Posted by: @bristoljoe

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I don't know if other people have noticed this , although the cops are good, i think our overall delivered heat has gone up compared to our gas consumption (without a full year its more difficult to tell) I don't know if the HP is over estimating the delivered heat (and therefore inflating the COP figures.) or perhaps its a combination of having a generally warmer house than we did and now not using the wood burner as much as it seems like the dirty option compared to HP, whereas it used to feel greener compared to gas. 

This heat delivered by heat pumps thing is a bit of an enigma. I am off mains gas, and used to have oil CH. In a typical heating season, I might use 1200L of oil, at 10.35 kWh per litre x 80% boiler efficiency that is 9936 delivered kWh to heat the house, which I don't remember as being cold at all. I have just passed the first anniversary of having the heat pump installed, and it has used 10,068 kWh, which at a COP of say means it delivered a staggering 30,204 kWh of heat, three times as much as the oil did, to achieve much the same level of heating.

When I have brought this up before, no one has come up with an answer. Perhaps I am being really thick, but from where I am standing, something definitely doesn't add up. 

@dangermousie I have only the vr700 I think it's called which is the weather comp unit and the main vaillant controller. I don't have the sensocofort or an app. I do have wiser thermostats but this only really monitors room temps and is only an on off control to the heat pump.

The wall unit for the arotherm, the one with the twist dial, you can look in the yeild figures and in here it give working figures for hot water heating and cooling if you had it installed. 

@cathoderay I agree this is difficult and I have asked those on the open energy monitor forum to compare vaillant reading and their heat meter readings. those that replied said they were not wildly out. 

But that made me think that generally they measure OK but some units might just be off, miscalibrated or something. Like yours or mine.

Heat perception is a difficult one. As I have noticed that I some time can feel quite cold or too hot even although the temprature is a stable 20 degrees . But when we had gas we had very little record of the house temp. 

Is your pump far from the house? We have 30m of 28mm pipe work outside and the insulation supplied was really poor. I realised there was a good few hundred watts being lost . This would mean the delivered heat measured at the pump vs the heat needed to keep the house comfortable would be off. 

Did you old oil boiler do hot water ? If not this would cause a difference in heat supplied/required  between oil and hp. 

Your cop might be lower than you think too. Do you know what your typical flow tempratures are? 

Might be combination of things but your number do seem very off. Worth talking to your installer or a different service engineer. 

A change from oil to hp should in almost all circumstances save money so worth getting to the bottom of it. 

I too live in the NE of Scotland. I find the energy consumption on the app very accurate to my actual meter usage. I have also seen a huge difference since my installer has been back to adjust the settings. My house is never below 22 deg 24/7. At the moment my consumption is approximately 24 kw per day. The settings have to be correct for your property or it will eat electricity. My heatcurve is at 0,4 and still playing with it, I may try and go lower to get more efficiently which at the moment is around 4.4 to 5. I need longer to compare running values with my previous ground source pump but so far looking much the same if not better.

Arotherm plus 12 kw with sensocomfort 720f, and weather compensation 

Hi @Murchison2003

That's great to hear, I noticed ours wasn't to far from actual useage also.  It's interesting to hear about your heat curve.  We have two for this house presently 0.5 for downstairs and 0.3 for upstairs.  I have been trailing the adaptive heat curve and it seems to be working well.  Strange as Vaillant tech support said not to use it in the UK.  It seems to be doing its thing okay here in the North East of Scotland.  

One caveat, it is only running on the upstairs at present due to the way the system is setup.  I am waiting on the installer coming back to modify a things to allow it to work on downstairs also.  I think my installer quite likes having a bit of a geek as a customer, we are both learning lots!  

@bristoljoe - the old oil system and the new heat pump system both did and do the same work, heating and DHW. The heat pump has only about 1.5m of external pipework with some but not very good insulation. 

I agree heat perception is a tricky one, especially in an old leaky building like mine because of draughts, which are less now than they used to be as I seal some of the leaks. Nonetheless, my memory of the oil CH era is that I didn't feel cold (or too hot), just 'about right', and that has also been the case over this winter, with the heat pump. Another thing to consider is age - I am older now that I was (!) and typically the old feel the cold more. But while there may be a few degrees difference in room temps, my overall perceived level of comfort is pretty much the same.

And yet the heat pump appears to need to deliver over three times more energy to achieve the same comfort level. It just doesn't make sense.

Because of this glaring anomaly, cost comparisons are tricky. However, if we use my actual annual consumption figures, oil is significantly cheaper. To achieve comparable comfort levels, I have used just over 10,000kWh of electricity over the last year using a heat pump, which costs £3,400 at today's price cap (which will go up), with oil I typically used around 1200L per annum, which at yesterday's boilerjuice.com price per litre of 74p is £888 per annum (and oil prices are currently falling). Even at last year's typical higher price of around £1 per litre, it is still only £1200 per annum, still significantly cheaper.       

If we look instead at estimated energy produced, things look different, and but still just favour oil. 1200L at 10.35kWh per litre at 80% boiler efficiency = 9936 kWh produced at a cost of £888 = 8.94p per kWh; while for the heat pump, 10,000kWh at a SCOP of 3.3 = 33,000kWh produced at a cost of £3,400 = 10.30p per kWh. Oil is still cheaper, but the margin is less.      

But there is a major problem with the last paragraph: the glaring difference in energy produced anomaly, 9936kWh for oil, and 33,000kWh for a heat pump. I really can't make any sense of that at all, to the extent that I think the 8.94/10.30 pence per kWh numbers may even be meaningless. On the other hand, I do know exactly what actual costs are at today's prices: heat pump £3,400 per annum, oil CH (if I still had it) £888 per annum. From my bank manager's point of view, who cares not a jot about COPS and all that other heat pump voodoo, oil is significantly cheaper.   

Put another way, heat pump price per kWh produced may be around the same as oil price per kWh produced, but the heat pump needs to deliver over three times as many kWh per annum to deliver the same comfort level, and so ends up being much more expensive.

I still think I must have made a huge blunder, because the energy delivered anomaly just doesn't make any sense at all! 

Advertised COPs and COPs calculated from manufacturers' own monitoring equipment built into heat pumps are always going to be suspect, human nature being what it is. As I've pointed out elsewhere, 'human nature' led to dieselgate, all done by one of the most respected European car manufacturers. I find it impossible to believe that heat pump manufacturers are immune to such influences, and must at times find themselves sorely tested. There is already some evidence of less than honest marketing, in the use of headline kW ratings based on ideal conditions that bear little resemblance to actual performance in winter conditions. MCS, rightly dubbed the Keystone COPs, couldn't police a goldfish in a glass bowl, so the manufacturers get away with it. I call this whole can of worms compressorgate. It is a can that is waiting to explode.

My own calculated 24 hour trailing COP for what it is worth is based on Midea's reported lifetime total energy consumed and produced: total energy consumed now minus total energy consumed 24 hours ago divided by total energy produced now minus total energy produced 24 hours ago. The results are in the right ball park (see chart below), but having said that, I know, based on an external dedicated energy meter that only supplies the heat pump, that the Midea energy consumed is, rather bizarrely, an over-estimate of actual use, by a little over 10%. But what if the energy produced is also an over-estimate, by a little bit more than the energy consumed over-estimate? The COP then becomes magically inflated. Who knows what is really going on? Without dedicated expensive and complicated third party monitoring, which is itself not perfect, there is no way of knowing.

All that said, here is my calculated 24 hour trailing COP, plus energy in/out and ambient temp for the last week: 

@murchison2003 Hi. As before, I’m not necessarily replying just to you, but I am adding my three ha’p’orth (showing my age!) which might add a little something to the general conversation.

Having previously had a solid fuel central heating system, costing in the region of 2 1/2 thousand pounds a year, but including hot water as prices were a year or so ago, I can only say that my heat pump so far does not disappoint. Yes for sure, during January and December, I was using about 200 quid’s worth of electricity for each other’s two months.

But I can already see that it will be rather less than that for this February, and I note - from last autumns numbers - that it will come down to well under £100 by April or May, and considerably less than that during the summer. Compared to my previous average of £200 a month for the whole 12 months, this can only be a win situation. 

I agree with other comments I have read somewhere on this thread that it is very important how you use your system.

It’s absolutely no good just turning it on and off as if it was an oil or gas system with flow temperatures of 60 C or above. Plus, as we should all be getting to know by now, installation, installation, installation. If you have a leaky old house that it isn’t viable to do radical insulation work on, there is no reason I heat pump shouldn’t provide the same kind of COP, as this is based on power, put in, and kilowatts of heat put out.

If you have a leaky old house that it isn’t viable to do radical insulation work on, there is no reason why a heatpump shouldn’t provide the same kind of COP, as this is based on power put in, and kilowatts of heat put out. Unless the thing that is happening is that you have to set the flow temperature of your heat pump emitters right up in order to get a cosy temperature. But that is not the fault of the heat pump. If the rating of the heat pump is not sufficient to provide the desired level of heat, that is something to take up with the people who did the heat loss calculations on your house, and the heat pump that was chosen to do the job.

Final point, honest! I really do have to argue the point with the whole calculation for a COP!! Whatever any manufacturers says, the COP is simply the ratio between the energy that goes into the system, compared to the energy that comes out! It cannot be, as a number of sources suggest, the electrical input plus resultant kilowatts of heat output, divided by the input value. This gives you ridiculous figures like a COP of 4 to 1. This is not only wrong, it is deliberately misleading! And utterly meaningless, unless these are the figures that everybody uses; and even then it will only be a relative figure between different installations. This acronym, COP, stands for ‘coefficient’ of performance. In this application, it is virtually meaningless.

The true ratio is between actual amount of electricity used, an actual kilowatts of output. And then you should decide whether you’re looking at the total output of the installation compared to the input, or only the Heating. It depends what kind of Heating you had before, and how your hot water was produced. My current figures for the whole system, which I have had since the end of last July, is a true COP/ratio of 2.3:1 for the system as a whole, and 2.55:1 if I just use the Heating values. The figures come out at closer to 4:1 if I use the manufacturers’ way of calculating the figure. This is simply misleading, and meaningless as far as I’m concerned.

When you are, for example, making a calculation for resistance heating systems, i.e. night storage heaters, the figure comes out at almost exactly 1:1 - 1 kW of electricity, produces 1 kW of heat, end of. If you use the ridiculous equation, favoured by manufacturers, night storage heating comes out with a value of 2:1, which is just plain wrong!

That’s it, that had to be my final word 🤷🏼‍♂️😁 (ps. I could start in on weather compensation/heat, curves, et cetera, I was told to leave it off by the installers, because that’s what they were told by Vaillant. In fact, I was told not to adjust anything, which naturally I have completely ignored! It is certainly true that probably the majority of people will simply not be a—sed to fiddle and adjust and experiment. Good luck to them. But if you might be able to save a couple of hundred quid a year, why wouldn’t you do that? That’s at least five bottles of really decent single malt whisky…) 

(with apologies for typos, and errors in grammar. My phone, unilaterally and arbitrarily, decides to change spellings at the last minute, at the point of sending. Although it is very true, that installation and commissioning of a system is incredibly important, it should have read insulation, insulation, insulation. But I’m sure you are all clever enough to read through the errors 🤦‍♂️🤣🤗🤨🥃

@cathoderay this sound like a nightmare. 

the heat delivered must be wrong, there are reasons for 20% increase in requirements, weather, losses out side the house envelope (poor insulated external pipe work.) but your 3 x figure is crazy. if that was indeed being delivered your house would be perhaps 10degrees warmer - quite noticeable. 

are there losses with the hp that were not present with oil? how much was the system changed? if you got new rads, are the underfloor sections of pipe work insulated? they could be heating the cold floor void? - could the HP compressor and internals have not had insulation put on properly during install/ service . either way losses accounting for twice what the house was using seems unlikley 

another option is the current internal heat meter/ estimater is just wrong.  if the actual delivered heat is more like the oil set up your cop is in reality about 1 point  something. so essentially you would have two issue, inaccurate heat delivery metering, and something causing a terrible COP.  

How hot do your radiators typically run? how big is your house.  

i think to solve this you need more data. do you have a dedicated electricity meter for the HP? or are you using the increase in your overall usage? if the latter there may be another item or electrical fault eating up the electric. An independant elec meter for the pump is not too expensive £50 plus fitting. 

they are expensive but a class 2 heat meter costs about £200-300 to buy, then needs installing (but will quickly pay for itself if it fixes your issues.). this would diagnose if your pump is indeed delivering this staggering amount of heat.   if not could direct you to why its using so much electricity.  

good luck you have a real financial incentive to get to the bottom of this. 

@yogabob 

i agree the manufactures COP calculation are  only aproximate, but for Vaillant at least, they don't quote heat delivered they quote the 'environmental yield'. this is what has been extracted from the air. so it would be right to add the energy from electricity used to the calculation for the COP. 

I think the real issue is that the figures they give for environmental yeild and electricity have quite large error margins and these compound when calculating COP to make the COP figure pretty inaccurate. 

I feel to be satisfied i will need to add an independent heat meter to my system to see what the performance really is. but i don't really have the cash. 

@yogabob

You are perfectly correct that COP is measured as heat energy out divided by electrical energy in.

The way that a heat pump works, is that it uses a quantity of electrical energy, most of which is converted into heat energy, to extract a larger quantity of heat energy from the outside air, the combination of both being the specified heat energy output.

Vaillant, in their wisdom, refer to the energy extracted from the outside air as Yield, so their calculation of COP becomes:-

Electrical Energy In + Yield / Electrical Energy In = COP

Many other manufacturers use the easier to understand:-

Heat Energy Out / Electrical Energy In = COP

I hope this makes things clear.

@bristoljoe - it is completely crazy, just doesn't make any sense. I have an old leaky high heat loss building, listed so not easy to improve this side of things, upgraded rads to match the heat pump output at relatively high leaving water temps (needed to keep the rads to a manageable size), all run on weather compensation. Because of some insulation improvements in recent years, the total building heat loss will now be a bit less than it was when I had oil CH.

I do have a dedicated external energy meter supplying just the heat pump, that is how I 'know' Midea over-estimate energy usage. I have also looked at third party energy out monitoring, flow temps reasonably easy to get, but the stumbling block is getting the flow rate, the meters are as you say hundreds of pounds, and most are invasive, and more importantly, obstructive, ie reduce flow, a bad idea on a heat pump system. I haven't ruled out getting an ultrasonic non-invasive flow meter, can be got from China for a little over £100, but I am not sure how accurate they are. I also have a plate heat exchanger between the primary heat pump circuit and the secondary rad circuit, so in an ideal world I would have two flow meters, twice the cost, twice the complexity... 

Posted by: @bristoljoe

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this would diagnose if your pump is indeed delivering this staggering amount of heat

But it 'must be', if COPS mean anything at all! I 'know' the heat pump consumed 10,000kWh over the last year, so if a COP of 3 means what it claims to mean, then it 'must' have delivered 30,000kWh of heat to the house. Yet the house is as it was when it got only 10,000kWh (from the oil CH). It just doesn't make any sense...

I may start a new thread on this conundrum.