@jamespa - taking into account the usage of the wood burners and the energy profile that they chuck out over an evening, the divide by 2900 figure gives me 11.63 KW, the divide by 2 16.9 and the divide by 3 11.24 - these all having been corrected by 13/10.5. 

I can see where the 2900 figure comes from but where do the 2000 and 3000 correction factors come from ? (I did search, but without success).

With regard to the thermal store, yes I am aware of this issue - the thermal store runs reasonably hot and is a totally unsuitable way to use a heat pump. 

The installer who came out (but seems to have disappeared) said that the manifolds would benefit from replacement on account of the fact that they don't have flow meters and the mixer valves are no longer necessary (as you stated). To be honest, the manifolds we have are a  pain in the neck as we have experienced leaks and I am unable to get the mixers to drop the flow temperatures sufficiently (they sit at about 45 degrees at present). That the actuators are forever causing issues would go away as they would be removed and flows set via flow valves.

thanks for the information that you have been feeding.

Ironically, our village is currently in the midst of a power cut .... thank goodness for battery backup and the capability of it to drive most of the light loads in the house  and so keep me internet entertained !

Posted by: @ian33a

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o the 2000 and 3000 correction factors come from ? (I did search, but without success).

Me, I invented them (starting from 2900) to help with people on this forum who were getting silly quotes, and allowing for the fact that some oversizing isnt a disaster and anyway heat pumps have discrete steps in power (eg Vailant 5, 7, 12) and of course many people operate some kind of night time setback.  Only a tiny amount of science behind it, but useful to give people some pretty hard limits to exclude silly heat loss surveys which still appear to be common (as in if your heat pump installer is suggesting that the loss > gas consumption/2000, probably best look elsewhere).  2000 could probably be 2500.

Posted by: @ian33a

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The installer who came out (but seems to have disappeared) said that the manifolds would benefit from replacement on account of the fact that they don't have flow meters and the mixer valves are no longer necessary (as you stated). To be honest, the manifolds we have are a  pain in the neck as we have experienced leaks and I am unable to get the mixers to drop the flow temperatures sufficiently (they sit at about 45 degrees at present). That the actuators are forever causing issues would go away as they would be removed and flows set via flow valves.

Sounds like he has his head screwed on!  He is right, ditch the actuators and mixing, balance the loops for the desired differences in room temperature using flow adjusting valves, then let weather compensation do its job!

@jamespa thanks - that clears up my question on where the numbers come from - although I would be interested to understand why it may be acceptable to change the 2000 factor to 2500?

So, with my numbers using oil consumption coupled with your calculation method coming out at 11.24 11.63 and 13.49 (using a factor of 2500 for the latter) and 16.86 (using a factor of 2000) and my HeatPunk figure of 12 - is it fair to say in your mind that there is a reasonable correlation between what is being measured from oil usage and what HeatPunk is saying and that these could be used as a basis for a discussion with heat pump installers (once I can get somebody willing to actually set foot in the house and have a chat!) as a starting point for a heat loss analysis?

Posted by: @ian33a

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So, with my numbers using oil consumption coupled with your calculation method coming out at 11.24 11.63 and 13.49 (using a factor of 2500 for the latter) and 16.86 (using a factor of 2000) and my HeatPunk figure of 12 - is it fair to say in your mind that there is a reasonable correlation between what is being measured from oil usage and what HeatPunk is saying and that these could be used as a basis for a discussion with heat pump installers (once I can get somebody willing to actually set foot in the house and have a chat!) as a starting point for a heat loss analysis?

 

Yest it is fair to say thats a reasonable correlation and in this circumstance I would be tempted to believe heatpunk.

I totally agree its a reasonable starting point, even then you may have problems with installers that ignore fabric upgrades they cant see or those that use unreasonably high ACH.

Posted by: @ian33a

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@jamespa thanks - that clears up my question on where the numbers come from - although I would be interested to understand why it may be acceptable to change the 2000 factor to 2500?

Well consider a 7kW house, in principle 20300kWh/year.  Perhaps subtract up to 20% (unlikely) for fairly extreme part time heating - 16240 .  Now take a gas boiler that is actually condensing with 110% 'efficiency' (obviously not strictly efficiency, just how the declared calorific value is calculated - but anyway very unlikely because of the (bad) way plumbers set up gas boilers) - 14700.  So that would be a case of divide by 2000 to get loss.  However the probability of both these occurring is very small, so somewhere in between is a reasonable point at which to raise suspicion, even if its not a hard limit.  Furthermore if dividing by 2500 leaves you just above a size boundary, so you are pushed to the next, its perhaps time to think harder/get some more evidence.

Like I said not terribly scientific , but its only intended to weed out the silly quotes.

With half hourly meter readings I plotted daily average OAT vs daily consumption.  I did a few other checks, but as I say with gas its easier.

@jamespa - Thanks ever so much - your patience and help has been much appreciated.

As a now retired engineer, I hate to have to accept blind faith numbers without reasonable science behind them. That my HeatPunk numbers broadly line up with the oil usage calculations gives me the confidence to have a meaningful discussion with an installer .... if I can find one who fancies visiting me !

@ian33a keep the faith. I am also a retired engineer and sympathise with your problem.

For me it was.a 2 year journey which culminated in an two paragraph, informal RFQ that basically told prospective installers what the loss was (with evidence) and what system configurations I was prepared to accept.

Of course some couldn't cope with this approach, but the ones that engaged were good. They had to go through the motions to satisfy MCS, but they found ways to interpret the rules to get the right result.

I ended up with two quotes that realistically I could have accepted, either of which I could have chosen on price and technical grounds, so it came down to proximity. 

I count that as a good result, the (very simple) system is great in operation, far better than my boiler, and the price was pretty much the lowest I was quoted.  

Posted by: @jamespa

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Of course some couldn't cope with this approach, but the ones that engaged were good. They had to go through the motions to satisfy MCS, but they found ways to interpret the rules to get the right result.

Same here lol

The fact the house had been heated for 40 years by a 12kW ground source heat pump could provide a bit of a hint about the actual heat loss...

I also had 5 years of data about the actual run time of the heat pump recorded by home automation...

After this I installed 200mm rockwool exterior insulation, double glazed windows, 400mm blown in fiberglass in the loft, etc...

My heat loss calculations still pointed towards 12kW, this time considering it would only run during the day to maximize photovoltaic self consumption, so already about 2x oversized...

I'm also installing 20kW log boiler disguised as fireplace...

Drum roll 🥁🥁🥁🥁🥁🥁

Every single installer went full retard, some of them wanted cascade, also all of them wanted buffer tanks, and I could only talk one down to "only a 16kW Mitsu with huge electric backup" after about two weeks of emails.

That's because if it is not powerful enough to heat the house to 21°C when it's -7°C outside (which never happens) they can be liable, so they play it safe.

I ordered the 16kW LG R290 from internet, put it in the garden, done. It's the exact same machine as the 12kW so the low end of the modulation range is the same, about 3500W, but it has 15kW cooling power. Nice. Also 10k€ cheaper than the Vaillant installer quote.

@jamespa Well, something along the lines of "three buses coming along at once" : Yesterday evening I approached two companies who are "emerging" on this website. First thing this morning I rattled the cage of the installer who visited last week and went quiet on me.

I got an invite to a 1:1 web based discussion with one of the companies (which is scheduled for tomorrow), the cage rattling worked and I got an estimate from the people who visited last week, and I spoke with the other company that I approached yesterday and they are visiting in a week from now to do a exploratory investigation and a heat loss calculation.

It looks like I may be getting somewhere afterall.