Hot water temperature control

[johnmck66]

Anyone know how I stand legally by taking out the thermostat from my immersion heater and fitting a PID controlled temperature controller using quality components. I.e. PID controller with comms interface, thermocouples SSR power switching.
I am looking for a more finite temperature on my domestic hot water.

 

[Lectrician]

Get one of the types with a seperate thermostat and overheat cutout - change the thermostat for the probe, leaving the overheat in place.

Ideally, leave the immersion exactly as it is and place the probe somewhere else - a pocket could be fitted to the cylinder if there is not anything suitable (like a disused coil etc).

I would not want to remove the thermostat if it was a combined thermostat and overheat cutout - regardless of how "quality" your controler is, it is going to be ugly WHEN it fails.

 

[Gees]

Anyone know how I stand legally by taking out the thermostat from my immersion heater and fitting a PID controlled temperature controller using quality components. I.e. PID controller with comms interface, thermocouples SSR power switching.
I am looking for a more finite temperature on my domestic hot water.

Do you mean FINE control?
http://www.eolss.net/ebooks/Sample Chapters/C18/E6-43-03-03.pdf

Thats a bit deep for me!!

There are probably commercial stats available that will do the job but one question? How do you get the sensor unit INTO the water cylinder?

 

[holmslaw]

..

 

[Lectrician]

We did the panel manufacture for a small cheese making vat - It had 4 immersion elements heating water which was pumped around the tank in a kind of sandwich.

This needed finite control (as in precise).

We fitted stainless steel elements with thermostats (no overheat), and had two pockets installed on the tank for an overheat cutout and the probe from a temperature controller.

The controller was capable of turning on all elements to get upto temp, but would then attempt to use just 2 elements to keep the temp stable.

We have done very similar things with water for circulation in beer brewing vats, and for caustic wash tanks in dairys for cleaning pipe lines and pasturisers.

 

[Lectrician]

I asusmed open vented, or that he had not decided to remove PRV's etc.

anyway.....

good old myth busters.

http://www.youtube.com/watch?v=68p4ngS-yME

http://www.youtube.com/watch?v=JmJoyuUJj2Q

 

[brig001]

Why control the tank when you can control the temperature of the water instead?
http://www.screwfix.com/search.do;j...tton.x=0&searchbutton.y=0&searchbutton=submit
Maybe ask on the plumbing forum for advice on this.

I don't know if you are using this to control the immersion heater or a boiler, but if you tried to get finer control with a boiler, your gas consumption would go up because of increased cycling.

 

[electronicsuk]

Why control the tank when you can control the temperature of the water instead?
http://www.screwfix.com/search.do;j...tton.x=0&searchbutton.y=0&searchbutton=submit
Maybe ask on the plumbing forum for advice on this.

I don't know if you are using this to control the immersion heater or a boiler, but if you tried to get finer control with a boiler, your gas consumption would go up because of increased cycling.

About to say the exact same things myself. Control the temperature by mixing cold and hot water, not by adjusting the temperature of the water in the cylinder. Besides, it needs to be kept hotter than typical bathing temperature to prevent any possible growth of legionella bacteria.

 

[johnmck66]

I was merely questioning the legal implications as regulations apply.

As for safety measures I already taken those factors into account with high temperature alarming and relevant protection etc, etc.

I have reasons for precise control, which for now prefer to keep to myself.

Thanks for all your replies, all comments will not go unnoticed.

I have many years industrial control experience.

No gas on premises by the way.

 

[electronicsuk]

I was merely questioning the legal implications as regulations apply.

I'm not sure exactly what statutes would apply here. Certainly there are requirements for unvented cylinders, but as for vented... you might be better asking in the plumbing forums.

 

[Stoday]

One fact that hasn't been mentioned: hot water rises. In fact, heating forms a hot top layer and as the tank heats up, the hot layer increases in thickness from the top down. A bit pointless using a PID to control the immersion heater.

The tank will have to be stirred enough to keep all the water at the same temperature before it's worth using a PID controller. The immersion heater should be located in the bottom of the cylinder and 6kW would be a more suitable power.

Hot water should be stored at 60°C or more to avoid the growth of bacteria, particularly legionella.

 

[Lectrician]

A shunt pump is best for that.

 

[ricicle]

A total waste of effort and resources using such a control system for basic domestic hot water.
You would get better results just from adjusting the times that your hot water is on down to the minimum time possible to suit demand, and if possible checking the accuracy of the thermostat every so often.

 

[Lectrician]

I dont think this is for domestic HW......

 

[ricicle]

I am looking for a more finite temperature on my domestic hot water.