Quick answer: A good industrial dehumidifier control design decides four things before wiring: what to control (RH, dew point or a process signal), where the sensor goes (in the controlled zone, not at the unit outlet), who decides (the unit's own controller, a PLC, a greenhouse computer or the BMS), and what the BMS sees (run, fault, alarms and data). For simple sites, dry contacts for enable and fault are enough; for monitoring and coordination, use Modbus or BACnet with an agreed points list. Stage several units with deadbands and time delays so they do not all start and stop together.
Quick answer
- Control variable: RH for most rooms; dew point where condensation or low humidity matters.
- Sensor: in the zone that matters, away from discharge air.
- Integration: dry contacts (simple), 0–10 V/4–20 mA (analog), Modbus or BACnet (data).
Choose the controlled variable
| Variable | Use when |
|---|---|
| RH | Rooms with fairly stable temperature: warehouses, offices, storage |
| Dew point / humidity ratio | Temperature varies; condensation risk; low humidity targets; cold stores; BESS |
| External process signal | Drying processes, production lines, greenhouses controlled by a climate computer |
Sensor location
| Location | Effect |
|---|---|
| In the controlled zone at product or crop level | Controls what matters (recommended) |
| Return air of the unit | Convenient; can differ from the zone |
| Unit outlet | Wrong for control: dry discharge air turns the unit off too early |
| Duct (supply) | For high-limit or supply-air dew-point control |
Local control, external enable, or full BMS control
| Arrangement | How it works | Good for |
|---|---|---|
| Local control | Unit's own humidistat and sensor | Single units, simple rooms |
| External enable | BMS or PLC enables/disables; unit controls to its own setpoint | Schedules, interlocks with HVAC |
| Remote setpoint / full control | BMS writes setpoint and stages units | Multi-unit sites, coordinated HVAC |
Staging several units
- Lead–lag: one unit runs first; others start if humidity keeps rising after a delay.
- Rotate the lead unit to even out running hours.
- Use deadbands (for example 3–5 % RH) and minimum on/off times to protect compressors.
- If one unit faults, the next starts automatically.
Alarm list
| Alarm | Action |
|---|---|
| Unit fault (compressor, fan, heater) | Start standby unit; service call |
| High humidity in zone for a set time | Check doors, load, units |
| Drain fault / tank full / pump failure | Stop unit to avoid overflow; clear drain |
| Sensor fault or out of range | Fall back to safe mode; replace sensor |
| Filter dirty (pressure switch) | Clean or replace filter |
| Communication loss | Unit runs on local setpoint; alarm at BMS |
Interface options
| Option | Gives | Notes |
|---|---|---|
| Dry contacts | Enable in; run and fault out | Simplest, very robust |
| Analog (0–10 V, 4–20 mA) | Humidity reading out or setpoint in | One value per wire pair |
| Modbus RTU (RS485) / Modbus TCP | Many data points and settings | Common in industrial equipment (Modbus specifications) |
| BACnet | Building automation standard | Common in commercial BMS (ASHRAE BACnet); often via a gateway |
Related: modbus specifications, ASHRAE BACnet.
Confirm which interfaces each model supports before design; for cabinet and BESS units, see dehumidifier BMS/EMS integration via RS485.
A practical points list
| Point | Type | Direction |
|---|---|---|
| Enable / disable | Digital | BMS → unit |
| Running | Digital | Unit → BMS |
| Common fault | Digital | Unit → BMS |
| Zone RH and temperature | Analog / register | Sensor → BMS |
| RH or dew-point setpoint | Register | BMS → unit (if allowed) |
| Drain alarm | Digital / register | Unit → BMS |
| Running hours | Register | Unit → BMS |
Commission with trend data
Run the system for at least a week, including humid days, and trend zone humidity, unit states and alarms. Check for short cycling, units fighting each other or HVAC, and slow recovery after doors open. See industrial dehumidifier installation site readiness and our industrial dehumidifiers.
FAQ
Frequently asked questions
How do I connect a dehumidifier to a BMS?
With dry contacts for enable and fault, or with Modbus or BACnet for data and setpoints, depending on the unit and the BMS.
Where should the humidity sensor go?
In the controlled zone, at product or crop level, away from the dehumidifier's discharge.
How do I control several dehumidifiers together?
Lead–lag staging with deadbands, delays and rotation of the lead unit.
Sources
- Modbus Organization, Modbus specifications.
- ASHRAE, BACnet (ANSI/ASHRAE Standard 135).
- ASHRAE, Fundamentals of psychrometrics.
