Posted by: @grahamf

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May I ask what kind of house you live in?

Sure, its a 200sq m 1930s house with (originally) solid walls, a couple of modest modern extensions and miscellaneous fabric upgrades such as partial IWI and 300mm of loft insulation.  Floors are still entirely uninsulated though.  The fabric upgrades caused the surveyors problems (basically because the ignored them unless they could see them,  even though I told them about them).  In addition at least one of the 2 double counted room to room, losses.  They both assumed ACH2-3 whereas the evidence is that its 0.5-1.

Here are the plots I did, based on half hourly meter readings over 2 years.  For the second year only (not the first) I operated the boiler as close to 'heat pump' mode as possible by turning the flow temp down to 50 (55 when it was really cold) and having it on 24x7 rather than timed.  This appeared to have the effect of reducing my gas bills by about 10%, although that might just be down to climate variations.  It definitely increased comfort.  Its a 15 year old condensing boiler so, when operated in condensing mode (which it was in year 2 of the measurements, but not in year 1) can reasonably be expected to have an output to input ratio (efficiency if you will) of 90%-110%.

I don't doubt that there was a bit of luck in mine, but at the same time my strong suspicion is that a bit of well thought through analysis of half hourly meter readings could reveal a lot more and be rather accurate if you look also at the dynamics and make some sensible allowances for partial heating based on sound thermodynamics (its surprising how little difference partial heating actually makes once you actually plug some numbers in).  I would be surprised if the likes of Octopus weren't working on this, it seems an obvious job for AI.

Posted by: @jamespa

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Posted by: @batpred

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It seems that instead of oversizing things a bit, people are being pressed to have exactly what they need for the whole house.

In 3 years on this forum I have seen very, very few cases indeed of under sizing of the type you are describing.  In contrast there have been dozens of cases of gross oversizing of the outdoor unit, which can have dramatic knock on effects.  Thus I very much doubt that 'people are being pressed' in the way you suggest, this is an unusual case not reflective of any norm reported here.  If you would care to post the heat loss calculation that might help understand what happened.  

In any case up sizing a radiator is a quick and relatively cheap operation so little or nothing is lost by doing 'after' the main install.  Why do your friends not simply do this if it matters to them?  See my comments above about what should be deducted from the cost and what they could reasonably be expected to pay imho.  If this were to happen and  based on what you have said, they would be in exactly the same position as if the radiators in question had been done with the main install.  So the question to my mind is why is it not happening if it matters?

Yes, I agree with your points.  However, the risks are different in nature.  If you oversize a heat pump, then the risk is that it is less efficient.  This has no impact at all on the installer and maybe only a marginal impact on the home owner.  There is also more in reserve for the occasional really cold few days.  On the other hand, if the heat pump is undersized then the home owner may be cold a lot of the time and then make a claim against the installer.  It leads to a whole world of pain.  Given the choice, most people feel safer oversizing.

Yes, you can upgrade radiators later, but that may well involve draining the system, so it is cheaper to do it all at once.  We tried to do it all at once, but our coloured Stelrad Vertical Ultra radiators were on a 14 week lead time!

Posted by: @grahamf

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 If you oversize a heat pump, then the risk is that it is less efficient.  This has no impact at all on the installer and maybe only a marginal impact on the home owner

That depends on the circumstance and your assertion is not necessarily true.  If for example if oversizing leads you to going from one heat pump to 2, the change is enormous. If it leads to you requiring a 2 fan pump rather than a one fan, and there is no good space for a 2 fan, then the impact is equally enormous.  Likewise its an enormous impact if oversizing results in floorboards being lifted (or worse still solid flooring) to upgrade pipework unnecessarily.  In general terms the difference is bigger the larger the loss.

The professional design approach (applicable as a principle to any engineering situation of this kind) is to establish the loss as accurately as possible, and in doing so get some estimate of the uncertainty.  From this you can make an intelligent decision whether the uncertainty needs to be reduced, or whether the information you have is good enough to resolve any critical design choices for example of the type above.  Any other approach is simply sloppy engineering and doing it properly is, in this case, not so difficult.  Fuel savings due to micro-zoning (in time or space) are nothing like as big as the manufacturers of controls have conned us into believing - do the math if you dont believe me.  With a condensing boiler or a heat pump they may even be negative.  Thus the correction factors for zoning and even more so the uncertainties in the correction factors are also smaller than we have been led to believe by those in whose interest it is to sell controls.

In my case relying on the survey results would have resulted in the need for a 2 fan heat pump or even 2 heat pumps, and extensive (and wholly unnecessary) pipework upgrades.  Getting a more accurate figure was thus essential to making a sensible design choice.

Posted by: @grahamf

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Yes, you can upgrade radiators later, but that may well involve draining the system, so it is cheaper to do it all at once.  We tried to do it all at once, but our coloured Stelrad Vertical Ultra radiators were on a 14 week lead time!

That's correct and is why I said above that the householder in question should not be charged for the draining and refilling if they were not told of the need to upgrade.  We still don't know why they have not just done the upgrade if it maters to them, rather than complaining about it!

Posted by: @jamespa

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Posted by: @batpred

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This made me smile, it seems a design fault of most ASHP systems, warming the house at a constant temperature all the time.

I'm not sure where you are getting your design information from, but its incorrect.  The standard design temperatures, as specified in MIS3005(D), are 21C in living areas and 18C in bedrooms, not the same all over at all.  If you want it colder still in the bedroom(s), just turn down the lsv, or if you wish fit a TRV (the former is preferable).

Thank you for sharing the design standards. 

What I mean is that, given it is healthier to have a cooler environment to sleep than when people are active, when the systems are being systematically being setup to maintain constant temperature, when each design is created, arguably it misses a default requirement. I had not even looked at the document you reference. I am not sure if this was done to maximise operating efficiency or the system but it does not facilitate user centered design. 

So I see a lot of anxiety about these assessments as they provide results that, in the case of boiler upgrades, users find difficult to adjust to their needs, budget and changes to the existing system. Would there not be cases where a user would like the pump to deliver hotter heating water to avoid resizing circuits, etc? 

From what I saw people are being asked to pay for these reports upfront. Is the report then just used by a single installer to create a proposal based on the products they use? Or is it available for the user to provide to other installers so they can make their proposals? 

@grahamf 

it changed my setup, i charge the battery at cheapest rate, or on PV Mch-Oct.

i have heat pump so have cosy tariff, i get 8h low cost electricity a day at 3 times a day, during these times i recharge the battery, I have configured the inverter to run the house on batteries in the expensive period and recharge on cheap rates

also the heatpump is set to 20C, with a 0.5C boost at 1pm cheap rate for 3h with water heating here too.

i tried water heating at other cheap rate windows, 10-12pm and 4-7am, but the HP COP was poor as the outside air temp is lower so HP had to work harder to produce 50C to heat the DHW tank.

ive been using trial and error all year optimising usages

@agentgeorge Optimisation is not something that can be done in a hurry! Patience is also a very useful virtue😉 Toodles.

Posted by: @jamespa

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That's correct and is why I said above that the householder in question should not be charged for the draining and refilling if they were not told of the need to upgrade.  We still don't know why they have not just done the upgrade if it maters to them, rather than complaining about it!

Well, in my friends case, I don't know what happened at budget stage but they travel a fair amount, so unlikely both were looking into it, but after the install, one partner was happy to wear an extra layer as it was reducing their carbon footprint, the other was somewhat frustrated with the change to ashp..

Anyway, we know that the assumption the heat pump will be running continuously is based on the fact a cylinder is assumed to be always part of the solution. This essentially means unless it is a massive property, the system is never going to be powerful enough to provide direct hot water for showers etc. And don't start me on the electricity capacity, we know these pumps run on a normal socket circuit like normal air cons.