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Dehumification System Control

Dehumidification System Control

Humidistats and Energy Saving for Dehumidifiers

DST offers everything from simple hygrostats to PLC-based moisture and temperature control. In most cases, if dehumidification installations are controlled well, you get a very short pay-off time in return. The Energy-saving brochure takes a look at control systems carefully adapted to suit the DST range of dehumidifiers. All variants are available fully assembled and tested. Investing in a good control system can result in considerable reductions in operating costs. At the same time, you are helping to preserve our environment – an important consideration if you hold environmental accreditation, or are thinking of applying for it.

One supplier

The process industry often makes stringent demands of climate – precise regulation is the name of the game. DST offers a number of systems to control both moisture and temperature. This means that you can avoid having to coordinate a number of installations: these will all be optimised and provided by one supplier.

Energy savings – three stages

Three DST control system stages are available. Stage one has been developed to cover smaller dehumidifiers. Stage two has been developed primarily for electricity and gas regenerated dehumidifiers, while stage three is mainly for steam and hot water regenerated dehumidifiers

EH3 Humidistat and Controller

  • Relative humidity % RH
  • Absolute humidity g/kg
  • Dew-point °Cdp
  • Temperature °C / K / °F

Two closing contacts: Possible to choose source from one of the four parameters above to each relay. Used for controlling one dehumidifi er in two steps or to control two separate dehumidifi ers. Can also be used for dehumidifying on one relay and tem pe ra tu re control on the other.

Display and diodes: 2 row display where two parameters can be monitored. Green “Normal” LED and red “Alarm” LED, switches at a set value of any of the four parameters.

Analogue outputs: 2 outputs with Vdc or mA, choose source from the PI-regulator or one of the four pa ra me ters above.

PI – regulator: Controls energy-saving on a three phase dehumidifier or a valve for a cooling coil. Set relative humidity, absolute humidity, dew-point or temperature and EH-3 will keep it constant.

Sensor: Capacitive type moisture sensor from Honeywell with an accuracy of <±2%RH and <±0.5° C. Each sensor comes with a calibration protocol

EH4 Electronic Humidistat

  • Two step humidistat with fast response sensor
  • Two independent volt-free control relays
  • Visible "High RH" alarm
  • Now also for humidification

Two closing contacts: Two independently programmable relays with adjustable hysteresis. Possible to use for both dehumidification and humidification. Suitable for Hi/Lo/Off control of one unit, On/Off control of two separate unit or On/Off control of one unit plus remote high/low RH alarm.

Display and diodes: High visibility RH display (15 mm). Neon lamps indicate relay operation. Display fl ashes if ‘High RH’ set point is exceeded. 

Sensor: Honeywell fast response capacitive type moisture sensor. Factory calibrated (accuracy < ±2%RH).

Optional: available for wall or duct mounting. 



Energy Saving & Humiditiy Control for Dehumidifiers

Energy Saving, step 1

A two-step hygrostat, e.g. EH-3, initially regulates down to approx. half capacity, then in the second stage it regulates down to zero. 

Energy Saving, step 2

A control system regulates the dehumidification capacity from zero up to full capacity by regulating the regeneration heater, in binary or linear fashion, depending on the unit and the type of heater (electricity, steam or gas). The moisture sensor controls the heater by means of a regulator. In other cases, the moisture sensor supplied is fitted externally and wired to the distribution box for the dehumidifier.

Energy Saving, step 3

The system regulates the dehumidification capacity from around 20% up to 100%. Wet air flow, rotation rate of the rotor (in some cases) and the heater’s power output are regulated in parallel, resulting in better utilisation of energy compared with simply regulating the heater. A moisture sensor controls the wet air flow and, in some cases, the rotor speed, via a regulator. The regeneration temperature is maintained at a high level which ensures more efficient dehumidification. 

Alternatively, the dehumidifier can be controlled by an external regulator which emits a 0-10 V signal to the dehumidifier.