tado° + Midea Air Source Heat Pump
Hi folks,
Not a question, just a success story.
We switched from a gas fired boiler to an Air Source Heat Pump (ASHP) a couple of months ago. We'd used tado° in our last house and requested to re-use the same stuff with the heat pump after we moved.
Now, I realise tado° is designed for gas fired boilers and not heat pumps (and a lot of the data in the app assumes as such), but I was really keen to see if we could make it work since we already had all the stuff.
The good news is that it does work very well as the ASHP's controller just expects an on/off from an external thermostat, so that part was relatively straightforward.
The advice we were given is that heat pumps are at the most efficient when they're running 24/7, and they "don't like" heating rooms from cold (given the significantly lower flow temperatures). The heat pump is using weather compensation to dynamically vary the flow temperature on curve of 50°C flow at 0°C ambient (and below) to 37°C at 7°C ambient (and above). We have tado° TRVs on most radiators and a couple of room sensors in rooms that don't have radiators (e.g. hallway). We set the TRV schedules so that pretty much every room (except bedrooms) are calling for heat almost all the time but we vary the temperature by time of day. For example, the lounge is set to be no more than 16°C overnight, 19°C during the day and then 21°C in the evenings. Similarly, bedrooms are set to 16°C during the day, 18°C in the evenings, off overnight, and 18°C when we wake up (and off overnight so we're not woken by the TRVs buzzing on/off).
We experimented with not running the heat pump at night (when the ambient temperature is coldest), but our energy usage on those days actually went up quite considerably, specifically because, I think, the heat pump was having to work so much harder to bring a large body of water from around 8°C up to 37°C or higher first thing in the morning. It seems counter intuitive but it's working well so far.
We make sure there is an overlap in the schedules where rooms are being heated to 19°C+ or allowed to drop to 16°C in order to ensure the body of hot water flowing through the central heating system doesn't drop in temperature too much.
Energy usage is currently coming in below what was estimated for our house - we're using between 8kWh on warmer winter days and 25kWh on the coldest days. It's a reasonably well insulated (cavity walls and 250mm in the loft), double-glazed, ~200sqm detached house built in the 1950s. Our energy performance certificate estimates around 16000kWh heat demand per year.
Happy to answer questions if anyone is curious or wants to know more.
Comments
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Fascinating Ben - thanks. With 37C output I would require around a fortnight's notice to warm up my north-facing lounge! It's your penultimate para that's the clincher for this - my 1930's build with barely a cavity will always be at a disadvantage. Impressed with 25kWh on cold days! What part of the world are you from please?
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How is the configuration of you heatpump and the heating system? Do you have a scematic picture?
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@Herres it's really very simple I think, there's a flow/return from the heatpump and a diverter valve that switches between the heating system and the hot water tank (it can't do space heating and hot water at the same time). The heat pump's controller is constantly monitoring the temperature of the domestic hot water (DHW) store, and if it drops below a threshold (40°C I believe), the controller switches the valve from the space heating loop to heating the DHW (the heat pump also then works harder as the flow temp boosts to 50°C). The external pump for the heating continues running to circulate water round the radiators if tado° is calling for heat.
The hot water cylinder also has an immersion heater that's run on a timer to boost the temperature up above 60°C for 2 hours to kill off any bacteria. I'd like to wire this in so it's controlled by tado°, but that's a little tricky as I believe that'd need some kind of relay.
The heating in the house is all radiators, we replaced 2 so they were sized appropriately. The heating flow and return is 28mm copper with 10mm drops off to the radiators. Flow rate is around 33l/m
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Oh one thing to add is that I think some Air Source Heat Pumps use hydraulic separation on the heating loop so you have a glycol and water mix on the heat pump side and then water (and inhibitor) on the space heating side with a heat exchanger between them. We don't have this because the ambient temperatures don't get cold enough here, plus glycol tends to go a bit "syrupy" and reduces the efficiency. The heat pump will regulate the temperature of the loop itself so as to prevent freezing.
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Interesting, thanks for your explication.0
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Hi Ben. Great to hear this system is working for you. I'm thinking of installing similar in my 1940s semi in the North of England. We get some really cold winters up here and I've heard the Midea units can struggle in those conditions. We've been advised to up size to compensate but I worry it will be very inefficient over the winter when we need it most. I'd be keen to hear your experiences. Have you had any sub-zero conditions since you installed the system?1
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Really glad to have found this post. We have solar PV that has been able to provide almost all our hot water to storage tank needs and I have been wondering what to do when our 15 year old oil fired boiler gives up. I have no intention of replacing it with another oil fired. ASHP are definitely something I would be looking at, glad to read they can work well in UK
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@BenL, thanks for posting this, super helpful. I'm about to get a Midea ASHP myself. Did you have a buffer vessel for yours? Typically during the day I might only have one or two rooms calling for heat, and it feels like it would make sense to have a buffer to draw off initially rather than the heat pump cutting in.0
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This is really interesting, though the thing I wonder most from this is - would it actually work better if the thermostat wasn't actually connected to the ASHP?
It feels like you need to jump through some hoops on the schedule to make sure the ASHP is never switched off by a lack of radiators requiring heat - but if the main thermostat wasn't connected then you wouldn't have to do that. You could have the radiator schedules set to what you want them to be.
Obviously, the main thermostat becomes pretty useless at that point, and I guess you'd need a radiator that wasn't Tado controlled because you always want one radiator taking flow for the balance of the system (at least I think that's a thing - I'm no plumber).
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@BenL Many thanks for writing this up! I'm looking to use my existing Tado on a new install of an ASHP, and so this has been a helpful read.
I wonder if you could share some more on how you have Tado set up? How is Tado wired to the ASHP? Is it doing the calling for heat, or just using it to control the TRVs?
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tldr: Just here to be a good citizen of the internet to say we've since ditched tado° and no longer use any heating controls.
Long version: we ditched tado° entirely in favour of just using weather compensation (so the heating is always on) and using semi-smart non-tado° TRVs as limiters in bedrooms only. Everywhere else is just wide open all the time. Now, we turn the heating on in Autumn, let Weather Compensation do its thing, and then turn it off in the spring.
The TRVs were modulating too much for my liking (could be mitigated by just setting them higher and using them as limiters not targets) and the wireless receiver would do strange things like turn the call for heat on/off repeatedly when the gateway lost connection to the internet (in doing so it actually destroyed a 2-port motorised valve).
So, it kind of got to the point where the tado° features we were using were limited, and it was creating more problems than it was solving.
The moral of the story is that correctly sized radiators and correctly tuned weather compensation is enough on its own. Geofencing is nice but not all that useful for heat pumps given the slow warm-up times.
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A year late in replying but yes, exactly that.
No, we turned off the tado° call for heat on the heat pump controller so that the heat pump was always on
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