steam output. Surface skimming

systems produce a negligible interruption to steam output because

heaters remain on during skimming, and because tanks that are

regularly skimmed require minimal or no tank draining and

flushing. Draining and flushing a tank causes steam output to

stop for the entire drain duration, which in some systems can be

as long as 60 minutes. All DRI-STEEM skim durations are user-

adjustable, allowing operators to change the length of time the tank

skims, as well as the frequency, often eliminating drain and flush

requirements.

Energy modulation also key to maintaining consistent RH

The other key mechanical aspect of maintaining RH output within

a specified range is to provide consistent energy to the heating

components. There are two ways to modulate energy delivery to

an isothermal humidifier: full, analog modulation, such as with

a steam or gas valve, or on-off modulation such as with a time-

proportioning electric element system.

Valve systems falter at low end

Steam valves, such as those used in a steam-to-steam humidification

system, modulate steam flow to heat exchangers in direct

proportion to demand signals. Theoretically, if the system demand

is 25%, the valve opens 25%. However, steam delivery is part of a

mechanical system that includes a boiler, valve, actuator, and steam

trap. So while in theory it would seem that a valve system would

provide the most directly responsive energy metering, it does not

due to mechanical limitations of the system’s components.

To provide peak performance, steam valves require supply steam

to be at a consistent pressure. Supply steam can be controlled with

a pressure reducing valve, which converts an inconsistent supply

pressure to a steady, lower pressure, eliminating one source for

steam fluctuation. Steam pressures may drop when a bucket steam

trap empties, reducing steam output. But the main issue with

valves is low-end controllability. If very tight RH control is essential

with a steam valve system, specify a valve with a high turndown

ratio (50:1).

Systems using gas valves cannot burn efficiently when demand

is low. This is why many gas valve systems switch to on-off

modulating control below a certain demand point. For example,

a gas system may be fully modulating until demand reaches 25%,

Output control basics

On-off control

On-off control is the simplest control scheme

and does exactly what its name implies: the

output device turns fully on, then fully off.

Residential furnaces and air conditioners

often use this type of control.

In a humidification system, an on-off

humidistat has a differential between the

on and off switch points. The differential is

established at a range sufficient to prevent

output short cycling. In other words, the

humidity level has to fall a little below

set point before the humidistat closes and

energizes the humidifier. Once the humidifier

is energized, the humidistat stays closed

until the humidity is a little above set

point. This creates an operating range that

prevents the humidifier from running for

very short periods of time.

Modulating demand signal control

With modulating demand signal control,

a modulating humidistat or a building

management system sends a signal to the

humidifier, which then produces a directly

proportional output. For example, if a

humidistat operating between 4 mA and

20 mA sends a 4 mA signal, the humidifier

produces no output. A 12 mA signal causes

the humidifier to operate at 50% of capacity,

and a 20 mA signal causes the humidifier

to run at 100% capacity. Humidity set point

is adjusted at the humidistat from within a

building management system, or by using

the humidifier controller keypad.

1 2 ... 53 54 55 56 57 58 59 60 61 62 63 ... 83 84

Komentáře k této Příručce

Žádné komentáře

DriSteem Vaporstream Specifikace Strana 58

Komentáře k této Příručce

Související produkty a manuály pro Odvlhčovače DriSteem Vaporstream