3-way zone valve

Hallo,


I have a problem write a program to contol a 3-way zone valve for my heating installation. This valve has 3 connections (common, open, close). Now to open the valve 100% you must place power for a time of 180sec then power off and the valve stil on 100%.
If you want to go to 50% you place power to te open wire for 90sec and release the power.
How can i calculate and memorise the time and position to open or close the valve?
I have al ready the function to calculate the temperature wat i need but i have no idee to command the valve.

Can somebody help me?

Thanks
Jacques

Probably no need - all three way valves I have worked on (honeywell/danfoss etc) have all had position limit switches for the purpose you describe - why not post the valve details .

Using time "on" in not a good idea. Right now the valve takes 180s, but in future with a little usage, it might be 185 or 175 or 200. What if you have a complete malfunction of the valve and it does not move at all, how would you know?

Yes, use limit switches to detect when the valve is Open or Closed. If the switches are not already on the valve, then add some external switches. Now it will be simple. Give an Open commmand until the "Opened" limit switch closes (energizes). Give a Close command until the "Closed" limit switch closes.

Firstelectric,

The reason to know the position is, as Jacques found, that for a motor-operated valve, you must somehow know when the valve is 100% closed or 100% open. Otherwise, you have no way to know when to stop the motor, and it keeps trying to turn and may burn up.

As for the 50% position, if you really want to know that one, then add another limit switch at the halfway point.

3-way valve

Hallo,

Thanks for all your ansers.
I have post the manual of the valvemotor.
I use this valve for floorheating. The max temp for floorheating is 45°c. I calculate the temperature that i need in the room and then i maesering the watertemperature of the heater. The difference of these two values is the percentage for opening the 3-way valve.
exampl.
heatertemp=60°C
floorwatertemp=30°C -> 60/30=0,5 = 50% valve open

thanks,
Jacques

Curious

10baseT said:

Probably no need - all three way valves I have worked on (honeywell/danfoss etc) have all had position limit switches for the purpose you describe - why not post the valve details .

Click to expand...

So what does one do when the desired output is 37%?

You need a position feedback on the valve. You might be able to run without that by doing 1 second moves and monitoring the change.

What's needed is heat/cool PID.

You would never do that Peter , when using an A , B , A+B type valve , the dynamics of the system are much too complicated . As the volume to A is reduced and B increased , then the return temperature from circuit A increases , and from B decreases , and the total flow through the system increases , it would be a complete waste of time to move to say 37% , and if you did , because let us say circuit B was calling for heat , then what happens to circuit A ? The lag in the system with hot water would be so big as to make positioning and temperature close on impossible.

3 way valves are generally only used to select , not to proportion flows - and are not intended to do otherwise (though I am probably talking out of my hat in this case )
The majority of these valves are fitted with position limit switches to enable the control system to sense the valve position . Individual zone temperature control would normally be achieved with capsule type thermostats.
Perhaps the original poster could post a simple line drawing of what he is trying to achieve ?

Peter Nachtwey said:

So what does one do when the desired output is 37%?

Click to expand...

Doesn't this complicate things immensely?
As I remember, flow through a valve isn't linear at all, and, not being linear, would require some system modeling & control better then PID to get better control afforded by deadband control?

It is , that is why the valve isn't used in this way , normally these valves have a ball inside to select the outputs - so the thing would be completely non-linear from about 0-10% open would equate to 0-100% of flow .

Jacques said he's heating floors. Once when I was in Salt Lake City, I checked out a 6 million dollar house as if I was a prospective buyer (wanted to see how the other half lives!). It had hardwood floors with hot water running through them. This was just to keep the floors cozy warm. Not part of HVAC.
If that's what he's doing, control might no be that tight.

Just a question here... If flow is what you want to control, wouldn't flow be what you would want to measure and feed back to your control?

CroCop said:

Doesn't this complicate things immensely?
As I remember, flow through a valve isn't linear at all, and, not being linear, would require some system modeling & control better then PID to get better control afforded by deadband control?

Click to expand...

First, I consider a 3-way valve a valve that can shift to three positions. Asbuild's valve only lets water flow or not.

Second, that valves I use for servo control should be linear.

Third, Asbuild thinks he can get some sort of proportional control. What hasn't he told us.

I am interested in how the system is designed and how one will control this floor heater. It seems to me that that floor area closest to the source of hot water will be much hotter than the other parts of the floor no matter what one does. I would think there would need to be many parallel pipes. If one can only add 60 degree C water without mixing, I think the floor would be too hot or too cold. There must be a way of mixing water so the temperature can be 40 degrees c.