Feature Notes
Air Handing Unit Humidity Submodule with 3 x Triac Outputs (3T version) with 2 x 0-10V DC Outputs (AOP version)
HUM / DIN / 3T /... HUM / DIN / AOP / ...
Main Features Provides Control of a Humidifier Works in Conjunction with a SeaChange AHU Controller to ensure correct interlocks Can also be used to provide modulating De-Humidification control Cascade control

Summary Features

General

This Humidity Controller is an AHU Submodule,and must be used in conjunction with a SeaChange AHU Controller; it can be used to control staged Humidifiers with up to 3 stages of operation or to control 0-10V DC Humidifiers.

In order for the Humidity Controller to function, the system must be fitted with an Intelligent Return (or Supply) Air Temperature and Humidity (T+Rh) Sensor; this is wired to the Network, and Registered to the AHU Controller. The Humidity Controller will then automatically acquire this Humidity value over the network. An Intelligent Supply Air T + Rh sensor may also be fitted; this will give upper and lower limits on Supply Air Rh if required. See section “Return,Supply Air and Cascade Control”.

Modes of operation

The Humidity Controller may be used in a number of different ways to control humidity.

On/Off DeHumidification Control

This is the most common method of controlling humidity in commercial buildings. The Humidity Controller controls humidification, but the AHU Controller controls De-Humidification in an On/Off manner with a hysteresis dead-band. This is the most energy-efficient method of humidity control.

Close Humidity Control

This method gives closer humidity tolerances, but is a less energy-efficient method of control. Here, the Humidity Controller assumes responsibility for Humidification and De-Humidification, and sends De-Hum demand signals to the AHU Controller which override the AHU’s temperature controls.
Various advanced techniques are available for complex plants or exacting control requirements; contact SeaChange for further details.

Dessicant AHU Evaporative Cooler

This Humidity Controller can also be used to control the Evaporative Cooler in a Dessicant AHU, including control of the reservoir dump valve. This application is outside of the scope of this document; please contact SeaChange for further details of this application.

Registration

Registration is the simple process by which logical connections are made between Controllers in a SeaChange system; it is done at time of commissioning and involves pressing buttons on the Controllers in a specific sequence (for further details of the registration process, see our publication “Commissioning Guide”).

The Humidity Controller must be registered to an AHU Controller; this is done by putting the AHU Controller into Configuration Mode, and registering the Humidity Submodule to it. This automatically enables all necessary demand signals, interlocks, temperatures etc. to be exchanged between the Controllers across the network.

The module is registered to it's AHU controller by putting the AHU controller into config mode and then pressing the registration button on the Humidity Controller. Registration is confirmed by the status LED on the module flashing once. Only one Humidity controller is supported per AHU.

The AHU controller must be AHU3d1 or later to support a Humidity controller. For Close Humidity control or use of the DeHum output option the AHU controller must be 4a1 or later.

Description of Features

Humidity Control

This Humidity Controller can be used in a variety of different ways to control humidity; it may also be used to provide cooling via an Evaporative Cooler as part of a Dessicant AHU; this application is not covered by this Data Sheet; contact SeaChange for further details.

On/Off Dehumidification Mode

This is the most common (and most energy-efficient) method of humidity control. The AHU Controller performs De-Hum control, whilst the Humidity Submodule takes care of Humidification. The Humidification control method is continuous control using a Fuzzy Logic loop, so that increasing deviation below Humidification setpoint will result in a proportional increase in steam / water vapour into the supply air. The Dehumidification control is On/Off, with a hysteresis band to avoid cycling. When humidity levels rise above the Dehum setpoint by half of the deadband, the cooling coil will be overriden to provide maximum cooling (and hence De-Humidification). This will continue until the humidity has fallen to (Dehum setpoint - 1/2 deadband). when the cooling will revert to temperature control. During this process the heating temperature loop stays active to reheat the supply air if necessary to maintain supply air temperature.

Parameter Settings for On/Off Dehum mode

RHSP and RHDB must be set in the AHU Controller; RHSP sets the nominal DeHum Setpoint, and RHDB defines the width of the Hysteresis Band.
SPRH must be set in the Humidity Submodule; this defines the Humidification Setpoint. Ensure that there is a Deadband left between SPRH and (RHSP - half of RHDB) to ensure that cycling does not occur. In the example given, SPRH is set to 50%, RHSP to 60% and RHDB to 5%, thus giving a 7.5% deadband between Humidification and DeHum.

Set SPDB in the Humidity Submodule to zero; this ensures that Dehum Control in the Submodule is disabled, which would otherwise conflict with the AHU Controller’s control regime.

Close Humidity Control Mode

If a more accurate control over humidity levels is required (at the expense of energy efficiency) Close Control may be adopted. Here, the AHU Controller performs only temperature control , whilst the Humidity Submodule takes care of Humidification and Dehumidification. Both Humidification and DeHum cycles employ continuous control using a Fuzzy Logic loops, so that increasing deviation below Humidification setpoint will result in a proportional increase in steam / water vapour into the supply air.

The Dehumidification control loop will cause the AHU Controller to override its temperature control, a Maximum function is applied to the 2 cooling demands (one from the temperature control loop, one from the humidity control loop) and the highest demand will be used to set the Supply Air Temperature setpoint, thus as dehum demand rises, the Supply Air Setpoint will be depressed, gradually condensing out increasing amounts of moisture from the Supply Air. During this process the heating temperature loop stays active to reheat the supply air if necessary to maintain supply air temperature.

The problem with this approach is that the rate of condensation from a coil is a non-linear process, and it is possible that, for significant periods, the Humidity loops will settle in a state where the cooling coil is partially open, providing minimal dehumidification but still requiring re-heat by the Heater Battery.

Parameter Settings for Close Humidity control mode

RHSP and RHDB must be set to zero in the AHU Controller; this will disable the AHU Controller’s own DeHum function (see On/Off DeHum control mode). The DHDM parmeter in the AHU Controller must also be set to 1; this enables the AHU to receive DeHum demands from the Humidity Submodule which will override the AHU Controller’s temperature control.

SPRH must be set in the Humidity Submodule; this defines the nominal Humidity Setpoint. Set SPDB in the Humidity Submodule to a non-zero value; this ensures that Dehum Control in the Submodule is enabled, and also ensures a Deadband exists between Humidification and DeHum. In the example given, SPRH is set to 50%.

Return,Supply Air and Cascade Control

Return-only control

If a Return Air Intelligent T+Rh sensor is wired to the network and Registered to the AHU Controller (with no Supply Air Intelligent sensor fitted), Humidity Control will be based on the Return Air Humidity sensor.

Supply-only control

If a Supply Air Intelligent T+Rh sensor is wired to the network and Registered to the AHU Controller (with no Return Air T+Rh sensor fitted), Humidity Control will be based on the Supply Air Humidity sensor, provided that the RTMD parameter is set to 1.

Cascade control

If both Supply and Return T+Rh sensors are fitted, Humidity Control will be via Cascade Control (provided that the RTMD parameter is set to 1). This means that the Supply Air Humidity Setpoint is determined by the Return Air control loop, within upper and lower Supply Humidity limits set on MXSH and MNSH. This feature can be useful for preventing air with extreme conditions of humidity being introduced into the space, but the limits must be set with caution as they may conflict with the other control functions. Typically, Cascade Control should not be used in conjunction with On/Off Dehumidification mode.

Setting the RTMD parameter to 2 will help prevent “integral wind-up” action in the Return control loop. If the Supply loop is continually at 0 or 100% for long periods, the Return loop will saturate (the “integrating” part of the fuzzy logic loop will wind the output up to maximum) and will take some time to de-saturate. If instability is experienced, try setting RTMD to 2; this will lock the Return loop’s output if the Supply loop becomes saturated.

Return-only control, Supply monitoring

If Return-only control is required, but the Supply Humidity needs to be monitored (but not used as part of the control regime) the RTMD parameter can be set to zero. This means that the plant will control to Return humidity, even when a Supply sensor is fitted, but the Supply Humidity may be monitored.

Setpoint Trim using an external potentiometer

If a 10Kohm potentiometer and a 1Kohm resistor are wired into terminals 5 and 6, the pot will apply a +/- 5 % Rh trim adjustment to the current setpoint when in Occupancy.

Control Mode

The Humidity controller can operate in one of three modes determined by the setting of CMDE control mode.

Driver mode CMDE=0

If the humidifier (Evaporative Cooler) is being used in conjunction with a Dessicant Wheel controller

Closed Loop Humidity Control CMDE=1

The Humidity controller controls the connected humidifier to maintain the Return Air Humidity at Humidity setpoint. The measurement of Return Air Humidity is provided by an intelligent TRH sensor type RHR which must be registered to the AHU controller. (The Humidity setpoint has a deadband associated with it and the controller also provides a network variable output which could be used to control de-humidification this will only become operative if CMDE=2 is selected).

The controller may also be used to control the Supply RH, register an RHS sensor instead of the RHR sensor.

If BOTH Supply and Return RH sensors are registered and the parameter RTMD (return mode) is set to 1 or 2 then the control changes to cascade control with the Return Humidity control loop being rescaled by MNSH, MXSH to create the Supply Humidity setpoint. With RTMD set to 2, if the Supply Humidity loop output reaches 100 or 0 the return humidity loop is locked to prevent un-necessary 'integral type' wind up.

Closed Loop Humidity Control CMDE=2

The Supply DeHum control now becomes active, the dehum output level can be created either from the Supply DeHum loop working to a setpoint offset DHOF from the Supply Humidity setpoint or from the InterCoil temperature control loop which becomes active if a temperature sensor is fitted. Here is a fuller description of control options and how to set up for Close Humidity control.

The Humidity control loops control the connected humidifier to maintain the Return Air Humidity at Humidity setpoint as described above with CMDE=1. If only a single TRH sensor is being used the Supply Loops are used to provide Humidity and DeHumidity control using RHSP and SPDB to create the setpoints. The DeHum output is sent to the AHU controller to modulate the cooling battery.

Water Reservoir Control

The second, channel 2, driver output can be used to control the reservoir solenoid valves. The output will change to 5V (50%) when the supply water solenoid is required and then change to 10V (100%) when the controller has been running the humidifier for a continuous period of 2 hours (configurable using RDLY 0- 10hours). It is intended that a Sontay RM2 relay module is connected to the output and the supply solenoid is switched using the normally open contacts of the first stage relay, and the drain solenoid is switched using the normally closed contacts of the second stage. The second stage can be thought of as 're-circulation mode'. When this stage is on the drain solenoid will be off thus re-circulating the return water.

Options and Product Code

Air Handling Unit Humidity Submodule

HUM / DIN / 3T / [driver option]

Driver options

HUM / DIN / AOP / [driver option]

Driver options

SC Controls Ltd

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