Has anyone been to check what is going on with the secondary side of the system with the UFH? I’ve not read all the posts recently. The minimum modulation of the 14 to the 11.2 is not that much I think, but can’t remember.

i just can’t help think that diagnosis over the internet with information that is only from the pump to the buffer and no idea what happening on the house side is be tricky at best. 

needs someone to come and fully inspect it all in my view. 

Posted by: @davidnolan22

↑

Has anyone been to check what is going on with the secondary side of the system with the UFH? I’ve not read all the posts recently. The minimum modulation of the 14 to the 11.2 is not that much I think, but can’t remember.

I haven’t looked at that side yet. But so far, the only thing that’s changed is that we’ve had the heat pump changed and COP is getting worse. 

I can see further tweaking will be beneficial but before I do that I want to figure out why we’re in a worse situation with the COP when nothing else has changed (aside from the weather but we were getting better COP in these temps previously). 

Part of me feels like we’ve shot ourselves in the foot getting the heat pump changed.

Posted by: @sandman1600

↑

Posted by: @davidnolan22

↑

Has anyone been to check what is going on with the secondary side of the system with the UFH? I’ve not read all the posts recently. The minimum modulation of the 14 to the 11.2 is not that much I think, but can’t remember.

I haven’t looked at that side yet. But so far, the only thing that’s changed is that we’ve had the heat pump changed and COP is getting worse. 

I can see further tweaking will be beneficial but before I do that I want to figure out why we’re in a worse situation with the COP when nothing else has changed (aside from the weather but we were getting better COP in these temps previously). 

Part of me feels like we’ve shot ourselves in the foot getting the heat pump changed.

 

 

 

Im really gutted for you, there are loads of Ecodan 11.2kW machines out there and its a very popular and well renowned make, so it should work well.   The current weather isnt particularly helpful for diagnosis!

Looking at the graph, I would say that the pattern of COP over the same period (up in the middle, down at either end) is actually rather similar to mine - which should give some comfort.  However overall the value is still low.  I guess this might be suggesting that the switch may not have made an obvious difference.  If this turns out to be the case it wouldn't be surprising given the weather - the greatest difference is more likely to be at a steady 6-10C).  Can you clarify the meaning of the the bar and the black line.  Also if you would like to post some more plots with the other parameters, Im happy to comment, but at the same time accept you may be having doubts about advice received!

For me there are still principal questions now: 

• low COP at the heat pump - why?  
• what effect is the buffer having (and is the first linked to the second)?

There really aren't many reasons for low COP at heat pump (and Mitsubishi publish comprehensive specs so its easy to check - although quite challenging with the current weather).  Thus Im still wondering if the buffer is somehow contributing to this.  Some recent data plus some measurements of temperatures art the buffer may clarify.  Id particularly like to calculate cop when on to understand how much cycling is affecting things (if it is, doing something to increase the cycling period may have a significant effect).  It may be difficult to diagnose fully until we get a prolonged spell of fairly constant temperature, which might now be next season, but Im sure some progress can be made now

@sandman1600 I’ve been following this thread and although I understand your misgivings there is no way swapping an oversized heat pump for a smaller one is going to be the cause of worse COP. In my mind the problem is in the system design not the heat pump.

Keep your nerve, it may be a journey but I’m sure it will be worth it. 

the reason why cop is bad is the delta t's on the primary circuit are small, so its not giving out much energy by the mitshi calculations.  nobody knows what the delta t's are at the manifolds or on the secondary side. but, it sounds like the heat pump team think their responsibly stops at the buffer. they might be right. if you've got delta t's of 2 at the manifolds, then someone needs to slow the water down and look at total system volume. no one knows what the flows through the house are. is the flow rate still 28?

Posted by: @davidnolan22

↑

the reason why cop is bad is the delta t's on the primary circuit are small, so its not giving out much energy by the mitshi calculations.  nobody knows what the delta t's are at the manifolds or on the secondary side. but, it sounds like the heat pump team think their responsibly stops at the buffer. they might be right. if you've got delta t's of 2 at the manifolds, then someone needs to slow the water down and look at total system volume. no one knows what the flows through the house are. is the flow rate still 28?

I must say Im also coming to the conclusion that there is a problem of this nature.  OP has optimised the initially high flow temperature and its now reasonably low (given that there is, sadly, an almost certainly unnecessary buffer).  Thus, like you, I suspect that water flows are wrong.  I suggested he putting some temp sensors on the buffer ports to understand whats going on, for me thats the most likely next step.  Unfortunately I think installers see buffers as the solution to all problems involving potential mismatches between heat pump and heating system, as opposed to the cause of a high proportion of the problems reported on this forum.

[quote data-userid="6617" data-postid="44648"

The DHW COP is the worst we've had yet strangely. And there were no big drains on the water yesterday. It's like it's heating less frequently but having to use more energy to heat when it does kick in. I'll give it a few more days to see what it performs like.

How large is your tank you have reheat set at 5Cish depending on how much water you use you may not need to reheat.  Ignore what the tank temp is reading there could still be plenty of hot water available.  If you run a tap for a bit it could cause a reheat that will be very inefficient to raise it 5C.

We only heat overnight for 90 mins at 00.00 lasts all day even if the tank says it’s 20C there is still plenty of hot water for bath at 6.30

We only have the hot water schedule set for 2 hours 00.00 to 02.00 so it can’t reheat.

Posted by: @davidnolan22

↑

the reason why cop is bad is the delta t's on the primary circuit are small, so its not giving out much energy by the mitshi calculations.  nobody knows what the delta t's are at the manifolds or on the secondary side. but, it sounds like the heat pump team think their responsibly stops at the buffer. they might be right. if you've got delta t's of 2 at the manifolds, then someone needs to slow the water down and look at total system volume. no one knows what the flows through the house are. is the flow rate still 28?

Thanks. I still need to check this out. It's taken all my mental capacity to wrap my head around the heat pump. So it should be as simple as just adjusting the flow rate on each circuit on the manifold to lower it..? Is it best to try this a bit at a time to see how it goes? And then how do I judge if it's helping things? Just from the COP?

Flow rate according to the Mitsubishi panel currently is between 21 and 23.

Honestly I don't think there's much point in me questioning this with the people that installed the pump. They seem to have a very limited, narrow field of knowledge and no overall understanding. One actually admitted he'd never worked on an underfloor heating system before. 

Posted by: @jamespa

↑

I suggested he putting some temp sensors on the buffer ports to understand whats going on, for me thats the most likely next step.  Unfortunately I think installers see buffers as the solution to all problems involving potential mismatches between heat pump and heating system, as opposed to the cause of a high proportion of the problems reported on this forum.

Thanks James, this is still something on the to-do list. I know there's more diagnostics to be done. I was just hoping the new pump would stabilise things a little so the immediately worsening COP had me jumpy.

@gary The tank is 210 litres. I work from home as a baker so I can use a lot of water during the day but using the old MegaFlo and oil boiler, we never seemed to run out of (REALLY..!) hot water so maybe you have a point. It's certainly something we can take a look at. Thanks!

@sandman1600 

you need to measure whats going on really before you make loads of changes. If you can measure the temp of the flow and return to and from each manifold when the pump is running in steady state and see if it’s different from the primary flows on the mitshi controls.

if the delta t of the primary is still 2-3, but the delta t at the manifolds is more, then you need to open up the secondary flows more. But if it’s the same, the you probably need to play with pump speeds and slow the water down so it can transfer some heat.  But, and it’s a big bit. You don’t know if you’ve you 10 or 25 litres a minute going through the secondary side.  The problem can be of you say only have 15 litres a minute going through the house, then 7-10 litres just go straight back to the heat pump via the buffer. This narrows the delta t and shuts the pump off. 

You ideally need the same flow on the secondary side as the primary, which is a pain to know with a buffer.  I’ve got a low loss header which is a pain in the ass and I’d love the installer to bypass it 

I remember you saying all the pumps were on max, I doubt you need them all on max, but it’s best to try to measure whats going on.