Hi @cathoderay

Do you have a thermostat switching the secondary water pump on and off? What is the speed setting of the secondary water pump?

Are there any zone valves on your system?

@cathoderay you don't need a heat exchanger. Freedom supplied my system and I don't have that.

Posted by: @batalto

@cathoderay you don't need a heat exchanger. Freedom supplied my system and I don't have that.

What is this heat exchanger anyway?  I thought that it was part of the heat pump...

@kev-m - the IR thermometer gives my oral temp as 34 degrees, I am normally 36 degrees using a traditional mercury thermometer, not sure of the emissivity of human oral mucosa, but on the face of it the IR thermometer isn't far out.

Midea are Chinese and huge globally, mostly white goods and AC, but relatively unknown in the UK, though they appear to have plans to change that. I think I'm right in saying Freedom are the only UK importers of Midea ASHPs, and so in practical terms, at least for us end users, they are in effect 'Midea UK'.

I'm pretty sure the LWT and RWT sensors are in the heat pump box, can't see any external sensors. On the Operation Parameter pages, they are actually labelled as TW_O PLATE W-OUTLET TEMP and TW_I PLATE W- INLET TEMP. Maybe plate means plates in the compressor?

I think the readings from my system from yesterday are a reflection of poor heat exchanger performance. The primary heat pump circuit water is still warm because it hasn't lost heat to the secondary rad circuit, which remains cooler than it should be. That's how you can get a RWT at > 40 degrees, and rad temps in the 20 and 30 degrees range.

@derek-m - the room stat controls the Midea controller which then controls the secondary circulating pump (and the primary pump). Room stat calls for heat, Midea controller starts both circulating pumps and then a few minutes later the compressor starts. The secondary pump is currently on its max constant pressure setting. No zone valves. 

This morning's readings: ambient 9 degrees, AHSP LWT 43, RWT 39, heat exchanger LWT 40, RWT 28 (both these taken using IR thermometer on black insulating tape on pipework), rads mostly 20 something degrees, a few 30 something degrees, rooms at or mostly just below design temp. All readings taken after system running for a while (in fact, the room stat is pretty much calling for heat all the time, it's in the kitchen and set to 18.5 degrees, the kitchen only gets to 19 degrees (the point at which the stat stops calling, 0.5 degrees swing) when it gets some solar gain.

@batalto - interesting. My installer's sub-contracted plumber clearly wasn't very familiar with heat exchangers (set it up with same direction flows not contraflows), suggesting they are not a standard item on most (non-Midea) systems. The heat exchanger manufacturer (who I contacted to confirm the flow should be contraflow) also asked why the system needed one. Yet the Freedom/Midea installation manual VERY clearly says (page 6):

"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"

"There are no short cuts" and "you will void the warranty" make things very clear.

But it turns out that is the Sept 2020 edition of the installation manual, which I guess my installer was using, or at least remembered that from previous installations. Yet the Sept 2021 edition of the installation manual that wording has disappeared, though the diagrams continue to show a 'header, buffer or heat exchanger' and it is treated as if it is a routine part of the installation.

@kev-m - the heat exchanger sits between the primary heat pump circuit and secondary rad circuit, keeping the two separate. It's part of the Freedom installation kit, and is highly visible in all their installation manual diagrams. Here's the diagram (and the no short cuts wording) from the 2020 installation manual:

I am beginning to get the impression Freedom are still on the learning curve (maybe that's the polite wording) with Midea heat pumps. The output data in their calculator is misleading. They don't seem to know whether you must have a heat exchanger or not. They don't know the 12kW, 14kW and 16kW units are interchangeable. And finally, their tech staff won't deal with end users. It's only conjecture, but could that be because they know they won't be able to answer the questions?    

@cathoderay they put a low loss header in my system. Next time we have a plumber in, I'll be having it removed. It's not needed and it's a cause of heat loss and therefore makes things inefficient 

Hi @cathoderay

The PLATE description for the temperature sensors refers to the plate heat exchanger that is located within the heat pump unit.

@batalto - having a secondary circuit also means having a secondary circulating pump, more £££ with no direct heat gain, ie system is more expensive to run. COPs don't routinely include these costs, which are not trivial (this has come up somewhere on the forum before). I think there may be a question about the primary circulating pump in the heat pump, whether it is capable of circulating to a rad circuit. Somewhere in the Freedom installation manuals it says max 12m run (each way, so 24m there and back), any more and you need to contact them. My ASHP to DHW tank and heat exchanger is just under 12m, but the rad circuit is much much longer.

@derek-m - that is about as close to the compressor output as you are going to get, isn't it?

Hi @cathoderay

The plate heat exchanger within the heat pump unit has the hot refrigerant gas on the inlet side and the central heating water on the outlet side. If you look at pages 21 and 22 of the attached document it is the item labelled Evaporator, though this is actually incorrect, since this is the Condenser.

Page 4 shows a system layout without any of the three items that Freedom specify as essential, so you may be correct about their level of expertise.

I do believe that the 12m mentioned in previous posts relates to the pre-pressure of the expansion vessel as described on page 72. I would expect that the water pump in the external heat pump unit should be adequate for your average home system, and would only require additional secondary water pumps for larger systems. It is dependent upon the water pump being able to move the required quantity of water around the system against the restrictions created by the height of the building, the diameter and length of the pipework, and the volume of water to be moved.

The password for the document is midea2020.

Posted by: @derek-m

you may be correct about their level of expertise

Indeed. Looking at page 72 of the Midea manual, the 12m figure is not the pipe run length, it's the vertical height ("Height difference is between the highest point of the water circuit and the outdoor unit’s expansion tank"). It seems to be about hydrostatic pressure, not pipework length, and so resistance. Yet the 2021 Freedom installation manual has this:

"The pump in the unit is strong enough to push the water a maximum of 12m each way to the hot water cylinder and
The low loss header. If your pipe length is more than 12m of 28mm copper please call us first"

The Midea manual has no other relevant occurrence of 12m or 12 m.

@batalto - I now have a USB wireless adapter for my PC and it can see the Midea Controller (again, the SSID shows as net_c3_xxxx rather than midea_c3_xxxx, but so similar that I am sure it is the Midea Controller) and I can connect to it in Windows by entering the password and it says connected, but no dice in the Midea app in the android emulator. It can't connect automatically, and when I try to connect manually it fails. A wireless connection is visible, called rather unhelpfully 'Wireless' but it seems to be my ISP via my wired/wireless router, if I turn it off I lose internet in the emulator, turn it back on and I get the internet back again (though all a bit odd, this 'wireless' connection remains even if I remove the USB Wifi adapter, leaving only a wired ethernet connection between the PC and the router...). But no sign of the net_c3_xxxx connection in the emulator, even when Windows shows it is connected... Thought it might be my firewall, so turned that off briefly, but emulator still only see the wired 'wireless' connection. Also tried cold rebooting etc. Still nothing.

It looks as though the Midea app doesn't work on an emulator, unless anyone has experience to the contrary.

cathodeRay 

@cathoderay just borrow a phone and do it that way. Once it's connected you can just use the emulator to log into the app. You'll save yourself a lot of hassle just using a phone. All you need the phone for is giving the midea controller the password for your WiFi - that's ALL you need it for.

@batalto - OK, will do next time I have a friend round with an android phone. But I'm still a bit confused:

Posted by: @batalto

All you need the phone for is giving the midea controller the password for your WiFi - that's ALL you need it for.

When I connect (in Windows) I put in the default Midea password (which gets accepted), not my Wifi password. Perhaps that happens behind the scenes, but if I do it on someone else's phone, then won't their password get used? Perhaps I'm just being very thick...

cathodeRay