‘Oversize’ may become more common as the heating requirement becomes a smaller portion of the demand, due to warmer weather and/or better building fabric. I sized our unit (5KW) on the time taken to (re)heat a tank of hot water (without an additional immersion heater) -that being the larger of the two demands. Based just on the heat requirements we could have gone a size down. The cycling, as we have come in to the shoulder months has noticeably impacted the efficiency, but it may also have had the same effect on the smaller unit (as both have the same minimum continuous power output). A small gain in the DHW efficiency may outweigh a slight loss in space heating efficiency…
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I’ve added the links to the other tools and improved the performance on mobile of the new heat demand tool.
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Looks really good Trystan.
I’ve tried this on my heat pump (Farnham, Surrey, Daikin Altherma, 11kw) which I know is very oversized. But I don’t get any data. Does it require me to add some extra details somewhere? I couldn’t work it out.
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The heat loss tool requires room temperature data
Thanks Glyn. Obvious when you say it.
I don’t have internal temperature sensors logged in the system. Can I add a time-series in manually to make this work?
My house is always within 0.5C of 20.5C, so I could just put in a record of 20.5C or it would be handy to have an over-ride in the tool to be able to add a fixed room temperature? I get the purest view that it’s a bit of a bodge, but someone estimating their heat loss they would have a good idea whether temperature in their own property has been maintained 24/7.
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Yes good idea, I will add this in.
Another minor update to the tool, it’s now possible to edit capacity figures that set the lines on the graph directly in the tool rather than having to switch between the form and the tool.
I’ve also added an option to provide a ‘max capacity test result’ which may be different from ‘datasheet capacity’. E.g @ColinS’s 11kW Daikin which we believe can’t reliably deliver more than 7.8 kW during heavy defrost conditions, having the option to include this line illustrates that the data sheet values are in question at least. (Link to data: ASHP sizing for Freezing Conditions - #63 by TrystanLea)
Ultimately I’d like to move test results like this to a heatpump make/model specific page, with a link to the period under which the test was performed so that those interested can double check the test.
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The max capacity test result line should probably be called ‘Be careful designing for accurate heat loss above this line’.
Interestingly the East Midlands 11kW Daikin Altherma 3 gave 10.35 kW over ~6 hours at -4.8C outside here and it doesnt look maxed out… and the COP doesnt look low enough for a booster heater to be on?? interesting result @ColinS
https://emoncms.org/app/view?name=Altherma&readkey=dfb6fbf82b5eb4f396ba1e8acb146d66&mode=power&start=1705541700&end=1705564785&cool=1
Or 10 kW over 3 hours here at -2.5C https://emoncms.org/app/view?name=Altherma&readkey=dfb6fbf82b5eb4f396ba1e8acb146d66&mode=power&start=1705628330&end=1705639070&cop=1&carnot=0.441
Hi Trystan,
That 11kW Daikin is not an Altherma 3 Monobloc like Colin’s.
It is a hydro split system.
They can’t be compared to each other like that?
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Recently featured on Hacker News - should drive a lot of interest 
One thing that came up was export of raw data in an agnostic format - is that possible?
(Just need to get a heat pump now…!).
This is really great and much easier to use than my hacky scripts 
.
One bug I observed: When I press auto fit, it automatically resets the x axis to 23 K DT even though I saved DT at 32 before. Then entering 32 K as DT again will shift the fit line so it’s no longer correct (or better the fit line stays where it was, the data shifts).
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Hi Tristan
Thanks for the changes, looks good, and in line with what I have calculated outside the system.
Just need a proper cold spell in the data on here. I should try and see if I can get the 2.5 years of historic data out of the EoH project, I believe it’s in an open portal somewhere, but not an easily accessible format (to me at least), JSON I believe.
Doesn’t solve my problem of oversized heat pump, but at least I can’t be accused of manipulating the data in Excel 
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@TrystanLea thanks for the altherma split data. The flow temp is the same as mine but defrosts are far less frequent. I suspect the evaporator is better sized to get this result.