@broadsman I've made it well-known, but I have been incredibly unimpressed with Samsung's terrible customer service and support.

Really glad to hear things have gone with Havenwise. @hcas (the guy behind Havenwise) has been doing a great job!

Posted by: @editor

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@broadsman I've made it well-known, but I have been incredibly unimpressed with Samsung's terrible customer service and support.

I didn't realise that Samsung even had customer support.  In my 'discovery phase' I asked them several questions and got precisely zero replies.  Even worse than Daikin who replied but, on almost every occasion, said 'ask your installer'.

I am still having issues with my Daikin Altherma 3 8kw. So I am looking to see if I can pull some information together to help resolve it. So all of you with the Altherma 3 8kw or 6kw, PLEASE HELP. 

So to outline the issue briefly. I run my ASHP in full weather dependent mode, with only one zone, ie the whole house . During the winter the default setting is 45c flow temp at -1.2c, with 25c at 16c . I have the default delta T of 10c as per the Daikin recommendation, but also because anything else would make the problem worse.

So at the coldest times my Heatpump should be able to output 7.8kw of heat according to the Daikin specification. However it does not, it is limited to 4.88kw. This is the limit placed on it by the settings in heating mode. The output is driven by the delta T and the flow rate. My flow rate when it’s running in settled mode,( ie has been running for a while ), is ~7lpm, actually it jumps around between 6.9lpm and 7.1lpm, but that’s all. When heating domestic hot water it’s fine and obviously is running off a different algorithm or instruction and can go as high as 24lpm.

My contention is that my Altherma is no different from anyone else’s Altherma and therefore this should be a problem for all Altherma’s unless they are somehow being operated differently. The only difference I have been made aware of is the homely app, apparently according to one user , the homely is able to vary the flow rate in heating mode and thus increase output. I have looked at a lot of the charts on the openenergymonitor site and what I see there seems to substantiate two things, firstly that resting flow rate does seem to be around the 7lpm for most altherma’s and secondly that I don’t see, or haven’t spotted any one getting over the 4.88kw.

So what I am hoping to get from people is that either they too have hit this limit or that they haven’t. Now if they haven’t I would like to understand the conditions that let their Altherma get above the 4.88kw of output. Clearly if they too have hit this limit what impact has it had for them on trying to reach temperature. From my experience the problem only matters with the temp below about 10c after 10c, the 4.88kw is enough .

Would appreciate your input. Thanks.

Are you sure the limit is not imposed by your emitters or pipework?

What is the design ft, loss and dt?

Have you tried reducing the flow to return DT which, at any given ft, will increase the emitter output (because the average room to rad dt is increased) and should cause the heat pump to increase flow rate, if it can within the water pump capacity given your pipework (and if it can't you may have found the problem)

What happens if you increase the ft thus increasing the emitter output?

Have you got a buffer tank between heat pump and emitters.

Has the throughput been throttled by insufficient diameter pipework or at the lsvs.

This feels like it may be a system design problem not a heat pump problem, which may be fixed by changing heat pump operating parameters.

@jamespa James thanks for your response. Neither emitters or pipework are a problem, I have 22m pipework with drop to 15 at rads. Emitters are big enough. It is clear to me that the problem lies with the heat pump in heating mode. Interestingly I was just re looking at the Daikin spec for the altherma 3, and I hadn’t noticed this before, but it says  the minimum flow rate for heating is 12 lpm , which is certainly not the case for me or anyone else, mine , as I notes runs at ~7lpm.

And no buffer tank, there was originally but that has all gone along with the hive controller.

You have à vaillant heat pump I see, which probably works differently and maybe does have a variable flow rate in heating mode, which the Daikin doesn’t have, once it’s into a run.  

OK, so the Daikin I believe by default adjusts flow rate to maintain roughly the set DT, although I think it might also have a fixed flow rate setting (which may be selected, but presumably not as you say you have 'set' the DT to 10 and you can only 'set' dt if the water pump adjusts it's speed in a feedback loop, otherwise it's determined by the heat output from the rads and the flow rate and is not something you can 'set' - that's just basic physics nothing to do with make of heat pump).

What happens when it hits the limit.  Does dt rise, fall or stay at 10.  This will give a clue to what's happening 

@jamespa . Hi James. With the daikin neither dT nor flow rate are controllable by the user. Daikin recommend a setting of 10 for radiators. It’s important to understand that if dT goes down, heat pump output goes down. Now in my experience the dT once it’s reached 10 never goes above 10, but it can and most often does drop below 10, which obviously further restricts output. Once a Daikin is just running the flow rate barely changes and this is where the physics comes in, because the heat output of the pump is determined by the delta t multiplied by the flow rate and if you can’t increase flow rate or delta t then you can’t increase heat output. So taking the max heat output at a delta t of 10 and a flow rate of 7, you get the 4.88kw of heat, which is someway of its supposed output of 7.5/7.8 kw.

i do have to query your assumption about the heat pump responding to the emitters, it doesn’t. The heat pump is driven simply by the return temperature, ie the delta t. The delta t will of course be influenced by the heat the emitters can take out of the water as it passes by, but that is their only influence. And I know you know this but just to remind folks, there are effectively two delta t’s the heat pumps delta t and the one for the emitters which is different.

Ok I'm not going to get into a chicken and egg discussion because it won't progress things. 

Irrespective of which comes first DT flow to return is determined by flow rate and rad emission, and the latter is determined by average DT rad to room.  You can't really 'set' flow to return DT, it is a consequence of these factors, unless your heat pump has a control loop specifically to do this, eg by varying the flow rate.  So unless it does this, dt flow to return will vary (this assumes that the principal control loop is the ft control loop, which if you are operating wc it is). 

I'm presuming, from what you say, that your house isn't warm enough at outside temperatures less than 10C, ie below this oat the iat falls.  However you also say flow to return dt remains at or below 10C and flow rate doesn't vary.   The only way these can all be the case is if the emissions from the radiators don't rise above 4.9kW even though the oat and IAT have fallen, which means that the flow temperature must start falling as the oat and iat falls, rather than rising in accordance with the design WC curve.  Is this what happens?

I'm assuming incidentally that you aren't being limited by thermostats or trvs, ie these are set above the target temperature, and your heat pump is operated 24*7.

If the above is an incorrect interpretation of the problem you have or your operating conditions perhaps you could clarify exactly what problem you are experiencing in terms of your house

@jamespa James, no the dT is set at 10, but it moves all the time, never above 10, but always below can go as low as 2. Yes at low temperatures , so say around 0c, the living room will get to about 13c , unless I also get some solar gain. And the lower dT goes the lower the heat pump output. The flow rate however does stay pretty flow moving between 6.9-7.1.

But the reason for my post is to try and capture other Daikin altherma’s experience to test the hypothesis that all have this fundamental glitch.

Posted by: @terry1812

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But the reason for my post is to try and capture other Daikin altherma’s experience to test the hypothesis that all have this fundamental glitch 

Noted.  There are plenty of 8kW Dawkins on openhearpump monitor that deliver around 8kW which is why i'm asking questions around the problem.

However since I'm not a Daikin owner I wilk refrained from further comment.

@jamespa James, i haven’t seen those ones that do deliver 8kw, so if you can point me in their direction that would be helpful.