as far as I can tell from reading that, its a fixed speed pump for the primary side, locate inside the outdoor unit. Based on no pump control connections on the PCB (just pump power) and pumps speed in a picture on p25. pump power curves on p26 and p27. So I don't know how you'd set it up to do anything better than what yours is doing, which , as your compressor amps confirms, is more or less doing full-off-full-off repeatedly. One to ask your installer about.
re the high flow temps at cold small rads - yes that makes sense.
But - if you do the DT6 * flow rate 1.3 - your output is only 9 or 10kw? because its a fixed speed pump and you have a separate primary loop, the flow rate that the heat pump sees is 100% determined by the hydraulic resistance of the primary loop. Nothing to do with the radiators. If you want to increase the output that the heat pumps is capable of sending into the primary - without increasing DT (I'm assuming the heat pump's controller doesn't want to go much over DT5 or DT6) you need to increase primary flow rate - which in your case, is all about how the primary loop is physically built. pipe sizes, bends, components that may restrict flow, etc. another one for your installer?
@iancalderbank The manual you are referring to is for a previous generation devices. The current ones have a later high-efficiency version of the Wilo pump. I am not sure it is suitable material.
@mphb thanks - do you have a link to the latest manual? also if the later pump is higher efficiency but still fixed speed its still the same conversation.
The Wilo high-efficiency pumps are set up to adjust to demand so it is very unlikely for them to run steady.
Annoyingly, the Wilo high-efficiency pumps do not give out data easily, which makes me wonder where the HP gets it data from. Probably an internal flow meter. I am running a hydraulic-separated system with a plate heat exchanger between a short loop to the heat exchanger and DHW tank and my UFH circuit. I have a very fancy 2021 high-efficiency Wilo Stratos Maxo pump for my UFH circuit on the other side of the plate heat exchanger. The Stratos Maxo actually produces a "heat produced" (or cold produced if RWT > LWT during defrosting) number on the basis of one internal temperature sensor and one external PT1000 sensor. It does not do Modbus out of the box though and it needs another 200€ module that I am not willing to buy - yet.
I am tracking the heat produced that the Wilo pump gives me against the electric energy the HP tells me it uses for heating. My simple division gets me to monthly COP's of 5.5 (for February and March) which I dare to question since we still have quite some insulation to do (well built 1980's in Germany).
On page 82 it actually states options on S2 depending on Pump (Wilo / Grundfos) and how they are run.
So open up the hood to see how our pumps are run!
Update II:
In paragraph 6 on page 82 it gives us part of an answer: "The pump is controlled via a digital low-voltage pulse-width modulation signal which means that the speed of rotation depends on the input signal. The speed changes as a function of the input profile. The relationship between external static pressure and water flow rate is described in Part 2, 7 “Hydronic Performance”." These lead to the tables on page 59 that I cannot access =).
This post was modified 2 years ago 4 times by MPHB
I have remarked on this many times, because it is almost always 1.3 something m^3/h (Midea's chosen unit) and it does seem odd that it doesn't vary, because it is the obvious thing that should vary to control output, if you want to keep the delta t fairly constant at around 5 degrees. Here's a quick plot of flow rate over the period for which I have minute data (data collected every minute). As you can see the vast majority of the readings are in the 1.3 something range:
I think that you will find that the flow rate will only change by an appreciable amount if the speed of the water pump is varied. What is controlling the speed of your water pump?
Thank you all for your contributions. Getting the right manuals for the exact heat pump one has is tricky. For a while I believed I had the correct ones, but on at least one point I probably didn't, the infamous dip switches that set the output may not apply as the manual suggests (it has been suggested the 12, 14 and 16kW units are all identical hardware, actual output is set in software by three dip switches, now I am not 100% sure, am going to check tomorrow when the box is open for servicing - @batalto, you might want to check this too if you are ever tempted to dip your switches). The pdf "Midea-M-Thermal-Split-R32-ENG-eng.-data.pdf" linked to above for example is for split units (an easy mistake to make) whereas mine is a monobloc unit.
That said, the "The relationship between external static pressure and water flow rate is described in Part 2, 7 “Hydronic Performance”" does appear to lead to Part 2 Section 7 on page 48 which has two charts with flow rate on the x axis and outside pressure on the Y axis. As I have said many times, I am convinced the Chinese do things this way because they want us to live in interesting times.
I think that you will find that the flow rate will only change by an appreciable amount if the speed of the water pump is varied. What is controlling the speed of your water pump?
The first sentence - of course, which means my flow charts suggest the speed of the pump mostly isn't varied very much, if at all. I'm not sure what controls the pump, see above. By normal charting procedures, they show how the flow rate affects outside pressure, not the other way round, which I find vaguely alarming, or, as the Chinese would have me think, interesting. But whichever it is, it doesn't seem to throw any light on how the pump is actually controlled.
On a more general note, I was going to suggest we move this very welcome discussion and flow of information to another thread, and keep this thread for the actual guide. But thinking about it, I think leave things as they are, and then I will add an index to the actual 'how to' posts at the start of the thread once they have all been posted. Any views on this very welcome.
Midea 14kW (for now...) ASHP heating both building and DHW
Whilst the covers are off the unit, I would suggest that you obtain details of any items of equipment that you can. Locate the pump and flow meter, check that any temperature sensors have good thermal contact and adequate insulation. Look to see if the water pump has both a signal cable as well as a power cable.
Apologies for causing confusion with the wrong engineering data sheet. I am running monoblock myself as well as I hope/suspect most do. The same engineering data sheet for Monoblock can be found here:
It is basically the same with sheet the same tables in the hydronic performance section on page 59. It covers the whole range from 4 to 15 kW machines.
If one could tab into the pulse that the pump apparently receives it should be easy to get and plot regular flow rate numbers.
Apologies for causing confusion with the wrong engineering data sheet.
It's very easy to do, I've done it myself. You have to check, re-check and then triple check. The model numbers are long and confusing, and even the images, which are often the give-away, can be too generic to be of use.
It is basically the same with sheet the same tables in the hydronic performance section on page 59.
I see they are now using ESP (extra-sensory perception), that should certainly make for interesting times. Only later did I spot ESP is in fact External Static Pressure. But the charts are still confusing, basically they say at flow rates between ~0.5 and 1.5m^3/h , the ESP remains steady, at higher flow rates it falls in linear fashion. I'm not sure that makes us any the wiser, though it might be enough to make my ears pop.
Midea 14kW (for now...) ASHP heating both building and DHW
@cathoderay I believe you need to look at it differently : for a flow rate of 1.5m/H, the system (i.e. the pump plus the head loss due to the HP itself) can cope with an external pressure drop requirement of up to 80kpa. to achieve higher flow rates than that, the external pressure drop (head loss due to the pipework) has to be made lower. that's normal behaviour for a pump.
as was mentioned before - whilst the lid is off with your service engineer - as much detail of the pump as you can . a key give away for a speed pump with variable speed that is controlled externally (to the pump)( is TWO cables (one power, one control). Fixed speed pump (or one that does variable control internally to the pump) will be only 1 cable (power).
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