drop the nest, you are on a hiding to nothing. it gives no feed back to the pump about required temperatures..

stick with the heat pumps own controller and app

@alec-morrow so I understand the logic, but need the data to confirm. Do you see my point. Running the ASHP at 5+ COP for 24hrs (even with step back) might cost more than How I am running now with Nest. 
Where is your evidence for the “hiding to nothing” statement?

It’s understanding I defer to, I’m a heating engineer.

Turning things off and on inherently create inefficiencies in regularly used spaces. That was tolerable before variable flow temperatures became the optimum way to maintain comfort temperatures.

on-off necessitates a higher than necessary flow temperature to compensate for the off period 

@alec-morrow understand your point. And I’m sure you are an experienced heating engineer. And know what you are talking about. But as an ex-scientist and now IT geek, I need the data. That’s why I’m comparing across two years with two different control systems. Not sure it’s statistically accurate though. 

Posted by: @julianc

@alec-morrow understand your point. And I’m sure you are an experienced heating engineer. And know what you are talking about. But as an ex-scientist and now IT geek, I need the data. That’s why I’m comparing across two years with two different control systems. Not sure it’s statistically accurate though. 

Julian,

I fear your experiment will only work if the weather and temperatures are the same for each year. I suspect that they may not be. 🙃 

@derek-m it’s a good point well made. Not sure what else to do?

Posted by: @julianc

@derek-m it’s a good point well made. Not sure what else to do?

You can look up degree days for both your years and adjust.  There are a couple or three sites but this one will do it.

DEGREEDAYS.NET "https://www.degreedays.net/?gclid=Cj0KCQiAr5iQBhCsARIsAPcwROMVQCTUetrrnT6MWK48r7Vh62Ae8WkVR1GT8aMQux3alSWiR3AJQfMaAgsDEALw_wcB"

Heating & Cooling Degree Days – Free Worldwide Data Calculation

Heating degree days and cooling degree days for thousands of locations worldwide. Download free data in a simple spreadsheet format.

You could also plot outside temp vs energy consumed on a scatter diagram and compare the two years. Like I did here to compare using thermostats with weather comp. 

Posted by: @julianc

@alec-morrow understand your point. And I’m sure you are an experienced heating engineer. And know what you are talking about. But as an ex-scientist and now IT geek, I need the data. That’s why I’m comparing across two years with two different control systems. Not sure it’s statistically accurate though. 

oh dear…  I feel for you! 

There have been comparisons done by people here, savings of not using an On-Off has been seen here to be around 20-25%

Posted by: @julianc

@alec-morrow so I understand the logic, but need the data to confirm. Do you see my point. Running the ASHP at 5+ COP for 24hrs (even with step back) might cost more than How I am running now with Nest. 
Where is your evidence for the “hiding to nothing” statement?

Hi Julian,

The problem with any home based test is that there are so many variables that are not being measured and hence cannot be taken into account in the final results.

Since you believe in maths and physics, maybe I can prove to you that what Alec is saying is actually true.

Looking at the data for Kev's system, the heat demand at an outdoor air temperature of 7C is 4304W at a water flow temperature of 34.3C, and a COP of 4.6, which would require an electrical energy input of 936W. So if his heat pump runs constantly for 1 hour then the energy used would be 936Wh.

If instead of running continuously for the full hour, the heat pump runs for 40 minutes and then stops for 20 minutes, then the heat emitted into the property would be 2689W at the above water flow temperature. So the indoor air temperature would start to fall.

To maintain the indoor air temperature requires that 4304W is emitted during the 40 minute period, which would equate to a heat energy output of 6456W from the heat pump. To achieve this level of output the heat pump would need to operate at a water flow temperature of 39.2C, at a COP of 3.93 and electrical energy input of 1642W. Because the heat pump is only running for 40 minutes, the power used is 1095W.

So if running the heat pump at a higher temperature but for a shorter length of time uses 1095Wh, and running it continuously at a lower water flow temperature uses 936Wh, then the energy consumption is almost 17% greater with the on-off method.

I hope this answer your question.

@derek-m thank you Derek. Fantastic explanation. I do take your point about all the variables too. 
I will think on this more. But it suggests I need to end my annual Nest control trial and move over to weather compensation sooner. 
Thank you

@julianc I think I remember you saying you'd bought a Daikin maintenance and service pack. Which one did you get and has it proved to be a good investment ?