I’m after advice for a wall thermostat to maximise the use we make of the solar heat we generate from our thermal panels. Here’s the issue:-
In an Alpine climate, on sunny days, our solar system generates lots of lovely hot water. However, production stops when we run out of cold water to heat, and when this happens I’d like to use the excess to start the UFH, using the wall thermostats connecting to the bottom of the water store tank. We can already achieve the same manually when at the building by looking at the temperature stats on the water store, but we’re often not there so would like to do this automatically, and be able to monitor over wifi.

Currently we have 3 (non wifi) thermostats over the building (one on each of the 3 floors), and they are set to start the heating when the building is used most of the time (post 4pm, and pre 9am). On cloudy / foggy / snowy days I want to keep the heat in the tank, so it’s ready for night time heating / DHW, when it’s needed most. Note the DHW and UFH comes from the same tank – see below.
I’d like to find a Wifi connected smart wall thermostat that connects to our Akvatherm 1000ltr water store, so we can:-
1) Control Wall Thermostat remotely via Wifi, and be able to set rules such as: if temp > 35 degs at bottom of tank between 10am and 5pm then direct heat to UFH.
2) Control the immersion heaters on the water store remotely (the Akvatherm water store has 2 immersion heaters, 6kw each – one for DHW, and the other for heating backup), and check they are working properly.

I looked at the Nest system, but not sure if this will work for what I want to do (but maybe it does…). There seems so many thermostat variants out there, and am very confused which one would work for our situation. HELP!

Description of system & environment
French Alpine chalet for 12 pax (170m2 – 6 bedrooms), situated at 1350 meters. Heating & DHW load required early morning and post skiing (post 4pm). Usually most people are out in the day. Some weeks have zero occupancy, so much reduced DHW load – in these weeks, we have very little cold water to heat for the solar panels to heat.
Power generation: Solar array of 17.5m2; woodburning fire (16 KW); 2x 6KW immersion heater electric backup for DHW & heating
Heat Storage: water storage tank (Akvaterm 1000 ltr) plus thermodynamic store of 250ltr acting as a pre heater. The Akvaterm supplies DHW from the top of the tank, and feeds building UFH from the middle of the tank (as per manufacturer’s spec)
Other: x3 wall thermostats to control UFH. Currently set to times when heating is most required (morning / evening, with lower temps in the day). No direct link from thermostats to water stores, but it would be good to have this.

S.T. = +1

sounds like OP needs a three-way temperature-controlled diverting valve, on a stub in the bottom of the DHW cylinder. When the latter gets up to temp, the valve switches and sends the solar feed to a separate thermal store for the UFH.

or something...

http://cgproducts.johnsoncontrols.com/met_pdf/977320.pdf

gg

Posted By: Ed DaviesI can't really see the problem that ST and gg are worrying about as the stratification in the heat store should be enough to keep things apart suitably.

If we change 'stratification' to 'gradient', then you need quite a large gradient, around 40°C I would think. This probably does not happen unless the vessel is very tall. Would have to try and model it to see if what I mean makes sense.

Do you know your DHW usage? i.e. how much water at 50 or 60° do you take out of the vessel every day.

Posted By: Ed DaviesI can't really see the problem that (...) gg (is) worrying about as the stratification in the heat store should be enough to keep things apart suitably

Well, apparently not, since OP says :

Posted By: gohuwgoproduction stops when we run out of cold water to heat, and when this happens I’d like to use the excess to start the UFH, using the wall thermostats connecting to the bottom of the water store tank.

To me (neophyte...) this suggests that the capacity of the thermal storage (or more to the point, the upstream SHW tank feeding into the thermal storage) is too low, for OP's solar thermal potential...

Whence my agreement with ST's proposition of needing a second storage to separate the DHW from the heating...

(at the time of my suggestion, I had not devined that OP *was* actually using a second storage for his solar HW)

gg

Posted By: gohuwgoIn an Alpine climate, on sunny days, our solar system generates lots of lovely hot water. However, production stops when we run out of cold water to heat, and when this happens I’d like to use the excess to start the UFH, using the wall thermostats connecting to the bottom of the water store tank.

This can probably more easily be achieved using the solar controller. Most have a heat "dump" or "diverter" function which can be activated when the main thermal store is satisfied. This output could be used to start the UFH, overriding the heating controller &/or room thermostats. Although you would need to think about how to avoid over-heating.

Posted By: gohuwgoWe can already achieve the same manually when at the building by looking at the temperature stats on the water store, but we’re often not there so would like to do this automatically, and be able to monitor over wifi.

Remote monitoring is a lot easier than remote control. Do you really need remote control? Do you really want to be sat there waiting for the tank temperature to get to the right point before remotely throwing the switch? What happens if you're at work, on holiday, ill, etc?

From a technological point of view, remote control over the internet is almost trivial. The problem is integrating all the different pieces of hardware with different electrical interfaces, voltages, polarities, etc and controlling this from a common software platform. You either do it yourself as Ed describes or pay a lot of money for someone else to do it. In the latter case you will likely be forced to change a lot of the hardware to make it compatible with their software!

And watch out for them removing support at a later date. Product life cycles in consumer electronics are a lot shorter than those in houses & heating systems.

David

Posted By: gyrogear: “To me (neophyte...) this suggests that the capacity of the thermal storage (or more to the point, the upstream SHW tank feeding into the thermal storage) is too low, for OP's solar thermal potential...”

If the store is large enough to deal with the evening and next morning's DHW and UFH needs, or whatever the criteria are, then it's large enough. Making it larger just to store more heat because it's available is pointless - much better to move the excess available heat to storage elsewhere like in the floor slab, walls, etc, where it's more useful. That's the control problem which the OP is asking about.

Posted By: davidfreeborough: ”You either do it yourself as Ed describes or pay a lot of money for someone else to do it. In the latter case you will likely be forced to change a lot of the hardware to make it compatible with their software!”

If a completely DIY solution is too much then maybe something can be done using:

https://openenergymonitor.org/emon/

I haven't yet explored what they do properly yet but they do do some control functions. I think MQQT (which they use) integrates with IFTTT somehow.

I share DavidF's scepticism of basing the system around some web service that could go away any time. I feel this sort of thing ought to be able to run autonomously, without an internet connection, in a reasonably sensible manner and that any connection is just used for monitoring and tuning. Having a third party involved is a potential source of headache but sort-of handy to get round the hassles with IPv4 and NAT, etc. Beyond that I don't see the point.

Posted By: Ed DaviesIf a completely DIY solution is too much then maybe something can be done using:

https://openenergymonitor.org/emon/

I haven't yet explored what they do properly yet but they do do some control functions. I think MQQT (which they use) integrates with IFTTT somehow.

Thanks for that posting, Ed. They didn't do much in the way of control as far as I knew so your post prompted me to check. Things appear to have moved on. As well as the MQQT interface they also seem to interface to Lightwave RF - https://guide.openenergymonitor.org/integrations/lightwaverf/ - which may well mean emon etc could be used to meet the OP's requirements.