Posted by: @dunlorn

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@drew-pa. At risk of sounding like one of the Four Yorkshiremen, I dream of a monthly consumption like that, 760kWh - you were lucky!  
I live in a c100yr old four bed detached in the Cairngorms, around 175m2, solid stone walls and suspended floors. Never going to be a passivhaus it's true but we've installed secondary glazing throughout and are zealously chasing out draughts to try and improve matters and we've a C-rated EPC (79 score). We've 2 x 12kW Samsung heat pumps operating on a master and slave basis.

During December we managed to consume an eye-watering 2536kWh, with a daily peak of around 130kWh, that's around twice a typical daily figure for November or over the last week. Obviously not sustainable. I ended up switching the slave heat pump off as I'm not convinced it's adding much value - the controller shows its output temp consistently some 6° C lower than the master (so presumably just lowering the buffer tank temperature) and heat power generated is recorded as virtually zero which may be a measurement issue. Neither unit gets anywhere near their WC set point. 

 

Like you I've seen a significant improvement in efficiency over the last few days as temperatures have risen to 3-4°C or so. Nevertheless I'm far from convinced the system is set up optimally and I'm currently waiting for a visit from the installer and Joules. I'm not holding my breath. 

 

Simon

 

Wow, that's a lot of energy.  Do you know the heat loss of your house?

I sometimes wonder about the value of EPCs. My house is about the same size as yours, has a D rated EPC but uses well under half the energy (less than 1000kWh heating and HW in December). 

I've no faith in the EPCs either - we've had two in the past year (needed for gov't fund contributions here in Scotland). The most recent said heat demand 43,000kWh but the previous one (with less done) said 34,000kWh!

We've an air tightness test being carried out next week (arranged by the supplier of our secondary glazing) and I'm planning to see what more the firm can offer by way of properly calculating demand and prioritising sensible benefits, ie not externally cladding the entire house. I'll post any learning.

Simon

Please do.  I'm no expert but it's often said that draught proofing is as important, if not more so, than insulation.  

@dunlorn 

Hi Simon,

wow that’s some big numbers right there.  I’m amazed at the difference in since of installed capacity.  I know I think ours is a little under sized but we are still hitting good numbers and we are 1/3 of the installed capacity that you have.  I’m still learning all about this industry/technology and find all this stuff fascinating.  We found a good local company that did our install, can’t recommend them enough.  

I notice you are in the cairngorms, we are north of Elgin on the coast if you are every around this way and want a look at our system.  

ATB

Drew

Hello again,

Thanks for all your input.  It appears we have a system that is almost working well.  

it would appear that I have made an error in my COP calcs.  I had divided yield by energy consumption using traditional logic.  Well it turns out that Vaillant use a different calc.  I have attached a screenshot from their documentation to highlight this.  

Vaillant use the following. 

(Yield + Energy consumption)/ Energy Consuption = COP.  (Roughly). 

I have attached two photos of our Figures for everyone to see. It would appear we have had a COP of 4.2 since the start of the year.  I really cant complain!   The COP for the system since install is 3.88.  

oh well the learning continues!  

Posted by: @drew-pa

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Hello again,

 

Thanks for all your input.  It appears we have a system that is almost working well.  

it would appear that I have made an error in my COP calcs.  I had divided yield by energy consumption using traditional logic.  Well it turns out that Vaillant use a different calc.  I have attached a screenshot from their documentation to highlight this.  

Vaillant use the following. 

(Yield + Energy consumption)/ Energy Consuption = COP.  (Roughly). 

I have attached two photos of our Figures for everyone to see. It would appear we have had a COP of 4.2 since the start of the year.  I really cant complain!   The COP for the system since install is 3.88.  

oh well the learning continues!  

It can be an expensive learning curve. 😡 

At least you can bask in the warm glow of having an efficient system. 😎 

@drew-pa Thanks Drew, I'll let you know if we're over that way. We're in Kingussie so happy to do likewise if you're heading south anytime.

Simon 

Hi,

Hope you are doing well. Do you have more up to date spreadsheet you could share? Please advise.

Good evening all,

Here is the latest version of the spreadsheet.  All data is taken from the new Vaillant app to create a level playing field.  I realise there will be errors in the data gathered, but at least it's hopefully constant.  The changes made earlier this year to the system appear to have made a big difference to the performance of the system.  I will do a proper write up of the system and how it is now in a little while.  

ATB

Drew

@drew-pa Hi, I am new to the forum and about to go ahead with ASHP install into a new self-build near Inverness and currently favouring Vaillant and was very interested in your posts and especially the set up and electricity consumption you are experiencing.  My house is around 230m2 with UFH to ground and first floors and was interested in which Vaillant schematic should be used, buffer vessel sizing, UFH circulation pumps yes/no, HW cylinder type eg Vaillant or other etc any advice would be greatly appreciated.  In tandem with the finalising ASHP spec I am also trying to establish best Solar/battery combo and your electricity consumption spreadsheet is a great starting point, thank you.

@neilhighland it won’t really matter what heat pump make you have installed although vaillant do seem to be the preference for heat geeks.  What is more important is the heating system design, correct pipe sizing for flow rate, correct spacing of ufh pipes in each area for the heat loss, the heating circuit being run as one open loop with no zoning no wiring centres or actuators and multiple pumps restricting flow.  Any of these things will restrict efficiency and will mean you have to run at a higher flow temp and you will have paid for a load of unnecessary equipment.

@gary thanks Gary, I am certainly coming around to that way of thinking, UFH has been designed already and I am happy with that but had always thought that I would need some individual 3rd party room temp control but I take it the most efficient will be weather compensation control via ASHP and room adjustment via manual flow control on UFH circuits?  Thanks again for advice.