UKH

Hello UKC Hive mind,

Looking for ideas on whether it's possible to monitor the temperature and amount of hot water in a domestic hot water tank. 

We currently use gas to heat it so know that an hour of water heating will give us about 2-3 days worth. We're about to get solar panels/battery and a diverter which will power the immersion if and only if there's surplus electricity generated. Basically the immersion will only trigger if the battery is full and the sun is providing power that would otherwise get fed into the grid. The immersion/water tank are acting like a second battery. 

Because the amount of time the immersion will run for will be dependent on the sunlight each day and thus variable it would be great to know what temperature the hot water is and how much before getting a nasty cold surprise. 

Any ideas on whether this is possible and if so what kit I'd need to achieve it?

Many thanks in advance.

Fiona 

I have a Raspberry Pi monitoring my CH and water tank, so it’s possible. As for knowing the amount that’s trickier, but I wonder if it’s necessary. The thermocouple (for the Pi) is behind the tank thermostat located about 2/3 of the way up the tank. If that reads anywhere near 50C I know there is enough hot water for a bath. The water at the top is going to be hotter than the bottom, but think that it will be a gradual change so monitoring one point will give an indication of the amount. I’m surprised you can save 2-3 days worth as my old insulated tank ‘leaks’ about 40W/h (but is due to be replaced with a new one).

For a "quick and dirty" solution, Screwfix sell multi-meters which have a thermocouple input and come with a temp. probe. Bodge said probe under the insulation on the tank, and read it before deciding on whether to draw a bath.

(Although the pi linked above gives much more info w.r.t. system performance)

Do a Google search for a "digital LCD thermometer" lots of results for around £3

This is what I use for the same purpose and as above poster said try to get the probe about 2/3 height. Gives a constant readout

Ideally you want a tank with pockets into which you can insert thermometers, but this won't be possible to retrofit.  But placing the probes underneath the insulation, in good contact with the metal of the tank, is going to give you a decent enough measurement.  Owl Intuition do a nice system that integrates with smartphone and, I think, could also integrate with the heating system.

Having said that, if you are on mains gas and grid connected, I would strongly encourage you not to bother with the solar diverter.  It's not going to save any appreciable amount of money, because the price per kWh that you pay for gas and the price you get for exporting electricity are more or less the same.  You will probably never pay for the extra cost of the diverter and its controls.

And it's actually carbon positive.  As long as we still have gas contributing to the UK mix (which is sadly going to be the case for a long time to come) then the best thing you can do with an excess kWh of electricity is put it back into the grid, saving a CCGT somewhere from having to generate it.  Your gas boiler is quite a bit more efficient at turning gas into heat than the CCGT is at turning gas into electricity so you're actually increasing total CO2 by not exporting.

Those diverters should never have been allowed for any property on both mains gas and the electricity grid.  They used to be financially quite beneficial (back when we didn't bother to measure export, so self consumption was effectively 'free' energy) but they don't even have that going for them now.

Hi Fiona,  If it’s an “Eddi” you are using, it has indicator lights on it.  If two blue lights are visible, your water has reached maximum temperature.

It has an associated device “Harvi” which, as far as I’m aware, will give you the info you require, and I think also will switch the incoming power between locations.  It was out of stock everywhere when we bought the Eddi, so we don’t have one.

Would stick on temperature indicator strips be of use? We have them on some pipes at work. 

Your set up looks pretty cool. 

I think our tank is pretty well insulated.  If we put the water on for an hour then we'll get the next two mornings with toasty showers, the third morning will be OK for a quick shower. It will stay pretty toasty for about 48 hours. 

Thank you that looks like a good option, simple & cheap and idiot proof for my pityful DIY skills

I assume you mean like the things you stick on a fish tank? That might work, most of the pipes going too/from the tank are lagged so finding a bare bit of pipe might be tricky though. It would also need a bit of trial and error to work out what temp the water was based on the pipe temp but certainly food for thought if a digital LCD thermometer doesn't do the trick. 

Looks like the digital LCD thermometer option  should do the trick. 

Hi Fiona I have this exact setup. The battery will charge first and this is enough of an indicator of how much has gone into the immersion depending what time that's done. On the app you will be able to monitor battery charge etc. The immersion is set to a max temp so once at said temp it will stop drawing and your setup will start exporting to the grid. So no temperature with this but you'll just get to know your system.