Daikin Low Water Leaving Temperature

I wonder if someone here can help

We bought a house which has a slightly ageing Daikin EKHBRD-ACV1

We've had some renovations done and replaced the radiators downstairs with UFH controlled by a heatmiser wired system. This is controlled by wireless thermostats - which work fine - just opening/ closing the manifolds on demand.
There is a wireless demand switch back to the ASHP
Upstairs we have Tado TRVs which communicate to a Tado wireless receiver

Both the UFH and the Tado system seem to work properly - the LEDs all come on when they should

But they're not getting hot water from the ASHP. There is water flowing according the UFH manifold flow valves

The problem seems to be that whatever leaving temperature I set on the Daikin controller, the leaving temperature doesn't exceed about 30C

Hot water is fine

What could be causing the low leaving temperature?

(If this all sounds a little heath robinson, it is - the builder who installed most of it didn't get a heating engineer in - which was one of the many reasons we parted ways)

Thank you

A couple of issues come to mind based on your info.
Hot water may be ok due to the electric immersion heater doing all the work and your low leaving temp could be due to any number of issues, poor pipework design, lack of maintenance, shortage of refrigerant, diverter valve not working, control parameters incorrectly set even undersized system dating back to initial installation.

I would suggest that to get to the bottom of the issue, you contact Daikin service department and pay for them to come out and diagnose/set up the system correctly

Thanks very much for the reply Frank
We're working with a local company, but they've not had any experience with a unit this old. They've been in contact with Daikin and they're not entirely sure either..
But your suggestion to get in contact directly makes a lot of sense - I'll give that a go
Thank you

Hi mandraki - I'm interested to hear how you get/got on: I've a similar issue and I've had engineers out a few times but no one seems to be able to resolve the problem. I have a Daikin Altherma LT split (indoor unit: EHVH08S26CB9W, outdoor unit: ERLQ006CAV3) and it has never delivered a COP better than about 2. The domestic hot water is fine: the refrigerant temperature gets up to well over 60 degrees Celsius without any difficulty, and it heats the hot water to about 48 degrees without the back-up heaters kicking in.

The problems happen with the UFH: the system doesn't seem to be able to get the leaving water temperature up to much more than 28 or 29 degrees. The delta_T across the UFH is about 5 degrees with a flow rate of about 1.5 - 2 l/min. I live in Ireland so the outdoor temperature in winter ranges typically 2 - 10 degrees, which should be fine for this system.

I suppose I'm starting to wonder if a COP of more than 2 is realistically achievable.

Quote:

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Originally Posted by tdownes

Hi mandraki - I'm interested to hear how you get/got on: I've a similar issue and I've had engineers out a few times but no one seems to be able to resolve the problem. I have a Daikin Altherma LT split (indoor unit: EHVH08S26CB9W, outdoor unit: ERLQ006CAV3) and it has never delivered a COP better than about 2. The domestic hot water is fine: the refrigerant temperature gets up to well over 60 degrees Celsius without any difficulty, and it heats the hot water to about 48 degrees without the back-up heaters kicking in.

The problems happen with the UFH: the system doesn't seem to be able to get the leaving water temperature up to much more than 28 or 29 degrees. The delta_T across the UFH is about 5 degrees with a flow rate of about 1.5 - 2 l/min. I live in Ireland so the outdoor temperature in winter ranges typically 2 - 10 degrees, which should be fine for this system.

I suppose I'm starting to wonder if a COP of more than 2 is realistically achievable.

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What are the Leaving Water Terperature (LWT) and Return Water temperature (RWT) when the system is heating the DHW (tank)?
Is the LWT the same when the diverter valve changes over to Heating?
Do you have a blending valve on the UFH manifold?

With poor temps on Heating I would be looking for any areas where the flow can bypass/blend, i.e. through the Bypass valve etc.

Thanks for the reply Frank. No, the LWT and RWT are different when the system is doing the DHW - by that I mean that the system's sensors return different values. The LWT for the DHW is not something that I can easily see how to set: the LWT for the UFH is the one I have access to. The blending in the bypass valve is an interesting thought: It's on the boiler side of the UFH manifold and I've had to change it's setting from the manufacturer recommended value to ensure I get reasonable flow rates through the UFH loops - the changed setting on the bypass valve meets all the requirements (I got an engineer to look at it).

There's no blending valve on the UFH manifold, so I guess that's not causing the problem.

Sorry - to give a better picture, the LWT and RWT when the system is doing the DHW vary as the tank is being heated, and gets up to an LWT of about 50 and an RWT of about 47 or 48 before the BUH's kick in. I don't think I've ever seen an LWT of more than 30 or 31 when the system is doing the UFH even though the desired LWT is typically set at 35. I've played around with changing the desired LWT but it hasn't made much difference to the COP.

How are you calculating the cop? is the outdoor correctly sized, are flow rates correct as per the original design spec?

If you are getting decent flow temps on DHW heating then I would say the there is no issue on the refrigerant/ heat exchanger side.
It certainly says to me that the problem is on the valve/blending side.
Can you disable all UFH manifold heads apart from one and then see what your flow and return temps are?

I'm calculating the cop in two ways: the first is by looking at the total electricty consumed/energy produced figures given by the user interface. The second is an instantaneous cop calculated by looking at the flow rates and the delta T, together with a (good to within about 10%) estimate of the kW being used by the system. There are some occasions, always when the system is using a lot of kW, that the cop gets to around 3 - 3.5 (which seems OK to me, at outside temps of 2 or 3 degrees).

Good question about the sizing of the outdoor: I'll take a look, though the outdoor and indoor are paired properly. The floor area being heated is about 75 square metres.

Quote:

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Originally Posted by frank

If you are getting decent flow temps on DHW heating then I would say the there is no issue on the refrigerant/ heat exchanger side.
It certainly says to me that the problem is on the valve/blending side.
Can you disable all UFH manifold heads apart from one and then see what your flow and return temps are?

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That's really reassuring regarding the refrigerant/heat exchanger side of things, and probably explains why the service engineers never found anything. The blending issue sounds really interesting - I'll try what you suggest: I might have to wait a while until the weather warms up a bit though because the flow rates have to meet a minimum requirement (12 l/min) to ensure that defrosting doesn't cause the system to freeze ...

Quote:

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Originally Posted by al

How are you calculating the cop? is the outdoor correctly sized, are flow rates correct as per the original design spec?

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On the sizing of the system, one symptom seems to be the following: when a stat starts calling for heat the system starts up. For the next 30 - 40 mins the compressor seems to operate at a high power state, consuming about 3 kW. After that though, it drops to using about 1kW. It is in this low power state that the COP is poor (1.5 - 2 pretty much irrespective of the outdoor conditions). The LWT drops in the low power state, usually never having met the desired LWT (even while in the high power state).

Quote:

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Originally Posted by frank

If you are getting decent flow temps on DHW heating then I would say the there is no issue on the refrigerant/ heat exchanger side.
It certainly says to me that the problem is on the valve/blending side.
Can you disable all UFH manifold heads apart from one and then see what your flow and return temps are?

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Today's a really mild day so I've been playing around a bit with the manifold heads. The short answer is that the LWT gets to the desired temperature, even if it's 35 degrees, with only two loops open. If I choose the longest loops then the RWT is around 8 degrees lower than the LWT.

However, the system doesn't maintain the LWT at the desired temperature: after about 30 or 40 mins the LWT drops to around 28 or 29 degrees.

The situation is made dramatically worse if I open the bypass valve to the recommended setting: in this case the LWT is never reached at all.

Thanks again for all your comments: I'm going to get an engineer in again - the problem so far has been that all the engineers I've spoken to seem to think that a COP of 1.5 - 2 is all I should expect, but this isn't what Daikin have told me and it isn't what other friends who have heat pumps are experiencing.