Emerson Liebert iCOM, Manual

Page: 43 / 172

Operation
35 Liebert
®
iCOM
®
for Liebert DSE
™
PI —If PI Control is selected, the percent humidification/heating requirement is calculated by
combining two methods, proportional and integral. The proportional term is calculated in a manner
similar to the previously described Proportional control.
The integral term (sometimes called “reset action”) is calculated by measuring how much and how
long the air humidity has been above or below the setpoint. If the actual air humidity has deviated
from setpoint, the percent requirement is slowly but continuously increased until the total is
sufficient to bring the return room air back to the setpoint.
The control helps to ensure humidity setpoint is achieved while efficiently operating the equipment.
From an idle state (compressor[s] Off, chilled water valve closed, etc.), the call for
humidification/dehumidification is based on proportional humidity deviation from setpoint. As
humidity deviates further from or closer to setpoint, the call for humidification/dehumidification is
increased or decreased, respectively. The amount of humidification or dehumidification applied
depends on how far the actual temperature has deviated from the setpoint on the proportional (P)
band.
The integration (I) time works with the proportional band in PI Control to stage call for components
before the room humidity deviates far from the setpoint. The “I” portion does this by doubling the
current “P” deviation for every time the “I” has elapsed.
3.5.2 Humidification
Infrared Humidifier
There are two types of infrared humidifiers: small pan (IFS) and large pan (IFL). The operating mode
of each is similar, however, some of the variables or timings differ.
Infrared humidifiers are started at 100% humidification request, and stopped at 0%. Infrared
humidifiers cannot be driven in proportional mode.
An autoflush system automatically controls a water makeup valve to maintain proper levels in the
infrared humidifier water pan during humidifier operation. If humidification is needed and 15 hours
have elapsed since the last time the humidifier was on, then the humidifier is not turned on until the
valve completes an initial fill of the humidifier pan. This pre-fill is about 30 seconds for a small pan
and 60 seconds for a large pan. The valve continues to fill and flush the pan for about 4-1/2 minutes
for a small pan or 7-1/2 minutes for a large pan. Pan size is selected based on unit specifications and
is preset at the factory.
During humidifier operation, with the flush rate set at the default of 150%, the valve is opened
periodically to add water to the pan (about 45 seconds every 7 minutes of humidifier operation for a
small pan, or 80 seconds every 10 minutes of operation for a large pan). This adds enough water to the
pan to cause about a third of the total water used to be flushed out of the overflow standpipe located
in the humidifier pan. This action helps to remove solids from the pan. The flush rate is adjustable
from 110% to 500% in 10% intervals. Default is 150%. If the water quality is poor, it may be desirable
to increase the water flushing action above the normal 150% rate. Also, if the supply water pressure
is low, the flush rate adjustment can be increased so that sufficient water level is maintained during
humidification.
Table 8 Parameters for infrared humidifier control
Parameter
Small Pan
(IFS) Default
Large Pan
(IFL) Default
Humidity in Last xx Hours 15 hours 15 hours
Fill Time 33 seconds 56 seconds
Humidifier On Time 440 seconds 576 seconds
Flush Rate 150% 150%
NOTE
The flush rate parameter, Infrared Flush Rate (Service Menu, Options Setup), is adjustable
from 110%-500% because the fill valve is controlled by time. It uses a factory-installed integral
float to prevent overfilling if the humidifier drain or condensate pump fails.