@owenmc1984. RE: hi Owen, I'm new on here and have I believe the same set up as you in a similar sized house which was a new build (timber frame) in 2018 and is very well insulated. I'm finding it more costly than I expected - using about 8000kwh per year. How does...

Good morning all.  Just joined after reading some very helpful topics in my journey to understand the ASHP & Solar systems we acquired when we bought a house at the end of the last year.  I can see it will be a fairly steep learning curve but I'm up for the challenge.   

Our ASHP is a Mitsubishi Ecodan 14.4 with a FTC2 Controller supplying under floor heating throughout.   I have a number of (probably quite basic) questions which I will raise as a separate topic. 

Thanks in advance for your support.

Hi, in the mid 1970s, as a spotty teen I was glued to 'A House for the Future' on Granada TV. Scroll forward 50 years and I'm now living in my retirement project and we had our ASHP installed last summer. 

Mark from Ireland here. Moved into new build in tipperary last june and trying to figure out this air to water system on here. Very knowledgeable forum i can see.

Hi, first post on here but have been following some of the threads already. I had a Midea 16Kw monobloc fitted last summer and I am trying to gather as much data as I can so that as I make improvements I can see the impact. If anyone else is using the Midea smartphone App it would be good to know if COP is simply the Heating Output over the Heating Electric consumption?

I've put a rather clunky schematic of the setup I have in the image below.

@alan-m - Welcome. You will find a lot of stuff on monitoring Midea pumps on the forum, some of it from me, but many others, many of whom are more knowledgable than me, have also contributed. Some general points:

1. the app is crap. MSmarthome's proper name is MDumbhome. Most people ditch it. I do currently use it to record daily energy in and out on a weekly basis but it has to be done manually (in the History pages, start getting there via the top right hand three dots).

2. no one really knows (except Midea, and perhaps Freedom, but they aren't telling) how they generate the kWh figures. On my own system, the Midea app tends to underestimate consumption by about 5% most of the time, according to an external dedicated energy consumption meter that supplies only the heat pump. Perhaps it also over-estimates energy out, who knows. 

3. COP is total energy out divided by total energy in, so on the face of it, it can be calculated from the app data. The app doesn't do it, you have to do it manually. Since the resulting figure is Midea marking it's own homework, I take it with a pinch of salt. I do however have reasonable confidence in the external energy meter, so I do have a 3rd party way of checking how creative Midea are with their energy accounting. Nonetheless, a 5% underestimate of energy in and say a 5% overestimate or energy out could inflate the COP by 10%, meaning a Midea COP of 3.3 means a real COP of 3.0.

4. I and @derek-m (one of the leading and very knowledgeable forum contributors) have spent forever and a day trying to access the Midea wired controller data on the LAN (local area network). All said and done, we have made little progress. The python code is as @derek-m put it so well written by sadists. I am currently about to move over to trying to get the data over modbus (a communication protocol) over a wired connection. Progress or lack of it will be documented here on the forum. 

5. One of the major flaws in Midea units is their output falls significantly at lower ambient temps. All ASHPs do this, but Midea units are notably poor performers in this respect.

6. Your diagram has what looks suspiciously like a LLH (low loss header), appropriately appearing as a 'black box'. The general consensus is that these are the devil's work and should be binned. @batalto has some useful before and after data showing improvements in efficiency after removing a LLH.

@alan-m - if you like the sound of what @cathoderay is saying, you might want to get an energy meter installed to monitor the electricity supply to the heat-pump and the solar-thermal pump systems.

Obviously, the sooner you have an independent measurement of energy consumption, the easier it will be to track the effects of any changes you decide to make.

What you'd be looking for is something like the Eastron SDM230 energy meter.

This is powered by the mains that it's monitoring, and has internal memory to retain readings and configuration settings during a power outage.

It is MID certified, which means that the particular unit you are buying has been tested and is certified as accurate enough for billing purposes in UK/EU.

It has additional terminals which allow data to be read using an external device/logger. In particular, this model has an RS485 interface which supports the Modbus protocols that @cathoderay alluded to earlier. That provides you with a level of future-proofing to add on whatever else he and @derek-m may suggest at a later date.

The meter will need to be be housed in a DIN-rail enclosure, at least 2-modules wide, and must be installed by a qualified electrician.
There is no harm in requesting a wider DIN enclosure. That would allow space to install additional monitoring units, trips, indicators and whatever else you might want in future.

@cathoderay Thanks for the welcome. Certainly agree that the app is very limited and, like you, I am transcribing data from it into a spreadsheet for analysis. There is indeed a Low Loss Header and additional pump in the heating circuit. I have seen many comments about how this may be a source of inefficiency, so whilst frustrated that my installer included it I see it as an opportunity for future improvement. On the whole I am delighted with how the house is being heated (using weather comp), even in the couple of cold snaps we have had this winter (and it gives me endless opportunities to tinker with how it is set up).

@transparent Thanks for the suggestion. I was thinking of waiting for the summer and then installing some of the openenergymonitor equipment to break my dependency on the Midea app data. It is another cost but seems on the face of it to give more accurate and trustworthy data. In the mean time I might have an old eco-eye monitor somewhere that I could use to measure the actual KWh of the unit and pumps.

Posted by: @alan-m

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On the whole I am delighted with how the house is being heated (using weather comp)

That's good news, and weather comp is indeed the way to go. What is remarkable is how many people come to this forum not using weather comp, and in some cases not even knowing what it is. This is 95% an installer problem: they don't tell the householder how to set up their heat pump properly, and some installers/brands take it even further, they disable weather comp.

For others reading this thread, who are unsure, weather comp is very simple. A house loses heat at a rate that depends on the outside temperature. It loses more heat in cold weather, less heat in milder weather. To stay in equilibrium ie stay at a set target temperature, it therefore needs more heat added in cold weather, and less heat added in milder weather. Weather comp is shorthand for adjusting the heat pump output according to the outdoor temperature so that its output is as close as is possible to the current loss at the current outdoor temperature. This is normally done by adjusting the leaving water temperature (LWT, the temperature of the heated water coming out of the heat pump), hotter temp means more heat.

A linear (straight line) relationship between outdoor temp and heat loss is assumed (a certain change in outside temp by say one degree always results in the same amount of change in the heat loss). Setting a weather comp curve (curve is used in a very generic term for a line on a graph) is then as simple as setting two points on that line, and upper and a lower one, and the line joining them takes care of all the intermediate points.

Here is Midea's attempt to make it seem much more complicated than it is:  

T4 is outdoor temp, T1 is LWT. T4H1 is the lower outdoor temp, and T1SETH1 is the corresponding higher LWT you set at that outdoor temp, and T4H2 is the upper outdoor temp, for which you set a lower LWT, T1SETH2. On a Midea unit, these are set on the 'For Serviceman' pages, a sort of backdoor tradesman's entrance into parts of the controller where the sun don't normally shine. My current settings are 58@-4 / 35@15 which is shorthand for setting the leaving water temp to 58 degrees when it is minus 4 outside, and 35 degrees when it is 15 degrees outside. It is worth noting that most 'curves' flat line to the left of the left hand set point and to the right of the right hand set point.

The consequence of using weather comp is that the pump runs steady and low all the time, rather than fast and furious in fits and starts. This has a major impact on overall efficiency, because heat pump efficiency, the COP or coefficient of performance, is very dependent on LWT. This difference in efficiency is far from trivial, as this recent chart from my delinquent Home Assistant set up shows: 

On the left hand side, with mildish outdoor temps, the COP is around 3.3. Over the next couple of days, when outside temps fell to at or around zero at night, the COP falls below 3, then, on the right hand side, as it gets milder, the COP climbs up again, almost reaching 4.

It is important to be aware that lower outdoor temps are a double whammy for heat pumps: not only do they have to produce more heat to heat the house, but they have to do that while their efficiency is compromised. The end result is sky high bills in cold snaps, but, hopefully, also much lower bills in milder weather, because it both has less heat to produce and it can run more efficiently, with, at the end of a full heating season, the two cancelling out. At least, that's the idea. It's also why you should not file for bankruptcy on the basis of your energy use during one week of cold weather.       

@cathoderay This is a brilliant explanation - if you're not a teacher, you should be. 

@dockray - thanks, that is very kind of you.