5 degrees (average) outside and I am running at a heating COP of 3 so far, flow temperature of 40 degrees (average). My estimate is I'll use 41kw today to heating based on the formula trendline for my past performance.

Posted by: @batalto

5 degrees (average) outside and I am running at a heating COP of 3 so far, flow temperature of 40 degrees (average). My estimate is I'll use 41kw today to heating based on the formula trendline for my past performance.

Hi Batalto,

Based upon the Midea data that you supplied previously, along with your heat loss calculations and heat emitter data, the energy consumption figure would appear to be approximately correct, but the calculated water flow temperature should be approximately 49C at a COP of 3.3.

I wonder if like Kev, the flow and return water temperature sensors are not indicating the true temperature.

@derek-m I think it's the difference between lab conditions and actual... Much like MPG claims with cars. Real world experience says you'll never actually get that. Also the losses in the system won't help such as my low loss header

Posted by: @batalto

@derek-m I think it's the difference between lab conditions and actual... Much like MPG claims with cars. Real world experience says you'll never actually get that. Also the losses in the system won't help such as my low loss header

The spreadsheet that I produced and sent to you some time ago, incorporated the data that you provided about your system. At an ambient temperature of 5C, the calculated energy consumption would be 42kWh as against your estimated 41kWh, but the water flow temperature would need to be 49C. So unless your heat emitter data was incorrect, I would expect your water flow temperature to be much higher than 40C.

If you have a suitable thermometer then try measuring the temperature.

@derek-m yes but that data came from the manufacturer about their performance based on lab testing. I can imagine in the real world the system is simply less efficient than they really claim. However I can test the temperature easily enough. There is a thermometer about... Somewhere

My estimate is based on the real world trend line from my results. Hopefully it should be more accurate, but the r of that data is something like 75, so it's not 100% accurate and certainly has error bars.

@batalto 

In the spreadsheet the required water flow temperature is calculated based upon your heat loss data, your estimated total heat output from the heat emitters and the indoor air temperature, it therefore is not dependent on the manufacturers data.

Posted by: @batalto

@derek-m yes but that data came from the manufacturer about their performance based on lab testing. I can imagine in the real world the system is simply less efficient than they really claim. However I can test the temperature easily enough. There is a thermometer about... Somewhere

My estimate is based on the real world trend line from my results. Hopefully it should be more accurate, but the r of that data is something like 75, so it's not 100% accurate and certainly has error bars.

Hi Batalto,

I am not trying to prove anyone wrong. My objective in producing the spreadsheets, was for people to have a model, showing how their system could possibly perform if correctly installed and optimised. This would allow any large deviations from the anticipated performance to be identified and possibly investigated and rectified. People who suspect that their system is not operating efficiently, need something against which they can check the performance. I very much doubt that the vast majority of installers of domestic heating systems, fully understand how to accurately measure temperature, and where and how such measurements should be made to ensure maximum accuracy. If the control system is not receiving the correct information from the various sensors, then how can you expect it to control your system at its optimum.

The data published by manufacturers should have been obtained by testing in an independent testing facility, using calibrated standard test equipment, so will be more accurate than anything that can be achieve in normal operation.

Much of my career has been spent achieving the best accuracy in the measurement of numerous variables, particularly temperature, pressure flow and level. Whilst working on a new build power station in Pakistan, one of my task was to set up an on-site calibration facility, so I made an in depth study of Metrology, to enable me to ensure that the calibration of the site test equipment achieved the required level of accuracy.

@derek-m as ever I'm always appreciative of the knowledge on this forum. All I was trying to say is that all models are built on a range of assumptions. I'm finding that real world outcomes will give me the best idea of what the system is actually doing. That said I do have a meat thermometer. Perhaps I'll just test the inlet and outlet temperatures.

However I fear if the heat pump isn't accurately measuring it's temperatures what hope do I have!!!

@batalto 

Hi Batalto,

Your ASHP will still operate, even if the temperature measurements are not accurate. From the point of view of the heat energy output of the ASHP, and hence the determination of the COP value, the important parameters are the volumetric flow of the water, and the Delta T between the water flow temperature and the water return temperature. If these two temperature measurements are consistently offset from the true value by say 5C, then the heat energy output measurement should be reasonably accurate within the specified tolerances. Of course inaccuracies in the heat energy output measurement could occur if the Delta T varied due to variations in the readings rather than a true change in temperature.

I would suggest that you locate the temperature sensors in question, and see where and how they are installed. If they are just zip-tied to pipes, particularly plastic ones, then this could lead to inaccurate readings and also delay the reaction time, which could lead to further inaccuracies in heat energy output and COP measurement.

Posted by: @batalto

5 degrees (average) outside and I am running at a heating COP of 3 so far, flow temperature of 40 degrees (average). My estimate is I'll use 41kw today to heating based on the formula trendline for my past performance.

I'm heading for about 40kWh today but average temp has been 3C (I think I'm a bit further north!).  I've also been tinkering with the compensation curve and have overshot room temps again; it's 22-23C in the house at the moment. 😐 

@derek-m I think the sensors are integral. The only external sensor is in the hot water tank. Perhaps @grahamh can help. He seems to be the man who knows the Midea units better than anyone else

@kev-m we are now at 49kW used and the average ambient has dropped to 4°

Heat delivered 145kW COP: 2.95