Heat Pump defrost cycle explained.

[@BenIsInSweden]

Good video! I think one of the other things worth mentioning is that defrosts are also affected by how close to max capacity the heat pump is running, as some people seem to think that they will always need frequent defrosts below 6C, but of course, there's some nuance. For example, in the 0C-5C defrost sweet spot, a properly designed system for space heating will have defrost cycles occur less frequently compared to when the heat pump is running at max capacity (e.g. DHW, or in a poorly designed system for the UK climate). And maybe getting a bit too detailed, but as the coil is now much warmer after defrosting, it can reclaim some of the energy used for defrosting when it switches back to heating. What blows my mind is that people use defrost cycles as an anti-heat pump excuse, yet are perfectly fine with a gas boiler constantly "wasting" heat through the flue - something that's entirely unavoidable. but hey ho! haters have got to have something to hark on about.

[@jfinnie78]

I suppose the reason they're cited as being an issue is that most people buy a heating system to keep warm, rather than to avoid heating the outdoors. So while it is true that boilers will lose heat through the flue, they're so massive that the system is still going to heat the house enough; that's never come up as an issue. Defrost cycles can cause the system not to do the job it's supposed to do, and that the video is being made and has the lengthy section on death spirals says this >is< an issue people are sadly finding. There's quite the drive at the moment to try and remove volumisers and buffers, which probably isn't helping either. Looking from the outside in, it seems that there is a bit of a design knifeedge being walked at present in terms of trying to tightly optimise the heatpump size, maximising sCOP (installer vanity?) and removing (arguably) unnecessary equipment, perhaps not helped by having incomplete data from the manufacturer as to what level of defrost losses they might see at different outdoor temperature / humidity levels. I think the difficulty facing homeowners at the moment is that given these things >can< happen, how can I be sure I don't end up with a system where they >do< happen. And it's not clear what the answer to that is. Given that even some of the best seem affected, perhaps the most important factor is having confidence that if you do have an issue, that the installer will still be there and be motivated to sort it out for you.

[@BenIsInSweden]

@jfinnie78 like with many things, there are often processes that seem wasteful but overall beneficial - e.g ice cars burning more fuel before getting up to temperature. Defrosts just seem like a "gotcha" for many that don't understand that when properly done you'll likely never notice it in a detrimental way. E.g. I can hear when any of my a2a heat pumps go into defrost if I'm near them, but it never results in an uncomfortable home etc. There is an issue that is amplified by Americans but that is pretty unique to American houses, with the poor building design putting the air handler and all the duct work outside the heating envelope, something that TC criticises in his furnaces are oversized video. That means for the defrost there is never enough heat for the inside unit to collect to perform the defrost effectively. Which is where you hear they need heat strips or some form of backup to provide the heat, and that they "blow cold out the registers". And you will get Brits repeating that without realising that it's a unique issue to American homes. The defrost spiral of death is definitely a thing, but is a result of something gone wrong with the installation to cause the unit to be undersized.

[@jfinnie78]

@@BenIsInSweden I've got a couple of A2A units in my home that I mostly use for cooling in summer (and emergency heating, don't really like the warm airstream effect) and I note that at least here in UK it's incredibly hard to get A2A units that would be small enough for typical rooms, which I think is one reason why defrost isn't an issue with them. My whole house heat loss at -2 is probably in the 4kWh region according to gas usage, yet because of where rooms are using A2A for the whole house heating would need 3 or 4 units and that would see me at likely 8kW+ of capacity. There seem to be more issues with defrost cycles with A2W systems where it seems the optimal sizing band is really being squeezed.

[@Rowlysrenewableroadshow]

@@BenIsInSweden this is so true the US hvac market is totally different to the uk heat pump market. For many states their cents per kWh are 50% that of the UK market and their reasons for having heat pumps are often a bi product of needing cooling during summer, along with a limited natural gas network heat pump CoP is not as critical.

[@NilsKall]

Interesting and professional video! Thank you!

[@AllElectricHouse]

Interesting video, I've always wondered how the defrost cycle works. I'm sure last year we ended up in the "death spiral". Seemed like the heat pump was working really hard, frosting up and then never really getting the house warm. I've changed things a little this year and so far seems better.

[@Belrmar]

My first guess would be underestimated the required power output or too small of a system volume, I'm probably wrong tho

[@M0j0]

Perfect timing! Thanks for the reassurance. Our 11kw Daikin altherma 3 monobloc is having it's first winter at our well insulated 6bed semi. We had 3 defrost cycles per hour at -2c and was worried it was faulty. The back up heater was kicking in at times which spiked consumption to 6kw from around 2.5kw tick over at -2c. .. But I've turned that off to see if the inside temp doesn't drop off too much. We prefer between 18c and 20c constant. Today it's 3c outside so can't test if turning the back up heater was a good or bad idea :)

[@timballam3675]

Having a lower flow temperature can cause problems increasing the required volume we had an extra volumiser specked on out 7kw Daikin Altherma 3 monobloc because we wanted a temperature of 18C backing down to 16C at night.

[@jeanh9641]

Thank you. A very informative video.

[@JohnBailey-n6w]

Good explanation, system volume is important!

[@Rowlysrenewableroadshow]

Absolutely!

[@raiphkay6829]

Samsung 8kW Gen 7 - just before a defrost cycle 72dB of noise. Thought it would walk off into the sunset ... Tried to record the noise the next day - only 60dB. I'll have to wait for colder weather to catch it doing it again. Are all HPs as 'quiet'?

[@Kasey84]

Please is there anyway I can email you a video of mine, I’ve never seen it do what it was doing I immediately cut it off because all I could see was what I thought was smoke, it’s 26°F here where I am.

[@janice9628]

Good explanation. My heat pump has been running in defrost mode off and on for a few days but the fan hasn’t been coming back on. I had someone check it, and they said it was okay due to the low temperature. Should I get a second opinion?

[@Alibloke]

Any clue why my Daikin opens the three port valve on the first defrost of the day and pulls heat from my hot water? I've a reasonable system volume with 15 rads + a 20L volumizer, though I do have 10mm microbore downstairs.

[@Rowlysrenewableroadshow]

Some heat pump decide where to pull heat from depending on current temperature. For instance if your heating water temp is low it may decide to use your domestic hot water as defrost source.

[@MarkCullen1]

Thanks, interesting. Clear explanation and presentation. (Camera seems a bit low, just mentioning).

[@Rowlysrenewableroadshow]

Noted

[@MacNeilR]

How loud is your defrost cycle? Our lines run across the basement's ceiling and we find it quite loud in the rooms above when the defrost cycle kicks in and for this reason we don't run the heat pump when the temp drops below 3c. We've had the company that installed it to verify and they say that it's normal but I'm finding out that they only recently began to service heat pumps. I would be interested in knowing what the sound is like for others.

[@Rowlysrenewableroadshow]

Our systems are Monoblock meaning all refrigeration components are in the unit outside. Heat is distributed via water to the house therefore defrost is silent in the house.

[@MacNeilR]

Thank you, that's something I've not considered.

[@giollaliddy5817]

is it using much electricity when it defrosts?

[@johntisbury]

Yes it does. Not as much as when heating.

[@jfinnie78]

@@johntisbury Double whammy though, as not only is it using electricity, it's also removing heat from the house that will have to be replaced...

[@johntisbury]

@ a defrost is around 4 minutes in duration & does not impact the house heat. If it does then there’s a query about the design of the system. System water volume will absorb the defrost with no impact.

[@jfinnie78]

@@johntisbury Sorry, but that is magical thinking... Where precisely do you think the heat that melts the ice is coming from?! It may not have a >large< impact, but it will undoubtedly have >some< impact, not >no< impact.

[@johntisbury]

@ if it has an impact then the system is incorrectly designed period!

[@WilliamHennessy-c7u]

Very good video! My system went into a spiral death last week when it was -2, it sucked all thr heat out of the house leading to flow temperature dropping to 17degrees.. how do i increase the system volume?? Samsung joule generate 5. I had changed my setting to weather compensation flow temp (-2,35 and 15,20). System was working perfectly. Thank you!!

[@Abhishek8720]

I have the same heat pump as you, and encountered this last year. With the coming cold snap I am worried it might happen again? Did you manage to fix it?

[@WilliamHennessy-c7u]

@Abhishek8720 hi are you using weather compensation? If so what settings? The issue has not happened since but I am nervous.. currently -1 outside and the flow rate is 33degrees

[@henrikprebennielsen4612]

Hej Der vejrforhold, som er uegnet for luft til vand varmepumper, hvis du afrimer 4*4 minutter i timen UPS. 16 minutter , det kræver et godt isoleret hus, jeg slukker for min varmepumpe, når minus varmepumpe dage kommer, som os mig er slud og sne og ca. 3 graders varme, tak for din gode video. (tænder op i brændeovnen)

[@LauraSwabe]

We need a heat pump that contains a de-humidifier before the air enters the evaporator. Does anyone make one?

[@Rowlysrenewableroadshow]

Heat Pumps work in the same way a dehumidifier does. Although your idea makes sense in principle it would basically be a heat pump in front of a heat pump 🙂

[@grahamersguy]

Our heat pump was frozen solid this morning, front to back of the fins, it almost seems like it forgot to defrost. then about 20 minutes before daytime set back, it decides to defrost. was 10degrees below flow temp the whole night. It's a r290 pump, so not sure if that makes any difference. Here's the video I sent to the installer kzbin.info/www/bejne/qWSxiYOshZpkqdEsi=muxjI3tR2TRmoXjK

[@BenIsInSweden]

Was it still able to heat just fine? As yours is a Warmflow R290, looking at the owner's manual it states (Page 20) that it senses the build-up. Essentially what Adam is saying at 8:30 in the video, so it's not based on how iced up it is, but how reduced the performance is. If your home was still heated just fine, and it defrosted without intervention, then it's just normal behaviour. If your home was struggling to be heated before it defrosted then something might be up.

[@hidinginmidlands8344]

Great video, thanks! It highlights the importance of system volume. Is there a way to quantify the reduction of the maximum output power of the heat pump, say between the worst-case scenario (frequent defrosts) vs best-case scenario (no defrosts), all else being equal? Given the rumours that some manufacturers don't account for defrosts in theiir performance tables (for example, Szymon from Urban Plumbers suggested that about Vaillant recently: kzbin.info/www/bejne/l4e6f3epgqmXhqs), this could help size heat pumps correctly?

[@BenIsInSweden]

An installer would need to estimate/assume the drop in output as a percentage due to defrosts, e.g for Szymon's case assuming defrosts take up 10% of the time, the 6.4kW output would be reduced to 5.76kW. And I don't know if Vaillant publishes data on the defrost strategy of the Arotherm Plus, which would make accurately accounting for them difficult. That is why I think in Szymon's case, it's the insulation isn't up to scratch, but I guess we will find out. My concern is that Szymon didn't mention OpenEnergyMonitor being installed on that one, which had it been, the data would have revealed what the problem was. Hopefully going forward it has been, as then it will show what the heat loss is of the property at the design temperature (if it reaches it this year), to prove whether, Szymon was spot on with the heat loss, or the poor insulation messed things up. Ironically, I asked ChatGPT what manufacturers include defrost cycles in their output tables, and the first one stated that typically will is Vaillant 😂

[@jfinnie78]

@@BenIsInSweden Is your math wrong? You appear to only be accounting for the lost heating from the time the heatpump isn't running. But the defrost not only prevents you heating, it is also removing heat during that time, which means that some of the heating time after the defrost time is also effectively lost, as it is making up for the lost heat.

[@BenIsInSweden]

@@jfinnie78 it's just an example/assumption as I said I don't think vaillant publish defrost data to work from, 10% isn't a hard and fast amount, its just easier to work with and is in the ball park. Not all heat used in the defrost cycle goes to waste either as the coil is still hot from the defrost so it will recover some of that heat in reducing the temperature of the coil again back down to below ambient.

[@JBLHPJ]

its not steam coming off the heat pump, its water vapour. there is no way the heatpump is boiling the ice off fins

[@Rowlysrenewableroadshow]

Fair comment, thanks for pointing it out. 👍

[@sygad1]

isn't water vapour the gaseous phase of water, which occurs at 100°C? How do you get water vapour at lower temps, genuine question

[@davideyres955]

@@sygad1it is water vapour that is then condensing out into water droplets because it’s colder than the dew point for that level of humidity in the vapour. Basically the same thing as clouds. All air has some degree of water vapour in it. It’s stays in the air and dosnt condense unless the temperature is below the dew temperature like on a metal car in the morning on a high humidity day.

[@henrikprebennielsen4612]

Det fleste har backup, på måske 3,000 Kilowatt tilskud, UPS Der nogle forbruger der har fået efter regninger på 25000 kr. i DK.

[@Rowlysrenewableroadshow]

Yea sure we have backup heaters, I always say they can be your best friend or your worst enemy. When you need them they’re great but if they run uncontrolled the customer will receive huge bills…..!