Ecodan taking 30min to switch over from DHW to heating

[joth]

I have an 8.5kW Ecodan R32 with the FTC6 controller.

I'm (now) on Octopus Go, so trying to get as much DWH and heating action in the cheap hours of 0030-0430

Currently I have the loxone system call for heat and turn off my "DHW setback" at 0030.

 

I find it takes about 30mins, to 1am, to get the cylinder up to temp. Then the system sits idle for about 35mins before firing up the UFH zone.

 

Anyone else seen this long change over time? Any idea why it is there, or how to reduce it?  having the system sit for 30mins idle during the cheap rate is going to be an issue as it gets colder.

 

Ideally I'd run in parallel, have the "mid position" value use it's mid position and get the UFH circulating at the same time as it is running the DHW cycle, but I know it doesn't support that so I'd happily run the two serially, so long as I can remove this dead time between them 

 

Worse case I can disable ASHP from heating DHW at all during cheap rate and just sling on the immersion on then instead, 5p/unit is comparable to gas even without the ASHP COP but it does feel a, er, copout.

 

 

[Dan F]

I really doubt there would be support for running DHW/UFH at the same time, but may be wrong.  The change over times seems like a question for Ecodan technical support, I can see why it's fustrating though.  How are you triggering UFH?

[Dave C]

21 hours ago, joth said:

I have an 8.5kW Ecodan R32 with the FTC6 controller.

I'm (now) on Octopus Go, so trying to get as much DWH and heating action in the cheap hours of 0030-0430

 

 

Snap! (well, I have the 5kW Ecodan - but otherwise I'm doing exactly the same dance around trying to do as much on Octopus Go as possible).

 

30 minutes does seem slow - I haven't timed the switchover on mine exactly but it feels more like 5-10 minutes, which is a lot more reasonable.

 

Couple of ideas:

 

1) How sure are you the DHW is fully up to temperature? Might seem like a silly question, but ... when my Ecodan was put in, the installer hadn't set the pump speed(s) high enough - so the heat pump ran for ~30 minutes then cut out to prevent overheating. In my case, the DHW wasn't done after 30 minutes, but you do have a more powerful heat pump! If that's happening to you,  30 minutes might be enough to get the DHW nearly done, then it cuts out for a while? (Solution was just turn the pumps up!)

 

2) What's the max temperature you're aiming for on DHW? Is it possible the flow temperature when it's finishing off the hot water is too high for the UFH so it waits until things have cooled down?

 

3) Have you timed how long it takes to switch from UFH to DHW? If that's quicker, then bit of a hacky work around, but ... you could set the UFH to run from 00:30, and set the DHW to come on (overriding UFH) at 03:50 or so - that way you get 3h20m of UFH on cheap rate, then your 30m of DHW on cheap rate, and if the heat pump sits around in a mood from 04:30-05:00, well, who cares!

 

16 hours ago, Dan F said:

I really doubt there would be support for running DHW/UFH at the same time, but may be wrong.

 

Yeah - the Ecodan/FTC manual has a promising setup option for "simultaneous DHW+heating" but when you investigate the details, all that does is allow running the heat pump for heating and firing up the immersion for DHW at the same time ... they really don't want to run DHW+UFH simultaneously.

[joth]

Cheers both! Interesting to know I'm not alone!

The 30mins is based on the power consumption graph. e.g. here you see the DHW run from 00:30 to 01:17 and then it's all systems idle until 01:52 the UFH starts running. So yeah, 35mins idle ?

The tank temerature graph also lines up with this - it reaches target temp right on 01:17 so isn't any overrun while the pumps circulate to get it finally to temp or anything.

 

[yes, my domestic base-load of 400W sucks, that's a different conversation though]

 

I'm using the "dry contact" Z2 input to call for heat on UFH, and the "smart grid boost" dry contact to fire up the DHW. This is not ideal as smart grid boost pushes the target temp up to 56ºC. I think the ideal would be to just take it to about 50, and have another option to really boost it to 56 when we have lots of guest over or masses of excess sun or whatever.

I enable both these relays simultaneously at 00:30 so it's the built in priority in the FTC6 that runs DHW first then the UFH zone.

Having it run both at the same time was sort of a joke, but I think the immersion may actually be my best option here.

 

[ProDave]

Have you been up to witness exactly what it is doing during this time?

 

Could it be the water circulating through the system has been up to 56 degrees or more when doing DHW, then it switches back to space heating, and the water in the system is still hot and it takes that half an hour for it to cool down to heating temperature and put any demand on the heat pump.

 

Ours does something similar (different ASHP) but for a while after finishing DHW heating, the water in the system circulates at above heating demand temperature and if say only one UFH zone is actually calling for heat it can take a while for it to cool down before the ASHP next comes on.

 

The obvious way to test this or at least make sure you are getting the most out of the limited cheap rate period, is time the DHW cycle to happen at the end of the cheap period, not the start or the middle.

[dpmiller]

where is the UFH call signal coming from? Do I presume correctly that you aren't using a normal wiring box?

[joth]

24 minutes ago, ProDave said:

Have you been up to witness exactly what it is doing during this time?

 

No! It's a good question, I was hoping for an easy answer here rather than have to do that.

 

25 minutes ago, ProDave said:

Could it be the water circulating through the system has been up to 56 degrees or more when doing DHW, then it switches back to space heating, and the water in the system is still hot and it takes that half an hour for it to cool down to heating temperature and put any demand on the heat pump.

 

 

Ah good thought, I think it could well be something along these lines. This is the UFH flow temp at the same time

 

There's a small slug of 23ºC water at the moment the DHW turns off 01:17, then at 01:52 it starts running the UFH proper. If for some reason that initial slug is just as the electronic mixing valve shuts down, it will indeed take a bunch of time for the water to cool if it's just circulating in the primary circuit and low loss header. (I definitely wish we'd put a large buffer tank in, as then this would be filling that up, rather than most likely being wasted to outdoors in the external pipework.)

 

And again I think you're right that running the DHW at the end of cheap rate is going to be the only/best way to solve it. I've not programmed it to do UFH first and if that reaches target it will do a "boost" on the DHW. I need to program in an extra test that if the tank middle stat temp is too low (below 40?) it will force override the UFH with 30mins of DHW from 0400-0430

 

Thanks!

 

16 minutes ago, dpmiller said:

where is the UFH call signal coming from? Do I presume correctly that you aren't using a normal wiring box?

 

No it's driven from Loxone miniserver relay outputs, so I can make as complex control logic as I care on all this. (Although trying to KISS as far as I can, future me will be grateful for that) 

 

 

[joth]

Just to close the thread here: setting the DHW to heat at 4am for 30mins mostly solved this, giving me 3.5 hours of cheap rate heating (octopus Go) followed by 30min DHW heat up with no time wasted in system cool down.

 

One thing I found was my dry-contact relay control was a bit blunt and also messed up historic charts making it hard to see what was going on (as I was descreasing the thermistor reported resistance to emulate a "setback" temp, which causes it to report a higher tank temperature than actual).

 So I've switched to a 100% software approach: the Home Assistant Ecodan integration works very well to set target temp and also enable "force heat hot water mode".  So I now have very fine control, based on the electricity price, PV generation, number of people staying in the house, and forecast sunshine for the coming day, I can tweak the target temp from 40 right up to 55C, set force heat mode, and turn on the immersion heater as needed.

 

Here's a few days of it working nicely. (Spare room was in use on the 19th so you can see the elevated target temp at work, and some extra showers in the day causing a larger DHW draw off)

 

 

 

I've made a similar algorithm for house heating --- if it's really cold out and the house mean temperature is falling behind target I sling on a variable number of the electric bathroom UFH and towel rails in the cheap rate too, just to boost up total consumption during cheap rate. (likewise if the PV starts making a lot of excess -- very unlikely in December!!)

 

Edited December 20, 2021 by joth

[Luke1]

2 hours ago, joth said:

Just to close the thread here: setting the DHW to heat at 4am for 30mins mostly solved this, giving me 3.5 hours of cheap rate heating (octopus Go) followed by 30min DHW heat up with no time wasted in system cool down.

 

One thing I found was my dry-contact relay control was a bit blunt and also messed up historic charts making it hard to see what was going on (as I was descreasing the thermistor reported resistance to emulate a "setback" temp, which causes it to report a higher tank temperature than actual).

 So I've switched to a 100% software approach: the Home Assistant Ecodan integration works very well to set target temp and also enable "force heat hot water mode".  So I now have very fine control, based on the electricity price, PV generation, number of people staying in the house, and forecast sunshine for the coming day, I can tweak the target temp from 40 right up to 55C, set force heat mode, and turn on the immersion heater as needed.

 

 

 

Thats very interesting, my Nibe allows me to set a schedule which can increase the DHW to luxury for certain periods, likewise the heating can also be scheduled to move the setpoint up and down. I'm now also making much better use of night rate electricity to heat the DHW and put as much heat into the house over night as possible. (My night rate is over 2 separate periods hence the wild swing in flow temp)

How do you determine an increase in number of people in the house, to increase DHW temp?

 

Nice to see someone else using Home Assistant too. It can make some nice graphs to track use etc.

 

[joth]

1 hour ago, Luke1 said:

How do you determine an increase in number of people in the house, to increase DHW temp?

 

 

The main logic is in Loxone miniserver (I just use Home assistant to do analysis/logging, and SW interface to things Loxone doesn't have native support for -- Z-wave roof windows, ASHP and MVHR controls, media devices, etc).

The logic is driven  from the alarm integration, for each room: "if the alarm is night armed, and the given bedroom door is closed but any motion is sensed within the room, assume that room is in use for the night" . Logic resets at 2pm each day, or something.

 This is a very useful signal to disable automatic blinds and lighting in that room (we've had some "exposure" to the neighbourhood first time we had guests and the blinds opened automatically at 9am!) and I can count up the number of rooms in use to gauge extra hot water needed.