Air Mixing with Belimo Driven Louvres

Many Potato Stores over the last twenty years have been fitted with motorised louvres (to provide “Air Mix” capability) driven by BELIMO type actuators.

The most common model employed is the Model SM240 (15Nm). While this an inherently good product it is sadly miss-applied in the Potato Store role.

Belimo SM240 Actuator 15Nm

The weakness of the Belimo actuator is in its core design that is a slipping clutch that protects the motor against excessive loading. i.e.: It is designed to STALL! Air Mixing systems which use a “Time Pulse Movement” (the majority) have to rely on all of the louvres moving an equal distance on each time pulse. If they do not the louvres quickly become out of synchronisation and no effective air mixing can take place. Worse still, there is a very real danger of structural damage to the building fabric. This normally takes the form of a blown out main door or louvre vent blades. The classic symptoms of this are huge difficulty of opening the fan house door because the fans are struggling for air.

Because the Motorised Louvres required for Potato Stores are normally fairly large the loading required to move them (mechanically and against air pressure) is beyond the Belimos' 15Nm capability.

Farm Electronics can provide a Retro Fit solution to the Belimo type louvres that can give good Air Mixing results.

The method of achieving this is as follows.

All the Belimo drive motors must be exchanged for the Belimo “SR” type which are physically the same but allow the actuator position to be determined by a proportional 0-10volt input. We also recommend using GM240A-SR model that at 40Nm is more than twice the strength of the SM240 that enables stiffer louvre linkage to be operated.

Belimo SM24A-SR Actuator 40Nm 0-10v Proportional Control

A new PLC interface needs to be installed which sits between the Store Controller and the Belimo louvre motors. This PLC converts the “Louvre Time Pulses” into a “Voltage Pulse”. The Belimo motors are now instructed to go a pre-set voltage angle. This means that even if a particular Belimo motor goes much more slowly it will eventually reach its correct position (or degree of opening). The existing wiring to the standard Belimo motors can be easily modified to operate with this system without any additional cables being required.

PLC Air Mix Time Pulse to Analogue 0-10v Converter

The cost of a conversion of this type would be around £2500-3000 for a typical 6 louvre system. (that is replacing the Belimo motors and fitting the PLC interface)

While this might initially seem expensive it will transform the performance and efficiency of the Belimo Air Mix System, and compared with replacing the controls and louvres themselves, very cost effective.