@toodles should it be tied shut like that.

Posted by: @david999

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@derek-m I was out looking again and no ice but was wondering if this pipe being cable tied is the cause.

The sensor to which I refer is located inside the unit and should be attached to the pipework coming out of the evaporator.

@david999 the OAT sensor on the back of my 8kW unit looks the same as yours. I think the actual sensor is towards the open end of the pipe and the cable tie will be holding the pipe tight to the cable back into the unit.

@sjn that makes sense

Posted by: @allyfish

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@derek-m interesting video. Stateside the defrost mode in A2A systems enables direct electric heating of the incoming air to avoid loss of heating function. Having got rather fed up over two winters with my A2W system doing exactly that - losing heating function during defrost, I've just enabled the 3kW immersion back-up heater on my system LLH, which was never wired up properly at install, or commissioned. Supplementary back-up heating will enable 3kW of direct electric heating during defrost if the LWT is below 38degC. I'm hoping it will help maintain target LWT during periods of regular defrost, and mitigate the time the ASHPs needs to reach LWT after defrost, but I may need to wait until next winter now to determine that. 😉

Achieving efficient defrosting is a problem with which a sufficiently large volumiser would probably assist, rather than using an immersion heater. When operating in heating mode the water in the volumiser is heated and therefore stores thermal energy, this thermal energy can therefore be used during the defrost cycle which should help reduce the possible cooling of the heat emitters.

Producing the thermal energy gradually using the heat pump should be more efficient than using an immersion heater during the defrost period.

@david999 Ah, that I don’t know, the one on ours has a tube or sleeve over it ‘pipette style’ and suspect that yours may follow the same scheme but on the other hand, it may be protective packaging and that it should just rest over the clip on the case. Perhaps you have access to the installer’s manual where you could determine which is the case. Regards, Toodles,

Why would a sensor for external air temperature be placed in the airflow being drawn through the fins?

Placing it within a sleeve might provide mechanical protection, but to me, it still seems to be a strange location.

@toodles yup I can feel the sensor inside so likely ok. Have swung a camera around to watch how it manages the ice. At 76 it’s nice that you keep an interest in these things, I’m 66 an engineer and still learning new stuff but it keeps you alive I say. 😊

@derek-m The nearest we have to a buffer is the LLH which I don’t think could hold more than a few litres at most; when the Daikin (no extra heating element involved) goes into defrost mode, the cycle lasts about 4 - 5 minutes at most and then the radiators start warming again. The radiators (10 plus towel rail) during a very cold day will drop to a ‘cold water; sort of temperature for those few minutes and then back in business and rarely have I been aware such a cycle is going on at all! Regards, Toodles.

@transparent Surely, if you need to know the OAT, the best place for the sensor is close to the air inlet for the pump? After all, that is the air that is about to enter the system. Regards, Toodles.

@toodles I installed so much insulation that when the installer moved a faulty room stat to another location he wired it wrong and it was two days before we realised the heating was off.

@david999 Indeed it does; I reckon that being so nosey and inquisitive keeps me going!😉 Regards, Toodles.