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

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:

Hope to see you all there!

@chiefmac @nealmurphy @Jeffus