Posted by: @kev-m

@Markc, very interesting.  Was your house warm enough with the lower flow?  To use the car analogy quoted by someone else, you have better mpg but you're driving further.

How do you scale the MELcloud output to look like that?  I could post some of mine but they won't look as neat as yours.  My overall consumption is similar but much spikier as I've been varying the room temp using the thermostats. 

Have you looksed at the csv output?     

The house was equally warm, maintaining 22º for both 50º and 35º flow.

I've photoshopped the screenshots together to make them more readable.

I did look at the CSV output but it seems to totally ignore the date selectors and I always just get the first 4 months worth of data which is useless.

@markc it's important to remember COP isn't just a function of power used, it's also of heat delivered. When you have a cop of 3.5 Vs 2.5 you are delivering far more heat. Looking at your figures at 2.5 you used 22kw so delivered 48kw of heat. At 3.5 you used 24kw but delivered 84kw of heat. Almost double.

Posted by: @batalto

@markc it's important to remember COP isn't just a function of power used, it's also of heat delivered. When you have a cop of 3.5 Vs 2.5 you are delivering far more heat. Looking at your figures at 2.5 you used 22kw so delivered 48kw of heat. At 3.5 you used 24kw but delivered 84kw of heat. Almost double.

Good point but where has the extra 36kWh gone? If 48kWh is enough to heat the house - which it is -  why hasn't this been delivered at a COP of 3.5?      

@markc 

Hi Mark,

The difference in heating energy used (as shown by the graphs) is easily explained, in the first case with the water flow temperature at 50C, when the system initially switched over from DHW heating to CH, the heat source for the radiators was actually the hot water tank rather than the ASHP.

Comparing individual days is very difficult, since no two days are identical. When I look at my data for the 21-10-21 compared to the 3-11-21, I find that there was over twice as much solar PV generation, so on the 21-10 your home would probably have received more solar gain, hence less heating required. Our energy consumption on 3-11 was 1.5 times that of the 21-10.

Posted by: @batalto

@markc it's important to remember COP isn't just a function of power used, it's also of heat delivered. When you have a cop of 3.5 Vs 2.5 you are delivering far more heat. Looking at your figures at 2.5 you used 22kw so delivered 48kw of heat. At 3.5 you used 24kw but delivered 84kw of heat. Almost double.

The higher COP did deliver more heat yes you are correct.

Given that and thinking about it, selecting individual days that had the same outside temp is not accurate enough.

If for example if the days prior to my examples, 20/10 was warm and 02/11 was cold the heating would have more work to do to get up to temp.

@markc 

The actual air temperature is just one factor, solar gain, not just through the windows, but on the building fabric itself can have a marked effect on heat loss. Also wind and rain can dramatically increase heat loss and hence heat demand.

Here are my figures based on a 6 day test. All factors the same except for flow temperature and outside environment.

Room thermostats were at 22ºC so there will have been moments where the ASHP had no call for heat.

50ºC flow temp with average outside temp of 11.6ºC. Average COP of 2.7. 286kWh of heating produced. 100kWh of energy used.

35ºC flow temp with average outside temp of 7.8ºC. Average COP of 3.4. 478kWh of heating produced. 130kWh of energy used.

So if my maths are correct, if I had been running the ASHP at 50ºC during the period 02/11 - 07/11, I would have used 177kWh as opposed to 130kWh.

Outside temps for each of the testing days.

19/01 - 24/10

02/11 - 07/11

Posted by: @derek-m

@markc 

That is fine Mark, whatever suits you best.

Hi @derek-m. How would you like to go about us setting up my compensation curve? 

Posted by: @markc

Posted by: @derek-m

@markc 

That is fine Mark, whatever suits you best.

Hi @derek-m. How would you like to go about us setting up my compensation curve? 

Good Morning Mark,

Whatever is best for you. We can do it via the forum, direct e-mail, telephone or possibly Skype or similar. The choice is yours.

Posted by: @derek-m

Posted by: @markc

Posted by: @derek-m

@markc 

That is fine Mark, whatever suits you best.

Hi @derek-m. How would you like to go about us setting up my compensation curve? 

Good Morning Mark,

Whatever is best for you. We can do it via the forum, direct e-mail, telephone or possibly Skype or similar. The choice is yours.

Skype is good. I'll send you a direct message with my username.

I’ve managed to gather data for a couple of six day periods where the average outside temp was 11ºC.

I was running the ASHP differently in each period.

10/05 to 15/05

Running at 50ºC flow, 

ASHP controlled by multiple thermostats calling for heat when required. (so like a gas boiler would be controlled)

Indoor temp 18ºC for 20 hours and 22ºC for 4 hours in the evening.

73.9kWh energy consumed.

231.8kWh energy produced.

COP was 2.9

08/11 to 13/11

Flow temp controlled by the compensation curve 

Thermostats calling for heat constantly (all set at 25ºC)

Indoor temp maintained at 21ºC-22ºC for 24 hours.

64.3kWh energy consumed.

297.4kWh energy produced.

COP was 4.3

From what I have experienced, using the compensation curve delivers a much more consistent and comfortable level of heating.

UHF is constantly warm under foot, whereas with the on/off schedule it was cool for the majority of the day.

The large thermal mass of my UFH no doubt helps running the system at a constant 22ºC be more efficient compared to an on/off schedule.