Exh Fans and Blowers Auto control_Which temperature value should be MASTER

Hi;


In our corrugator plant where the building is pre-fabricated (140M X 130M) and height starts from 6m to up to 13m max, there are many Exh fans and blowers for cross ventilation for which an automation is needed to switch off/on these fans automatically for energy saving point of view.

The outside of department, the temp rises up to max 47c in summer. Inside of department, temperature rises up to max 42c. But if out temp drops below 42c, there is almost 5-10degc temperature difference in between out and inside. For example, this time out temp is 26c and inside temp is 32c & Humidity is 39% and feeling is well. In summer season, the relative humidity also rises upto to 85%. So if for example the inside temp is more than 32c but humidity is > 50%, the Exh fans & blowers should also be working.

As normally operators have no time, no one switch off the fans if temperature is normal, so we are going to install PLC to manage the operation. I am confused which temp value should i consider the MASTER value or BASE value to initiate the work. I am thinking to use this formula;

Avg value = (Outside temp + inside temp + humidity)/3

Then use this average value to start stop the fans. In this way if any of above value changes, system will operate the fans accordingly.

Please share your views. If anyone has already done such kind of project, please share his expert opinion.

Hi;


Any Idea?

It might make sense to zone them if you have lots of fans this would give better control. for example if the fans are reasonably distributed across the area then zone them so each zone is controlled independently based on the readings in that zone.
Although I have not worked on this type of ventilation I have worked on cooling systems for food production and we always control each zone independently even though a particular production floor is open.

I don't do a lot of HVAC controls so my suggestion may not work.

But i don't think your formula there will work. You can't add parameters of different units together, i.e. temp and humidity.

Personally I'd try the following:

Work out temperature difference between in and out. If it's greater than a setpoint, say 5 degrees, then FansEnabledOnTemp = True.

Do another condition for humidity. If humidity is more than a setpoint of 85% then FansEnabledOnHumidity = True.

If both FansEnabledOnTemp and FansEnabledOnHumidity = True then run the fans.

You'd want to add start and stop delays to both conditions, as well as deadbands to stop the fans from cycling on and off too quickly, i.e. if Humidity setpoint is 85 then subtract 5%, to make a stop setpoint of 80%. I always do this kind of thing automatically in code so there's less chance of someone mucking it up.

Does the facility run 24/7? If not then consider adding time controls too to make sure the fans go off at night (although in the temperatures you mention I'd probably only want to work at night!!)

What PLC will you be using?