Posted by: @stuartornum

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This leaves installers in an interesting position... with Homely providing arguably the best controls (that you can buy) in the market (IMHO), couple that with a Midea/Riello/Samsung etc... why bother with the "premium" brands such as Vaillant, Viessmann, Stiebel Eltron etc... I mean, Riello is owned by the same parent as Viessmann (Carrier).

Thats a fair observation, although some of the 'cheaper' brands (eg Samsung) with very basic controllers seem to have caught up in price certainly with Vaillant. Whether that's price gouging or a retail price which differs dramatically from the price to installers I cant say.  It would probably be perfect for installers and consumers if the market split into heat pumps and flow temperature controllers, so you could pick the two individually according to the situation and also so installers dont have to cope with very different interfaces, but I doubt that will happen.

Ideal is an interesting brand also.  Well established in UK with (like Vaillant) a large existing field network,  clearly a strength if you want to get into the market.  Their R32 model looked suspiciously like a Mitsubishi, albeit with their own controller.  I'm reliably told that their R290 model is Midea; I don't know if it has the same (Ideal) controller as the R32 but I do know its modbus compatible so presumably could work with Homely - possibly not ideal for Ideal.  I'm not sure where that leaves Freedom, who up till now appear to have effectively been Midea UK.

The market still has a long way to go before its anything like mature.  Its a pity that the 'grant harvesters' are damaging the reputation of both the technology and the industry.  Of course it may be a minority of installations that go sour; people who are happy with their installations tend just to get on with their lives so we probably don't hear much from them!

Hi @stuartornum 

“ When it's -3c and you have a 300L cylinder, it'll take at least 2.5 hours to heat the tank to ~55c. That's 2.5 hours your house has no heating. If you size the HP for your heat loss, it will struggle to get the house back up to temperature.

3. Bigger heat pumps generally have better COP figures.”

you can obviously extrapolate figures to the worst case scenario. But your post,which is addressing ‘Mr & Mrs Confused’ appears to imply it’s a typical situation when it clearly is not.

I have a 8.5kwh heat pump and a 250 ltr cylinder it takes 45 minutes to take the thermistor up to 48c (why go to 55c) the top-of-the-tank thermistor is usually 5 or 6c hotter.

Regarding over sized Heat Pumps it’s not a good idea at all. If for only one reason the bigger the Heat Pump - the bigger and earlier the cycling. Our moderate climate means a he highest number of days the HP has to operate above +8c outdoor ambient. Larger heat pumps have a larger minimum output so will cycle earlier.

@sunandair Bigger heat pumps with bigger loads. Don't forget about the pipework and flow rates. The more powerfull the HP the higher the flow rate required. Samsung 5kW - -2 degrees, 35 WO flow required to deliver 5460W is 14.3 lpm. 8K unit - 22.3 lpm to deliver 8240W. 12K unit 33 lpm to deliver 12360W. So pipe sizing and layout are critical. As flow rate increases so does pressure loss. Don't forget all other system components - higher flow rates - higher pressure loss. Most installers just look at the pipework - should be OK. Remember that the HP is just one of many components.

@raiph yes…. And with higher flow rates comes potential for background noise. But I must admit I don’t know much about pressure loss. 👍

Is this what you mean 

Look at pressure-drop.online.

Posted by: @stuartornum

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Posted by: @toodles

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Sounds rather like what my Homely controller does right now! Regards, Toodles.

Big fan of Homely! One of the reasons being... it's not pure weather comp, it uses room influence.

I have Homely on my setup, currently turned off as it doesn't play well with other devices being on the modbus (floods it). I've asked Homely several times for an API... fingers crossed.

I believe Homely is in the best position to be v2.0 for weather comp. Here's some features/data I'd like to see added:

1. An API (a local API would be even better)
2. Multiple zones (I know people are against zones generally, but the feature would still be nice)
3. Ability to change max/min flow temps without having to call them and ask them to make the change manually (I believe this feature is coming)
4. Release anonymised performance data of heat pumps
5. Ability to use different sensors, for example it uses the OAT of the HP itself... which may be in direct sunlight... I'd like to push my own OAT to Homely.
6. Ability to dynamically change the heat requirement
7. I don't believe they ask for the properties heat loss, they may determine this themselves over time based on the heat requirements... I'd like to be able to modify this dynamically (via the API)

That is really interesting what you mentioned about contacting homely directly to change max/min flow temps.

Our installers [allegedly] designed our system at 45C. I noticed when the homely was installed that it had the maximum set (or defaulted?) at 50 which I have constantly been querying with the installers who insist their design and heat losses are correct.

I had some isolated instances where it would seemingly overshoot in Oct/Nov so my installers contacted them and set it back to 46C. The installers told me that this was due to a software fault but again I do not believe that this is accurate- I think they simply called them and asked for it to be set back to stop me complaining. Cue cold weather and it wasn't sufficient to get the house to 20.5 (our set indoor target temp). I had to contact homely who put it back to 50C, said it needs to be at that set point to heat the house sufficiently, and no issues since. Generally COP in coldest weather at 45 was 2.75. Now it is around 2.55 when set at 50 so all in all I'll take the warmer house...

The red herring I believe is the design temp rather than anything to do with homely. I believe that we've been mis-sold that element and was highly sceptical when the installers said that it would be that low, taking into account their proposed emitter changes, and our house not being particularly well insulated. But, when is this max flow temp even set? The installers said there's no option to select or change this when commissioning; indeed the installer app does not allow for this to be changed as you say.

I don't get why they'd even set up the controls in this way to force you to call them when this needs tweaking. The chap from Homely who called me the other day (in response to the max flow temp issue) said he can't keep up with demand and enquiries. I do like Homely but I dislike things like this which seem as though they can be easily solved...also seems odd they have a load of end users on a forum like this, posting reviews on the app stores etc but they don't provide any feedback via any of these platforms. That might be helpful...

Posted by: @benson

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But, when is this max flow temp even set?

It's set by the installer when setting up the Hub, you physically cannot miss it. The reason why I've had to change it a lot recently is due to customers having UFH and a liquid screed that needed heating up slowly... If I put 40c down the UFH for any reasonable time it would bust the drying floor! Hence the need to gradually increase it.

Posted by: @sunandair

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Regarding over sized Heat Pumps it’s not a good idea at all. If for only one reason the bigger the Heat Pump - the bigger and earlier the cycling. Our moderate climate means a he highest number of days the HP has to operate above +8c outdoor ambient. Larger heat pumps have a larger minimum output so will cycle earlier.

I would like to agree with you, I really would. However, the data (my HP) shows otherwise. Oversizing is not as detrimental as people are led to believe. For reference, my heat loss is 4.5kW and I've got a 8kW (more like 7.6kW) heat pump. Now, it's worth noting each property is a snow flake and should be treated as such. Emitters are an important factor to consider, I have UFH in most of the downstairs and reasonably sized radiators upstairs (not huge ones!). I'd say this setup is not uncommon.

You mentioned short-cycling, when comparing my HP with other top performing HP's (especially during the shoulder months), their HP control strategy is stop/starting the HP more than my own WC program. Images below are from the 17th of December.

My day job (nothing to do with heat pumps btw) is to question everything and look for improvements. When someone says "Don't oversize the HP"... I want to see the data/research supporting that statement. If anyone knows of any research papers please do post below.

I'm sure in some circumstances, oversizing is bad. However, in my (not uncommon) setup, it's proving to be beneficial. Therefore, (IMO) the statement "Don't oversize the HP" should be dropped until more data/research has been analysed, which in turn will arm installers with more knowledge and that is ultimately the endgame, the installer needs access to the best possible data, research and tools in order to do a better job. (I think we can all agree on that)

Posted by: @stuartornum

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Posted by: @benson

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But, when is this max flow temp even set?

It's set by the installer when setting up the Hub, you physically cannot miss it. The reason why I've had to change it a lot recently is due to customers having UFH and a liquid screed that needed heating up slowly... If I put 40c down the UFH for any reasonable time it would bust the drying floor! Hence the need to gradually increase it.

Interesting, and as I suspected. Thanks.

Posted by: @stuartornum

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Don't oversize the HP" should be dropped until more data/research has been analysed, which in turn will arm installers with more knowledge and that is ultimately the endgame, the installer needs access to the best possible data, research and tools in order to do a better job. (I think we can all agree on that)

Although i agree that the evidence that oversizing causes performance problems is at best shaky (albeit there are some logical arguments why it might) performance isn't the only possible issue with oversizing, as I point out above.  

The right approach, surely, is to work out the correct size then make a decision based on all of the factors.  What is wrong, equally surely, is the common practice of oversizing by default (often by 'rule of thumb').  This appears to be all too common in the industry at present.

Posted by: @jamespa

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The right approach, surely, is to work out the correct size then make a decision based on all of the factors.  What is wrong, equally surely, is the common practice of oversizing by default (often by 'rule of thumb').  This appears to be all too common in the industry at present.

Yep, can’t disagree with that. I must admit, I was highly motivated by performance and everything else was an afterthought.

Posted by: @stuartornum

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Posted by: @jamespa

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The right approach, surely, is to work out the correct size then make a decision based on all of the factors.  What is wrong, equally surely, is the common practice of oversizing by default (often by 'rule of thumb').  This appears to be all too common in the industry at present.

Yep, can’t disagree with that. I must admit, I was highly motivated by performance and everything else was an afterthought.

Understood. 

You suggest (I think) that your data shows that oversizing is positively beneficial to performance in your case.  Have I understood that correctly and if so how does your data show that?  As you say this is an area where we do need data!