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Bugger, no hot water?


joe90

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Just tried to do the washing up and water not hot, wifey then says “oh forgot to tell you my bath was not very warm “ I had just had a shower and was fine couple hours ago. Found the ASHP had gone into defrost mode (first time that I have ever noticed this). We have had a few very cold days and noticed the ASHP running much more that normal. I guess that the system was in DHW mode when it went into defrost mode so “stole” hot water from the DHW tank! I have put the immersion on, switched the ASHP off and collected logs for the wood burner. 

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Strange.  Mine only takes a couple of minutes to defrost so can't steal much heat from the tank.  Mine has been working fine these last few days with -9 nights and -2 days.  But just above 0 is worst for defrosting.

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3 minutes ago, PeterW said:

Don’t switch the ASHP off as it will soon defrost (mine is 10 mins max) and soon back to full power. 

It had not only defrosted but the fins were quite warm and still running on defrost, 

 

3 minutes ago, ProDave said:

Strange.  Mine only takes a couple of minutes to defrost so can't steal much heat from the tank.  Mine has been working fine these last few days with -9 nights and -2 days.  But just above 0 is worst for defrosting.

yes, never seen it defrost before. Will leave it off till the morning so I can monitor it when I get it running again.

 

How does an ASHP go into reverse? Does it have valves to reverse the flow?

 

I did mention a long time ago when planning mine that I wish it would just turn off before frosting rather than waste heat defrosting.

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2 hours ago, joe90 said:

It had not only defrosted but the fins were quite warm and still running on defrost, 

 

yes, never seen it defrost before. Will leave it off till the morning so I can monitor it when I get it running again.

 

How does an ASHP go into reverse? Does it have valves to reverse the flow?

 

I did mention a long time ago when planning mine that I wish it would just turn off before frosting rather than waste heat defrosting.

I was out in the garden once when mine defrosted.  you could see the ice build up.

 

The compressor and fan slowed and stopped.  There was a whir whir click as the 4 port valve changed position, then the fan and compressor re started.  After less than a minute you could see the ice melting and a puff of "steam" blew out.  Shortly after the fan and compressor stopped the click and whir as the valve changed position again and it re started as normal.  I was really surprised how quick it all happened.

 

I don't know if it only took heat from the house or whether it turned on it's inbuilt willis heater to aid the process.

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6 minutes ago, Temp said:

How do they know when to defrost? 


Some have air flow sensors (ice stops the airflow through the vanes) and others have thermistors in the vanes themselves that sense the temperature of the vanes as they ice up. In some instances they get warmer (airflow at -10°c replaced by solid ice at 0°c) but they sense rate of change of the temperature. It’s a pretty complex part of the control system. 

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30 minutes ago, ProDave said:

The compressor and fan slowed and stopped.  There was a whir whir click as the 4 port valve changed position, then the fan and compressor re started. 


ah, my compressor was running but not the fan ???. Will report back when I fire it up in the morning.. thanks all for your input.

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5 minutes ago, joe90 said:


ah, my compressor was running but not the fan ???. Will report back when I fire it up in the morning.. thanks all for your input.

You didn't accidentally unplug something when you had a nosey in there earlier?  Unplugged fan would cause it to ice up, then fail to defrost.

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Mine spent the day frosting and defrosting.. on either Thursday or Friday (can’t remember which now everyday is Groundhog Day).
It only took a few minutes to completely defrost, but with so much moisture in the air it only took about an hour to frost up again. 
With all the frosting a defrosting, it had icicles about a foot long. 
 

 

Edited by Gav_P
Typos
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While our temperatures have been cold for down here, they are not really cold, hovering between 0°C and 4°C.

With our relatively high humidity, this is the worse temperature range for an ASHP.  Not cold enough, for long enough, to condense moisture our of the air and lock it up as ice, and not hot enough to reduce the density of the air, and hence the amount of gaseous water in the air is at a maximum.

 

We knew it would happen @joe90's, just seems the last few winters have been exceptionally mild, and it is probably just a statistical fluke (stochastic) event, probably would not have noticed it via the house temperature, just that it happened when the ASHP was trying to heat the water.

Possibly, as a solution, in this type of weather, running the DHW cycle at the coldest time i.e. <=0°C, would produce less icing when the ASHP is working at its hardest.

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4 minutes ago, ProDave said:

You didn't accidentally unplug something when you had a nosey in there earlier?  Unplugged fan would cause it to ice up, then fail to defrost.

Nope, eyeball only. Let’s see what tomorrow brings, beddy  buys time ?

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10 hours ago, SteamyTea said:

While our temperatures have been cold for down here, they are not really cold, hovering between 0°C and 4°C.

Just done my Sunday morning ritual of processing my weather and energy data.

Mean temp has been 2.9°C and the mean RH has been 98%

Min Temp 0°C and Min RH 29% (probably last night as there is a hard frost this morning)

Max Temp 5.2°C and Max RH is 100% (this is where the sensors tops out, so it may have gone higher, as odd as that sounds)

 

Clipboard01.jpg

Edited by SteamyTea
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My A2A units stop the fan for the initial part of the defrost so I wouldn’t worry too much about that as long as it starts back up afterwards!

 

But I concur with the above, they’ve been defrosting much more the past week or so, very damp/foggy here

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I had a quick look at this with an ASHP defrosting and pulling the flow temperature down on the UFH flow for about 5 minutes. What was interesting is the flow dropped to about 15°C, but the return from the slab stayed pretty constant at 25°C during defrost so the slab was giving heat back to the ASHP to defrost. When it restarted the flow soon returned to normal. 
 

Need to get some proper monitoring in place tbh.! Thinking of building a 10 channel logger ... 

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2 minutes ago, JOE187 said:

Still  -4c here East sussex neighbours Air source iced up with the freezing fog yesterday and last nights cold temps, not a good advert for heat pumps!

Still -4 here. No ice forming at all and I am not aware of the ASHP defrosting for some time.

 

It is at or just above 0 with high humidity (fog) that is the problem region.  We don't seem to get that often here.

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Right chaps, ASHP behaving ok, light frosting and slowly bringing the buffer up to temp fir the UFH. DHW already hot because of immersion overnight ?.

 

I think I panicked when I saw it defrost as I had not seen it do that before and unfortunate that it was in DHW mode, recent bath and shower meant little hot water to defrost with. On further thinking my defrost mode pumped hot water through the fins but the fan was not on, if it was then the cold air would suck the heat from the fins even faster, so perhaps defrosting without the fan on is the best way.

 

Interesting that on one of the coldest nights without UFH the house temp dropped by less than 1/2 a degree, so insulation works (but don’t tell zoot ?).

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Glad to hear (in a nice way) that other people's heat pumps are icing up as I only have experienced mine for two weeks and it seems to ice up regularly and I thought I had problems that I did not know how to sort out!! Glad you got yours sorted @joe90 

 

 

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