Thank you gentlemen/people (can't be too careful now) perfectly reasoned arguments that fit the observed evidence. The only fly in this ointment is why the manufacturer does not mention this in it's otherwise clear and technical explanation of defrost. Taking a "tiny bit of heat from the HE at the end of the process" is the only mention. One would think if they were setting out to make such a video then the simplest route would be to say "we are briefly going to steal some heat from the house or DHW to defrost the HP" But they don't.
Sigh....split jury, should never have studied law!
@abernyte - you really can’t be too careful.... alas there is possibly another complication in the evidence..... @davidnolan22 has a Low Loss Header fitted and he has been discussing poor recovery after defrosts (presumably the poor recovery is of room temps via the heating circuits and isn’t a failure of the heat pump)
A Low Loss header is entirely capable of masking the size of the cooldown during a defrost if the flow rates are not balanced on both sides of the LLH.
If the exit flow to his rad circuit and his 2 UFH circuits does not match the flow rate of his primary pump then it is entirely possible that the heat pump just sees a smaller cool down temperature than is actually happening. A small distortion might not be a problem But it mightn’t be worth investigating.
If the chilled water from the defrost was sent in to the secondary circuit (radiators and UFH then there could be SLIGHTLY hotter water sent straight back to the return thermistor to give a false reading.
This graph shows our heat pump during a defrost and you can see quite a high temperature drop compared to David’s graph
This graph is very clear and our system has no LLH or buffer or separate circuits. In other words there is no opportunity for distortion (or mixing)
here is the same graph where ive tried to sketch the DT as an overlay to show what the flow Andy return temps would have been like had ther not been a defrost. Hopefully you can better see the true drops in temps for both flow and return.
As was said earlier these defrosts could be repeat events every hour which could significantly upset the heating continuity of the home.
ive posted David’s graph below for comparison and I hope it can be seen the temp drop does not look that severe, when in reality it is likely to be just as large a temp drop as my defrosts.
So @davidnolan22 this was one thought I had and perhaps you’ve done it. Regarding recovery after multiple defrosts- Have you checked with thermostats what the temperatures are on all your connection ports on your Low Loss Header? This might give you an indication where the dominant circuit is or if the circuits are well balanced.
Hi, ive read that a few times, I think I get what you mean
Yes, was definitely struggling to heat the house this winter at several points. But, I'm not sure if it was the defrosts that were the problem are the system design and how I was running it. My system was "designed" to run closed loop with fixed flow of 45 degrees. But my house would drop in temperature intolerably when it got close to freezing. When all the zones were calling for heat and the fixed flow was set to 45, it struggled like mad. The house dropped and I could never get it back.
But having worked through the "design" it seems that my emitter power was quite different in each zone. Overall I have 17Kw of emitter power at DT25 with an 11.2Kw heat pump. When all the emitters were open at the same and I was calling for 45 degrees, it could never get close, it sent the compressor to 120hz constantly and defrosted every 20 mins. And as I was running zones, the fabric of the house never got properly warm and the rooms were constantly going up and down in temp, and if the house got stuck too cold in minus weather, I could never get it back.
As for defrosting. On the old set up: all the systems flows kept running with defrost.
I then changed how I ran the system, all stats set to max and opened it all up all the time, only called got 28-34 degrees, but ran it constantly, and the house heated a lot better and held its heat. Ive only had a few minus days or periods since, but its been no problems with those temps with flows of 32 to 35, when its 3-5 degrees I'm running 26-28 degrees, no major cycling issues. With calling for lower flow temps it did defrost less and settled the whole system down, ran much calmer and less noisy and used less power.
However, the installer made some changes to try to help defrosts. but we, and I include the installer who designed everything, we're still trying to get me to 45 degrees. The changes they made were to swap the initial 35mm piped header for a larger volume low loss header and zone valve off this to close the secondary flows if possible with defrosts. This was (I think) to increase the volume in the primary circuit so the pump had more energy to defrost and not need to use the secondary flows.
I spoke to Mitsubishi, who said that the secondary flows should close and the pump should be OK to defrost of the primary loop as it only needs 9 litres or so to do this in our climate.
Anyhow, after the changes nothing has changed other than a small blending problem that has irritated me more than ruined the system. But now I think what's happening is that as I'm always running very cool water, the pump needs more energy than is currently in the primary circuit to defrost and has to keep the house flows open.
So in summary, I still don't full know if the Mitsubishi heat pump is meant to defrost on the primary loop if its got sufficient energy or not. I need to wait until next winter to full tests my system to see if the deforesting issues I had re surface, or I can ride through them. If I can't then I'm going to have to come up with a plan, a 3 piped buffer, or volumiser placed somewhere.
Do you think your drops look so much as your running at 40 in the picture and I'm running at 30. And, you retuns drop, but I've got 170l system volume and I get about on lap of the full circuit in a defrost so the return water does not drop until after the defrost finishes and its stole some from the UFH mainly. I think I've got this system pretty well balanced across the header now... Wow... long post. Time for a beer.
This post was modified 4 weeks ago by davidnolan22
Yes, was definitely struggling to heat the house this winter at several points. But, I'm not sure if it was the defrosts that were the problem are the system design and how I was running it. My system was "designed" to run closed loop with fixed flow of 45 degrees. But my house would drop in temperature intolerably when it got close to freezing. When all the zones were calling for heat and the fixed flow was set to 45, it struggled like mad. The house dropped and I could never get it back.
But having worked through the "design" it seems that my emitter power was quite different in each zone. Overall I have 17Kw of emitter power at DT25 with an 11.2Kw heat pump. When all the emitters were open at the same and I was calling for 45 degrees, it could never get close, it sent the compressor to 120hz constantly and defrosted every 20 mins. And as I was running zones, the fabric of the house never got properly warm and the rooms were constantly going up and down in temp, and if the house got stuck too cold in minus weather, I could never get it back.
As you say, your system appears to have plenty of emitter capacity for your HP size, if you’ve got 17kwh capacity at DT25. 17kw capacity becomes 4.98kwh output capacity at 32c flow temperature which is more than the minimum operating output for the heat pump model you have. So even when your flow temp is set to 33c there shouldn’t be any significant cycling.
I then changed how I ran the system, all stats set to max and opened it all up all the time, only called got 28-34 degrees, but ran it constantly, and the house heated a lot better and held its heat. Ive only had a few minus days or periods since, but its been no problems with those temps with flows of 32 to 35, when its 3-5 degrees I'm running 26-28 degrees, no major cycling issues. With calling for lower flow temps it did defrost less and settled the whole system down, ran much calmer and less noisy and used less power.
However, the installer made some changes to try to help defrosts. but we, and I include the installer who designed everything, we're still trying to get me to 45 degrees. The changes they made were to swap the initial 35mm piped header for a larger volume low loss header and zone valve off this to close the secondary flows if possible with defrosts. This was (I think) to increase the volume in the primary circuit so the pump had more energy to defrost and not need to use the secondary flows.
I spoke to Mitsubishi, who said that the secondary flows should close and the pump should be OK to defrost of the primary loop as it only needs 9 litres or so to do this in our climate.
So the issue of recovery after/during several defrosts may need to wait for a cold spell before you are able to test. But the issue of volume may be a factor. The latest thinking on design sizing of volume seems to be requiring over 20 ltrs volume per 1 KWsize of the heat pump. So for 11.2 model that would be 11.2 X 20. That would make for a 224ltr design volume.
Under floor heating is perfect for slow release of heat but they are not very good at adding volume.
I noticed on the sketch you sent earlier you had a circuit volume of 150 litres does this include the volume of the new, BIGGER LLH? What exactly is the volume of the new LLH. Reason for asking is that LLHs tend to be fairly small in volume eg 2 to 15 litres. (If it’s not very big you wouldn’t really benefit by converting it to a volumiser)
So if you’re not thinking of extending the radiators any time and why should you, then you might benefit from adding 50 or more litre volumiser * if the recovery problem persists.* This would give you a surplus supply of hot flow-temperature water.
I also noticed on the sketch that there wasn’t a primary pump before the buffer I guess there is one since the ecodan doesn’t have an internal circulator like other makes.
regarding placement of the volumiser if you needed one… (and since we are on the thread talking about correct placement of a volumiser)
I still think it should be placed on the Flow side after the DHW valve. That would be in position C on the attached sketch.
Special note: And since the tank would be constantly carrying high water temp it very much should be placed within the insulated envelope of the home. (Even insulated tanks lose heat over time.)
reason being the chilled defrost water has a chance to mix with the flow temp water in the tank before entering the emitter circuits.
Please feel free to discuss this hotly debated topic further….
Anyhow, after the changes nothing has changed other than a small blending problem that has irritated me more than ruined the system. But now I think what's happening is that as I'm always running very cool water, the pump needs more energy than is currently in the primary circuit to defrost and has to keep the house flows open.
So in summary, I still don't full know if the Mitsubishi heat pump is meant to defrost on the primary loop if its got sufficient energy or not. I need to wait until next winter to full tests my system to see if the deforesting issues I had re surface, or I can ride through them. If I can't then I'm going to have to come up with a plan, a 3 piped buffer, or volumiser placed somewhere.
In all this discussion, sorry I forgot to ask do you still run it in fixed flow temp or are you now working in Weather Compensation mode. Do you ever bother with Auto Adapt?
One key point I think is quite important is that LLHs and buffer tanks rely on balancing the flows entering and exiting the tank but they introduce inefficiencies if there is a blending or mixing problem. The other issue is you have no knowledge of the flow rate through the various other zones since the flow meter is installed on the primary side of the circuits.
They are supposedly rarely needed but obviously serve an important role where they are needed.
A volumiser on the other hand actually relies on blending and mixing when the situation of chilled water needs to be warmed before it enters the under floor heating circuit. I believe that radiators cope with recovery better than high mass underfloor heating.
This post was modified 4 weeks ago 2 times by SUNandAIR
Do you think your drops look so much as your running at 40 in the picture and I'm running at 30. And, you retuns drop, but I've got 170l system volume and I get about on lap of the full circuit in a defrost so the return water does not drop until after the defrost finishes and its stole some from the UFH mainly. I think I've got this system pretty well balanced across the header now... Wow... long post. Time for a beer.
Possibly 40c vs 30c flow has something to do with it…. Inevitably temp is what melts quicker. But what the graphs seem to show is both our Flow temps (LWT) appear to drop to similar degC fall 12c for yours and 15c for mine. The flow temps also both take about the same length of time to recover:- 16 minutes for your lwt recovery and 16 minutes for my lwt recovery. What is really different is that your RWT hardly drops more than 2c whereas mine drops 5c and takes 26 minutes to recover to its former 35c return temperature.
I have similar volume to yours but no UFH and no LLH. So yes perhaps your linear under floor heating means the feedback in temperature drop might be a lot longer.
And as you say, this might be robbing your heated slabs of some of the carefully built up heat your system had created. So is it not a fair question that this defrost-pause in heating followed by the “robbery” of heat with each cold influx from the defrost is what’s stopping your systems recovery to your target room temperature? just to be clear what now happens if you run your heating system at a LWT of 45c or maybe even 35c? Perhaps a WEATHER CURVE that is higher by only a few degrees might be all that you need to regain the room temps you’re after.
This post was modified 4 weeks ago 2 times by SUNandAIR
Yes, was definitely struggling to heat the house this winter at several points. But, I'm not sure if it was the defrosts that were the problem are the system design and how I was running it. My system was "designed" to run closed loop with fixed flow of 45 degrees. But my house would drop in temperature intolerably when it got close to freezing. When all the zones were calling for heat and the fixed flow was set to 45, it struggled like mad. The house dropped and I could never get it back.
But having worked through the "design" it seems that my emitter power was quite different in each zone. Overall I have 17Kw of emitter power at DT25 with an 11.2Kw heat pump. When all the emitters were open at the same and I was calling for 45 degrees, it could never get close, it sent the compressor to 120hz constantly and defrosted every 20 mins. And as I was running zones, the fabric of the house never got properly warm and the rooms were constantly going up and down in temp, and if the house got stuck too cold in minus weather, I could never get it back.
As you say, your system appears to have plenty of emitter capacity for your HP size, if you’ve got 17kwh capacity at DT25. 17kw capacity becomes 4.98kwh output capacity at 32c flow temperature which is more than the minimum operating output for the heat pump model you have. So even when your flow temp is set to 33c there shouldn’t be any significant cycling.
I then changed how I ran the system, all stats set to max and opened it all up all the time, only called got 28-34 degrees, but ran it constantly, and the house heated a lot better and held its heat. Ive only had a few minus days or periods since, but its been no problems with those temps with flows of 32 to 35, when its 3-5 degrees I'm running 26-28 degrees, no major cycling issues. With calling for lower flow temps it did defrost less and settled the whole system down, ran much calmer and less noisy and used less power.
However, the installer made some changes to try to help defrosts. but we, and I include the installer who designed everything, we're still trying to get me to 45 degrees. The changes they made were to swap the initial 35mm piped header for a larger volume low loss header and zone valve off this to close the secondary flows if possible with defrosts. This was (I think) to increase the volume in the primary circuit so the pump had more energy to defrost and not need to use the secondary flows.
I spoke to Mitsubishi, who said that the secondary flows should close and the pump should be OK to defrost of the primary loop as it only needs 9 litres or so to do this in our climate.
So the issue of recovery after/during several defrosts may need to wait for a cold spell before you are able to test. But the issue of volume may be a factor. The latest thinking on design sizing of volume seems to be requiring over 20 ltrs volume per 1 KWsize of the heat pump. So for 11.2 model that would be 11.2 X 20. That would make for a 224ltr design volume.
Under floor heating is perfect for slow release of heat but they are not very good at adding volume.
I noticed on the sketch you sent earlier you had a circuit volume of 150 litres does this include the volume of the new, BIGGER LLH? What exactly is the volume of the new LLH. Reason for asking is that LLHs tend to be fairly small in volume eg 2 to 15 litres. (If it’s not very big you wouldn’t really benefit by converting it to a volumiser)
So if you’re not thinking of extending the radiators any time and why should you, then you might benefit from adding 50 or more litre volumiser * if the recovery problem persists.* This would give you a surplus supply of hot flow-temperature water.
I also noticed on the sketch that there wasn’t a primary pump before the buffer I guess there is one since the ecodan doesn’t have an internal circulator like other makes.
regarding placement of the volumiser if you needed one… (and since we are on the thread talking about correct placement of a volumiser)
I still think it should be placed on the Flow side after the DHW valve. That would be in position C on the attached sketch.
Special note: And since the tank would be constantly carrying high water temp it very much should be placed within the insulated envelope of the home. (Even insulated tanks lose heat over time.)
reason being the chilled defrost water has a chance to mix with the flow temp water in the tank before entering the emitter circuits.
Please feel free to discuss this hotly debated topic further….
Anyhow, after the changes nothing has changed other than a small blending problem that has irritated me more than ruined the system. But now I think what's happening is that as I'm always running very cool water, the pump needs more energy than is currently in the primary circuit to defrost and has to keep the house flows open.
So in summary, I still don't full know if the Mitsubishi heat pump is meant to defrost on the primary loop if its got sufficient energy or not. I need to wait until next winter to full tests my system to see if the deforesting issues I had re surface, or I can ride through them. If I can't then I'm going to have to come up with a plan, a 3 piped buffer, or volumiser placed somewhere.
In all this discussion, sorry I forgot to ask do you still run it in fixed flow temp or are you now working in Weather Compensation mode. Do you ever bother with Auto Adapt?
One key point I think is quite important is that LLHs and buffer tanks rely on balancing the flows entering and exiting the tank but they introduce inefficiencies if there is a blending or mixing problem. The other issue is you have no knowledge of the flow rate through the various other zones since the flow meter is installed on the primary side of the circuits.
They are supposedly rarely needed but obviously serve an important role where they are needed.
A volumiser on the other hand actually relies on blending and mixing when the situation of chilled water needs to be warmed before it enters the under floor heating circuit. I believe that radiators cope with recovery better than high mass underfloor heating.
HI, yes, I forgot to add the primary pump! its on the return from LLH
I never bother with Auto adapt, I run the system all open, but run fixed flow where I control the flow temp, I'm looking to change this by next winter, but I just wanted to make sure my system was working. So, I'd look at the weather over night, set the flow manually and the change it in the day as it warms. This has given me a good idea about what temps do what at what weather. The weather comp on the R32 I struggle with, as my system tops out at 35-36 degrees, I can't get it higher. And the difference between a flow of 32 and 34 is really quite a bit. The temp probe on the back of the unit gets colder during a cycle due to it cooling as the unit does and this drives the temp up 2-3 which on my system is a really big change.
@davidnolan22 assume you have the flow rate set at 5, my system is the same I can't get it above 42C when its freezing outside, if I close off some loops it can get there, its just under sized I probably should have an 11.2 rather than an 8.5, when I did heat loss on heat punk it comes out as nearly 10kw but was surveyed at 8kw.
I dont wish to go back over material you may already have covered, but its perhaps worth observing that another forum member (@cathoderay) for several years couldn't work out why his house wouldn't warm even though all the indications were that the heat pump was oversized not undersized. Its not clear that its fully resolved but is looking a lot like it was a flow rate mismatch at the PHE used as system separation, resolved eventually by opening up some valves.
If you have any form of system separation its not inconceivable that you have a similar or related problem. Just saying but please accept my apologies if you have already been through all of this.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Its not the integral tank, so I have a separate pump.
My data from the second 1/2 of the winter is that 11.2 should be OK to cover this house.
I can not get my water above 36 degrees if its 10 degrees outside, let alone freezeing. The power gets lost in the 17kw of emitter capacity. The installer shoulder have spaced out the pipes a bit more in parts of the UFH.
it's the eveness of the spec. If your going to oversize, do it evenly. BUT, and it's a big BUT, having spent many hours and weeks playing with things, I've think I've got this in a place that a). can live with and b) is working well. But in very cold weather, the bedrooms still run 2-3 degrees cooler than the main house. But for the 2-3 weeks of the year that's its very cold, I think I can live with that.
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