I started with a Hive thermostat because I had that with my previous LPG setup. I wasn’t happy with it because it’s too fine-grained for the heat pump i.e. it stops heating when 0.1c over target and starts again when 0.1c under; my HP has a high start-up cost so I don’t want it starting a lot.
So I called Samsung support who recommended I get a different thermostat with a wider “dead zone” i.e. maybe +/- 0.3c.
I bought openenergymonitor.com‘s wifi mqtt relay thermostat via the Shop link at the top of this page but before I fitted it I was accepted to join a pilot trial for shifting energy demand for heat pumps away from peak times. This pilot asked all participants to use a Tado thermostat which they provided and installed for free. I don’t like the Tado, I think the Hive was better, and look forward to the end of the pilot so I can replace it with the new one that’s gathering dust.
The external thermostat (smart or not) wires into the connections in the bottom of the large indoor control unit. You can use a conventional thermostat too but if you want the thermostat to be in a different room you may as well get something wireless.
Don’t get a Horstmann! My mum inherited one of these when she moved into a new house and it there was nothing intuitive about it at all!
Interesting comments about thermostats - in general any commercially available thermostat will be incompatible with the need to run ASHPs on long cycles. They all seem to be designed to manage systems that have gas or oil fired boilers that can be turned on and off pretty often without hitting their performance. So as you say, narrow dead zones (as you put it).
In addition to that, they’re mostly ‘smart’ these days which can mean anything. The first ones we had were Warmup devices which would kick in anything up to an hour early to get to the desired temperature in time. Useless when you want to run the ASHP on the cheap overnight Octopus Go tariff. The ‘smartness’ wasn’t overridable so they’re gathering dust in a box somewhere.
They were replaced by Tado’s - you can override the smartness on them, so they only call for heat on the schedule. We’ve set the desired temperature higher than we want, so that they don’t oscillate about the set point, turning the ASHP on and off. A compromise but hey… We don’t find the Tado’s too bad btw, except for some weirdness on the display of the temperature graphs and that we don’t think the humidity readings are correct.
Looking at the wifi mqtt relay thermostat though, gave me a duh moment though!! Because our thermostats are wired, I’ve been looking for an off the shelf standard thermostat but of course I can use the wiring for a DS18B20 - two wires are enough - so by putting the relays in a din rail enclosure next to the wiring enclosure, I can wire them to the UFH wiring centre and site the DS18B20s in the back boxes where the thermostats are wired to. I’d have to cover the back boxes with cover plate, probably modified to get some airflow but then we’d be able to manage the setpoints and have a much wider dead zone.
Apologies Ian that this is almost certainly no help for you I hope you do eventually get to the bottom of how to manage your system.
That’s kind of how were are using the Tado - when heating to a temperature, the first hour in the schedule is set high, then the rest of the schedule is set to the real desired temp.
Apart from that, the other things I don’t like about Tado are:
it overshoots for instance we keep finding ourselves too hot and it still calling for heat at 20.6 when 20.2 is set. I’m going to try reducing the 20.2, see what happens.
I can’t find a way of changing the boost time so it seems the boost only works for 30 minutes. On the Hive we could boost for up to 2 hours.
On the other hand the Hive only allowed setting temps in 0.5c increments so Tado beats it there.
I like your idea about using existing wiring. I have none unless I reuse some wiring a previous inhabitant put in for surround speakers.
Edit: I also liked the Hive’s ability to advance to the next item in the schedule i.e. the heating’s due to come on in an hour but I can bring that start point to now.
I have some BLE temp and Humidity sensors and a small wifi relay board to do the switching. Logic/schedule comes from Home Assistant with the Generic Thermostat component. The old thermostats are still there in parallel so if the IOT stuff goes down (even though local not cloud) I can still control the heating!
We have a massive insulated slab with UFH, so overshoot happens a few hours after we’ve pumped more heat into the system! But we seem to have found a happy medium where the setting gives the overshoot we need!
Surely if you have Tado’s in place then they are switching the 2 wires to the wiring centre and you can use those?
I’ve been experimenting with a Sonoff temperature and humidity sensor (SNZB-02 - SONOFF Official) - they are really tiny and could be stuck on a wall, or just stood on a shelf. You need the zigbee hub to capture the data of course and you’re also, like the Tado’s, reliant on their cloud. For the worried amongst us Tado is in Europe, so covered by incredibly stringent privacy regulation. Sonoffs work through the cloud in China.
So now I have 2 solutions!! Thanks for the prompt.
I have do something similar, using an old Pi with a bluetooth dongle to read the values from BLE hygrometers and posting them to emoncms. The average temperature is then used to adjust the flow temps of the heat pump and to turn it off when not needed (by poking manufacturer’s cloud service).
Only trouble I have is when a battery dies in one of the sensors; I’ve just purchased a pack of fresh ones!
I currently use a simple Honeywell radio controlled relay switched “thermostat”.
I am considering using a “smart” European 240 vac Thermostat.
The USA uses smart Thermostats with a 24vac rating.
Do I need a transformer, or a Samsung Thermostat convertor, to provide 24vac for European smart Thermostats?
Some Heat Pumps can be controlled by a continuous voltage or Pulse width control.
Samsung provide a “Thermostat convertor” using the F3/F4 control lines allowing continuously variable , not only switched, power control.
Be careful what you wish for ‘smart’ doesn’t necessarily convert to intelligent when coupled with an ASHP. You could end up with the worst of all worlds. ASHPs need to run long and not be cycled on and off - many, if not all commercial smart thermostats will end up cycling due to very narrow dead zone as Christian mentioned. You’ll also find that if you want to make sure your ASHP is running only on a cheap overnight tariff, then the ‘smartness’ will thwart you. Our initial thermostats would turn on anything up to an hour before the scheduled time in order to get the rooms to the desired temperatures.
Would be interesting to hear from anyone that has found a commercial thermostat where you can adjust the dead zone to make sure that the ASHP runs efficiently. I’ve looked around and haven’t found one - so we use one where some of the 'smart’s can be turned off and we manipulate the schedule and target temperatures to meet our needs and the structure of the build. Ours isn’t a typical build at all - minority sport, this energy saving business - so there aren’t commercial thermostats on the market to suit our situation. And yes, I’ve looked in more energy conscious countries but still haven’t found anything. We’ve effectively got about a 1000 old fashioned storage heaters in our slab which unlike them is highly insulated…
So, the best bet for anyone trying to optimise a similar system would be to go the DIY route, as @borpin has done.
My “installer” has just E-mailed to say that " a new replacement “manager” has been appointed to replace Tony Dunn , the former “manager”, who was blamed , and fired, for the fiasco in installing my Samsung Heat Pump.
The new “manager” is trying to get Samsung to “inspect and repair” my Samsung Heat Pump.
Eight months and counting!!
The "instability " I have encountered with the Samsung could be reduced with the provision of a “Continuous” Thermostat control.
A suitable control could be interfaced using the Samsung “Intesys” KNX to F3/F4 converter. F3/F4 is the Samsung RS485 control bus.
Any Thermostat using a continuous KNX interface could then be interfaced to the Heat Pump.
At risk of being off-topic, I mostly Avoid thermostats because I run the house heating “normally Off”, “unless there are Renewables Available”, “except when it gets too cold”. The default heating plan is to go out for a walk, and the house quite often feels warm enough when returning to it.
I avoid thermostats because “a thermostat is a hypervigilent sales rep for the electricity company” which always tries to turn up the heating just in case someone might want it. I prefer to use heating mainly “if necessary”.
After that puritanical greener-than-thou claim, I did run the gas central heating for an hour this morning (and to get a hot bath) and I do presently have the air-air heat pump ( 0.7kW electrical 2.2kW thermal ) on in the room which I am in aiming for 21C at its built-in thermostat. Room temperature looks like about 19 or 20 C. It was about 14C in here overnight unheated.
I totally agree with your comments about the unexpressed, hidden, motive of the Energy companies in trying to get the user to spend as much as possible on Energy.
The Energy companies well know the importance of energy saving , but have an obvious motive to get the user to spend as much as possible on their energy!
I also, take long walks , with my walk preceded by Switching my Samsung Heat Pump into outing mode.
Outing Mode drops the Flow water Temperature to 15 C.
I also, further, have invested in an all over Thermal insulation outfit, with a not to fetching Thermal vest complimented with an equally not fetching industrial thermal Trousers.
Very interesting thread. I don’t yet have an ASHP but I have been researching towards getting one and shared the concerns expressed here over whether common smart thermostats were suitable such as Tado, Nest, Drayton, etc…
FYI - The Tado supports both ye olde call for heat control which would likely overshoot but also supports OpenTherm and eBus control. These are modulating control methods designed to prevent overshooting but not all heat sources e.g. older boilers supports this method of control and I have not been able to establish if any ASHP systems do.
Tado themselves say they do support ASHP but there is support and there is optimised for and clearly it sounds like it is not optimised for ASHP.
Resideo probably better known here as Honeywell have a new Evohome Smart Thermostat they claim is designed to specifically support ASHP as well as traditional boilers. See -
This based on their claim is interesting but I have not seen any independent reviews to substantiate this yet.
@iantelescope You apparently have a Samsung ASHP. I have been considering a Samsung Mono HT Quiet along with their ClimateHub but I cannot find any installers in the London area I would have confidence in. Would you or anyone else here have any suggestions?
With regards to Samsung ASHP any thoughts over whether to just stick with their own thermostat?
