What are the design principles informing the, ' which pump and UFH design' question

[akjos]

15 minutes ago, PhilT said:

Interesting piece of research by Brendon Uys. Just to clarify does the third option suggest a monobloc ASHP can pump the heating flow by itself? Mine (Ecodan R32) has a pump just inside the house right next to it - is that in addition to it's own pump? There is also another pump near the LLH dedicated to the radiator circuit. Is that a sub optimal config?

Some monobloc heatpumps have a pump inside the unit (ex. Midea), but others don't and need an external pump (ex. older Samsung, not sure about the newest gen).

Pressure drop across your whole heating system needs to be calculated, but if it falls within the capacity of the pump head, you can run the whole heating from the one pump (be it inside the unit or outside).

BUT that's only the case if you don't have any 4-port buffer, LLH or CCT which create hydraulic separation. If you do have any of 4-port buffer, LLH or CCT, you essentially have a primary and secondary circuit, then your circuits are separated and each needs its own pump. Primary circuit is from heatpump to 4-port buffer, LLH and back, and secondary circuit is from the separation to your heating emitters and back.

Edited January 25, 2023 by akjos

[PhilT]

30 minutes ago, akjos said:

Some monobloc heatpumps have a pump inside the unit (ex. Midea), but others don't and need an external pump (ex. older Samsung, not sure about the newest gen).

Pressure drop across your whole heating system needs to be calculated, but if it falls within the capacity of the pump head, you can run the whole heating from the one pump (be it inside the unit or outside).

BUT that's only the case if you don't have any 4-port buffer, LLH or CCT which create hydraulic separation. If you do have any of 4-port buffer, LLH or CCT, you essentially have a primary and secondary circuit, then your circuits are separated and each needs its own pump. Primary circuit is from heatpump to 4-port buffer, LLH and back, and secondary circuit is from the separation to your heating emitters and back.

thanks for that - the installer told me the LLH and secondary pump (both inside house next to DHW tank) were necessary for my microbore fed rad circuit. It's obviously nothing like the ideal circuit described by Brendon Uys but it's achieving a COP of at least 3.4 which seems quite good under the circumstances although I might try longer WC operation at reduced flow temps.

Edited January 25, 2023 by PhilT

[akjos]

1 minute ago, PhilT said:

thanks for that - the installer told me the LLH and secondary pump (both inside house next to DHW tank) were necessary for my microbore fed rad circuit. It's obviously nothing like the ideal circuit described by Brendon Uys but it's achieving a COP of at least 3.4 which seems quite good under the circumstances.

 

Makes sense. Microbore has a high pressure drop due to the small pipe diameter (meaning your pump needs to work harder to get the required flow rate through) so you need the additional pump. Your installer seems to have done the correct thing to hydraulically separate your circuits with a LLH, as otherwise the two pumps would work against each other and could lead to premature failure.

[IanR]

49 minutes ago, JohnMo said:

Not sure it does say a different conclusion, but that report is now very old and only really applied to fix speed heat pumps.

 

With regards the aspect being discussed here, Buffer tank effect on CoP, the report off the "Kiwa GASTEC at CRE" government website states: "Very little difference was seen in the predicted COP between the different configurations. (Indeed the errors in the predictions probably outweigh the difference, so this should not be relied upon for decision making)".

 

Where as the "Brendon Uys" suggestion shows a 28% reduction in CoP.

 

They are coming to different conclusions, with regards to buffer tank effect on CoP.

 

49 minutes ago, JohnMo said:

Report are written early 2000s when most heat pumps didn't modulate.

 

Recommendations states - for Installers Buffer tanks are unlikely to be required when the heat pump can modulate (i.e. if the heat pump is not fixed speed).

 

The report was first written in 2008, and does address that inverter heat pumps are less likely to require a buffer tanks, as you have noted. But there are still good reasons for some installations to have buffer tanks, so I am interested on their potential effect.

 

It's unfortunate that the "Brendon Uys" report has been written as if to prove what he felt was already the case, as well as advertise his services. When his findings did prove what he already believed top be the case, he didn't seek to explore alternative buffer/volumeiser configurations that were less onerous in the system CoP, such as not installing the buffer "outside".

 

Neither report is conclusive, but I feel the "Kiwa GASTEC at CRE" report takes a more balanced approach. There's no denying there will be greater loses from including an additional volume of warm water within the heating system, although that would hopefully be within the thermal envelope for the majority of installations. For a 4 port buffer there would also be an additional (low energy) pump that needs to be accounted for, although with the benefit of stratification if correctly sized.

 

You pays your money and you takes your choice - it's just a shame there's not more conclusive data for the home owner to rely upon.

[JohnMo]

Main differences I see

Brendon is actually using a modulating ASHP, trying to simulate real conditions, and controlling heat absorption rates within the simulated house.  This goes a long way to represent real life conditions of wanting your house a set temperature. 

 

The Kiwa is testing with electric immersion heaters, and seems not to report or include output monitoring or compensation.

 

As you say

 

52 minutes ago, IanR said:

You pays your money and you takes your choice

 

[JamesPa]

1 hour ago, IanR said:

Neither report is conclusive, but I feel the "Kiwa GASTEC at CRE" report takes a more balanced approach. There's no denying there will be greater loses from including an additional volume of warm water within the heating system, although that would hopefully be within the thermal envelope for the majority of installations. For a 4 port buffer there would also be an additional (low energy) pump that needs to be accounted for, although with the benefit of stratification if correctly sized.

As I stated above there is the additional factor to consider, namely the temperature loss in the flow across the buffer tank, which will reduce system efficiency.  The penalty, based on my WC model, is about 2% per degree C.  Assuming that the buffer is inside the thermal envelope and well insulated, with a delta T across the heat emitter of 7C and little stratification in the buffer, that would be something like a 7% penalty.  If the delta T is smaller, or there is material stratification, then the impact is less, if the buffer is poorly insulated or outside the thermal envelope then more.  Figures and model based on Mitsubishi 11.2kW.  A well insulated 2 port buffer (sometimes called a volumiser) in the return would have negligible efficiency impact so far as I can see.  That's surely(?) the way to go if the sole reason for a a buffer is to increase the system volume.  

[IanR]

23 minutes ago, JamesPa said:

That's surely(?) the way to go if the sole reason for a a buffer is to increase the system volume.  

 

Certainly de-risks an install, allowing an over-sized heat pump to be installed to mitigate potential errors in energy loss calcs (more important for retrofits than new builds), allowing zoning of heat emitters, and improves DHW heat-up times.

 

27 minutes ago, JamesPa said:

As I stated above there is the additional factor to consider, namely the temperature loss in the flow across the buffer tank, which will reduce system efficiency. 

Can you talk me through this, and what buffer/volumiser configuration you are considering with this - I assume your volumiser in return flow. I'm also assuming you are considering this as additional to standing losses. 

[JamesPa]

1 minute ago, IanR said:

Can you talk me through this, and what buffer/volumiser configuration you are considering with this - I assume your volumiser in return flow. I'm also assuming you are considering this as additional to standing losses.

'As I stated above there is the additional factor to consider, namely the temperature loss in the flow across the buffer tank, which will reduce system efficiency. ' refers to a 3 or 4 port buffer where there is flow/return mixing.  In this case the flow temp has got to be higher to compensate for the mixing in the buffer, which reduces the temp to the emitters from that exiting the HP.  HPs have lower efficiency at higher flow temps, and this degradation is additional to the standing losses. 

 

On further consideration I think my post above underestimates the effect.  In a 4 port buffer with little stratification (ie near-perfect mixing) the flow temp has to be raised by an amount equal to the delta T across the emitters to maintain the same emitter output, not half as much stated above.  So if delta T across the emitters is 7C then the flow temp (with perfect mixing) will need to be increased by 7C to get the same output at the emitters.  That's a 14% penalty on system efficiency according to my WC model.  Not insignificant.

 

There is no mixing in a 2 port buffer, and if its plumbed into the return any residual heat loss is less, so in this configuration the penalty due to increased flow temps vanishes.

[JohnMo]

2 minutes ago, JamesPa said:

any residual heat loss is less

And if it's in the thermal envelope those losses go in to the house and are not wasted heat loss. So zero loss 

[Mr Blobby]

 

AFAIK the panasonic controller regulates the heat pump flow/return temps in one of two heating modes : WC or fixed flow/return temps.

So what exactly does Brendon Uys mean when he describes the heat pump as controlling the temperature in Test 3?  Has he set up test 3 with a fixed flow temp of 35C?  That would be convenient.  And would return a good COP but has nothing to do with the buffer tank.

 

Brendon Uys has changed two variables in his test 3 (6 below), he has reduced the flow temp setting and removed the buffer tank. 

 

Surely a more scientific approach would have been:

1: Flow temp 50C + Buffer

2: WC + Buffer

3: Flow Temp 35C + Buffer

 

4: 50C no buffer

5: WC no buffer

6: 35C no buffer

 

If, as I suspect, Brendon Uys has examined the COP from 1,2, and 6, and reduced the flow temps to 35 C when he removed the buffer then of course he will get a better COP.  But that has very little to do with the buffer tank and everything to do with the lower fixed flow temps.

 

Why not test the system with all combinations, to include a fixed flow rate of 35C and a buffer?  That would return better COP, although it may be at 36C to maintain a steady simulated house temperature after the buffer losses.  But at least the COIP would be better than allowing the HP to increase the flow temps.

 

Edited January 25, 2023 by Mr Blobby

[IanR]

1 hour ago, JamesPa said:

refers to a 3 or 4 port buffer where there is flow/return mixing.

 

OK, now I understand, this wasn't referring to your own 2 port, in the return line.

 

It may be my narrow experience of just one installation designed and installed, but wouldn't a 4 port buffer that is allowing mixing be either poorly designed or incorrectly sized for the required flow rates (or both). 

 

I had assumed all 4 port buffers for ASHP space heating were designed and sized to allow stratification. Should your model not be based on a correctly designed system? You would have to allow for the energy to power the additional pump though, should be around 25W, but could be as much as 55W.

 

 

59 minutes ago, Mr Blobby said:

Has he set up test 3 with a fixed flow temp of 35C? 

 

He did state "with compensation curve" I believe, but then only tested in a steady state, so effectively a fixed flow temp @ 35°C

 

59 minutes ago, Mr Blobby said:

That would be convenient. 

 

Indeed.

Edited January 25, 2023 by IanR

[JohnMo]

34 minutes ago, Mr Blobby said:

Surely a more scientific approach would have been

No. To many variables. 

 

The house side of things stays the same, same energy loss on each test, same flow into the simulated emitter.

 

 

He sets up up test 1 fixed flow to match a low temp as it enters the heating emitters equal to design flow temp at min outdoor temp.

 

Test 2 same test but with WC engaged so at the test temp of 7 degs outside, the flow temp is lower, but with a slight uplift due to buffer.  The flow temp into emitter is always the same temp.

 

 Test 3 same as 2 but no buffer, flow temp in to emmiters the same as previous tests.

 

So test compares the cop at the same weather conditions and heat going into the house. Only two variables fixed flow temp and or a buffer with weather comp.

[ReedRichards]

3 hours ago, IanR said:

It's unfortunate that the "Brendon Uys" report has been written as if to prove what he felt was already the case, as well as advertise his services. When his findings did prove what he already believed top be the case, he didn't seek to explore alternative buffer/volumeiser configurations that were less onerous in the system CoP, such as not installing the buffer "outside".

 

 I agree.  It seems such a pity that the opportunity to do some good science by exploring other configurations was wasted.  It looks to me is that there are two differences between tests 2 and 3; apart from the removal of the buffer the heat pump uses a different control method rather than using weather compensation.  And obviously the volume of water in the system between test 2 and 3 is changed whereas it could easily have been maintained.    

[JohnMo]

11 minutes ago, ReedRichards said:

obviously the volume of water in the system between test 2 and 3 is changed

Test 3 has less water in the system, so would be more susceptible to short cycling.  So wouldn't that make test 3 perform less well or what's the point of a buffer.  But in test 3 CoP gets better. More water may have improved CoP further.

 

Question

If you have a buffer why not record your own findings and post them. It's better for us to see real life installation, rather than experiments.

 

So what is the a temperature change across the buffer or is there no change in flow or return?

[JamesPa]

1 hour ago, Mr Blobby said:

If, as I suspect, Brendon Uys has examined the COP from 1,2, and 6, and reduced the flow temps to 35 C when he removed the buffer then of course he will get a better COP.  But that has very little to do with the buffer tank and everything to do with the lower fixed flow temps

Unless of course it was possible,  solely because of the removal of the buffer tank and thus any temp drop across it, to reduce the flow temp from the HP whilst maintaining the same flow temp at the emitters (which is the variable that needs to be fixed to compare like with like on a fair basis), but he doesn't say that. 

 

As @JohnMo says, it would be great if those with buffer tanks (2, 3, 4 port) post their own findings.  Temp drop and buffer configuration would be good to know.  

[ReedRichards]

Here you are, @JamesPa.  I have a 4-port buffer integrated with and underneath my hot water cylinder.  My LG therma V 12 kW heat pump is set to do Weather Compensation but a Drayton Wiser thierd party controller overrides the LG one.  I have two zones, one for most of the house and one for the 3 smallish bathrooms.  The heat pump reports its output and input flow temperatures.  I have personally insulated the pipes between the heat pump and the buffer using Kingspan phenolic insulation and that appears to be effective.  It also makes measuring the temperature actually at the buffer inputs and outputs rather difficult, will you accept the heat pump temperature data?  This only updates about every 30 seconds so I think some of the details about what happens are lost.

 

At the moment it is warm out and my heat pump operates in 20-minute cycles.  At the start of each cycle the inlet and outlet temperatures are typically around 35 C.  When the room thermostat calls for heat the internal heating pump circulates water from the buffer for a approximately two minutes.  The external pump then comes on.  This runs for another two minutes before the compressor turns one during which time the inlet and outlet temperatures fall by a few degrees as the cooler water from the heating system reaches the heat pump.  In the next stage the outlet temperature starts to increase, initially on its own.  The outlet temperature lags about 5 degrees behind.  This morning it got to 40 degrees out 34 in and the main zone cut out as warm enough.  This left the smaller bathrooms zone which is required to be warmer at this time of day.  This got to 45 in 40 out before the heat pump cut out even though the thermostat was still calling for heat and the pump was circulating water around that zone.  The maximum power drawn was about 3.5 kW for a 12 kW heat pump.  In principle the maximum output temperature should be 41 C at 5 C outside. 

 

A few minutes later and both zones now back on, both pumps running but compressor still off.  Flow temperatures have dropped to 36, 36.  now 37, 33 as compressor comes back on, then 37, 32,  then 37, 33 main zone off, then 39, 35, then 40, 36 , then 41, 37, then  42, 38, then 43, 39, then 43, 40, then 44, 40 and compressor off.  maximum power about 2.5 kW.  Internal pump on bathrooms zone runs for a couple of minutes longer.  Now no call for heat although the bathroom thermostat is 1 degree short of its target temperature (main zone at target).  The second cycle, which I recorded completely, ran from 07:25 to 07:45.

 

So at the moment the heat pump has the difficult task of maintaining the temperature in most of the house whilst trying to warm up three smallish bathrooms.  But this is the real world.           

[JohnMo]

Just compared @ReedRichards figures with the Brendon test, and interesting that the flow temp in test two is 38 to 40 and the flow temp in test 3 is 35.  Almost exactly the same figures. But more importantly the use of a buffer is causing the heat pump to run hotter than it would without a buffer.

 

For your bathrooms it may be worth increasing the loop flow rates a little so they are putting more heat in to the floor. Higher flow rate would give a higher mean flow temp, without increasing the actual flow temp.

[JamesPa]

7 minutes ago, ReedRichards said:

Here you are, @JamesPa.  I have a 4-port buffer integrated with and underneath my hot water cylinder.  My LG therma V 12 kW heat pump is set to do Weather Compensation but a Drayton Wiser thierd party controller overrides the LG one.  I have two zones, one for most of the house and one for the 3 smallish bathrooms.  The heat pump reports its output and input flow temperatures.  I have personally insulated the pipes between the heat pump and the buffer using Kingspan phenolic insulation and that appears to be effective.  It also makes measuring the temperature actually at the buffer inputs and outputs rather difficult, will you accept the heat pump temperature data?  This only updates about every 30 seconds so I think some of the details about what happens are lost.

 

At the moment it is warm out and my heat pump operates in 20-minute cycles.  At the start of each cycle the inlet and outlet temperatures are typically around 35 C.  When the room thermostat calls for heat the internal heating pump circulates water from the buffer for a approximately two minutes.  The external pump then comes on.  This runs for another two minutes before the compressor turns one during which time the inlet and outlet temperatures fall by a few degrees as the cooler water from the heating system reaches the heat pump.  In the next stage the outlet temperature starts to increase, initially on its own.  The outlet temperature lags about 5 degrees behind.  This morning it got to 40 degrees out 34 in and the main zone cut out as warm enough.  This left the smaller bathrooms zone which is required to be warmer at this time of day.  This got to 45 in 40 out before the heat pump cut out even though the thermostat was still calling for heat and the pump was circulating water around that zone.  The maximum power drawn was about 3.5 kW for a 12 kW heat pump.  In principle the maximum output temperature should be 41 C at 5 C outside. 

 

A few minutes later and both zones now back on, both pumps running but compressor still off.  Flow temperatures have dropped to 36, 36.  now 37, 33 as compressor comes back on, then 37, 32,  then 37, 33 main zone off, then 39, 35, then 40, 36 , then 41, 37, then  42, 38, then 43, 39, then 43, 40, then 44, 40 and compressor off.  maximum power about 2.5 kW.  Internal pump on bathrooms zone runs for a couple of minutes longer.  Now no call for heat although the bathroom thermostat is 1 degree short of its target temperature (main zone at target).  The second cycle, which I recorded completely, ran from 07:25 to 07:45.

 

So at the moment the heat pump has the difficult task of maintaining the temperature in most of the house whilst trying to warm up three smallish bathrooms.  But this is the real world.           

That's excellent data thanks. 

 

In summary (I think) your are saying that the output of the buffer on the flow side is about 4-6C below the input to the buffer on the flow side.  You don't say what the deltaT is across the emitters, but given you are running at 40+C Im guessing that they are radiators with a design delta T of (say) 7.  That's roughly consistent with a tank where there is some stratification, but also quite a lot of mixing.  If your delta T is less than this, then there must be more or less complete mixing in the tank.

 

According to my weather comp modelling (which is based on Mitsubishi not LG), the penalty for the 4-6C increase in flow temp needed to compensate for temperature drop across the buffer is in the region 8-16%, depending on some other factors.   Of course the buffer is doing some positive things which will tend to increase efficiency, particularly reducing short cycling and helping with defrost.  I have not seen any data on how much short cycling really matters, so cant estimate these. 

 

Im attaching version 2 of the model which addresses a factor previously omitted and mentioned earlier in this thread, namely that the delta T across the emitters will vary as the load varies, unless the pump speed adjusts to compensate.  As I surmised this makes a small difference, but doesn't affect the general trends.  The main findings in summary are this:

 

• WC makes about 25% difference at 55C, 20 at 50C, 15 at 45C, 10 at 40C and 5 at 35C (all flow temps)
• A linear approximation to the perfect WC curve degrades the performance by 2% or less
• The 'Lizzie' adaption to a linear WC curve (whereby the flow temp never falls below 37C) degrades the performance by between 1% (at 55C) and 6% (at 40C).  Obviously this adaption makes no sense at 35C
• A 1C uplift to the WC curve degrades performance by 2-3%
• The degradations above can more or less be added together

The simulation is based on radiators, it can be adjusted for UFH by changing the emitter coef. (to 1 I am told).

 

Hope this is of interest

WC Simulationv2.xls

[ReedRichards]

Sorry, I should have mentioned that I have only radiators.  Their nominal target drop across them is 5 C at the maximum rated flow temperature of 50 C but it's extremely difficult to check that they are well balanced because the output temperature from the heat pump is rarely constant because it is very rarely cold enough outside to require this.   And the flow rates are so large that the flow is quite audible in those radiators immediately downstream of the pump (which is how I knew which zones were on).  The audible flow is something I like least about my heat pump heating; the external oil boiler that preceded it gave me completely silent heating inside the house.

 

Buffer or not, my heat pump seems to be trying to maintain a 5 degree differential between flow and return without knowing that it could do better using less power to maintain a smaller differential (assuming it is capable of using less power).  My reading of the Brendon test was that Load Compensation was not invoked until part 3 of the test, although I'm not sure how much difference it would make in that case.  My heat pump looks as if it has the potential to do better with Load Compensation although I don't know quite how that works with multiple zones.  Reducing the temperature differential the heat pump aims for (by eliminating that in favour of a better means of control) would also have the effect of reducing any adverse effects of mixing.  Even if there was a setting I could change to say: "aim for a 3 degree differential instead of 5" looks like it would be beneficial at the moment.

 

I have not looked at @JamesPa's simulation yet; I'll do that now.     

 

  

[JamesPa]

Thats more good data thanks.  5C delta T across the emitters and 5C delta T across the buffer is consistent with more or less total mixing (ie no stratification) in the buffer.  I have seen many state that this is likely, you have given us data which seems to show that it is what happens.   Hopefully others will also post data.

 

In general a smaller delta T across the radiators, achieved by cranking up the pump speed, will give higher efficiency.  But of course pumps can only go so fast and pipes can only accept a finite flow.  Also faster flow = more mixing in the buffer (if you have one = higher flow temp required at the HP).  Having said that if mixing is already more or less complete the dominant factor will be first one

Edited January 26, 2023 by JamesPa

[ReedRichards]

Thanks @JamesPa.  My internal pump is a Grundfos 3-speed pump.  It's normally on setting 2 because setting 3 increases the system noise level and I don't like the noise; and because the installer set it up to be on setting 2.

[IanR]

@ReedRichards, Can we clarify where you are making your temp measurements?

 

4 hours ago, ReedRichards said:

The heat pump reports its output and input flow temperatures.  I have personally insulated the pipes between the heat pump and the buffer using Kingspan phenolic insulation and that appears to be effective.  It also makes measuring the temperature actually at the buffer inputs and outputs rather difficult, will you accept the heat pump temperature data? 

 

 

From what you've said, none of your measurements are at B, C, H or J. But I get confused whether you are measuring across the emitter ie. either D to G or E to F

 

I've made a guess below at what your Space heating plumbing might look like.

 

3 hours ago, JamesPa said:

5C delta T across the emitters and 5C delta T across the buffer is consistent with more or less total mixing (ie no stratification) in the buffer. 

 

I believe @JamesPa believes you are providing measurements across the buffer ie. B to C, H to J, or perhaps A to D and G to K.

Edited January 26, 2023 by IanR

[PhilT]

1 hour ago, ReedRichards said:

Thanks @JamesPa.  My internal pump is a Grundfos 3-speed pump.  It's normally on setting 2 because setting 3 increases the system noise level and I don't like the noise; and because the installer set it up to be on setting 2.

I think mine may be the same - is it this one? Would be interesting to try a lower speed. My flow temp difference is only 3degC at 35 up to 4degC at 50, and it's quite audible, although not excessively

Edited January 26, 2023 by PhilT

[ReedRichards]

5 hours ago, IanR said:

@ReedRichards, Can we clarify where you are making your temp measurements?

 

 

From what you've said, none of your measurements are at B, C, H or J. But I get confused whether you are measuring across the emitter ie. either D to G or E to F

 

I've made a guess below at what your Space heating plumbing might look like.

 

 

I believe @JamesPa believes you are providing measurements across the buffer ie. B to C, H to J, or perhaps A to D and G to K.

 

I'm not measuring anything, I'm going by what the heat pump reports at A and K but I hope that A and B are at almost the same temperature, as should be L and K.  The drawing of my heating system is accurate except insofar as "Manifold" is two 2-port valves, one for each zone.    Points B, C, J & K are well-insulated and the insulation is fixed in place so measurements there would be difficult.  I have tried to make measurements at E and F across radiators but I only have a single thermometer and the water temperature never holds constant so it's difficult.

 

@PhilTMy pump is a UPM3 Flex 25-75 130 AZA.  The pump itself is not noisy and makes a low humming sound but water in nearby pipes and radiators makes a rushing sound when water is flowing through them.  I tried it on setting 1 for a while and that makes the system a little quieter but only a little.       

[IanR]

36 minutes ago, ReedRichards said:

I'm going by what the heat pump reports at A and K but I hope that A and B are at almost the same temperature, as should be L and K. 

 

Thanks for clarifying. I've got the same issue taking measurements, I'd need to peel back the insulation to get to somewhere to measure, and it will need taping up to put it back so won't look the same again.

 

I've avoided going down that rabbit hole of data logging so far, but am now looking at what it will cost to buy a multi-channel temp logger and some probes.

 

9 hours ago, JamesPa said:

5C delta T across the emitters and 5C delta T across the buffer is consistent with more or less total mixing (ie no stratification) in the buffer.

 

I don't believe you can infer that, from the temps provided.

Edited January 26, 2023 by IanR