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15C0233-00 Rev A
SSC4500DX
9/23/2020
Humidity Control:
The internal humidity will be continuously monitored, displayed, and alarmed. The interior of the
cabinet shall be maintained between a maximum of 60% RH and a minimum of 20% RH. There
are typically (2) distinct processes involved in the control of RH. If the RH is high,
dehumidification is required; if the RH is low, moisture is added to the airstream. The
refrigeration cassette of the cabinet is designed to operate with a 55°F evaporator leaving-air
temperature, IE a dew point temp or maximum RH of 60%. Therefore, from a control point of
view, there is nothing to manipulate to lower the humidly by design.
The humidity level of the cabinet has a minimum value of 20%. This is a user-defined value that
ranges from 20% to 40% with a default value of 20%. If the RH is below the MIN RH VALUE
SETPOINT, humidification is required. The physical hardware to raise the humidly involves
several mechanical components: 1) A water tank with LOW LEVEL SWITCH, and WATER
PUMP. 2) A condensate pan with HIGH LEVEL SWITCH, SOLENOID VALVE, and HEATER.
If the measured RH value goes above 60% RH, the display screen will change to red and the
alarm condition will be displayed along with the date of the alarm, the time, and corrective
action. The REMOTE ALARM RELAY will be energized during this alarm condition.
If the RH drops to an RH value that is below the MIN RH SETPOINT, the humidification will be
automatically initiated to raise the internal RH value to the MIN RH SETPOINT plus 2%. The
LOW LEVEL SWITCH in the water tank will be verified, a 10-minute ON-DELAY timer and the
condensate pan HEATER will be activated to pre-heat the pan before water is added. Once the
timer has expired, water can be added to the pan. The HIGH LEVEL SWITCH verifies that there
is no excess water in the pan. Water can now be added to the pan. A PULSE RELAY is
activated with an ON-TIME of 1-sec and an OFF-TIME of 10 min. During the 1-second on time,
both the WATER PUMP and the SOLENOID VALVE are activated. This cycle will repeat until
the internal cabinet RH is at the MIN RH VALUE plus 2%. Once this RH value is achieved, the
PULSE RELAY will be stopped and a 15 min OFF-DELAY timer will be started to completely dry
out the condensate pan so there is no standing water.
The water level in the de-mineralized water storage tank is automatically verified prior to starting
the humidification process. If the LOW LEVEL SWITCH is activated, the display screen will
change to amber and the alarm condition will be displayed along with the date of the alarm, the
time, and corrective action. The REMOTE ALARM RELAY will be energized during this alarm
condition. The humidification process will be delayed until the water tank is refilled.
