Daikin: Defrost cycle pulled heat from DHW

[alibloke (Ali)]

Here’s an odd one. I have dhw set on “comfort” from 3am to 7am to take advantage of off peak tariffs. This morning was my first proper defrost since install in April last year and it appears to have opened the three port valve to take heat from the dhw. Tank temperature dropped from 50 to 44 degrees.

I’ve never seen this before, any ideas what’s going on here?

Link to my emoncms if you want to look in detail:
https://myheatpump.uk/app/view?name=DaikinEDLA08E2V3&readkey=4b67a63aec8b77bd655bab9680b01203

[Timbones (Tim)]

Your system details

If the volume of the radiator circuit isn’t very big, it might be better to use the hot water cylinder for defrosts instead. Means hotter water to defrost the coils, and the radiators won’t drop in temperature during the defrost.

I guess this is a setting within the Daikin? I can’t find any other systems doing this, though I think I remember a Samsung unit also defrosting from DHW.

[meatballs (Ben)]

How are you determining DHW is on?

[alibloke (Ali)]

We have 15 rads and a 20L volumizer, seems odd in comparison to other systems.

[alibloke (Ali)]

This is an ESPAltherma monitor which includes the three way valve. Also the dhw temperature dropped significantly during the defrost at 6:11am:

[meatballs (Ben)]

Ah well that correlates well I guess.

I have noticed similar behaviour (at least from the sensors), but I still used backup heater during that time and it was unclear if the ESBE valve was actually opened as the flow temp dropped so much:

Daikin Heat Pump ESPAltherma / HomeAssistant installer bundle for emoncms

Erm not sure I have the best logic for it, as my main concern was stopping it tagging DHW periods in the middle of the day when it was defrosting. There’s a potential that this could tag a DHW defrost against climate stats: espaltherma_dhw_on: friendly_name: "Altherma DHW On" value_template: "{{ states('sensor.espaltherma_esbe_valve') == 'ON' and states('sensor.espaltherma_defrost_operation') != 'ON' }}" I could probably check against the I/U operation mode on mine as it report…

I changed the logic for mine, as I was incorrectly tagging the DHW ON for defrosts to:

    espaltherma_dhw_on:
      friendly_name: "Altherma DHW On"
      value_template: "{{ (states('sensor.espaltherma_iuoperation') == 'DHW') or ( (states('sensor.espaltherma_iuoperation') == 'Heating + DHW') and (states('sensor.espaltherma_esbe_valve') == 'ON') ) }}"

Previous was

        #      value_template: "{{ states('sensor.espaltherma_esbe_valve') == 'ON' and states('sensor.espaltherma_defrost_operation') != 'ON' }}"

I have a hydrosplit unit so behaviour likely to different with backup heaters etc.

[Mld (Mark)]

My recently installed Daikin is doing the same thing. Every time it does a defrost it steals hot water from the tank. So with multiple defrosts a day I never have a full tank of hot water.

[alibloke (Ali)]

I had my three way valve checked out, no issues there. Annoyingly I haven’t had a defrost cycle since this issue so I haven’t been able to follow up.

[Mld (Mark)]

Its doing it daily for me right now. Got caught short yesterday morning with not enough hot water for morning showers as the defrost stole the hot water just before we got up.

Hot water schedule only, no reheat

Here is todays

[Mld (Mark)]

and for reference this is a scheduled hot water heat event

[Lakee (Tony Lake)]

Not sure about Daikin etc, but Panasonic now have a DHW for defrost option, to avoid cold rads/fan coils to improve heating comfort, if need be. If your diverter valve is actively switching to DHW position during defrost, then it suggests it’s something along these lines - if it’s not then maybe a faulty diverter valve, or odd pipework? Maybe ask your installer if there’s a setting and/or check valve etc.

[SarahH (Sarah Hanson)]

Another data point for you:
Samsung UK Tech Helpdesk tell me that for defrost heat Samsung Gen 6s use whichever heat reservoir happens to be in use when the defrost demand starts, thus (by default) DHW tank if a DHW cycle is in progress, and the emitter circuit (including any installed volumiser/buffer tank) otherwise.
So if you have a Samsung it might be wise to programme DHW cycles when defrost demands are least likely (e.g. daytime) if cooler hot water might be a problem for you (though surely a cold shower never hurt anyone… .).

[squarepeg77 (Jonathan)]

I am fascinated by this chart. My Daikin 9kW also switches the 3-way valve to DHW for some defrost cycles - when the DHW temp is much higher than house/flow temps, I suspect.

However I have never noticed an appreciable drop in the DHW tank temperature due to a defrost. It’s not actually using hot water from the tank, right? It’s just circulating water through the loop that goes through the tank, so it takes out a bit of energy, but surely not much in ~5-8 minutes?

[Mld (Mark)]

@squarepeg77

I am fascinated by this chart. My Daikin 9kW also switches the 3-way valve to DHW for some defrost cycles - when the DHW temp is much higher than house/flow temps, I suspect.

I am suspecting the same thing, as it looks like it does not happen on every defrost event.

@squarepeg77

However I have never noticed an appreciable drop in the DHW tank temperature due to a defrost. It’s not actually using hot water from the tank, right? It’s just circulating water through the loop that goes through the tank, so it takes out a bit of energy, but surely not much in ~5-8 minutes?

Good point, but it did leave me short of hot water for showers one day, which is what brought it to my attention, well more specifically my wife’s attention and then mine very shortly afterwards.

On the day we noticed the behaviour, it was doing multiple defrosts that day, despite it being a mild day (~15C). Its not done it since and we have plenty of hot water for showers without having changed anything.

[alibloke (Ali)]

so it takes out a bit of energy, but surely not much in ~5-8 minutes?

I could only fit in a 180L tank into my airing cupboard and need as much heat as possible to service the showers for the day whilst not boosting during peak rate times. I lost 6 degrees during the defrost that I initially posted about which is very annoying.

[Mld (Mark)]

180L tank here as well.

I will monitor the leaving water temp on a defrost event, alongside the tank temp and valve position to look for any correlation.

[Mld (Mark)]

Here is another example. The first hot water temp drop is a morning shower and then the second a defrost. I’ve added in the leaving water temp for reference.

I will keep an eye on defrost events with higher leaving water temps

[alibloke (Ali)]

Rather cold this morning, got down to under 2 degrees. Had two defrosts, the first took energy from the hwt. Emailed Octopus again and they replied with the following suggestions:

1. Settings: Ensure that the hot water priority settings are correctly configured. Sometimes, adjusting the flow temperature or the schedule can help manage how the heat pump interacts with your hot water tank.
2. Thermostat: If your thermostat is set too high, it may cause the heat pump to pull more heat than necessary. Consider lowering the temperature setting slightly to see if that helps.
3. Defrost Cycle: If the defrost cycle is occurring too frequently, it may indicate an issue with the heat pump’s operation.

Not very useful, I’ll bother them some more.

[Mld (Mark)]

Would be good to know what they consider is too frequent for the defrost cycle.

[Mld (Mark)]

Higher leaving water temp and this defrost cycle didn’t cause the 3 way valve to operate and no hot water was stolen!