control panel info help

[kdashc]

I am just looking for general information on control panels for closed loop water/glycol systems with a centrifugal pump and a heat exchanger. the water/glycol will be pumped through the system and heated up and then cooled back down with heat exchanger, etc.

Now i am assuming the control panel will be for controling the electrical motor the pump is attached to. My questions are what do control panels for this application exactly do. (ie check fluid temp, or press, or anything else and then shut off the motor or lower rpms or anything else???)

thanks for any help.

 

[DRWeig]

Hi kdashc,

I think you may have the cart before the horse here...

First, you decide what you would like the control panel to do -- write a sequence of operation. Then, the control panel is designed to accomplish your control strategy.

What can be done by a control panel? Virtually anything you can dream of.

Give us your operating scheme, I bet lots of suggestions will flow.

Good on ya,

Goober Dave

 

[kdashc]

drweig i think you misunderstood my post i am asking what is typically controled by a control panel in this situation.

The very generic situation being "closed loop water/glycol systems with a centrifugal pump and a heat exchanger. the water/glycol will be pumped through the system and heated up and then cooled back down with heat exchanger"

If anyone has any experience with this i would appreciate what to know what they typiclly do or see in order to control temp and pressure in the system.

 

[drawoh]

kdashc,

I agree with DRWeig.

What are you trying to accomplish with this water and glycol? What can go wrong with this water and glycol loop? When you answer those questions, you will have some idea of what conditions you have to monitor, and what settings you need to change easily.

I observe you are not a mechanical or chemical person. I suggest that you talk to whoever specified and designed this thing.

JHG

 

[kdashc]

Its a coolant system that the water/glycol is pumped through something to cool it down, and there by heating up the glycol, and then through an air cooled heat exchanger to cool the glycol back down. Its a closed loop system.

temperature is a concern, since the ambient air changes, should i be worried about pressure in a system like this? is it common to have a control panel that senses the temp and then if it goes over/under a certain temp then the pump is shut off, or is it common for the control panel to have a vfd and to just change the pumps flow rate?

 

[zeusfaber]

How much do you know about:

- The rate of heat you're being expected to reject

- The acceptable temperature range for the machine you're cooling

- The volume (hence thermal capacity, hence (with heat flow) time constant) of cooling fluid in your system

- The variability of cooling air temperature and flow.

If the acceptable machine temperature range is significantly wider than the anticipated cooling air temperature range, then there's a good chance you don't really need a closed loop system (the temperatures will tend to self-regulate). You just need your process designers to select their components properly and build in some adjustable valves so the system can be set up properly and adjusted later when all the pipes fur up. In this scenario, your control panel is probably just doing start, stop, maintenance lockout and alarms.

You should only start thinking about closed loop control systems if you need close control of machine temperature, or if there's really very little coolant in the system (in which case, you might ask why).

One silly semantic point (ignore if it will offend you): Closed loop fluid systems (that recirculate the same fluid) don't automatically need closed loop control (that measures a parameter and adjusts the system to maintain it at a nominal value)

A.

 

[drawoh]

... temperature is a concern, since the ambient air changes, should i be worried about pressure in a system like this? is it common to have a control panel that senses the temp and then if it goes over/under a certain temp then the pump is shut off, or is it common for the control panel to have a vfd and to just change the pumps flow rate?

Centrifugal pumps often are used for systems like this because they cannot cause an overpressure condition the way a gear pump might. Is it physically possible for you to change the flow rate? For example, can you change the voltage across the pump's DC motor?

We cannot answer your questions intelligently because we do not know what your cooler is for or where it is being used. Also, we do not know what control you have over the cooler design. Are you selecting the mechanical components? Are you designing the wiring and the control circuits?

What were you asked to do?

This is sort of like me stopping you on the street and asking you for input for my computer.

JHG

 

[IRstuff]

The bottom line, here, is that there is rarely such a thing as a "typical" configuration. Therefore, you need to decide what your application actually needs.

Is closed-loop really required? Most cooler applications that we have are simply on/bypass, i.e., when it's hot, you want the delta T to be close to zero relative to the ambient. When it's cold, you bypass the cooler to maintain sufficient warmth to keep the electronics or sensor paylaod happy.

As a point of reference, see:

http://www.portablechiller.net/portablestationcahnah913.jpg

http://www.thermo.com/com/cda/product/detail/0,1055,10130229,00.html

or do a websearch

TTFN

FAQ731-376

 

[eadwine]

The first question is, "What do you want this thing to do? Then the Control Panel follow suit. Just straight thru cooling with no temp. control? Process side temp control? Coolant side temp control? Temp indication only? Start-stop control only? Temp. control via CV"S or VFD"S? The list can go on and on. Process should be setting these constraints. Talk to them and let them make the call. Then all you have to do is implement the control scheme and the req'd. panel outputs will follow.

 

[jmw]

Water Glycol is a valuable refrigerant because of the low temperatures that can be achieved.
One concern is that if your concentration should change due to excess water getting into the system e.g. as can happen in some operations, refrigerant is a service - its vulnerability depends on what processes it services and how they are established. So, if you get too much water your freezing point may become elevated and you may actually freeze your system.
All sorts of things you have to think about and decide what goes in which control panel.
You could do worse than download a temperature concentration chart to see whether you have any risk areas.

JMW

http://www.ViscoAnalyser.com