@iancalderbank Thanks Ian, I didnt spot the link, the colour is quite subtle on my monitor.

So the latest in this saga, is that the neighbour still hasnt been given control of her heat pump via a local network and the company are unable to give her access via their internet portal because of poor broadband coverage.

I am trying to get them to guarantee the large heat pumps performance, in terms of the maximum number of cycles allowed per hour in mild weather. I suggested 3 per hour, they stated that the industry standard is 4. Does anyone know if this figure is correct?

I also found this quote in the MCS best practice guide which exactly mirrors her situation!

Key point:
Many installers use just one preferred
manufacturer for supply of heat pumps.
Whilst this has advantages with familiarity,
associated design, installation and
commissioning requirements, it could mean
that the heat pump becomes significantly
under or oversized if the nearest available
size is utilised. In such a situation it
may be advisable to seek an alternative
manufacturer’s product which is more closely
matched to the design load, or consult
the manufacturer and seek guidance (e.g.
increased water volume/install a buffer).
The Contractor responsible must weigh up
the pros and cons of their actions.

@bontwoody I'm not sure that there is a single, universally accepted "industry standard" for heat pump cycles per hour. I suspect different manufacturers might have their own internal guidelines and "interpretations", and some may recommend 3 cycles/hour while others might suggest 4. 

I suspect @sune or @heacol might now more definitively. 

@editor I'll defer to Brendon/Heatcol's encylopedic knowledge here when and if he responds in terms of how many compressor starts per hr is too many.... but....lets think about reducing them from a theoretical point of view: 

This is why sizing becomes absolutely vital. There's already oversizing "calculated in" to many systems because currently under MCS base temperature isn't accounted for because they refer to BS12831 for calculating the peak heat load and 12831 doesn't account for base temp. So for instance you house may only need heating once the outside temp drops to 15º, and the outdoor design temp (ie "really cold") might be -3º, giving a temp difference of 18. However the calc can mean, depending on the types of rooms in the house, that the starting temperature used for the calculation is 21º = temp difference of 24 - so that's already 33% oversized (not accounting for headroom for intermittent heating of course - ie heating up from cold).

You can work out base temperature from monthly bills via a regression calc on the degreedays website, or you can just record the outside temp every time it feels like you shoudl turn the heating on.  

Many manufactures will state that their heat pump is blah-kW. I guess this allows for comparison between makes, but an air source heat pump's output generally varies according to the flow temp required, and according to the outside air temp. So you need to know the designed flow temperature of your system and the external design temperature where you live. You then look up the output in the table which you should find in a tech manual. So we happen to supply Clivet heat pumps to engineers and here's the output table for the Evo I 41 unit. I've highlighted the max output at 45 flow temp, -2/3 outside as an example.

The types of system that Brendon teaches engineers to design will also reduce cycling. Not using weather compensation (ie delivering water that is too hot for the house), using TRVs, room stats and zones all increase cycling, whereas weather comp, open circuit, or open zone, flow balanced systems will tend to do the opposite. Engineers should be encourage to attend this type of training.

I also think that loading up extra heat into the house and hot water when electricity prices are low is a potential way to reduce cycling, as is the use of a volumiser - both are acting as a type of thermal storage.  

The only reference I can find in the MCS guide is how to reduce starts to no more than 6 starts per hr... there may be updates in the pipeline of course. Min Utilisation factors are being updated in the biomass standards for instance, which may have a relationship to the number of ignitions, which is the equivalent of compressor starts in heat pumps.

I realise I've not directly answered the question, hopefully Brendon will step in with his vast array of practical and technical knowledge!  

@bontwoody how did your neighbour’s saga finally conclude? Are they happy?

@editor Hi Mars, unfortunately I never got to find out. Despite my best efforts the neighbour could not get her head around how to set up weather compensation on her unit and started I think to blame me. I was rather busy at the time with my extension and couldn't keep popping around to try and sort out her latest experiment.

IMO the heat pump was oversized, but I think it could have been made to work moderately well with the right setup, unfortunately because the neighbour couldn't get broadband at her property, the company could not log in to remotely help her.

While I think the company's response was poor, I also don't think the lady helped herself either and was fixated on taking them through the available legal options to get some redress.

Weather comp is straightforward when in "ACONDTHERM" mode it has full weather comp, this mode uses high heat to reach desired room temp then backs off to try and keep temp .3˚C above or below set temp. The other option is EQUITHERM which uses weather comp, but you can also set your own curve (kinda like am aertotherm) which would probably be the best option, but requires time and a bit of tweaking. EG 

though it sounds like it, it's probably not worth the effort. 

@bontwoody I guess you never got the admin login details for the Acond unit ?

@deano Hi Dean, yes I did get the local interface working (Thanks for all your help).

I went through it with the owner and the concepts of weather compensation several times over multiple visits even writing help sheets. In the end my wife thought I was having an affair!

I explained the importance of changing one thing at a time and seeing the effect, but she just didnt seem to listen.

Things came to a head after her last experiment set the return flow temperature to 22C at all OATs. I tried to explain that the radiators would feel cold and that I thought she was mixing up flow temperature and room temperature. In response she said she had an IQ the size of a small planet and didnt need my help anymore, so I left it there. 🙂

Posted by: @bontwoody

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In response she said she had an IQ the size of a small planet and didnt need my help anymore, so I left it there.

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I take it you didn't reply that "in that case, you're talking out of Uranus"....

Taxi!

@majordennisbloodnok

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