Frozen Heat Pump

matelodave

If the OP panicked and turned the heatpump off when he saw frost, whether from the mains or shutting down the hot water and heating thermostats then it wont defrost itself unless or until it gets turned back on to circulate the heating fluid.

I really think that there's lots of speculation and even scaremongering going on unless we can establish when it frosted up and how long it stayed frosted up whille it was, or should have been running normally - interrupting it's operation by shutting its down could do it more harm than good, especially if left long enough for either the refrigerant or circulating fluid to freeze.

Older heatpumps (like mine) have a cranlcase heater to stop that happening but it does have the disadvantage of a continuous so called "vampre" load

As @NedS say's above they only defrost when the machine thinks it needs to either on a timed cycle or when it thinks its cold enough. That could be once or twice a day, once an hour or once evry twenty minutes or so depending on the settings

matt_drummer

It used 48kWh of electricity to generate 48kWh of heat?

Doesn't sound right to me?

Neither of my heat pumps got iced up to that extent before they defrosted.

But, it isn't clear whether the heat pump is actually defrosting or not.

Leaving it sitting iced up with no water flowing doesn't sound like a good idea to me.

the_lunatic_is_in_my_head

Thanks for the further comments, it had a thinish layer of white frost on this morning but was pulling the air through no problem and outside temp is above zero so it has now defrosted. Main lesson here seems to be don't panic and turn it off! 

matt_drummer said:

It used 48kWh of electricity to generate 48kWh of heat?

Doesn't sound right to me?

Sorry it was 38Kw used, 48Kw generated. The panel shows what it has used and what it has generated so on a summers day when the house is warm and we just need the hot water it will say it's used 2Kw and generated 6Kw, I assumed that means 8Kw of energy has gone into the water (perhaps minus what ever it uses to run the fan and do it's thing).

michaels said:

Max draw for a 12kw heat pump will be about 4kw, the 12kw is output not input.

Ours has frosted up too for first time ever  
May try asking it to run AC mode for a bit as the defrost cycles don't seem to be long enough to melt it clean

I just assumed 12Kw was the max it would draw, it was using 5.8Kw continuous power yesterday when I put the hot water on. One of those things where when it's working as it should I, perhaps foolishly, don't think about how it all actually works. 

Thanks @NedS, I see the defrost mode you mention under settings and will keep an eye on it all this evening once the outside temperatures drop again to see what is happening, hopefully defrost is running and as suggested it's become stuck in a spiral of not be able to fully defrost. 

QrizB

the_lunatic_is_in_my_head said:

Thanks for the further comments, it had a thinish layer of white frost on this morning but was pulling the air through no problem and outside temp is above zero so it has now defrosted. Main lesson here seems to be don't panic and turn it off!

Glad it's thawed and you are back in business.

Sorry it was 38Kw used, 48Kw generated. ... it was using 5.8Kw continuous power yesterday when I put the hot water on.

So it sounds to me as though it might have been using a direct electric heater to provide some of your heat. Otherwise you've got a COP of 1.2 which is sub-optimal!

on a summers day when the house is warm and we just need the hot water it will say it's used 2Kw and generated 6Kw, I assumed that means 8Kw of energy has gone into the water

It's more likely that, in those circumstances, operating the heat pump is using 2kW and there are 6kW going into the water.

NedS

QrizB said:

Sorry it was 38Kw used, 48Kw generated. ... it was using 5.8Kw continuous power yesterday when I put the hot water on.

So it sounds to me as though it might have been using a direct electric heater to provide some of your heat. Otherwise you've got a COP of 1.2 which is sub-optimal!

Quite possible - there is a setting in the Samsung controller (FSV #3032) whereby if the DHW cycle is unable to complete (i.e, reach the set point temp) within a set amount of time, the immersion heater will kick in to assist. If the set amount of time is set too low, the immersion will keep kicking in and affect efficiency as you say.

I know from my own heat pump, a normal DHW reheat cycle for me takes around 30mins, but can easily take 45-50mins if the tank is very cold to start and a defrost cycle occurs before it can complete. I set #3032 to at least 60mins to allow sufficient time for a DHW reheat before reverting to the immersion heater. It may need to be set higher (90mins) for larger water cylinders above 200L.

NedS

the_lunatic_is_in_my_head said:

Thanks for the further comments, it had a thinish layer of white frost on this morning but was pulling the air through no problem and outside temp is above zero so it has now defrosted. Main lesson here seems to be don't panic and turn it off! 

matt_drummer said:

It used 48kWh of electricity to generate 48kWh of heat?

Doesn't sound right to me?

Sorry it was 38Kw used, 48Kw generated. The panel shows what it has used and what it has generated so on a summers day when the house is warm and we just need the hot water it will say it's used 2Kw and generated 6Kw, I assumed that means 8Kw of energy has gone into the water (perhaps minus what ever it uses to run the fan and do it's thing).

michaels said:

Max draw for a 12kw heat pump will be about 4kw, the 12kw is output not input.

Ours has frosted up too for first time ever  
May try asking it to run AC mode for a bit as the defrost cycles don't seem to be long enough to melt it clean

I just assumed 12Kw was the max it would draw, it was using 5.8Kw continuous power yesterday when I put the hot water on. One of those things where when it's working as it should I, perhaps foolishly, don't think about how it all actually works. 

Thanks @NedS, I see the defrost mode you mention under settings and will keep an eye on it all this evening once the outside temperatures drop again to see what is happening, hopefully defrost is running and as suggested it's become stuck in a spiral of not be able to fully defrost. 

Yes, when working flat out like that, at ambient temps below 2C, it will frost up pretty quickly (maybe 30mins). The left hand display on the controller screen (heating side) shows the water flow temperature - you can easily spot when a defrost cycle is in operation as the flow temp will plummet as heat is taken to perform the defrost operation. The whole defrost cycle should take around 5mins after which the heat pump will resume normal operation, but of course will probably run flat out again heating the water flow temp back to where it needs to be.

You can also see when a defrost cycle is in operation on your Smart Meter IHD as your electricity usage will suddenly fall. The heat pump usage will drop back to 1kWh or below during defrost, so if it was previously drawing 4-5kWh, it should be quite noticeable.

michaels

I think all manufacturers have different 'rules' on when and how often to defrost.  Ours seemed to suffer in the recent sub -5 temps with a build up of ice that entirely blocked the airflow through the fins after which the efficiency really declined.

WE don't have the auxiliary unit heater enabled which may be why ours did not defrost sufficiently.  Today I tried running it on cooling mode for 20 mins which cleared all the ice and back to normal efficiency.

NedS

michaels said:

I think all manufacturers have different 'rules' on when and how often to defrost.  Ours seemed to suffer in the recent sub -5 temps with a build up of ice that entirely blocked the airflow through the fins after which the efficiency really declined.

WE don't have the auxiliary unit heater enabled which may be why ours did not defrost sufficiently.  Today I tried running it on cooling mode for 20 mins which cleared all the ice and back to normal efficiency.

I've no idea what logic Samsung heat pumps use, but my Samsung gen6 unit manages defrost cycles automatically. No idea how, but once the back of the unit is white with frost/ice, it enters defrost mode and takes heat from the circulating water to defrost the unit. As I mentioned previously, the key is having sufficient volume of hot water to be able to effectively defrost the unit. I'm not sure if other makes use auxiliary heaters. I think Samsung units support auxiliary heaters but they are not installed by default (at least in the UK) as far as I'm aware.

the_lunatic_is_in_my_head

Thanks again NedS, the flow temp when the HW on was around 56 but it seems to sit at around 35-38 for the CH, possibly just wasn't enough heat to defrost. 

Ticking over nicely the last 2 days so no damage thankfully and now know what to keep an eye on next time the temperatures are around zero. 

NedS

There was an interesting video posted on youtube a couple days ago, stressing the importance of system volume, which is particularly relevant to defrost cycles:

https://www.youtube.com/watch?v=VSep35GB15Y

Samsung recommend a minimum system volume of 50L for your 12kW gen6 heat pump. Realistically, something around 180-200L would be recommended and should ensure there is no issues performing system defrosts once temps drop down to around 3C or below.

The video explains how you can calculate your system volume, made up from water in the radiators, pipework and any volumiser tank.