Proportional Flow Control based on temp? PID?

I'd really like to make an on-demand water heater to replace my HLT eventually. The original plan was to mount a PID probe into the top of the heating tube near the unrestriced outflow, set my desired temp and control the input flow manually so that I don't under step my temp. However, I thought it might be even more slick to invoke a flow control valve so for strike water and run the element at 100%. My plan A would work OK for me because the flow rate isn't that important to me but if I find a cheap enough flow valve, I'd give it a try. Anyone know of any cheap sources? Many hundreds $$$$ from what I've seen.

As long the operation speed is not a problem I have a low cost solution.

You can use modulating valves from Honeywell or other vendors.
The operating speed ranges from 50-120 seconds (from closed to open)The price range is $80-120.00.
Control voltage, depending on model is 0-10V, 4-20mA, etc.



Cheers,
ClaudiusB

Watch Ebay for "Belimo" brand valves with proportional valve actuator, input is 24 VDC with 0-10V control signal. I have 5 installed on the phase 2 system and average cost was $10-$25 for the 1/2" ball valve versions. If you dont have any luck finding one PM me and I will check the spare parts shelf for one with a proportional actuator.

Very cool. I'll keep my eyes peeled. I still have to have my service upgraded before I get this going anyway. I want to run a 6000w element so I can get decent flow rates. Just for giggles though, does anyone have an estimate of a max flow rate that can be achieved with 6000watts and a 130F rise?

Keep in mind too that a vanilla auber PID won't be able to control analog outputs. You'll have to move up to slightly more expensive temperature controller. Love Controls offers some affordable solutions with current outputs.

I still have to have my service upgraded before I get this going anyway.

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Whenever you are ready for your service upgrade let me know...

It would be slow. We use these Titan Heaters in Guatemala model N-120 with has dual 5500 watt 208V elements run on 240 circuits. Running a standard shower you simply just use all hot or a crack of the cold water.

Niagara Industries Inc

Bobby_M said:

I want to run a 6000w element so I can get decent flow rates. Just for giggles though, does anyone have an estimate of a max flow rate that can be achieved with 6000watts and a 130F rise?

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Don't know how correct I am but I would take a stab at it using:
Power = Specific Heat * Fluid Density * Volume Flow * Change in Temperature, which can be rewritten as;
Volume Flow = Power / (Specific Heat * Fluid Density * Change in Temperature)
So that would be: Volume Flow = 6000 / (4185 * 1000 * 75) = 1.91*10^-5 m3/s = 1.15 ltr/min
(metric units ofcoarse)
That is the theoretical maximum but the it will be less than that because of effeciency, heat loss, etc.
Also somebody correct me if I'm wrong:cross: