You should not normally hear the hiss of water running through the pipes, have the radiators been bled? Are you located in Italy by any chance?

The heat pump is designed to run almost continuously during the heating season, but if you prefer to have it stopping and starting the choice is yours.

I think the vessel to which you refer is a volume cylinder, which again, may or may not be required.

Italy!? Umm, no, Warwickshire!

The radiators have been fully bled, but some of them have to be quite closed to force enough hot water to the distant parts of the house (which, frustratingly, are also the colder ones, being on the north side!) and so this means you can hear the water going through a restricted space.

Thanks, it seems that the intermediate vessel is basically just adding volume to the circuit, i.e. a buffer tank of about 18 litres.  Once I realised there was no membrane inside, it started making sense... took a lot of Googling that one!  Looks like it's standard fit for Daikin heat pump systems.

I've now set the standard temperature to 18C in all rooms, except for briefly (but slowly) warming up the bathrooms in the morning, and the lounge in the evening, both up to 21C.  I'm also lagging the warm water pipework and in particular the intermediate vessel, as that's basically acting as a radiator in the installation room (a.k.a. downstairs loo!) which is wasteful.

Well, we've had a new low today. 16kWh in, 26kWh out.  Nice and mild (about 9C) and windy, 29-32C flow temperature, so it should be ideal conditions really.  SCOP=1.6.

Daikin are coming out next Thursday...

Posted by: @rgledhill

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Well, we've had a new low today. 16kWh in, 26kWh out.  Nice and mild (about 9C) and windy, 29-32C flow temperature, so it should be ideal conditions really.  SCOP=1.6.

Daikin are coming out next Thursday..

I have a Daikin Altherma LT system and currently the COP is around 2.6-2.7 so it definitely sounds like you have a problem. 
But having said that, 16kWh in doesn’t sound excessive as a daily figure. That’s about what I am using daily (sometimes it’s a bit lower, maybe 12-14 is average at the moment) for a 117 sq m three-bed end of terrace. 

BTW how are you recording your figures for the spreadsheet? Are you noting them down in real time or is there a way to access historic data?

Just to be sure, is the “energy out” data definitely the total (including input) and not just the extra energy created? I’m pretty sure all Daikin units do give the total but it’s worth checking. 

I know there was some confusion with another brand of heat pump because the energy out data doesn’t include the input, so you have to add 1 to the apparent COP. 

Thanks Bob. I'm just using figures from the front panel screen, nothing special.  It doesn't say anywhere about the energy out details, but I'm pretty sure it's total energy out rather than additional energy.

Had the engineer visit today and he can't find a cause for the problem. No loss of refrigerant, and he's confirmed the hissing sound isn't normal.  All pipework and installation looks sound, so he's referred it to his manager, suggesting they do some diagnostics logging from the unit for a few weeks to try and get some more information...

And overnight the unit failed with an overtemperature on the sensor on the outlet from the compressor... looks like a misbehaving valve which isn't thoroughly opening, so they are going to replace the external unit, and also the heat exchanger as a precaution.  Fingers crossed this will sort it!  They did confirm that it's operating way below spec.

Daikin have been out today and have diagnosed either a faulty pressure sensor or a constriction on the pipe, since the pressure reading that gives the temperature for the indoor unit is much higher than the actual pressure, causing the external unit to work too hard to provide the inlet compressed gas. Basically it's trying to work at about 50-60C temperatures all the time!  They're logging the behaviour and will next isolate the cause of the problem before rectifying it.

I have to say, Daikin are being really good on this one.

@rgledhill Sorry to hear of all your issues, but I've also been impressed with Daikin's service levels. Hope they get it all sorted for you soon.

Thanks Alastair!  It's looking hopeful now.  It's basically been about 30-50% below COP since day 1, yet we're still seeing about COP=3 at the moment, so I'm really looking forward to seeing what we get when it's sorted.  Before switching to the latest approach (set all TRVs to 22C and use flow temperature and lock valves to set actual room temperatures), we were seeing as low as 1.2 on cold winter days!

Ok, finally the problem has been solved!!

It seems the original problem was a faulty pressure sensor or pressure control board, causing the system to run out of spec and blow the heat exchanger.  Once this was replaced, the system no longer failed but still ran at a max COP of about 3 even in warm conditions.

Over Winter, it ran a very low COP of 1.x, even for heating. This was due to a misconfiguration whereby the anti pipe freezing system would force the backup (resistive) heater to work as early as only -2C, even though it's a split system so only R32 refrigerant was outside, requiring no such protection.  Resistive heater = COP of 1.0 of course.

After a bit of a mishap where an errant Daikin engineer overfilled it with refrigerant (about 2.3kg instead of 1.5kg) causing another failure, they replaced the pressure sensor and PCB, put in the correct 1.5kg of refrigerant. Meanwhile I set the system to have a low flow temperature of 28-32C, weather dependent.

We saw the COP rise to about 3, but still well below where it should be for such a low flow temperature.

Problem was - the flow temperature was now TOO low, so although the fan and pump were on minimum speed, it still had spare capacity, and so was less efficient.

So now the system is configured for 34-38C flow rate, and in "fan coil" mode instead of radiators, which gets the system to maintain a 5C temperature difference across the heat exchanger.

And now - COP of 2.8 at 0C average, and nearly 5 at 8C average!  Success!!

So my advice is to not set the flow temperature below about 34C and you'll be fine.

Massive thanks to Daikin UK, who persevered until it was sorted, when they could have shrugged their shoulders and played blame ping-pong with the installer. Excellent service.