Air handling unit control cabinets
- Interlock: open valve → soft-start fan → supply air; reverse on shutdown. If the sequence is wrong, the cabinet will not execute.
- Temperature control: supply/return air temperature and humidity acquisition; PLC or dedicated controller closed-loop adjusts water valve position
- Freeze protection: when the low-temperature freeze switch trips, the hot water valve is forced fully open, the fan stops, and an alarm is raised
- Fan: VFD speed control automatically adjusts airflow based on temperature deviation; filter differential pressure alarm for maintenance reminders
- Components: Schneider / ABB / Siemens / Chint; brand can be specified, or customer-supplied components shipped to our plant
Specifications
The table below covers 80% of factory distribution room cases. Anything outside it we can still build — those are engineered items, quoted separately, with an indicative price the same day.
| Type | Floor-standing as standard, installed in mechanical rooms; wall-mounted for small fresh air units |
|---|---|
| Standard sizes (W×D×H) | 800×600×1800 / 1000×800×2000 mm, custom build available |
| Enclosure construction | 2.0 mm cold-rolled carbon steel; separate compartments for control and VFD sections; heat dissipation duct |
| IP rating | IP54 standard / IP65 optional (dusty mechanical room environments) |
| Operator panel | Temperature/humidity display, start/stop and mode selection, fault and filter alarm indicators |
| Environmental adaptation | Anti-condensation heater inside the cabinet when mechanical room temperature drops below 0 °C in winter |
| Rated operating voltage | AC 380V / 400V main circuit; AC 220V / DC 24V control |
|---|---|
| Control core | PLC (many I/O points / communication required) or dedicated temperature controller (few points) |
| Fan control | Variable frequency speed control (based on temperature deviation) or two-speed / direct-on-line, configured per unit model |
| Temperature and humidity acquisition | Supply / return air temperature and humidity transmitters, 4–20 mA; dew point and CO₂ optional |
| Valve interlocking | Water valve modulation (0–10V / 4–20mA), fresh air damper and exhaust damper on/off signals |
| Freeze protection | Freeze protection switch (low-temperature cutoff) forces the hot water valve fully open, stops the supply fan and raises an alarm |
| Interlock sequence | Startup: open valve → time delay → fan; shutdown: stop fan → time delay → close valve |
| Communication interface | Modbus RTU / TCP reserved for connection to building BA or a host system |
| Component brands | Schneider / ABB / Siemens / Chint; customer-supplied components accepted for factory installation |
| Two-pipe constant temperature type | Supply air temperature closed-loop control of the water valve; coil shared between heating and cooling; suitable for plants and offices |
|---|---|
| Four-pipe constant temperature and humidity type | Separate chilled and hot water valves control temperature; humidifier and reheat control humidity; accuracy ±1 ℃ / ±5% RH |
| Fresh air handling unit type | Supply air temperature control with freeze protection as the primary function; exhaust air interlock optional |
| Cleanroom air handling type | Constant air volume with variable frequency pressure stabilization (supply duct static pressure closed loop); differential pressure alarm for the high-efficiency filter section |
| Multi-unit group control | One cabinet controls multiple units, with rotation of unit count and centralized interlock management; connects to BA |
| Assembly standard | GB/T 7251.1 / IEC 61439-1 |
|---|---|
| Interlock verification | Verify start/stop interlock sequence and freeze protection override logic unit by unit |
| Routine tests (every unit) | Insulation resistance, power frequency withstand voltage, and closed-loop commissioning by energizing simulated temperature signals |
| Temperature rise | Independent air duct for the VFD section; temperature rise inside the cabinet ≤15 K |
| Documents with shipment | Schematic diagram, I/O point list, interlock sequence description, BOM, test report |
Five steps to specify your run
A configuration summary is generated as you go. It travels with your inquiry, saving a round of confirmation.
Build details
Systems have been in service for decades, and the failure points are always the same few: poor busbar contact, water ingress at the door seal, high temperature rise in the correction cabinet, and mis-phased outgoing feeders. The six hard rules below are written for exactly these points — every cabinet can be traced to them.
On startup, open the valve before starting the fan
Start/stop interlocks are hard-coded in the cabinet: if the sequence is wrong, it will not run — no coil freeze-up, no damper overpressure. This logic does not depend on the operator remembering it.
At low temperature, valve opens and fan stops
The freeze protection switch is wired into a hardwired safety circuit, so it still trips if PLC communication is lost: hot water valve forced fully open, fan stopped, audible and visual alarm. Better to run hot than to freeze and split the coil.
Temperature signals injected unit by unit
At the factory, a signal generator simulates temperature and humidity for closed-loop commissioning; the full control curve and alarm logic are exercised. On site, only sensor calibration is needed.
Isolated air duct for the VFD
The VFD sits in its own compartment with a dedicated air duct, so its heat does not bake the controller; even on hot days in the equipment room, the temperature rise inside the cabinet stays within 15 K.
Individual shielding for analog signals
Temperature and humidity 4–20 mA signals use individually shielded twisted pairs with single-point grounding, routed in separate trays from power cables, so readings do not jump.
Every point traceable
I/O point list ships with the panel: terminal, range, and alarm value for every sensor and actuator point are documented, so the BAS reads to the table.
Photos & enclosure construction
Below are photos taken in our own shop — from the complete unit down to the internal busbars and secondary wiring. Every build detail can be checked item by item.
Image key: 01–05 are shop photos (the numbers match the shot list). The line drawing shows the front elevation of the enclosure; dimensions match the specification table above.
Where these cabinets go
These are the routine applications — we can talk scheme and configuration directly. For the industry view, see the industry pages.
Process air conditioning for plants
The primary solution when workshop temperature and humidity affect the process (coating, electronics, printing).
Cleanrooms and laboratories
Constant air volume with stable pressure operation, high-efficiency filter differential pressure monitoring, and layered temperature/humidity control.
Constant temperature and humidity equipment rooms
±0.5 °C / ±3–5% RH control for precision equipment and metrology rooms.
Commercial air handling units
AHU group control for shopping malls and office buildings, interfaced with the building BAS.
Fresh air and exhaust air interlock
Fresh air damper modulates on CO₂ concentration, balancing energy savings with air quality.
Winter freeze protection
Standard protection for northern equipment rooms and fresh air handling units operating in winter.
Commercial terms
Specification dated September 2026; quotations follow this.
| Drawings & design | Free |
| MOQ | 1 unit (5 or more recommended for production) |
| Production lead time | 15-25 days after drawing approval |
| on-time delivery | 98% |
| Warranty | 12 months |
| Loading port | Ningbo / Shanghai, China |
| Component brands | Schneider / ABB / Siemens / Chint |
| Factory visit & dispatch confirmation | Factory visits welcome; finished-cabinet photos and video before dispatch |
| Capacity | 5,800+ units / year |
Documents for your engineering team
Selection manual, outline dimensions and RFQ checklist — for the customer's electrical engineer. All three documents are being organized by product line; download links go live once complete.
Six questions procurement and electrical engineers ask most
Why does AHU start/stop need an interlock sequence?
On startup, open the water valve before starting the fan: blowing air through a coil that has no hot water yet will freeze and split the coil in low-temperature periods. Shutdown runs in reverse order so residual coil heat dissipates before the valve closes. These sequences are hard-coded in the cabinet — the operator presses one button.
What does constant temperature and humidity require?
Temperature: split-range control of the chilled/hot water valve. Humidity: steam or electrode humidifier, with dehumidification by cooling the coil to condense moisture, plus reheat if needed. ±1 °C / ±5% RH is achievable as standard; ±0.5 °C depends on the room envelope and steam source, so we work that out together at the proposal stage.
How exactly does freeze protection act?
A freeze protection switch (capillary or low-temperature cutout) is mounted on the leaving-air side of the coil. Below the setpoint (typically 5 °C) it opens: a hard-wired circuit forces the hot water valve fully open, stops the supply fan, and triggers audible and visual alarms. It does not go through the PLC — it still acts if the controller fails.
Can it interface with the building BAS?
Modbus RTU / TCP interface is reserved, with the point list mapped to the BAS contractor's requirements; BACnet is handled by adding a gateway. Typical split of scope: we handle unit-level control, the BAS handles global scheduling and monitoring.
VFD or two-speed for the fan?
Choose a VFD for temperature-adaptive airflow and soft starting (better on both energy and comfort); choose two-speed if the budget is tight and only two stages are needed. VFD is already mainstream on large units — we build both panel types.
Can one cabinet control multiple units?
Yes. A group control cabinet centralizes unit staging and rotation, with the unit's own valves and fan on separate output circuits. Above 4 units, or when equipment rooms are spread out, we recommend separate cabinets plus supervisory scheduling; the topology is drawn out in the proposal.
Other cabinet types in the same main circuit
Related products use color-block placeholders for now (product photos not yet complete; they will be replaced together). Internal links will be filled in once live URLs are confirmed.
How this product is applied in the industry
Operating details, cabinet combinations and customization points are covered in the industry application page — go there directly.
Send us the unit drawings and we will hard-code the interlocks to them
Send us the AHU drawings or point list and we will provide a free control solution and interlock sequence diagram · Quotation within 24 hours. Direct from the source factory, MOQ 1 unit, 15–25 day delivery, 1-year warranty.
ISO 9001:2015 · CE(LVD+EMC) · CQC · IP65
When you write, include: single-line diagram or primary scheme, switch room layout, load list, and component brand requirements. You do not need complete drawings — capacity and cabinet type are enough to start.