Daikin LWT

I’ve recently had a Daikin 16kw HP installed.

I recently discussed switching to LWT mode only with Octopus who installed it. I’m struggling to find any documentation or understand how this works. Is the unit designed to be constantly on and adjust to the WD curve?

This seems counterintuitive…

We have Tado which I’m aiming to get rid of asap, and replace with the makoda.

We have a single zone now with UFH downstairs and radiators upstairs.

I think I’d need to turn the Tado on so it’s permanently on.

Then turn on LWT, with a potential lower temp between say 2200 & 0300 in the morning.

Is this how to run LWT?

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Sounds spot on.

Whats the model?

Daikin EDLA16D3V3 Altherma 3 Monoblock Air to Water Heat Pump 16Kw

I suppose my question is will this not use more energy?

Our -6 temp is currently set at 48 from memory.

If you can find the sweet spot for your comfort, emitter output (UFH, radiators) you may find running 24/7 at this point is cheaper than ramping up/down.

A few of us have this Daikin Altherma in 9/11/14/16 model designations. It’s the same unit with software restricted max output from what we can tell.

Seems to like flow temps around mid to high 30’s

Octopus and MCS are quite conservative on flow temps, so suggest putting tado to max, and lowering flow temperature until the house temperature drops/keeps in equilibrium.

Get a basic weather curve setup. Suggest no lower than ~32C at say 15C outside, and try no higher than 40C at -3C outside.

At design temperature (say -3C), the aim is to run 24hrs a day at lowest flow temperature possible.

Whats your dT set at? Ideally should be 5C (you can always change this), and is impacted by pipe sizing constraints. Lower the dT, the lower the flow temperature (massive factor in efficiency).

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Our dT is set at 5.

Upstairs has been fine, its actually the UFH specifically 2 rooms that have taken time to warm up.

We have a polypipe overlay system so the design temp of that was originally 55 with return of 50. Removing the actuators and balancing seems to have improved it somewhat.

I suppose if the flow temp is too high then overall LWT will work out more expensive to run?

I’ve tried to keep everything stable for the last week, rather than tweak.

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Have you tried opening the flow rate adjusters for each loop on the UFH?

I needed to re-balance our UFH once octopus had left.

You not only need to balance the loops amongst themselves, but against the radiators

That’s a great start if your pipework can take it.

What’s the maximum flow rate on max output you’re getting?

Do you know your heat loss (kW) at your design temperature?

I believe it was 11kw

I feel like the UFH is balanced well now. Just did upstairs and it’s fine.

Ideally like more flow in the 2 cold rooms, but the flow meters are open fully now.

“What’s the maximum flow rate on max output you’re getting?”

I think we get about 34l p/m there is a flow restrictor which doesn’t seem to do a lot tbh. I feel like the flow just bounces up and down. If that’s what you are asking.

We seem to have an issue with pressure loss which I plan to get octopus back out to try to rectify.

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Without knowing your specific setup, it might be worth considering you need to balance the UFH (the cold rooms?) against the radiators (the warmer rooms?) - maybe too much flow to the radiator circuit, starving the UFH? Just speculation, and it may not be that as all.

Was there this issue previously when you presumably had a boiler?

You could try restricting flow to the radiators (balance them against the UFH circuit)as they may have a lower pressure loss than the UFH.

34l/m seems border line for 11kW heat loss at dT5, but should be “ok”:

In fact the data sheet for the EDLA16 model specifically, states that it expects the max flow rate needed for max output to be:


See here the data sheet below for your model and the expectation flow rate:

Your pressure loss is indicated by the flow rate you’re getting at max pump speed/power in below image, and is much higher than shown on the data sheet on image above.

At dT5 with a flow rate of 46l/m the unit can potentially provide 16kW heat output (other constraints and factors may impact this however)

This indicates (from the information you’ve provided) that your pipework probably can’t cope with a dT of 5 (for what the model you have expects) as you’re saying a max of 34l/m is being achieved (presumably at max pump speed/power). You may need to increase dT to 6/7 to get the heat power required.

You can see going to dT6 with a flow rate of 34l/m increases available power output (at the expense of a higher flow temperature = lower efficiency).

That said, in another thread, I discussed finding Octopus :octopus: don’t power flush systems as part of the work, and my filter (x2) were badly clogged. My flow rate went from 22l/m to 34l/m when both cleaned out. Something to consider checking/assessing.

On a separate note: given your model indicates the presence of a BUH, do check if the BUH (backup heater for space heating) is kicking in and being used more that you think.

It has a CoP of 1.0, and IMO is very unlikely needed so can be safely disabled in the Daikin settings and the breaker flipped to the off position. (Both these point are reversible to be clear).

Do you have your data into EmonCMS (or better still published on heatpumpmonitor.org)?

Hope the above helps.


I think it was masked with the higher flow temperatures from the boiler tbh!

Lots of information to digest.

When they commissioned it they suggested a flow rate of 31l p/m.

I’ve just finished balancing upstairs and I kind of feel like it’s ok now.

There are 3 radiators supplied with microbore, I don’t think any of the runs are very long. In the coming months my plan is to get these upgraded.

I think that there is a slight adjustment I can make downstairs on 2 of the other circuits to slightly improve the perf of the other 2 rooms.

We had our system flushed about a year ago after an extension, prior to the HP installation.

I’ve only emon for our solar atm. No plan to extend it to the HP…

I think trying to drop the flow temp to see if I can maintain the equilibrium rather than increase/decrease heat and see if I can get LWT working.

My only concern is how low it will modulate down to, as the min today appears to be 1.3kw.

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Oh I might be wrong here, sorry!

I’d have to retest with the restrictor fully open and pump going - I find this hard to judge…

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If the 16 model of yours has same minimum input electricity attributes as the 9 and 11 models (and we believe it does as basically all components are the same), then mine and others on here never drop below ~920Watts at steady state and minimum output, so you should be expecting that kind of input power range.

Obviously you’re hoping to get as much output heat power as possible (high CoP), and flow temperature is by far the biggest factor on this.


Thanks for your help and information.

I’ll try LWT sometime next week after our initial heat and leave to run during the day with some of the settings you have suggested.

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Don’t think the BUH has run much… The booster heater has run a bit…

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Is that 1hr of BUH use? As in the below? (Just double checking the photo)

Daikin controller → Information → Running Hours → BUH

I would honestly disable its use (log in as “user profile” installer with code: 5678)

Then go to:

Daikin Controller —> Installer settings —> Backup Heater —> Operation —> “Restricted”

Then go back to main menu and “User Profile” —> “Advanced User (code: 1234)

I’m using the daikin heat and elec as my benchmarks to measure cop. I know these aren’t massively accurate but the best I can do without shelling out a chunk of cash for proper monitoring.

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Yes that’s correct, will disable tomorrow

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You should be ok, given you have a stated heat loss of 11kW, and the 16kW unit so there should be headroom there. See image below and yours is top right graph.

I will reiterate: when it gets to freezing in the U.K., we also have humidity very high, so these units frost up frequently and therefore need to defrost frequently.

This is normal, but around -2C to +3C capacity/output drops due to this (weirdly heat pump capacity/output increases or at least flatlines for a bit as it gets colder due to humidity dropping)

I don’t see it as an issue for you (but do keep flow temp below 45C at design temp as you can also see the capacity/output is also lower at higher flow temps, so not just an efficiency thing), but you can always reverse the parameter you’re changing for the BUH.

Well trying LWT with 40 @-3 and 30 at 15…

We had a really good run this morning but post the DHW cycle 1400 to 1500 it seems to be cycling.

Some of the spikes on the early run are due to the Eddi I need to put the CT clamp on the right feed, just not had time.

Know I’m only looking at a single view and will have to review COP comparatively to other days.

Compared to yesterday I think we’ll consume more energy for a similar day.

I’ve dropped the temp on the DHW to 45, still think I can get some better tweaks on this.

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