Posted by: @georgea

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Any recommendation to reduce the frequency of defrosts? I understand that these temps favour a lot defrosting (high humidity and temps 0-3C)

Thats a lot of defrosts although in fairness my Vaillant gets up to one per hour at times

I don't know what you can do, if there are plants or anything else causing humidity near by the move them, check that the airflow is unobstructed, thats about it sofaik.  Others may be able to help.  Do you live somewhere damp even for the UK?

Posted by: @jamespa

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Do you live somewhere damp even for the UK?

Cambridge, not the most humid place in the UK but there has been a lot of rain last few days so gardens are still soaked....

@georgea

It defrost more when working hard in cold/humid weather. The only way to get it to defrost less is to make it work less hard and produce less heat.  If it defrosts like that, keeps you warm and is at your design temp, then I would not worry about it, its not often at design temp. Its when ASHP are slightly undersized and they work that hard in more normal days that it becomes an issue. There has been some problems with units defrosting x 2 or 3 and then not outputting what they are meant to which can spiral temps in the house down, the machine works harder to raise the temp, its cant, defrost more..... That's a defrost spiral.  I''ve been in a few on them and have to manage my unit carefully and manually in cold weather 

@jamespa I decided to look at my Homely data for defrosts and the first of this season was on the 18th. November (I have only noticed 1 of them myself) but the Daikin EDLA03 8 kW Monobloc has actually had 9 since the 18th. The plot shows outside temperature at the times they occurred.

Considering I live within a mile of the River Thames (as the Fly Crows), this seems reasonable to me. A cycle takes ~8 mins. from start to finish; the radiators go cool for about ~ 3-4 minutes but otherwise, I would be unaware of the procedure happening at all.

BTW, I had an email today from Homely to say the beta testing of the new Homely programme starts today but I don’t know if my smart controller is in the trial or is one of the ‘control’ units they have decided on.

Regards, Toodles.

Posted by: @toodles

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@jamespa I decided to look at my Homely data for defrosts and the first of this season was on the 18th. November (I have only noticed 1 of them myself) but the Daikin EDLA03 8 kW Monobloc has actually had 9 since the 18th. The plot shows outside temperature at the times they occurred.

Regards, Toodles.

I wish I had only 9 defrosts in that timeframe.  I had 16 in the early morning of just the 26 Nov.

So far this month I've only had 1 defrost.

I'm already up to 10 today, it's played havoc with keeping the house up to temperatures and hammering the electric consumption.

Posted by: @njt

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So far this month I've only had 1 defrost.

I'm already up to 10 today, it's played havoc with keeping the house up to temperatures and hammering the electric consumption.

I suspect, but have no evidence, that defrost is very variable according to location and time.  There are places in the UK that are very humid and places that are very dry.  This is going to make a huge difference as is any front passing through.  Probably best not to worry unless its causing a problem that occurs frequently!  Obviously if it does cause a frequent problem that's a different matter!

@georgea 

You system isn't too different from mine. I don't have UFH and my house is a 2 bed mid-terrace so maybe a bit smaller. Heat loss 3.3 @ -3C though overestimated.

Is your emitter type UFH or radiator? I wouldn't expect fan coil with UFH. Try modulation at 4/5. Which may slow temp gain but with longer cycles isn't such an issue.

Your LWT of 39C could probably be brought down nearer to 36C at the cold end of the WD curve. There's plenty of flow rate capacity in the 4KW Daikin unless you have particularly restrictive pipe work.

Most of the time my LWT is ~33C with very low flow (7 l/m). WDC = 36C @ -5C & 26C @ 12C (I don't need heating above 12C OAT).

Posted by: @radwhisperer

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@georgea 

You system isn't too different from mine. I don't have UFH and my house is a 2 bed mid-terrace so maybe a bit smaller. Heat loss 3.3 @ -3C though overestimated.

Is your emitter type UFH or radiator? I wouldn't expect fan coil with UFH. Try modulation at 4/5. Which may slow temp gain but with longer cycles isn't such an issue.

Your LWT of 39C could probably be brought down nearer to 36C at the cold end of the WD curve. There's plenty of flow rate capacity in the 4KW Daikin unless you have particularly restrictive pipe work.

Most of the time my LWT is ~33C with very low flow (7 l/m). WDC = 36C @ -5C & 26C @ 12C (I don't need heating above 12C OAT).

Thanks for your response. 

I have UFH downstairs and radiators upstairs; and as I am in pure weather compensation there is no modulation setting. I was using madoka thermostat in milder weather and didnt find it comfortable. Indoor temp is now more stable, the only issue is the frequent defrosts when it gets colder. 

LWT of 39c is for outdoor temp of 3c, I'll try to come a bit lower (eg set 44-45c for -3) to see if it makes a difference. I dont have restrictive pipework and there are no zones in the system, everything is open. 

It is a steep learning curve for me if you imagine we had 3-4 frost days which are the first ones for the system....