First, deeply grateful to all who have in the past posted with such expert wisdom…
Now, to the questions… But first background:
Using an old non-condensing gas boiler; have tried to make the system globally more efficient by zoning and timing and geofencing with a vengeance- all with tado.
Now switching (at last!) to an ASHP. But the house’s inhabitants’ lives remain unpredictable and chaotic- so inclined to continue with tado- but use their “HP Optimiser”.
Three questions follow:
Simplest: has anyone experience of the tado HP optimiser? Putting aside zoning etc for a moment, how does it “optimise” compared to conventional manufacturers’ controls? (Can anyone convince me that its weather compensation, or anticipation of solar gain or learning is superior to, say, Samsung’s or Panasonic’s?)
Dread subject: Volumiser/Buffer. I appreciate that most readers will be anti-buffer. I’m convinced too. The problem is that most installers are pro buffer. Now, given that our circulating volume will change as TRVs open and close, is that somehow an argument in favour of a buffer (rather than a volumiser)?
Simplest: has anyone experience of the Panasonic M series? (Rather strange: its data suggests it pumps out the same heat regardless of conditions- for eg, whether its 7 or -7c, 12kW comes out, either at 55 or 35- can that be true?)
All answers/insights/brick bats gratefully received…
I am using a volumiser in my new home system to guarantee a minimum system volume, and an automatic bypass to guarantee a minimum flow rate. Seems to work well for me. I am trying to establish with some of my PhD research whether volumisers are actually the performance drag claimed. My current thinking is that overall microzoning plus the volumiser to enable that is a significant comfort and energy/footprint win.
I suspect that this is not unusual. The table Samsung publishes for my 8kW HTQ series ASHP shows that energy output is 8kW (or more) over a wide range of ambient temps and LWTs, and the only area where I’d get <8kW is at very cold ambient conditions (below -20degC). What does change significantly is the energy input to the compressor, hence the variety of CoP values.
Another data point: after removing all TRVs, binning off the Tado system and running the whole house as a single zone (open loop, no buffer), our 7kW Vaillant ASHP became cheaper to run and the entire house is at our chosen setpoint temperature, so comfort is hugely increased (never walking into a cold room).
For us, the Tado and micro-zoning was a complete waste of time and money.
Thank you. You’ll have seen that some are sceptical of the benefits of “microzoning”. I suspect that the difference lies in the efficiency of different homes’ insulation. Ours is poor, each room loses heat fast, a simple closed door can sustain a 5 temperature gradient, so there are good reasons to deliver heat only into the rooms actually being used (before it disappears out into the neighbourhood).
Does that sound cogent?
I suspect that if our insulation was better, we’d be able to heat up the whole place and hold it at a reasonable temperature, and then I might join the “chuck tado- waste of time/money” camp.
I guess the overall conclusion is: it’s a very complex system, indeed worthy of a PhD- and that’s why specifying is a challenge for the standard fitters under financial and time pressure…
Without somewhere to emit the heat that your heat pump is outputting, return temperatures will equalise with the leaving temperatures and it’ll cycle. Adding a buffer/volumiser into the equation only delays the cycle the first time until the additional volume is also heat soaked.
If you have zones constantly going in and out of existence, you may find that you’re also constantly cycling. Each time this happens, it seriously impacts the efficiency of the system and completely defeats the purpose of the zoning.
The ‘right’ solution to this is correctly sized emitters and a well calibrated weather compensation curve that ensures you can emit heat into each room 24/7 without any room overheating. A low flow temperature ensures that the cost of doing this does not become expensive.
Here’s where I’m at- if you think I’m miles off course, please let me know…
The facts:
Current ASHPs don’t have wide modulation ratios (pity!), English weather is very variable; most important: the heat calcs suggested a 22kW heat loss- which is completely divorced from the actual real data we have, which stem from our gas consumption…
Over a year, taking the hourly gas consumption from our smart meter, most hours the house received upto 7kWhs. There was only one hour in the whole year when we got more than 9kWhs…
I think that’s probably because of the micro zoning: there are basically three zones in the house: the core, which is always heated (kitchen, hall and bathrooms), the bedrooms and the living areas. So, if the heating is running at all, it heats two zones: the core and one other. Either way that means around 8 rads.
My hope is that we can manage with a 12kW machine; that if the heating’s running, there will be enough (poorly insulated) house to receive the heat (so it shouldn’t cycle too much); and if we’re cycling a lot then we can enjoy the luxury of opening doors in the living spaces on warmer days…
That’s the key: I’m aware of the danger of cycling, and I can see a way to reduce the effective insulation of our house (with more open doors) in a way we’d enjoy- and if that means we cycle less and heating costs less as a consequence, we’d be happy.
Are you planning on receiving the BUS grant as part of your install? If so, you don’t have the option of choosing a smaller heat pump then the survey suggests you require, you must either have the size heat pump as per the survey or get the surveyor to agree to adjustments which bring down the required size.
Assuming that’s not a problem, most heat pumps of that size seem to operate at a minimum level of ~900W input, for a minimum output of around 3.6kW. If you’re able to output 3.6kW through those 8 radiators then great, you could run the system 24 hours a day without cycling regardless of whether you’ve closed off other zones - if not then you already know you’ll have cycling problems when operating on that single zone.
To be clear, the main problem is having sufficient emitter space to get rid of the heat, the insulation in each room is not really a concern as the radiators should have been sized to the heat loss of the room anyway.
The first heat calcs were done without any real insight.
I’m hoping that I can get through the BUS hoop with the Cornish solution: lots of fudge.
As for the emitters, they’re (fortuitously) all K2s, so I’m optimistic on that specific score.
Over the last 20 years, I’ve fiddled with the “heating”- above all adding insulation, and tado. I know that I’m unlikely to get it right in one step now, and that some more fiddling will follow…
I’d be inclined to push back fairly hard on those heat loss calculations, if they result in a much larger ASHP than you really need.
There are countless tales of woe on this forum about oversized HPs and the consequent poor efficiencies due to excessive cycling. Many users have ended up negotiating a replacement smaller unit with their installers as a result.
Unless your house is very large and/or very poorly insulated (or you live on top of Bodmin Moor ), I’d be surprised if you actually need more than about 8kW. The MCS “rules” for calculating heat loss (and thus qualifying for the all-important BUS grant) are - or at least were (I believe that they are currently under review) - based on pessimistic ventilation flows. If you (or your installer) can demonstrate a lower ventilation component, you may end up with a HP better matched to your real requirement.
I agree with Sarah that you should try and get the heat pump to the smallest size possible, however I do think that you’re going to be in for a real challenge - a lot of people who went down this path wanted to go from a 9kW Daikin to an 8kW Daikin and that wasn’t easy for many of them.
Getting an MCS heat loss survey from 22kW to 12kW, where a part of basis of that is you not directly heating large portions of your house, might not be achievable. Without an agreed heat loss survey that shows 12kW (or any lower number) as appropriate, you can’t get a BUS grant on the system.
), I’d be surprised if you actually need more than about 8kW. The MCS “rules” for calculating heat loss (and thus qualifying for the all-important BUS grant) are - or at least were (I believe that they are currently under review) - based on pessimistic ventilation flows. If you (or your installer) can demonstrate a lower ventilation component, you may end up with a HP better matched to your real requirement.