Posted by: @pash44pump

↑

ACHs are as specified in the Freedom calculator that is based on room type.

I'm guessing these are the mcs defaults which are likely an overestimate, particularly for your lounge which has a large volume but relatively small surface area because it's double height and roughly a cube.

Personally they would 'note' the results for now and continue on the path already established.  The ufh design predates your ashp install so it's a moot point whether your ashp installer calculation for this matters, other than in so far as they affect the total load.

If you had a figure for annual oil consumption that would be really useful at this point.   If someone eg @cathoderay  can tell you what dip switches to change to convert your heat pump to 16kW I might consider holding this in reserve for an experiment when it gets really cold.

@jamespa I woke up this morning (at 4.45am!) thinking about exactly that and I have been looking into the ACH numbers on the Freedom Pumps xls. To me a number of 1.5 x per hour for ACH in a living room seems extraordinarily high and contributes more than half of the heat loss. If I change the default from living room (1.5) to 2006-2015 building regs (0.7), the Room Heat Loss drops from 4544 to 3222. I'm currently working through the rest of the house using 2006-2015 building regs. Ventilation in most rooms is simply trickle vents in the windows. In some rooms eg those with only Velux windows, there are no trickle vents. Will update when I have finished the spreadsheet.

Posted by: @jamespa

↑

My house noticeable exhibits oscillatory behaviour if I use any form of IAT based control which is why I run it on pure WC most of the time.  Its much more stable than it ever was with thermostat based control.  I depart from pure WC at the end of the season, when solar gain becomes a significant part of the energy input to the house.  Then I introduce a limiting factor set a little above the target temperature and based on a representative IAT.

So I would say by all means experiment with room influence on top of WC, but start with pure WC (which also means that you get the WC set up correctly)

WC is more stable because it modulates the inverter and thermostat based control has, currently, on-off behavior. It is not the information that is wrong, it is the way it is used. This is my point: that thermostat should modulate the inverter, which I believe is what will happen soon with heat pump manufacturers. To do this of course, you need digital thermostats, like the one used by the Midea wired controller, which relay the temperature.

Posted by: @cathoderay

↑

 

But (a) I am not sure what this adds over and above just getting the pipework emitters and balancing right and running only on weather compensation and (b) if you wait for the coldest room to get up to temp, what happens to the warmer rooms?

 

I also have the room on the longest pipe run not getting warm enough problem, running on pure weather compensation (with the room stat set very high ie always on). If I were to lower the room stat to 21 degrees and put it in the coldest room (which I can, its a wireless remote thermostat) it wouldn't do anything to warm the room up when it's cold. I am more persuaded the problem is a pipework problem, in effect there is an obstruction, but as the pipework is buried in a solid concrete floor I have no plans to start digging it up any time soon. I think some time ago I may have closed most of the other lock shield valves (I only have rads, no UFH) and it still didn't want to warm up fully. I live with it - there is some warmth from the rad, and as most of the time the doors in my house are open, warmth moves between the rooms.     

(a) The thermostat will work only if you exceed the desired temperature (in case WC does not work properly), to save you money.

(b) if you want independent control in each room, you have to install thermostatic valves. I don't know of any other way.

I cannot comment on your problem, since I don't have all the relevant data. It may be the pump is not sized properly or the piping is wrong or the room has too much loss. If the system is not correct, there is no way a thermostat will fix it since it just can't reach that temperature.

So now I have completed my heat loss calculations and I get a total property heat loss of 12502 against the installer's calculations of 8610. I have used 2006 building regs for all ACH numbers (0.7). 

@pash44pump 

Ok that's a bit concerning.  Is the difference down to the fact the as built spec for the building departs from the design spec?  If so it's possible that the ufh is not adequate (although if you got it to work with oil then that would counter this).

@cathoderay will have the output table for your midea and may also be able to tell you how to update it.

I really would like to know what your oil consumption was.

I'm not sure that the calcs change the course of action short term, but when it gets colder they help focus the experiment.  Installer will just say your calcs  are wrong so until you can prove otherwise probably best not introduce them at this stage (but reserve your position so you can later)

Did you get more info from installer on the other questions and have they agreed to redo the insulation/routing?

@jamespa Ok I have now found all my old oil orders and over a 7 year period, the average amount ordered was 2900 litres. The installer assumed an average of 3000 litres in the scope document. The house was always warm with oil/UFH.

I'm writing to the installer today as I was in information-gathering mode so didn't want to trigger them. 

Posted by: @tasos

↑

WC is more stable because it modulates the inverter and thermostat based control has, currently, on-off behavior. It is not the information that is wrong, it is the way it is used. This is my point: that thermostat should modulate the inverter, which I believe is what will happen soon with heat pump manufacturers. To do this of course, you need digital thermostats, like the one used by the Midea wired controller, which relay the temperature.

You have in a way touched on the essential difference between WC and room stat based control: the former is continuously variable between X and Y (the limits of the curve), while the latter is on/off. You might even say the former is analogue, the latter digital. Both achieve the same average result over a period, but the room stat method is rougher, with stops and starts, whereas WC is smoother. That is one reason for preferring WC.

The next question is which is the better stimulus, the inside air temp (IAT) or the outside air temp (OAT)? Given the OAT determines the IAT, all other things being equal, any change in the OAT will be ahead of changes in the IAT: first it gets cooler outside, then the house gets cooler, and in this way the heat pump can anticipate changes in the IAT my monitoring the OAT, and changing the output accordingly. If it waits for changes in the IAT, it will always be slightly behind the curve, so to speak. Thus, to my mind, using the OAT as the primary stimulus to control the heat pump's output make good sense.

I am sure there is no obstacle to using IAT in the same way as OAT, ie use 'room curve compensation', with a 'room curve' that sets the flow (leaving water) temp according to the current IAT. In fact, in effect, that is what my auto-adapt script already does. But it will always be slightly behind, and trying to play catch up, which is another reason for using the OAT as the primary stimulus.

That said, I think we both agree that this thread is about how to set weather compensation, not whether to use weather compensation. There is no reason not to discuss the latter question, but I am inclined to suggest it really needs its own thread. Why not start your own thread, with an opening post outlining your arguments against using weather compensation?    

Posted by: @pash44pump

↑

@jamespa Ok I have now found all my old oil orders and over a 7 year period, the average amount ordered was 2900 litres. The installer assumed an average of 3000 litres in the scope document. The house was always warm with oil/UFH.

I'm writing to the installer today as I was in information-gathering mode so didn't want to trigger them. 

OK that's great.  3000l = 30MWh.  This corresponds, almost certainly, to a loss between 10kW and 15kW.

I would probably ask the installer to produce the fabric parameters fed into the program.  You can compare those with yours and the actual and understand the differences.  This may give you leverage downstream if you need it.

This may be a relatively rare case of under sizing, but the get out for the installer may be the house not built to spec.  If it is undersized or marginal making sure it's used as efficiently as possible becomes more important!  Exit the buffer for example!

@jamespa how do you get from usage of 30MWh to loss between 10 and 15?

This now in answer to my request to provide input assumptions for the heat loss calculations

Posted by: @pash44pump

↑

So now I have completed my heat loss calculations and I get a total property heat loss of 12502 against the installer's calculations of 8610. I have used 2006 building regs for all ACH numbers (0.7). 

Posted by: @jamespa

↑

@cathoderay will have the output table for your midea 

I was just about to do that, and here it is. The CAP columns are the outputs at various OAT and leaving water temps (LWT , flow) in watts. As you may have picked up elsewhere, Midea units suffer from the optimistic badge output syndrome, in that the badge (label) output, in your case 12kW, can only be achieved in mild weather, when of course you don't need a high output. At lower OATs, the output falls significantly. At higher LWTs, which I have to use (all to do with the room size vs rad size), my 14kW falls to something just over 11kW at around zero OAT. At around zero OAT, your 12kW unit at 45 degree LWT achieves only 9428W. These temps are also those in which defrost cycles occur, and it is not entirely clear whether Midea's output tables take this into account. Note I use the middle 'norm' CL, or 'capacity level', because capacity level is never defined let alone explained. The table:

It is worth noting that the highest ever recorded hourly heating output from my heat pump is 10.25kWh (ie it averaged 10.25kW over that hour, it may or may not have peaked at a bit over that during that hour), and 11.52kW for both space and domestic hot water heating. This fits well with both my empirical (measured) heat loss, and the Midea output tables for my 14kW unit.

As @jamespa, I and others have already noted, standard spreadsheet heat loss calculators tend to over-estimate heat loss (I suspect half on purpose), mostly due to extravagant ACH assumptions, and, in the case of older buildings like mine, pessimistic U-values for walls. Since a monitored heat pump provides a way of measuring actual heat loss, I have done just that, and compared it to the standard (untweaked) Freedom estimate. At design OAT, the Freedom calculator came up with 12.3kW, while my actual heat loss is something just under 10kW.

But you have already tweaked your values in your Freedom calculations, and so the 12.5kW loss is probably not a bad estimate, and is certainly far better than the Evergreen guesstimate, unless and until Sustain and/or EasyMCS can demonstrate how and why their estimates are better.

Thus come this winter, when it gets down to around zero outside, you are likely to have a heat pump putting out about 9.5kW, to match a heat loss of around 12.5kW. Your room temps will not reach their design temps.

What's to be done about it? I suggest, now that you have a formal room by room heat loss calculation, check that the emitters are large enough. If they are too small, increasing the heat pump output won't make any meaningful difference, because the emitters simply can't emit enough heat. If they are inadequate, then the can of worms has suddenly got a whole lot larger. If they are adequate, then boosting your heat pump output, by changing the dip switch settings,  is certainly an option. If this proves necessary, then I think it might be worth getting your installer to do it, because if you do it, you may make yourself vulnerable to claims that you meddled with and compromised the system, and as a result not only do your installer have any duty to sort things out, but also your warranty is toast. If your installers do it, the responsibility in all its aspects lies with them.