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Buffer tank required? Samsung 12kW heat pump

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(@riponowl)
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Topic starter  

So I finally have the MMSP up and running and have some data from PassivLiving. Overall efficiency is at 3.65 which I am assuming is good for this time of year?

This is the graph from the last few days. The purple line at the bottom which is the heat output clearly shows the heat pump coming on and going off a fair bit but imagine that's more to do with the thermostat reaching temperature and switching the heat pump off. I'd been under the impression that it would just run constantly but it is actiing more like a gas boiler.

Anyway here is the graph, any observations gladly received.

image

 

 


   
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(@kev-m)
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@riponowl 

I think that's what's happening.  You can see the flow temperature dropping and rising in sync with the bursts of power.  That is likely to be due to your thermostat switching the ASHP on and off.  I don't think it's the ASHP cycling as the flow temp is dropping too much and the time period is too long.  It looks like you are running weather compensation as the flow temp seems to vary with outside temp.   

You could try turning your thermostats up a few degrees; your house will probably get hotter but the ASHP will run more steadily.  You can then adjust down the flow temperature if you need to, which will lower the house temperature. 

Your COP looks OK but could maybe be improved.

What's the trace at the very bottom? 

 

 


   
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(@riponowl)
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Topic starter  

@kev-m Yes, weather comp is set to 37-45. Thermostat up and flow temp down might work (and keep the wife happy). I don't what the trace at the bottom is, maybe someone on here can tell me.

Thanks for your help.


   
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(@kev-m)
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@riponowl 

the other thing I meant to say was that some of the ups and downs might be because of DHW. The flow temp seems to shoot up to 55 or so a few times a day.  Maybe the heating is running more constantly than you think.  Is your DHW on a timer?  Timing your DHW can improve its efficiency if you do it when it's warmest outside but it also stops the DHW interrupting the heating too often.  Each time it does, the heating stops and cools down and then has to work harder to bring the heating flow  back up.

Of course, the most important thing is to have enough HW when you want it.


   
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(@mike-h)
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Posted by: @riponowl

I'm having a Samsung 12kw monobloc heat pump installed today. The fitter gets part way through the install then tells me there isn't space for the buffer tank. He says he's checked with the office and my 7 rad system doesn't actually need one.

This doesn't sound right to me but without the technical knowledge I can't be sure.  Does anyone on here know if this is true?

 


   
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(@mike-h)
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I also have a 12kW Samsung ASHP, but I have a buffer tank. I have been trying to ascertain if it is required as it has been positioned 3 inches from the cover plate on the Tempest  cylinder thermostat. If the thermostat should require replacing, the buffer tank would have to be removed to allow replacement and then repositioned adding a day's work to the procedure. According to Fergal at Freedom Heat Pumps, installing a buffer tank or volumiser is mandatory as part of the warranty. One of the reasons that he gives is that during the defrost cycle the heat pump cannot access the volume in the secondary system, unless the thermostat is calling for heat and causing the central heating valve to open. However, Page 10 in the 2022 digital installation manual on the Freedom HP site seems to claim otherwise:

This relay configuration will ensure that the secondary pump runs whenever the primary pump runs AND the heating valve is open, ensuring that the system has the required minimum circulating water volume, without the use of large, expensive buffers or volumizers, and access to the secondary side when in defrost mode.
If the combined system volume of the primary + secondary circuit is less than 30l for a 5Kw or less than 50l for an 8Kw, 12Kw and 16Kw, you will still need a volumizer of buffer. Typically, will not be an issue unless working on a very small house/flat with less than 5 radiators or below 60m 2 floor area.

I find it quite confusing and wonder if anyone knows the answer. Despite the presence of the buffer tank I have also noticed cycling every 8 minutes after the pump has been in use for 3-4 hours, even though the thermostat is set 5 degrees higher than room temperature. @riponowl - are you still having issues with short cycling? 


   
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cathodeRay
(@cathoderay)
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Good luck trying to get any sense out of Freedom. I have found them to be remarkably unhelpful, arrogant dinosaurs would be the polite way to put it.

Their Midea (another ASHP brand) installation manual has changed over time. It used to say if you don't fit a low loss header/plate heat exchanger, then your warranty is toast, the current one doesn't. I think they probably just make up arbitrary rules and change them, hoping the smoke and mirrors they create will help them evade warranty claims.

    

Midea 14kW (for now...) ASHP heating both building and DHW


   
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(@batalto)
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@cathoderay I've spoken to their technical support a few times. They've told me they don't need a LLH it's installed to reduce system errors at the expense of efficiency. With a LLH they know the system will work 99% of the time right out the box and most users won't ever notice. Same as their recommended heat curve. It's purely to keep customers from calling as the rads are touch warm so people are happy

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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cathodeRay
(@cathoderay)
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@batalto - Freedom's 2020 Quick Installation Manual (page 6) for Midea ASHPs is very clear (up to a point - are LLHs, buffers and PHEs really the same interchangeable thing): "Every system will have a low loss header (buffer or plate heat exchanger) in the heating circuit, there are no short cuts. If you install the unit with no low loss header, you will void the warranty". My installer used that manual, that's why I have a PHE. It may also be why you had one originally.

In the more recent 2021 Freedom Midea Quick Installation Manual, it's not the warranties that get toasted, it's the above paragraph that's toast, making the Quick Installation even quicker. The thingamajig is still visible in the diagram, its the 'no short cuts' paragraph that has gone.   

 

Midea 14kW (for now...) ASHP heating both building and DHW


   
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(@batalto)
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@cathoderay it might be in the manual (or was) but they've told me it doesn't void the warranty as long as the system can work without. They add the LLH as it saves doing any actual calculations on if the system needs one or not. By adding it they by default don't need to check if it's needed - they said almost all of their installers are plumbers, so they just don't have the knowledge or capability to do that kind of technical analysis beforehand.

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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cathodeRay
(@cathoderay)
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@batalto - interesting. 

Midea 14kW (for now...) ASHP heating both building and DHW


   
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(@batalto)
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@cathoderay my own installer was a plumber. He had zero confidence to make any changes. I had to get someone else in, recommended by freedom actually

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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