Can I improve my COP?

matelodave

It really is a case of doing one adjustment at a time, giving it time to settle (a couple of days, rather than minutes or even hours) and recording what you did and what was the result.

There is no quick fix as it all depends on so many variable factors which interact with each other especially the weather and your lifestyle.

michaels

NedS said:

Exiled_Tyke said:

2. The big question for me remaining, I think, is do I run for longer (e.g. all day) at lower flow temperatures and possibly setting the ASHP to an even quieter setting (I note that the quietest one should be avoided as it won't run a defrost cycle on sub-zero days)?  Currently I have the system switching on (or to be more precise,  lifting the temperature from its set back) in the middle of the afternoon (when there is the greatest chance of a bit of spare, PV available in winter).  But would I be better of simply running all day and throttling the system back further?  I guess there are no easy answer to this one.  

Set backs are complicated, as there are many factors that are unique to your property and heating system. There was an excellent discussion here by retired physicist Michael de Podesta:

https://protonsforbreakfast.wordpress.com/2022/12/19/setback-should-you-lower-heating-overnight/

which concluded that there's not a lot in it, and whether or not it will save money probably depends on how efficient your heating system is when output is higher to recover the lost heat compared to continuous running.

To summarise, all else being equal, running a set back and then later returning to normal levels requires less heat overall (and therefore may cost less). However, if you are having to thrash your heat pump to recover from the set back, that may more than offset any savings you just made, so it depends.

A good analogy here is a car on a motorway trip. Driving at a constant 50mph is more efficient than driving half the journey at 40mph (setback) and the other half at 60mph to make up the lost time.

Conversely, if you have an oversized heat pump, you may find it easy to increase heat output to recover the setback whilst still operating in an efficient window. To use our car analogy again, imaging that car journey in a car with a top speed of 60mph vs a car that can easily do 120mph, where doing 40-60mph is all in the same efficiency range so makes little difference.

Of course the study above only really considers energy use and efficiency. It does not take into account ToU tariffs where applying a set back during an expensive period, and then recovery during a cheap rate period would almost certainly provide monetary savings even if the recovery were less efficient, as this would be more than offset in monetary terms by the ToU savings.

Problem is where comfort comes in you actually probably want to set back during the cheap times and boost during the expensive times. For me a set back so not about saving energy but about having cooler bedrooms at night.

NedS

michaels said:

NedS said:

Exiled_Tyke said:

2. The big question for me remaining, I think, is do I run for longer (e.g. all day) at lower flow temperatures and possibly setting the ASHP to an even quieter setting (I note that the quietest one should be avoided as it won't run a defrost cycle on sub-zero days)?  Currently I have the system switching on (or to be more precise,  lifting the temperature from its set back) in the middle of the afternoon (when there is the greatest chance of a bit of spare, PV available in winter).  But would I be better of simply running all day and throttling the system back further?  I guess there are no easy answer to this one.  

Set backs are complicated, as there are many factors that are unique to your property and heating system. There was an excellent discussion here by retired physicist Michael de Podesta:

https://protonsforbreakfast.wordpress.com/2022/12/19/setback-should-you-lower-heating-overnight/

which concluded that there's not a lot in it, and whether or not it will save money probably depends on how efficient your heating system is when output is higher to recover the lost heat compared to continuous running.

To summarise, all else being equal, running a set back and then later returning to normal levels requires less heat overall (and therefore may cost less). However, if you are having to thrash your heat pump to recover from the set back, that may more than offset any savings you just made, so it depends.

A good analogy here is a car on a motorway trip. Driving at a constant 50mph is more efficient than driving half the journey at 40mph (setback) and the other half at 60mph to make up the lost time.

Conversely, if you have an oversized heat pump, you may find it easy to increase heat output to recover the setback whilst still operating in an efficient window. To use our car analogy again, imaging that car journey in a car with a top speed of 60mph vs a car that can easily do 120mph, where doing 40-60mph is all in the same efficiency range so makes little difference.

Of course the study above only really considers energy use and efficiency. It does not take into account ToU tariffs where applying a set back during an expensive period, and then recovery during a cheap rate period would almost certainly provide monetary savings even if the recovery were less efficient, as this would be more than offset in monetary terms by the ToU savings.

Problem is where comfort comes in you actually probably want to set back during the cheap times and boost during the expensive times. For me a set back so not about saving energy but about having cooler bedrooms at night.

I agree, and everyone/every property is different. We are similar to you - we have an oversized heat pump and leaving it on low all night, even at it's lowest output, would result in the house being warmer than would be comfortable for sleeping. So we run setbacks, not through choice but because the heat pump puts out more heat than required. The fact that the heat pump is massively oversized also means we can recover from a setback relatively quickly and without compromising efficiency, so is not detrimental to our running costs.

michaels

NedS said:

michaels said:

NedS said:

Exiled_Tyke said:

2. The big question for me remaining, I think, is do I run for longer (e.g. all day) at lower flow temperatures and possibly setting the ASHP to an even quieter setting (I note that the quietest one should be avoided as it won't run a defrost cycle on sub-zero days)?  Currently I have the system switching on (or to be more precise,  lifting the temperature from its set back) in the middle of the afternoon (when there is the greatest chance of a bit of spare, PV available in winter).  But would I be better of simply running all day and throttling the system back further?  I guess there are no easy answer to this one.  

Set backs are complicated, as there are many factors that are unique to your property and heating system. There was an excellent discussion here by retired physicist Michael de Podesta:

https://protonsforbreakfast.wordpress.com/2022/12/19/setback-should-you-lower-heating-overnight/

which concluded that there's not a lot in it, and whether or not it will save money probably depends on how efficient your heating system is when output is higher to recover the lost heat compared to continuous running.

To summarise, all else being equal, running a set back and then later returning to normal levels requires less heat overall (and therefore may cost less). However, if you are having to thrash your heat pump to recover from the set back, that may more than offset any savings you just made, so it depends.

A good analogy here is a car on a motorway trip. Driving at a constant 50mph is more efficient than driving half the journey at 40mph (setback) and the other half at 60mph to make up the lost time.

Conversely, if you have an oversized heat pump, you may find it easy to increase heat output to recover the setback whilst still operating in an efficient window. To use our car analogy again, imaging that car journey in a car with a top speed of 60mph vs a car that can easily do 120mph, where doing 40-60mph is all in the same efficiency range so makes little difference.

Of course the study above only really considers energy use and efficiency. It does not take into account ToU tariffs where applying a set back during an expensive period, and then recovery during a cheap rate period would almost certainly provide monetary savings even if the recovery were less efficient, as this would be more than offset in monetary terms by the ToU savings.

Problem is where comfort comes in you actually probably want to set back during the cheap times and boost during the expensive times. For me a set back so not about saving energy but about having cooler bedrooms at night.

I agree, and everyone/every property is different. We are similar to you - we have an oversized heat pump and leaving it on low all night, even at it's lowest output, would result in the house being warmer than would be comfortable for sleeping. So we run setbacks, not through choice but because the heat pump puts out more heat than required. The fact that the heat pump is massively oversized also means we can recover from a setback relatively quickly and without compromising efficiency, so is not detrimental to our running costs.

But unless it also modulates very well don't you have periods like now where it runs 6 mins per hour in 2 three minutes bursts?

Exiled_Tyke

A couple more thoughts. 

1.  I can see why repeatedly heating up water is grossly inefficient.  But in my mind the reason for this is that it's not necessary to have a full tank of water at the highest temperature.  So it's better to heat enough water to a temperature to get through the day. For us that's mid 40s and usually by evening it's down to low 30s which is fine for personal washing but not for doing the dishes.    So to be clear heating from 30-40 uses less energy than 40-50 because of the lower COP at higher temperatures.   BUT it's not necessary to run the tank cold to get better effeciency - that's just wasting hot water.  BUT it is necessary to avoid repeatedly heating water to always have the highest temperature.   For us, if we run out (very rare) towards the end of the day then that's simply it. We wait for the overnight reheat to take effect. 

2. Did I miss something or has the Daikin app (ONECATA) changed.? I don't remember it having a Leaving Water Offset adjustment last winter.  But I'm loving the fact that I can experiment adjusting it without having to go to the controller and start editing the curves etc... 

NedS

michaels said:

NedS said:

I agree, and everyone/every property is different. We are similar to you - we have an oversized heat pump and leaving it on low all night, even at it's lowest output, would result in the house being warmer than would be comfortable for sleeping. So we run setbacks, not through choice but because the heat pump puts out more heat than required. The fact that the heat pump is massively oversized also means we can recover from a setback relatively quickly and without compromising efficiency, so is not detrimental to our running costs.

But unless it also modulates very well don't you have periods like now where it runs 6 mins per hour in 2 three minutes bursts?

No, we control ours by room thermostat so the heat pump cannot cycle and we can ensure longer run times. It's either on or it's off. Not recommended, but works well for us.

akwexavante

It's exactly a year since install and I've taken a set of readings from my Daikin set up.  I'm slightly disappointed at DHW is only 1.9 and space heating 2.9.

I have a Daikin and my COP in summer is poor because of the disinfection cycle.  I think once a week really is OTT. I asked if it was possible to change this to once a month, and i understand it's not possible within my system.

Heating is set to 21 degrees. At night, the set back is 18 degrees.

I tried this when my system was initially installed, and it was expensive, and it didn't work for me, so i just decided on a set temperature for the whole day and set it at that and i have a lower heating bill and a much better COP. My thoughts are that the three degrees for an ASHP is actually a big difference to manage efficiently.

If the actual problem is that bedrooms are too warm at night (This was my Problem) then turn down the rads in the bedrooms and close the bedroom doors but leave the room stat downstairs at 21.

I've learned to close ALL internal doors all the time to save money, regulate the temperature better room to room and get a better COP.

Alnat1

I turned off the weekly disinfection straight away.

If we die, I'm sure you see it on the news under the headline "Killer Heatpump"   

matelodave

Mine is also turned off,  - its a non-vented tank fed with mains water that is chlorinated so not stored for any length of time nor open to the atmosphere. So far we haven't had any problems and we've had our heat pump for 15 years.

If you heat your water above 50-55 degrees or the disinfection cycle is set to 55 or higher then its highly likely that the immersion heater will kick in as most ASHP wont heat above 55-55 degrees. I've disabled both the boost immersion heater and back-up heater so there's no possibllity of either getting turned on by mistake.

An immersion heater has a COP of 1 so keeping the hot water down to 50 or less will significantly improve your COP. Ours is set for 45 degrees and that plenty hot enough for most of our needs. We boil up some in the kettle if we need it hotter for greasy pots and pans. Also only heat once a day rather than keeping the water hot all the time.

Alnat1

matelodave said:

Mine is also turned off,  - its a non-vented tank fed with mains water that is chlorinated so not stored for any length of time nor open to the atmosphere. So far we haven't had any problems and we've had our heat pump for 15 years.

If you heat your water above 50-55 degrees or the disinfection cycle is set to 55 or higher then its highly likely that the immersion heater will kick in as most ASHP wont heat above 55-55 degrees. I've disabled both the boost immersion heater and back-up heater so there's no possibllity of either getting turned on by mistake.

An immersion heater has a COP of 1 so keeping the hot water down to 50 or less will significantly improve your COP. Ours is set for 45 degrees and that plenty hot enough for most of our needs. We boil up some in the kettle if we need it hotter for greasy pots and pans. Also only heat once a day rather than keeping the water hot all the time.

We do the same except out water is set to 47, might try 46C though and see if hubby notices...