thank you that's very good to hear, I will hopefully start the mods at the end of the week all going well.

alongside I plan to rewire so the main FTC display will be the one thermostat its downstairs in the centre of the house and the bedrooms will just act as temperature limiters

@rich I agree with your assessment that your pump is oversized, I have the same unit in a similarly-sized house with a design temp of 50° at -2.5 and I have come to the same conclusion. MCS heat loss assessments are notoriously pessimistic compared to how people find their houses perform, and EPC values are an over-generalised, rushed, stab in the dark. Unfortunately these are the figures that your plumbers supplied to Mitsubishi to get the OK for the system they put in. The SCOP value will assume far more heat is being supplied and probably has no idea of how much baseload all those pumps are drawing.

I slightly disagree with Derek’s statement that running at 33 at 0C is not a matter for concern in that it does show that you don’t need a large heat input at a low OAT but need even less for the vast majority of the time. I certainly find that my 8.5kW unit only runs continuously at 3°C or below, above that it cycles as it can’t modulate down far enough, and it cycled more frequently under WC than it does with AA. Rather than have the lowest flow temp but have pumps running circulating the heat 24 hrs a day, perhaps shorter defined on/off sessions charging the slabs at a higher temperature would work better for you. There are those who only run their HP during low-cost power periods but get enough heat in to last a whole day.

I suppose I should just point out that altering the pipework might well invalidate the Mitsubishi guarantee, if that is important to you. It is probably worth talking to them anyway whatever you do as they do seem to be quite customer friendly.

Thanks for the reply I haven't yet altered the pipework as decided the coldest part of the year is not the best time if anything was to go wrong,

I have to agree with you about the low flow temperatures not working out for efficient running mine suffers terribly and is cycled far to much at anything from about +2c  you can see the flow and return temperatures raising as the UFH can not give away any more heat and the heat pump is as low as it can go.

I think moving off weather compensation and having longer off times will work out more cost effective the issue I have at the moment is most of the pumps are not controlled via the FTC removing the pumps and turning the 3 remaining stats for temperature limiters leaving the main FTC as the one main stat goes hand it hand. Trying to rewire the pumps to do that will unfortunately be quite extensive.

In regards to the warranty this is not something I am really bothered about keeping I'm more keen on just having the simplest most efficient design 

Time for an update 

I had some time the last few days and with the warmer weather decided its now or never.

I'm no plumber but for a first go I am fairly happy, 4 pumps and the low loss header have now been removed.

I have had the system running for a few hours and am please to report monitoring the manifold l/min flow gauges before and after the mods there has been no loss in flow 😀 

I did then have to shut the system down as I have a leak that I will have to fix on Friday 

moving the dip switches to set up the new one zone I discovered several more errors like the PWM for the pump just being unplugged 

going forward I will look at balancing the system (upstairs return is much hotter) and changing my running style to auto adaption.

I've added some pictures 

Nice work - my system is almost identical to yours, I look forward to seeing if you get any efficiency benefits.

@rich congratulations. For doing this, and also on having the confidence in yourself to do this in winter. albeit you did check the forecast 😉

@rich

Well done.

@rich that is admirable. We’ll done. Looking forward to seeing how the system performs once you’ve balanced the rads.

morning all,

The system has now been running 24/7 since Friday in weather compensation mode and the house is sat at 21c downstairs 20c upstairs. 

so far we seem to have big electric savings I would put most of this down to the removal of all the extra pumps and control rather than heat pump as this still needs better control to get the most out of it.

I have slowed the upstairs flows to match the Delta T of downstairs as you can see the temperatures have become a lot better compared to the original. I am going to aliexpress some more cheap thermometer so I can better balance the system.

I briefly tried Auto adaption but this raised the flow temperature a lot, s this due to my heat pump constantly running around its lowest frequency (possibly oversized) I have used 540 code to see that I am getting a flow rate of 15 this seems ok but possibly a bit low for my heat pump?

today with it 5C outside I am still getting cycling so I am considering trying to schedule stops letting the slab cool slightly before adding more energy in what do you think?

please seen the before and after pictures of temps and flows

Looks good so far.  The cycling may be the low flow temps rather than the energy (although they are of course related).  Ecodans seem to struggle to maintain  LWTs in the low 30s.  When I'm running on WC I raise the LWT a bit more than is necessary and let the external stats limit the room temp, which does stop the ASHP periodically.  

Thanks yeah I am using the FTC controller as the stat so I am just trailing Advanced Auto Adaption however I have noticed this raises the LWT significantly 

Posted by: @rich

↑

Thanks yeah I am using the FTC controller as the stat so I am just trailing Advanced Auto Adaption however I have noticed this raises the LWT significantly 

I think auto adaption is best suited to fast response emitters, like rads or fan coils. It is essentially load compensation.