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Controlling air ventilation unit

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I have a house project and at the moment air exchange is not working properly. Ventilation system has 7 three-phase electrical motors, which are connected with belts to the rotors. Current system is very old and my aim is to improve it with Unitronics V350-unit which I already have.


I would like to do following:


- To control RPM of the motor with proper inverter.

- Measure temperature-, humidity- and CO2-levels. If possible, measure particles (smoke detector).

- Change settings based on current time, day and season.


I would expand system with remote control and monitoring later on.

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Hello Maakari,


You have many choices available to you.  You did not say what model of V350 you have so you need to post that here so we can see what its capabilities are on the hardware.  However, as a general statement, with 7 different driven motors involved you are probably going to want to set up communications with whatever VFDs you select to use.


1) VFDS - what do you need to do? Run all seven motors at the same time but at different possible speeds?  Ramp up one motor then when required bring up more and more motors until you are running 6 motors at full speed and just the last one a a variable speed?  Are you going to bring up all 7 motors all the time and make all 7 run the same speed?


2) Sensors - If you have 4 sensor types you need to monitor then you are goint to either need 4 analog inputs to be able to see these or buy sensors that have communications capability and look at all of them over whatever communications protocol you select.


3) Change settings - The V350 mhas a real time clock and UTC time control that if programmed correctly will allow you to make decision by 24 hour time, day, month, year.


If I might be so bold.....since you are looking to replace an old system that sounds like it has no controls at all other than an on/off switch thaqt you try to keep this an uncomplex as you can.  What do you need to respond to and how do you need to respond when it happens.  It is unlikely that knowing what the time is (other than building working hours/days of the week) is of much value.  Just because it is Febrauary 8 today is probably not important, season and month is not a good measure as to what to do.


Think about your project in detail and define what things are important to your process and write back.  We are not able to give useful help without you giving many more details about what, how and why.



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I have Unitronics V350-35-TU24 in use.


  1. I need to run all seven motors simultaneously with different possible speeds. Used variables for speed are dependent on usage of specific workspaces. There are several shops, offices and the bar in the building. I want to modify ventilation in order to reduce running costs. Right now the motor is only running on high speed, but I would like to reduce the speed for the night.
  2. Which kind of sensors would be generally recommended? I have discussed about active sensors with a friend. I'll likely use Ebay as a place to buy sensors.

Keeping the project simple sounds like a good idea. I will start with basic adjustments, leaving more complex solutions for later. V350-35-TU24 will be installed next to the motors and motor speed is adjusted with the inverter. Motors will run from 8AM to 4PM at full speed and for the rest of the time speed will be reduced to half.


I have some previous experience with coding and testing with V350-35-TU24. I need to find a good inverter to control 3-phased 380V-motors. Would you have any recommendations? All installations will be done by an electrician whom I provide the software to code with. :)


There will be one a document attached to the post. I'll update it regularly as the project progresses.


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  • 1 month later...

Since you are running fans almost any Variable speed drive will work.  I do not know what brands of VFDs are commonly found in your area, but as long as they have a communications protocol to use that you also have available in the V350 they will more than likely work.  You only have 485 or 232 communications in your PLC unless you purchase an adder card so anything with Modbus 485 or modbus 232 will work (485 would be common as 232 has such a short working distance).


In your pictorial you have a note for CO2, Temp, Humidity, that would be up to 3 sensors per zone.  Buying 7 VFDs anf 21 sensors and then putting it all otgether is going to make it difficult to pay for in electricity savings given the small size of all of your motors. 


Since you stated that you are intending to just run at full speed for a set time period and 50% speed at a different time period you have options to save you money.  You can run multiple motors off of a single VFD to lower the number of VFDs you need to run the system.  The obvious downside is that all motors connected to a single VFD must spin at the same speed as each other.  For example if wiring and process allow you to run 3 2.2KW fans on a single VFD you would need a VFD with at least 6.6KW of power capacity (it would be better to upsize slightly. Each motor would need a seperate overload, but with a dedicated overload per motor there is nothing wrong with doing this (as long as you can accet that when one motor is at full speed they all will be and they will all be at 50% at the same time as well.



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  • 4 weeks later...

Hi Maakari,


I do this sort of thing all the time.  At the risk of going outside your original scope, I suggest that it will be far easier and more economical long term to change your blowers to systems based on EBM EC units, or similar units from other makers.  Benefits are numerous with the main ones being far more efficient resulting in very quick payback; no belt maintenance issues; inbuilt variable speed simply controlled by 0-10v, 4-20ma, or bus; no electrical interference issues to deal with at all and will couple straight to your existing 3ph power with likely much lower CBs needed.


You can even have them direct linked to sensors to achieve what you want without any plc input, just having the plc monitor it.  eg  CO2 sensor drives the motor directly so that as it rises, speed increases.  Of course the plc can do this, but it involves more hardware and programming.  Is better, but more complex.  I understand that changing the blowers might be hard, but it will be well worth it.  Quieter, smoother, heaps better all round...can't stress this enough.  By the time you add in all the costs associated to put VFDs in correctly, and ongoing maintenance $s of what you already have, you will be a long way along the cost of changing.  And as well, your motors may not handle a VFD anyway.


On sensors, I recommend going with known brand names.  Speaking from horrible experience, although the pricing is often many hundreds of percent more, you will avoid hassles you might get with lower priced "bargains".  You can eventually get them to work correctly, but have spent ages achieving this when the big $ version just bangs straight in and works ok forever.  Ebay is useful, but on something so important quality is also vital....the usual ebay dilemma...sometimes stuff there is great, sometimes not so good!


Also, don't forget to have outside air intake adjustable via modulating damper.  You have required minimums/maximums to maintain, along with keeping it pleasant anyway.  I think you are going to find that it will end up more complex than you first thought, to make it great.


To finish, I usually end up with the EC's using b/n 1/3 to 1/2 the power for the same airflow.  On something running 24/7 these $s add up quickly.





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  • 1 year later...

I have never used Unitronics before. I am working on a project for a friend on his ancient commercial smokehouse (Eagle spring driven timers is what is used now. Ancient history!). Simple. All it is is controlling 1) an exhaust airflow damper infinitely variable from open/closed and 2) smoke flow damper infinitely variable from open/closed 3) temperature sensing and control 4) humidity sensing and control 4) a circulator fan motor 5) a time of day to start operation clock 6) start the smoke generator. There are 4 water valves that need to turn off/on during the process and for cleanup. I am envisioning the HMI to be through the wall and 20 feet away from the smoke chamber itself with a remote I/O brick at the smoke chamber. All the PLC needs to do is be able to select a recipe and display the 8 parameters of the smoking operation and allow the recipe to be tweeked up or down in value  from the saved recipe (Obviously it does need the ability to create new recipes and save them also). So after all this typing I would like to know what series HMI/PLC/touchscreen/remote I/O block would be recommended by people that have used Unitronics.

Thank you!

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Hi Protea,


before everyone can help, some questions.  How are your dampers controlled?  If they are already done with damper motors, what type/brand, do they use 0-10v, or 4-20ma?  Same for your other bits and pieces.  What runs them and what signals do they accept or output?


In some ways having all the control locally is easier, but you then have to use various types of multicores to your chamber, depending on what is needed.  Yours doesn't sound too large a job and personally I'd have all the control bits local, given the short distance involved.  Others here will likely disagree with this!  That's what forums are about.  But answers first, please. 




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