Most efficient way to run underfloor heating

dllive

Hi @matelodave . Im sure youve been eager for an update!   

Ive been making minor tweaks - leaving for a week - and then noting the COP and other readings. The worst COP has been 1.93, and the best 2.26.

Oddly, the best COP was achieved last week when it was very cold. I increased the flow temp from 37 to 40 degrees.
I can see the immersion tank uses 2kwh every 2 weeks. (presumably the fortnightly legionnaire cleanse).

Inside the house Ive left everything static (ie: heating is set to a constant 17 degrees downstairs, and upstairs the radiators are left at 3 on the TRV)

Im not sure what else I can try to improve the COP. Perhaps a COP of ~2 is to be expected at this time of year? What are you currently achieving?

My current settings on the Ecodan are: Target flow temp of 37 degrees (Ive took it off the comp. curve 5 weeks ago); and DHW at 45 degrees.

Ive also changed energy companies using the MSE Cheap Energy Club, so that in itself will save me money. 

matelodave

I'm glad to hear that it's working out for you and you've got a better idea of how it operates. TBH I'm not really sure how you can improve the COP a great deal at this time of the year. The colder it gets the more energy the heatpump requires to maintain the set temperature until it gets to the point where it can't and the heatoutput starts to drop. Most heatpumps are then set to switch in the boost heater (it's called the equilibrium point) - mine can't because I have it switched off. Also bear in mind that when it's everso cold the ouside unit will have to go into defrost mode to ensure that the heat exchanger fins don't ice up - it's usually done on a time/temperature basis so if its colder then it will do it more often than if it isn't. My unit is just outside the diningroom window so I can see when it starts to freeze and defrost and on cold dank frosty days it can build up ice quite quickly (make sure that the defrost condensate has somewhere to go and doesn't cause an icy slip hazard adjacent to the unit)

I cant actually measure mine because I dont have a heat meter and there isn't the capability in my heatpump to determine what heat it's producing. All I can do is log the power input (not as accurately as you can, I've only got a clamp on energy monitor) and I've got a data logger on the flow temperature. I should really be logging the outside temp as well to see how it's tracking. Mine is still set for weather compensation so the flow is varying between around 30-42 degrees.

We are using more electricity than usual because it's been a lot colder this Jan & Feb  than it was last year but we are still within my estimates (we've had a lot of days where the temperature hasn't gone above zero). I wouldn't get too hung up about COP, use it as an ideal target but it's not the ultimate measurement of performance because there are other things using the leccy as well as the heatpump - circulating pumps and possibly a crankcase heater which don't add to the heat output but will increase the consumption.

If you got a spare half an hour or so have a shufti at this to show the difficulties in actually getting definitive information on heatpump performance in a real life environment (it's a couple of years old now but it takes a long time - years, rather than days, weeks or even months to do a proper study and you need lots more info rather than just "leccy in versus heat out"

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/606829/DECC_RHPP_160428_On_performance_variations_v20.pdf

Keep your logging going for a whole twelve months to see how the COP changes over the year and what affects it

dllive

Thanks @matelodave

Ive certainly got more of a handle on how it all works. So much so that Im giving my neighbour a demonstration soon! (theyre interested in getting one).

Yes, Ill keep a log. Things will start to get interesting as we go into the warmer months! Hopefully my COP will creep up to ~3.

I will return here with an update in 6 months or so! (Im sure youll be on tenterhooks!  )

All the best

matelodave

Yes, I am keen to know how you get on as I'm sure are others, who may lurk on the thread but not necessarily participate.

In the end the more info that gets disseminated the better it is for us all to understand and optimise the performance of our systems rather than just leaving it to chunter away and not be satisfied. Although I dont have a Ground Source HP I'm an avid reader of the GSHP thread as well as the ASHP one.IMO you cant have too much info.

keep it up

ATB,

Dave

dllive

Hi @matelodave

Ive been keeping weekly logs of readings.

The COP is very slightly creeping up as we come out of winter. Its been ~2.2 past few weeks as opposed to ~2 in Jan/Feb.

Its currently set thusly:

Do you think - as the weather warms - I should switch to using the comp curve? The current comp curve (which isnt active) is currently set as:

My thinking is that - as the weather warms I dont want to be generating more energy than I need. So rather than a constant flow temp of 35 degrees, which may not be needed on hot days, the Ecodan uses the comp curve so it automatically changes when it needs to. 

Im not sure if that makes sense?

shinytop

Just read the whole thread with great interest as we've just (yesterday) had an Ecodan ASHP installed.  Radiators rather than ufh but the same system and controllers. Based on discussions so far you could use the curve but dial the whole thing down a few degrees using the big +- number so that max is 35 but gets lower as outside temp rises? As is is, the curve looks like it wouldn't hit 35 until it's about 15 outside. 

matelodave

shinytop said:

Just read the whole thread with great interest as we've just (yesterday) had an Ecodan ASHP installed.  Radiators rather than ufh but the same system and controllers. Based on discussions so far you could use the curve but dial the whole thing down a few degrees using the big +- number so that max is 35 but gets lower as outside temp rises? As is is, the curve looks like it wouldn't hit 35 until it's about 15 outside. 

Thats what I do, just leave the weather compensation on to do it's thing and use the offset to crank it down a bit - the flow temp has been just trickling away at around 30 for the past week or so although in the past couple of days it's been warm enough for the room stats to not even call for heat except first thing in the morning.

We'll soon be in the period when it's only heating the hot water tank. As I've said, have a minor tweak every now and again until you are satified that it's running at the lowest temp you are comfortable with and keep you log going so you can see how you are progressing.

Thanks for keeping us informed

dllive

shinytop said:

Just read the whole thread with great interest as we've just (yesterday) had an Ecodan ASHP installed.  Radiators rather than ufh but the same system and controllers. Based on discussions so far you could use the curve but dial the whole thing down a few degrees using the big +- number so that max is 35 but gets lower as outside temp rises? As is is, the curve looks like it wouldn't hit 35 until it's about 15 outside. 

Thanks - yes, Ill do this.

shinytop

Sorry to hijack your thread but how do you control your HW?  Ours is currently set up to be on constantly.  However, given that we currently still have electric showers and use a dishwasher, I'm thinking about using Matelodave's 2 hours per night method.  This worked for us before using the immersion heater.  I can't see the need to keep 250l of HW on the go unless that's somehow more efficient with the ASHP.  Any thoughts?  Matelodave?   

dllive

shinytop said:

Sorry to hijack your thread but how do you control your HW?  Ours is currently set up to be on constantly.  However, given that we currently still have electric showers and use a dishwasher, I'm thinking about using Matelodave's 2 hours per night method.  This worked for us before using the immersion heater.  I can't see the need to keep 250l of HW on the go unless that's somehow more efficient with the ASHP.  Any thoughts?  Matelodave?   

Take a  look at this: https://www.youtube.com/watch?v=sU_s1HtdV2o
And this:
https://www.youtube.com/watch?v=h6VpATOHbFU

(Matelodave may give a better and more comprehensive answer!  )