@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 thanks Mars

@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!  

@Sune

Thanks