Merlin Controls
Most fan array companies bundle controls with the fans and the bulkhead and sell you the whole thing. Merlin doesn't. We supply a field-installable controls package (Control Panel and QCB) that integrates with any AHU's installed EC fan array. The controls are the product.
Who this is for
OEM Reps (field retrofit)
You're replacing a failed fan section in an existing AHU at 11pm on a Friday. You need a controls package you can wire in fast, with IP54 plugs that survive a real mechanical room and MMPs you can reset instead of fuses you have to source on a Saturday.
Rep Platforms
You sell across multiple AHU manufacturers and product lines. You need one controls platform you can quote across all of them: same documentation, same BACnet integration, same field service experience, regardless of whose cabinet ships.
OEM AHU Manufacturers
You build air handlers. You've already engineered the bulkhead, the cabinet, the airflow path, and qualified your EC fans. What you need is a certified, scalable, A2L-ready controls package that integrates without forcing you to requalify your fan selection.
What ships in the box
Product photo · Pro Control Panel, front view, door open showing internals
PlaceholderHardware quality without the brain.
The PLC brain, plus everything an engineer wants to specify.
For specs no standard tier covers.
03 / Controls Architecture
Five sub-sections. Each compact. Each documented. Engineers writing sequences of operations should be able to verify Merlin behavior from this page alone.
Pro and Elite. Mode is selected by the Service role on the HMI, or via BACnet from the BMS.
Door-mounted Bypass switch transfers control to the front-panel potentiometer. For commissioning, testing, BMS outage.
Fixed speed command, no closed-loop modulation.
Closed-loop modulation to a CFM setpoint, measured via array-mounted airflow sensor.
Closed-loop modulation to a local static pressure setpoint, measured at the array.
Closed-loop modulation to a duct-mounted static pressure setpoint.
Efficiency-priority modulation behavior.
Hard ceiling on airflow regardless of demand signal.
Two independent chains, separately wired, separately reset.
High-priority chain (series)
High-limit thermostat, low-limit thermostat, freeze stat, door switches. Any open commands a full stop. Auto-resets when the chain restores.
Low-priority circuit
Fire alarm input. Asserting holds the system in a stop. Auto-clears when the fire alarm clears.
Each override is a programmable digital input, configured via the HMI by the Service role.
Override 1
A2L-compatibleProgrammable digital input with full behavior matrix (speed, mode, alarming, duration). Accepts A2L refrigerant detection signals, fireman's override sequences, smoke detector chains, demand-response, BMS-driven mode change, or any auxiliary signal the spec calls for.
Override 2
A2L-compatibleIdentical to Override 1. Two equivalent inputs so the spec can mix and match: one for A2L and one for fireman's override, two for redundant A2L, one for A2L and one for BMS-driven setback, or any combination the project needs.
Each override has a custom behavior matrix: speed, mode, alarming, and duration, all programmed by the Service role at commissioning.
Native protocol support plus legacy relay outputs.
Native BACnet MS/TP
PLC port J25
Device Instance default 5, configurable.
Modbus RTU
Internal
Between the PLC and the fan array.
50+ BACnet objects
Array · per-fan · system
Array-level (airflow, static, power, voltage, current, fan quantity), per-fan (15 alarm categories × 30 fans = 450 multi-state inputs), and system-level (running, Bypass position, control mode, Run Permissive).
Hardwired relay outputs
3×
For legacy BMS integration without BACnet: Array / Running / Alarm.
HMI mounted on the cabinet door. Basic on Pro, touchscreen on Elite.
Role · User
Role · Service
Three tiers, applied to controls
Hardware quality without the brain.
No PLC. No BACnet. HOA bypass switch, potentiometer, single safety circuit, Start/Stop. Same QCB, IP54 plugs, resettable MMPs, and multi-brand EC fan support as Pro. For projects that don't need the brain but won't compromise on the hardware.
Everything you actually need to specify a fan array.
PLC-driven, BACnet-native, seven control modes, two-level safety, per-fan diagnostics, basic HMI on the cabinet door. The tier most consulting engineers end up at, and the controls package most OEM AHU manufacturers integrate. Pro is the default; Essentials and Elite are the exceptions.
When the spec asks for things no standard tier covers.
Everything in Pro, plus custom I/O capability, balanced power operation across the array, the deepest diagnostic logic, and a touchscreen HMI. For premium custom AHUs, mission-critical applications, semiconductor cleanrooms, healthcare critical environments, and any spec that asks 'can it also do this?'
Integration & support
