Are there any problems using a smart thermostat with an Air Source Heat Pump (ASHP)?

Hiya @chiefmac !

That’s actually a seriously good question and is definitely one I’d not considered before!

I’ve had a look through the T&C for the Zero Carbon Heat Trial which you can check out right here if you’d like to - just in case I could spot any likely answers or clues. I couldn’t find anything obvious in there, but the full answer is probably a bit more complicated than usual.

If you weren’t on the trial, you probably could swap out the thermostat with a smart one without too much trouble, since all it really does is calls for heating when a room gets too cold, and calls for cooling when a room gets too warm. However, being on the ZCH Trial adds a few other factors into the mix like the Kaluza Flex Platform.

I don’t know the right answer to give in this sort of scenario, so I think the best I can do would be to call in some extra help from @Tim_OVO and @Jess_OVO for this one. They’ll probably need to check with a few other teams, but I’ll try to remember whatever answer comes back in case anyone else is interested.

Sorry it’s not quite the answer you were hoping for just yet, but I hope you’re OK with that.

@chiefmac To be honest, I don't think they'd ever know. The installers had the simple Honeywell stat with them to use but were happy to use my Nest stat to control it.

The best controls will be ones that don't allow the pump to cycle too often. I'm considering trying to let the Daikin box control things and utilise a smart radiator thermostat in any room where I want to have a change of temp through the day such as a bedroom. I will compare the energy usage with the pump on for the majority of the time with a scenario with the Nest's on/off control and see if there is much difference.

Hi @chiefmac,

So sorry for the delayed response on this one - we’ve checked in with the Smart Home team who have advised:

Yes -  you can change the thermostat as long as it doesn't 1) impact system performance or 2) prevent the data coming through to the project. The best way to validate this would be to discuss your options with your installer.

Hope this helps you decide on what to do about replacing your current smart thermostat - do let us know the advice your installer gives if you do decide to make a change. 

Thanks @Jess_OVO, that’s really good to know. It’s not something I’ll be doing immediately, but looking to soon. There are various reasons where it would be very useful to intelligently turn on and off heating in different rooms at different times in our house, so I think a Smart thermostat system could save us some money in the long run. I’ll let you know when I get this done. Thanks again.

Hi @chiefmac @nealmurphy and everyone - I’m looking to reinvigorate this topic because I’ve been doing research on it the last few days. Chiefmac did you come to a conclusion about which smart thermostat (“stat”) is best for your home, and the best way to set it up? I’ve been trying to decide which is best for our home because in a few months we’re changing downstairs from rads to UFH. So, downstairs we will have multizone UFH with a manifold and upstairs we will have rads, all connected to our low-temp Daikin ASHP. We want a smart thermostat to schedule and control the temperature in each zone/room from our phones, for the whole house. I’m easygoing on features like controlling DHW, “learning”, geofencing, etc. I’m unsure about the best way to set up the schedules, etc. since our heating has a slow reaction time and we want to minimise heat pump cycles. At the moment I’m focusing on Hive and Heatmiser. I’ve deprioritised Nest, Drayton Wiser, Tado, and Honeywell. For trial purposes we will leave the Kaluza connected. Are there any other brands you would recommend taking a closer look at? And is there any other advice you can share in terms of how to set up the smart thermostat, schedules, zones, etc.? Thanks in advance.

Hi @briannolan 

I probably can't assist too much as I don't have knowledge of Hive. I was looking at a potential switch from Nest to Tado as part of a Living Lab trial, but the benefits (smart TRVs for radiators) didn't seem to be worth the hassle as my system seems to be working OK for me with most radiators open fully and the thermostat controlling on/off times with some weather compensation from the ASHP.

Will be following with interest to see if there's any tips I can pick up.

@briannolan 

Have you looked to see if the Dakin app  controller might be compatible and if it would meet your needs? Never looked at it myself. I assume you are not already using it of course. 

https://www.daikin.co.uk/en_gb/product-group/control-systems/daikin-online-controller.html

@Jeffus - thank you, I appreciate it. I hadn’t heard about the Daikin app until now, but it looks like it’s only software. I could be wrong about this but I think I need additional hardware. Also, my heat pump isn’t listed as one of the compatible devices.

I did wonder how many pumps it covers and what additional dakin equipment in terms of senors might be needed. As it is a beta product it might be worth asking Daikin if they have any suggestions using their bits of kit. 

I only say this as there seems to be some consensus about using the manufacturers weather compensation controls with heat pumps? As soon as you add a 3rd party control you end up with two controllers attempting to work in sync to control the temperature. The Daikin controller will alter the water flow temperature as the outside temperature changes with weather compensation. The third party controller will be doing its own thing based on the temperature you tell it. I am no expert, i would want to know exactly how the two controllers were going to work together and if i was giving up anything in terms of efficiency vs increased control of scheduling etc. I don't know what the optimum solution would be in terms of running costs. Does Hive and Heatmiser work well with the Dakin weather compensation? 

Both Octopus and OVO have been talking about heat pump specific tariffs recently, depending on how your heat pump is currently controlled. It is not yet clear what controls they expect owners to have or if you would end up having to buy another piece of kit. 

Be really interested to hear how you get on. 

Well done for being so green! 

@Jeffus In the words of Greg from Octopus "Let's not try to have all of these special cases, it's bonkers!" His view is to let price be the single optimising factor, so use dynamic pricing and then let your EV, heat pump or whatever work with this rather than the other way around. It makes sense particularly if you've got both EV and heat pump vying for cheap prices at different times.

Agreed it makes sense, but in other interviews just today Octopus have spoken about the possibility of heat pump specific tariffs with their new heat pump offer and their own heat pump controls.

I would take anything greg says with a pinch of salt for the short term. Am sure it will change in the medium term in the way you say. 

Hi @hydrosam thank you for this. At the moment, as far as I understand, I have a Honeywell thermostat with one sensor telling the Daikin controller to turn the heat pump on/off. At least, that was what was installed for the trial - I wasn’t given an option of letting it run without a 3rd party thermostat. I’ve opened the TRVs on the rads all the way so that they don’t interfere with the Honeywell. And then my Daikin controller (model EKCB07CAV3) has pretty basic settings. From what I can tell, it is set to a 50C LWT target when the heat pump is switched on, which it never reaches. In the operation manual it talks about room temperature preset values and an eco:nighttime mode and weather-dependent heating, but even in installer mode I can’t access them.

So, I don’t know how the Daikin controller is handling requests for heat from the Honeywell. Maybe it’s as simple as the Honeywell asks for heat and the Daikin switches on full blast until Honeywell says stop. Maybe the Daikin controller is smarter than that to avoid cycling. I don’t know.

My plan is to swap the Honeywell for a smart thermostat, so that we can zone the house, set schedules for each zone, and control it with our smartphones.

As Neal said, that’s my main goal. I’m not trying to get the highest COP possible, I’m trying to spend as little money as possible, while being sustainable.

So, I’m hoping the thermostat switch won’t interfere with the Daikin side, but I’ll check with our installer, as you rightly suggested.

@briannolan The way the Daikin treats any 3rd party thermostat is a simple on/off. Any hysteresis is controlled within the thermostat, of which the basic Honeywell has none. Our new installer, from Reina Group, told me they tried the more intelligent Honeywell thermostats and they caused havoc with the heat pump cycling. It turns out the Honeywell I had also caused some degree of cycling which is why after some discussion/me telling them it worked better without the thermostat, we removed the thermostat and changed to run in weather dependant mode only. 

Unless you are moving to having a multi-zone system with underfloor heating manifolds, then a smart thermostat system will be controlling TRV’s. From what I’ve researched on heat pumps this can introduce further issues because the smart thermostat and heat pump compete between the pump trying to maintain a steady flow temperature and the radiators shutting on/off regularly interrupting the steady temperature. The way to improve this is installing a buffer tank with a primary circuit to the heat pump and a secondary circuit from buffer to the radiators. But it all starts to get expensive and complicated. But it can work.

So our systems would make a good comparison between a fixed LWT on thermostat vs weather dependant controlled as we have the same systems installed if you are up for sharing some data.

Have you been recording any of the meter readings to work out energy used and energy produced?

What is your heating schedule?

Do you know what the calculated heat loss for your house is? Mine was 8.5kw at -2C, since revised down to 7kw.

Another useful stat might be no. of starts vs running hours of the compressor. (Info>running hours>Feb 22> Compressor)

PS - spending as little as possible is also my goal, whilst being as sustainable as possible is also my goal. 

@hydrosam that’s interesting, thank you. We are changing to UFH with a manifold. Upstairs will be rads, so you’re right, they would probably be smart TRVs to call for heat to that radiator or not, depending on the schedule.

I have no problem with sharing data, but we’re about to start an extension so our data will be meaningless for the next 4 months. I haven’t been recording the data. Our heat loss was 8.3kW at -2.1C at installation. Our heating schedule is 18.0C 06:30-22:30 and then 15.0C at night 22:30-06:30. We experimented a bit with letting it dip in the afternoon, but that’s what it is now. Feb compressor LWT: 52h, DHW 12h, Total: 64h, 467 starts. In case the stats look strange, our system has a part that needs to be replaced, plus our remediation hasn’t happened yet.

I watched one of heat geek's videos on YouTube today, explaining why zoning using TRVs isn't always a good option with a heat pump. It's worth watching if that's your plan @briannolan .

@M.isterW thank you I found it here and watched it, it’s very good. I didn’t know the setback temp should be 2C lower than the comfort temp - mine was 3C so I’ll change it.

I also didn’t expect that having two rooms at the setback temp might result in using less heat energy, but a higher COP and therefore a higher cost. But it does seem to vary from one home to the next and depend on a lot of factors, like how much heat is transferred through internal walls and doors, whether the ‘on’ rooms can still get up to temp without putting pressure on the heat pump, etc.

So, it seems like one option would be to do the same as @hydrosam , basically run it in weather dependent mode only (without any thermostat or zones), and set a LWT target at the Daikin controller. That would heat the whole house, maybe with a setback LWT at night. And another option is to buy the thermostats and/or TRVs and do some trial and error until the system is running efficiently.

To everyone in this thread who hasn’t already RSVP’d, you should consider joining us at our next online event, the first LIVE ‘Share your experience’ with 3 guest speakers talking about their experience and learnings of heat pumps:

It’s on the 2nd of March at 5pm, it’s free, and you can even pre submit a question to be asked on the night here:

• LIVE 'Share your experience' online event - submit your questions to our 3 guest speakers! LIVE 'Share your experience'

Hope to see you all there!

@chiefmac @nealmurphy @Jeffus