PID configuration recommendations

[dwoodlock]

So over the last 6 months or so I put together a chiller system for the presses at our facility. some of them use in-die cooling.

I am programming with an s7-1200 controller, g120c drive, and ktp1200 hmi.

The system when operational will have about 300gallon capacity.

Currently I have just been operating the cooling loop in the holding tank, to see how quickly it will cool.

Bare in mind, this is my first project like this, and I just kind of threw it together, and thus far it works pretty well.

Cooling loop consists of (Pump) - (rtd) - (air/water exchanger) - (rtd) - (liquid/liquid exchanger) - (rtd).

My initial belief when I put it together was that I would use the VFD to control the pump speed on the cooling loop based on what the post loop liquid temperature was.

If I needed more cooling, slow the flow, if I need less speed it up. Varying the flow ratio's to achieve my set point.

Since I started toying with the system, I basically wrote some quick code to give it a whirl, and honestly just toggling the valve on the liquid/liquid exchanger that enables the glycol flow seems to work pretty well.

Wondering if anyone with experience and can throw in their 2 cents on this as far as what method they would use to manipulate the liquid temperature. (vfd with the circulation pump OR what I'm guessing would be called PWM with the glycol valve??)

Thanks in advance.

 

[linnemann]

PWM will almost always use more power than VFD (even accounting for efficiency), since you are accelerating to max speed every time the PWM turns on.

So if power consumption and wear on bearings/couplings etc. are not a problem then PWM will work fine.

I would go for VFD just to minimize wear and tear on the setup. Just keep in mind that the pump might have a minimum RPM where it can effectively cool the motor.

 

[rdrast]

I would keep the actual process water loop pump at a constant speed, or even better, pressure. Regulate the VFD speed to hold a target pressure in the supply, or a target supply/return differential pressure.

Then I'd use a proportional control valve feeding the glycol side of the heat exchanger, and control that based on the process water supply temperature.

 

[dwoodlock]

Thanks for the responses.