……and there is the irony, and lack of joined up thinking (system design!) in the UK
…and yet a fossil gas hybrid system is somehow allowed and also acceptable!
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You need planning for ANY air to air heat pump.
You also need planning for ANY water to air heat pump…
…unless it is being installed by MCS union labour.
That’s the rules that they have been permitted to write for themselves and that’s Ian Rippin’s stated objective. (ensure that there is only one way that heat pumps can be installed and that MCS governs that way of installing heat pumps)
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Interesting discussion, I’ve just had my heatpump installed, An Ecoforest EcoAir 3-12, but aside to that.
I am wondering when it does get to minus 2 (or below), the humidity should be much lower, and then the defrost cycles do less harm to the performance.
The problem is that at -2c the house heating requirement will be higher than at zero c so the heat pump will be working harder, with a larger DT between evaporator and outside air. If yours is oversized as many seem to be, then it still shouldn’t be a problem.
My system is at it’s limit at 0c - and reaches what I think is the maximum defrost frequency 30 mins on and 6mins defrosting, defrost frequency doesn’t seem to get worse at -2c but it does not produce any more power for me either.
I suspect you are right if you have a very low humidity sub zero day but that is not usual in our maritime climate.
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I’ve posted another test result from my EcoDan from last night, it met the datasheet output of an average output of 5kW and COP of 3, though time between defrosts seemed quite long! not really conclusive enough yet, just another datapoint: 5kW R410a Ecodan PUHZ-W50VHA2(-BS) maximum output testing - #7 by TrystanLea
@glyn.hudson also did a test at the same time on his Samsung 5kW (in the same village so similar conditions) and also achieved the same match to datasheet capacity 4.5kW on his, full details in his thread here https://twitter.com/glynhudson/status/1729591159146586180
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Another test result this evening, mine ran ~7.5% below datasheet suggested capacity over 3 hours at 0.84C outside 4.57 kW rather than 4.94 kW, I’m being overly precise here… roughly 10% below datasheet.
@ColinS had less favourable results 20-30% below I believe.
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Whilst we’re sharing 
Here’s a rare sight of my oversized Ecodan 14kW actually running all the time (can you see an Octopus Saving Session?)
Nominal CoP@Flow is around 270% and it did 285%. In the “Efficiency” chart you can see the gold line showing the manufacturer’s nominal CoP@flow:
When it’s trucking along it gets about 300%, but there’s a lot of defrosts in there so it’s paying the price of getting less efficient, then heating the ice and then getting going again.
You can see things went wrong around 14:00 when the air was getting warmer and it didn’t know whether to give up or not.
The outside temp was between 0 and 2 °C but the effective temp (which my control algorithm uses) was mostly between -3 and -1 °C. Dew point was -2 to 0 °C.
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Here’s @ColinS’s test from yesterday evening:
- Outside temp back of the unit: 1.32C
- Metoffice: 1.9C
- Metoffice dewpoint: -0.9C
- Metoffice relative humidity: 82%
- Average output: 8.7 kW
- 1st cycle: 9.9 kW (2.3 C outside)
- 2nd cycle: 8.7 kW (1.4 C outside)
- 3rd cycle: 8.2 kW (0.6 C outside)
- 4th cycle: 7.8 kW (0.6 C outside)
- Flow temperature peaked at 42C in the 4th cycle but averaged closer to 40C.
- Target flow temp was set to 50C to give the heat pump a clear signal to push as hard as possible.
- No backup heater running
Databook suggests output should be between 10 kW and 11 kW at these temperatures perhaps around 10.5 kW? So we are seeing 22-26% lower continuous outputs in those 0.6C cycles it seems:
Is that fair @ColinS ?
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Spot on Trystan. It’s worth pointing out that my radiator capacity (including 4 convectors) is 12 to 13 kw at a mean flow/return of 40c so the system is not emitter constrained. My house was definitely getting warmer last night with around 8.5kw input at about 1c so it is close to my ‘design’ capacity requirement of 9.8kw at -2c… which the Daikin data book says it should deliver. Grrr!
This evening with the same outside temperatures I am pushing it less hard - just 6.8kw and the COP has recovered from 2.3 to 2.9 along with larger intervals between defrosts.
I am still puzzling over the tech data Daikin supply - two pages after the capacity graph in the post above comes this table with wildly different capacity values and COPs for the same machine.
I took the MCS number and the graph as accurate when dealing with Daikin but now wonder what these other test standard results really mean. Do the other brands produce a similar tables to this?
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I noticed that a “show defrosts/ cooling” button has appeared, is this recent?
damage on my system for sat 2nd when it defrosted every 45 mins, -2C to -0.5C.
instantanous COP during the (short) stable periods is about 2.7, overall is 2.3 so the 10% hit on energy hits around 15% on COP.
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@TrystanLea Trystan - here’s the data for my NIBE F2040-8 (R410a) heat pump for a 6 hour period on Saturday when external conditions were between 0 and -1°C and freezing fog meaning relative humidity would be close to 100% (external sensor was reading around 98% but RH sensors are not very accurate at such extremes of the range). The evaporator frosts up very quickly on my NIBE under these conditions, with cycle lengths around 40 mins with a 2 minute defrost and 3 minute waiting period till the next cycle start. Flow temperature is nominally 35°C with peak heat output around 7kW falling to around 4kW at the end of the cycle due to the effect of the frost build up. COP is around 3.5 at start of cycle falling to around 2 at the end (average for 6h hours including impact of defrosts = 2.9). Input power was being software limited by the NIBE adaptive controls to an inverter frequency of 81Hz giving about 2kW power input (The NIBE F2040 8kW model will actually go up to 120Hz/3.5kW electric input so there is still plenty of capacity left). My house HTC is around 200 W/K measured - so with average inside-outside delta-T of 21K over the period it would need something like 4.2kW to maintain temperature (ignoring the effect of gains). Actual mean heat output over 6 hours was 4.6kW, hence why internal temperature was rising for the period. NIBE published performance curves for F2040-8 show “Max specified” heat output of 6kW at -1°C external/35°C flow temperature and nominal COP around 3.2 for same conditions - though it doesn’t state the RH assumption for the data.
Jez
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A note of interest for those with Daikin heat pumps, Daikin have an interactive databook tool here https://daikintechnicaldatahub.eu/en-GB/altherma-3-m/combination/
It gives outputs with and without the backup heater. The following example is with the backup heater:
Without backup heater:
- 11.08 kW at 0C
- 10.94 kW at 2C
Our results:
- 8.7 kW over 4 cycles including defrosts (1.32C outside)
- 7.8 kW on the last cycle at 0.6C outside
Im in contact with Daikin technical support that gave the above link. No light yet on why we’re seeing this difference in output. I will keep this thread updated with any developments. I’m definitely open to the possibility that we have missed something and that greater outputs are possible.
This clarifies at least that we should expect the ~11kW of output without the backup heater and COP’s should be around 2.44 (2C outside)
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Thanks Trystan, it will be interesting to see what Daikin say. I had a letter a few days ago from the receivers of UK heat pumps in Basingstoke who installed my Daikin, they had me listed as a creditor for the value of my installation. Curiously, as I’m not a creditor as the installation was completed. They must have suffered a lot as they told me last year that dealing with Daikin was a nightmare. Legally they were caught in the crossfire between unhappy customers and an unresponsive Daikin. Next year I have to find a decent Daikin servicing engineer…in the Aldershot/Farnham/Basingstoke area. …if anyone knows one please let me know.
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Wow, that’s interesting. I still haven’t heard back from my email to Daikin support - did you email/call/use a proxy?? Meanwhile, I’ll look at my EDLA09’s data with interest. It’s also an excellent source for all the manuals etc. on the other tabs on that link.
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I emailed I sent my email on the 7th of December.
Maybe you are confusing maximum output with mean output. I would expect the manufacturers data to give maximum output, but mean output in a defrost situation is going to be a lot less.
Hers’s a random sample from my Samsung 8kW.
The mean output is 5.5kW but the maximum is 8.2kW which is slightly more than the specified output under those conditions.
Guesstimating from your graph it looks like the peak output is over 12kW. Apart from the defrosts, the potential output reduces as the frost reduces the airflow over the heat exchanger.
On the face of it it looks reasonable to me.
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Thanks @billt
Im assuming that defrosts are included and that the capacity data should be mean output. Im pretty sure it should include defrosts…? We have had indication from another manufacturer that their data does not though… so you never know! Wish this was all a bit more explicit in the databooks!
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It’s not particularly clear in the EN 14825 standard, the only references to defrosts are:
…
and later…
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I have to say that the literature and test standards are highly ambiguous on what you would think is the most important design number for correct sizing of an installation. The MCS heat pump guide for example;
Heat-Pump-Guide.pdf (mcscertified.com)
Says on page 16;
3.4. Heat Pump Capacity
It is essential that a heat pump is selected to achieve the desired output for at least the design
conditions, if not slightly more onerous conditions which may not be the same as the nominal rating
of the unit. Lack of understanding of the variation in the performance of heat pumps at different
operating conditions has been identified as causing significant under-sizing in previous field trial reports.
For instance, the standard rating condition for ASHPs used to be air at 7oC and water flow at 35oC. However, in practice they may be required to produce water at approximately 55oC with
design ambient temperatures of circa -2oC. At these latter conditions **the output of many heat **
> pumps could be as little as 60% of the output at ‘standard’ (nominal) rating. For example a 13kW
ASHP may provide 13kW of heat at 7oC and 35oC flow temperature but it is unlikely to do this at an air temperature of -2oC and water flow at 55oC.
The actual output could be as little as 7-9kW and hence, if relied upon for the design of the system,
it will be vastly under-sized incurring the cost of expensive supplementary heating and/or lead to
issues of poor comfort.
This implies a massive output drop during defrost and yet there is no data that I have seen from any manufacturer that shows this drop. Try and spot the defrost affect below +4c on this Daikin graph for example.
As @TrystanLea has said the EN standard, on which MCS relies does suggest that defrosts are taken into account when stating the maximum capacities.
So on a key design point there is either something critically important that is completely missing in the manufacturers data (capacity with defrosts) AND/OR the test standard for capacity bears no relation to any realistic use in areas where the temps drop below 4c.
It makes me wonder whether something along the lines of the VW diesel emissions test defeat mechanism is at play here… but surely, that cannot be true as MCS would have picked up on it ?
Its like saying that the top speed of my car is 250mph … in a vacuum !
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I agree Colin.
There is a distinct lack of data and clarity about the most important aspects of how these heat pumps perform, stuff we need to know when making informed purchasing decisions.
Generally, it’s too late finding out what you wished you had known before buying once the thing has been installed and you come to use it in anger months later.
It’s all quite disappointing in many respects and it feels like the important stuff is hidden or not disclosed on purpose.
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