Posted by: @allyfish

@derek-m Hi Derek, the primary pump is the one in the ASHP, which for the Grant Aerona range is a fixed pump curve device. It's for exactly this reason the low loss header is needed, as the Grant ASHP requires a constant flow on the primary side, but the secondary side flow varies depending on the number of radiators calling for heat and the TRV settings. As the TRVs close down, or in the case of the smart timed TRVs, switch off, the system head increases and the flow rate decreases. The ASHP compressor and evaporator fan are variable speed control, in response to demand, but not the water pump. (Some ASHP manufacturers do speed control the internal pumps, which then negates the need for low loss headers and secondary pumps if the circuit hydraulic design can be accommodated with the in-built speed controlled pump.)

Hi Allyfish,

Thanks for the clarification, I wasn't aware Grant ASHP had a fixed pump curve. Not a very good selling point since the addition of added complexity in the form of LLH or buffer tanks can seriously affect the overall efficiency of the system.

@cathoderay

I had a reply from Hexonic, which stated that the nameplate is on the actual unit, but they did not state where. I have asked for clarification along with any available data on its heat energy transfer capability.

I am pleased to hear that you are now managing to warm up your home, even though it does mean that you are having to re-balance all your radiators.

Thinking about your cooler living room radiator, you state that it is supplied by a fairly long pipe run inside a concrete floor. Do you know if the pipes are insulated? Can you measure the temperature of the pipe before it enters the concrete and again where it exits? Also check that the TRV is fully open and not stuck in a part open position.

What are the temperatures like now at your PHE? Is your heat pump now cycling less?

Once your system is operating as well as can be achieved, it may then be preferable to set your water pump to the PP AA control mode for best overall efficiency.

@cathoderay

I have just received the following message from Hexonic.

Unless it is an RNI that is glued to the exchanger you can remove the thermal insulation from it. The nameplate is on the front cover where the 4 connections are.

If you want to make selections on your own or check different duty point for a particular unit, feel free to register at www.cairo.hexonic.com. This is our selection tool. When the registration process is complete and you click the verification link received in an email, mail me again so I can push it a little bit to grant you access to the selection modules.

If you wish I can delve deeper into the capabilities of your PHE, but if you are now happy with its performance I will not chase it any further for the time being.

I will have a look for a suitable flowmeter that is hopefully not too expensive.

Posted by: @derek-m

Do you know if the pipes are insulated?

I think so, but can't be sure. They were buried in the floor a long time ago (mid 80s). The point where the pipe enters the concrete definitely has visible foam insulation, what I am less sure about is whether that continues all the way to the living room. The bore may also be relevant: definitely 28mm where it goes into the floor in the kitchen, then probably 22mm to the dining room (only a short run, ~2m), and possibly even probably 15mm from the dining room to the living room, which is a longer run, ~7m. It is 15mm where it comes out of the living room floor, but I can't see the exit from the concrete as there is very well fixed down laid carpet and furniture on top of that. If there is a long 15mm run, maybe that adds significant resistance. On the oher hand, I don't recall problems with the living room rad with the oil boiler. Maybe there was a drop but not so noticeable given the much higher circulating temps. The living room never felt cold, quite the opposite. The temps - see below.

Apart from the living room, the rads are now generally more balanced, low to mid 30s upstairs and upper 20s to low 30s downstairs. Upstairs is mostly slightly over-temp by 2-3 degrees, downstairs at design temp. Bearing in mind the mild outside temps, this isn't difficult to achieve. I am going to close the upstairs LS valves another 1/8 turn and see what happens.

All the TRV valves are all fully open because the heads are off, and I have checked the 'plungers' aren't jammed in the closed position. 

The insulation on the PHE does seem to be stuck in place, I am reluctant to pull any harder because I suspect it may well tear. Looking at the Hexonic brochure, the LA 34 does seem to be the only one that is really quite close in pipe connection centres the the measurements I took, I think we can assume it is that model. If we look at the formula for the F dimension (height), it is given as 9 + 2.30 × NP millimetres. The measured F dimension on my PHE allowing 15mm  x 2 for the foam insulation is 70mm. Unfortunately that formula is ambiguous: is it F = (9 + 2.30) x NP or F = 9 + (2.30 x NP) but on the basis multiplication takes precedence it is probably the latter which means (cripes, I hope I can still do this!) NP = (F - 9) / 2.3 which using F = 70 gives NP = 26. I have no idea whether that is a credible number of plates. Perhaps, given measurement error because of the foam , if F is say 80 mm, then NP = 30.

The heat pump is cycling much less, it is mostly on. The current temps (now) are rather absurd because the compressor is in fact off at the moment: Midea Controller LWT/RWT both 33 degrees, the PHE secondary circuit is 30 in, 31 out, the downstairs flow to the living room rad is 26 where the 28mm pipe goes in, and 28 where the 15mm exits the concrete. I will check again later when the compressor is running...  

Interim update: the rads are approaching being balanced, its taking a while because it is so mild and the heat pump is not running for longish periods. Most of the rads are now within 2 degrees of each other, apart from the rogue living room rad which remains about ten degrees less than the others, and most of the rooms are at their correct temp, except the living room which definitely feels a bit cooler. Curiously or perhaps not, the balancing has meant all but closing the upstairs LS valves (all are 1 turn or less open) while leaving the downstairs LS valves mostly wide open.

I do wonder about the Proportional Pressure setting. If I have understood it right, it reduces the pressure (and so the flow) as the system resistance increases. The resistance trigger is supposed to be the TRVs closing because the rooms are warm enough, but in my case the TRVs are all still fully open (heads are off), meaning any resistance is a static resistance from the partially closed TRVs, This surely then means the pump decreases the pressure, reducing flow, which means the rads don't heat up properly - which defeats the object somewhat...  

@cathoderay

You are probably correct about running the water pump in PP AA mode, though it depends on how the pump actually performs.

A little information about linear opening valves, since the actual flow is not linear, but follows a square law.

% Open     % Flow

     1             10

     4             20

     9             30

    16            40

    25            50

    36            60

    49            70

    64            80

    81            90

   100          100

Obviously the actual flow rate is dependent upon the size of the valve and the pressure differential across the valve.

@derek-m - thanks for the figures. I knew the adjustment wasn't linear, useful to have a bit more precision. Given some of the lockshields only have maybe 4 full turns from from fully open to fully closed, it looks like one turn open gives you 50% of full flow. I believe the design including shape of the business parts of the valve may also have some effect on the flow (plugs vs saucers etc).

Now it is a bit cooler outside I am doing what I hope will be final tweaking. It's still not been cold enough here to put the system under any real strain, but I did notice some figures on the Midea Controller Operation Parameters some, of which made more sense than others:

Ambient: 10 degrees

Flow rate: 1.45M3/H

Heat Pump Capacity: 7.75kW   <= this being I think what the unit claims it's current output is

Power Consumption: 5242kWh    <= this is a mystery, see below

LWT/RWT: 44/40 degrees    <= about where they should be given ambient and using weather comp

Comp. Current: 5A     <= this being I think what the unit claims it is currently using (drawing from the mains)

The unit was in as steady a state as it ever gets.

The odd things are:

(a) given 5A x 240V = 1.2kW in, and 7.75kW out, the COP at the moment I took the readings was 6.46 which frankly I don't believe

(b) the Power Consumption of 5242kWh doesn't really make much sense, because the heat pump has its own metered supply so I know exactly how many kWh the unit has used sine installation, and that figure is currently just under 4000kWh. Yet the unit reports a consumption of 5242kWh. I did wonder if it might be the total kWh output (ie a running total of the kW output over time), but if that was the case, then I get another rather absurd (or perhaps very worrying) COP of 5242/4000 = 1.3. 

When I looked again after a couple of hours, the Power Consumption figure had gone up to 5244kWh, suggesting something had done 1 kW for 2 hours, or perhaps 2 kW for 1 hour, or any multiple that comes out at 2. But 1kW for 2 hours (ie one fan heater on a 1 kW setting for 2 hours, or whatever multiple that gets to 2) is unlikely to be enough to keep the house warm at 10 degrees ambient... 

Does anyone know what these figures are really reporting? Of have I just missed something really obvious?   

@cathoderay 

If Power Consumption is what is sounds like then around 1kW or therabouts consumed at 10 deg ambient to keep your house warm is definitely possible; it's in the same ballpark as mine.  My COP is over 4 at that temp so more than one fan heater!

If the Heat Pump Capacity is a one-off instantaneous reading of power being delivered it won't be reliable for calculating COP; energy delivered and consumed need monitored over a longer period. COP is hard to calculate accurately at the best of times.     

I don't know how the Midea controller works but there may be some other figures you can get out of it.  Maybe @Derek-m or @Batalto can help?

@kev-m I'd suggest he uses the app, but I believe there were some concerns on data security @cathoderay

Posted by: @kev-m

↑

If Power Consumption is what is sounds like then around 1kW or therabouts consumed at 10 deg ambient to keep your house warm is definitely possible; it's in the same ballpark as mine. 

I suppose that is plausible but it seems on the low side. Assuming building heat loss vs temp is linear, 12.4kW @ -2 / 0kW @ 20 degrees ambient, then at around 10 degrees ambient heat loss will be around 6kW. Assuming a COP of 3, and a consumption of 1kWh gives 3kW, or half what is actually needed.

I've just checked the Power Consumption figure again, and it is 5269kWh, about 25kWh over just over 12 hours, let's say average of 2kW per hour over the 12 hour period. It's been complicated by the fact the DHW has bizarrely come on, bizarre in that it is on a timer to only heat the hot water between 1300 and 1400 daily, and that will have upped the consumption, but nonetheless 2kW consumption x assumed COP of 3 = 6kW, about what the house needs at overnight ambients of say 10 degrees.

Currently, and for the last 15 mins or so, the system remains in DHW mode, primary and secondary circulating pumps and compressor all off. Go figure... (it's probably because the room stat isn't calling for heat, the DHW got up to temp, 50 degrees, so that went off, and there hasn't yet been a signal to turn the heating back on).

The figures I noted down yesterday evening were during a period (of around 10 mins) when the figures weren't jumping around all over the place. In particular, the Comp. Current remained at 5A, and the Heat Pump Capacity at 7.75kW (or very close to that figure, it did vary a bit, and this figure isn't hugely different from the estimated building heat loss given above, 6kW). Momentary COPs may not be possible, but steady state over ten minutes or so - surely that should be in the right ball park? But that gives an absurdly high COP, over 6, which I simply don't believe.

The other problem is the Midea claimed Power Consumption of 5269kWh is 25% or so more than that showing on the metered supply to the heat pump, which is 4075kWh )I slightly underestimated yesterday, 4075 is an actual reading). Unless the heat pump has managed to magic electricity out of thin air, or the separate meter is wildly inaccurate, which is unlikely, its readings tally with the main meter readings, then the Power Consumption figure makes no sense. Nor does it make much sense as a Power Produced (ie pumped out) figure. Given a 12 hour use of 25kWh as above, let's say average of 50kWh/day when the heating is on, and the total number of days since install when the heating has been on of say 120 days, that's 6000kWh (not a million miles from 5269) BUT that means a COP of around 1.14, which is either not credible, or if it is nonetheless correct, then the Midea unit is cr*p. 

Why is this all so effing complicated!?!

@batalto - true, my concerns about security remain. Furthermore, if the Midea Controller itself is putting out garbage, as it appears to be, then I can't see how the app would correct that, if anything it would obfuckstrate things even more.  

@cathoderay I've noticed my app shows the tank booster, even though it's disconnected. I believe that might be the cause of your error. You can see it at the top as the light blue. That value is actually zero as it's disconnected so it's impossible to actually turn on. My understanding is that the controller assumes this reading (as it's external) and the other two reasons are actuals measured from the HP.

@batalto - it's probably just me, but I am not sure I can make any sense of that chart apart from one thing - like me, you have your DHW desired temp setting at 50 degrees.

I assume, given the headings at the top, each bar represents one month but the numbers and usage don't make sense - 1 for Jan, 2 for Feb etc, which suggests your consumption (I am ignoring the light blue part of the stack) rose during the spring, and peaked in May. The DHW compared to heating use looks rather high to me, and if the bars are month total, then the usage, average around let's say 18kW, is far too low - I use more than that in a day. Perhaps it is an average for all the days in that month? But it doesn't say so. The Water Outlet Set Temp (green line) is also hard to make sense of. If, as it's name suggests, it is the desired ('set') temp set by the weather comp curve, then it seems very flat, but then so to is the ambient, so maybe they are right: ambient around 12 degrees, desired LWT varies between around 30 to 40 degrees. Perhaps it is showing a single month, and the bar numbering is the days of that month - but which month (it doesn't say)? Perhaps it shows 1st to 8th November, ambient might be about right, but why stop on the 8th, it's the 19th today.       

"My understanding is that the controller assumes this reading..." which is rather reckless! And begs the question how much else is being assumed. The only thing I can see in 'Operation Parameters' that might have something to do with tank boosting is 'Tank Backup Heater' (matches with TBH...) on page 2 of the display and that is set to OFF. None of the other parameters appear to be about tank boosting. Furthermore, if it is tank boosting, then I can't see why it is needed/assumed to be needed when the heat pump can get the tank, presumably DHW tank, up to temperature on its own. Even more baffling is why the assumed TBH (a) varies so much between bars and (b) on some bars, is the lion's share of the bar. 

I have to assume that the chart is, like most of HMG's covid charts, ultimately meaningless. That, of course, and with great respect, is no reflection on your choice to use the app, and look at the charts. It is just my personal assessment that I have no wish to force on anyone else! And I would love to be corrected, and see that the charts do in fact make sense, but I can't get there myself.