Hot water

[JonS]

I am in hot water over cold water in the mornings - secondary kids have a greater affinity for a morning shower then primary kids. The simple solution would be to extend the heating period, but I've sold the idea of adaptive heating based on tank temperature and occupancy.

For that I think I need to add an analogue input device (I only have digital) and sensor.

On the sensor front, what is the recommend device?
How would that connect to Idranet? direct connection or some circuitry ? Is there a circuit diagram someone could share?
Would I get better control with more than one sensor? Where should they be placed (top and bottom of tank, flow return from tank ?)
What is the best method to fix the sensor to the pipework? Assume once fitted it should be covered in insulation? Or does that impact responsiveness? Is that important?
I assume I leave the existing thermostat alone as protection, so maybe turn it up so it doesn't affect normal operation.

Wisdom from those who've done this much appreciated
Jon

[chris_j_hunter]

Cortex has a Thermal Store object - so have a look at how it works & what it needs ...

sensors wire to a QAI module - easy to do, need resistor to go with them - see datasheet ...

our 'tank has pockets for sensors - so they can be buried well into the tank, for best sensing, and so also under the insulation, of which more the better (*) - there are three of them, lower, middle, higher ...

we also have clip-on sensors (**) on pipes where they enter / leave the tank - they read accurately only when water is flowing ...

(*) one side effect of having sensors, is that it becomes v.obvious how much heat is being lost ...

(**) Rapid, clip-on temperature sensors / thermistors ...

http://www.rapidonline.com/electroni...m-lead-61-2040

http://www.rapidonline.com/electroni...sensor-26-7476

http://www.rapidonline.com/electroni...sensor-26-7477

[JonS]

Cortex has a Thermal Store object - so have a look at how it works & what it needs ...

sensors wire to a QAI module - easy to do, need resistor to go with them - see datasheet ...

our 'tank has pockets for sensors - so they can be buried well into the tank, for best sensing, and so also under the insulation, of which more the better (*) - there are three of them, lower, middle, higher ...

we also have clip-on sensors (**) on pipes where they enter / leave the tank - they read accurately only when water is flowing ...

Many thanks for the info and the links. I think there are a couple of pockets in the tank and prefer this method to clip on sensors if poss. I need to sus out the cable routing, module placement and get to grips with resistors!

One use for clip on sensors would be to see how long people are showering for ... and offer water saving advice over the intercom!!

Thanks
Jon

[M.Harrison]

Hi - I've done something similar and attached thermistors to the tank inlet / outlets (no dedicated places on the tank to fit). The details given in the Cortex help files mentioned above work spot on. To get round the issues with temperature changes due to water flow I set up a bit logic to trigger the heating. It feeds the inputs from the temperature senors to a mux to produce an average temperature output. This is passed to a threshold gate to compare to the trigger temperature and this is then fed (via a NOT gate to give a TRUE state when temp falls under the threshold) into a time accumulation logic gate which is set for ten mins. So the heating will only come on if the average tank temperature stays under the threshold for a minimum of ten minutes. So far this seems to work very well.

[M.Harrison]

Forgot to add to the above post - the heating trigger also goes via an AND gate linked to house Vacant state to prevent it from triggering when we're away...

[chris_j_hunter]

couple of thoughts ...

sometimes can use a Delay gate, sometimes with a MonoStable ahead of it, depending on signal, to do such timing (the Delay gate doesn't pass on if the source drops back before time is up) ... and another possibility is the Timer with Hold gate ... all horses for courses, of course, and the Accumulator can do transitions as well as time ...

we've added logic to in some situations run a pump for a short spell to improve readings of clip-on sensors, either before the (eg) Thermal Store becomes active, or within the delay / run-on period of that logical object ... our Thermal Store is heated from an ASHP and by solar, and running the latter's pump briefly can give best indication of tank water temperature - clearly, we'd prefer solar heating when it's available, and various sensors plus the weather forecast & other parameters (eg: how many in the house, when baths are wanted, house occupied, etc) can be used to best arrange the use of sources & get best efficiency / economy ...

[JonS]

thanks for the further tips. I'll keep you posted when I break my duck with custom logic. I've got some disruption in the airing cupboard ahead of me, before getting to the logic, the info on the physical side very useful.
Thanks
Jon