Mystery of consumption

[Garald]

I am spending much more on electricity that I had expected. The heat pump (which should be the main consumer of electricity) is operating at reasonable temperatures - and it claims a good COP and reasonable consumption.

 

However, notice how closely total energy usage tracks the energy the heat pump claims it is consuming - except that it's off by a factor of about 2.

 

The world according to the heat pump:

 

 

The world according to the energy company:

 

I have been away at a conference since the 24th; all lights (which are LED anyhow) are turned off.

 

What is going on here? Possible hypothesis:

- Some device (other than the heat pump) in the house is misbehaving grossly. Argument against: why would total energy usage mimic heat pump usage? I'll get a new fridge (the current has been having issues) but I doubt that's it.

- The energy company is lying. Somewhat unlikely, one would hope.

- The heat-pump applying to me about how much energy; for whatever reason, it has a terrible COP, and it lies about it. I would hope that's also not the case. Could it be the case?

Notice how the heat pump's statistics are only 'estimated': OTOH the figures for January and February obtainable in the machine itself (as opposed to the app) the ratio between power allegedly consumed by the heat pump and the total amount consumed in the house was similar.

- Maybe there's some sort of faulty wiring that makes me spend 2kWh for every 1kWh used by the heat-pump. How would this work?

 

Any more possibilities? How do I test these hypotheses?

 

 

 

 

Edited March 29 by Garald

[Alan Ambrose]

Taking a quick look, I’m not sure anything much is out of the ordinary.

 

Take the 25th - total consumption was 5.4, HP was 2.5, so rest of house (fridge etc) was 2.9. Our little place uses 4.4 when we’re not here and the heating and hot water is off. So your standby/background number looks good.

 

But the HP was still used for both heating and hot water on the 25th - so presumably it was cold enough that the ‘frost’ setting kicked in and presumably you didn’t turn off the hot water while you were away. Why not btw?

 

I don’t think a high of 21.3 on the 13th is so bad either. Our little place isn’t well insulated and we do a lot of heating with our log fire, but we still had 39.3 max one day. But that was £6.41 so not the end of the world - total for March will be about £90 which I can live with.

 

Your HP app will show CoP?

 

 

[John Carroll]

You have only shown the reduced consumption since the day you went away?, 5.4kwh on the 25th, a big reduction from previous?.

[ProDave]

In my house heat pump power consumption is only about 1/3 of total power used.

[PhilT]

Like Chuck McGill in "Better Call Saul" I went mad trying to find the hidden electricity! I acquired an energy meter and tested all the "always on" appliances in my house, and the intermittent appliance usage, before I came to the inevitable conclusion that they add up to much more than expected. My non HP usage is around 6kWh per day with only 2 of us in the house. Yours looks to be around 5kWh per day so I don't think you have anything to be concerned about.

Edited March 29 by PhilT

[SteamyTea]

20 minutes ago, PhilT said:

I acquired an energy meter and tested all the "always on" appliances in my house, and the intermittent appliance usage, before I came to the inevitable conclusion that they add up to much more than expected.

Yes.

I have managed to get my day (non space and water heating) usage down a winter average of 1.5 kWh/day and 1 kWh/day the rest of the year.

I one had a shock when my usage went up by 3 kWh/day, turned out to be a faulty fridge that was always running.

 

Two things to note about inbuilt ASHP monitoring, most are not very accurate as I suspect they used some fixed parameters i.e. electrical power consumption assumption, rather than actually measuring it.

Also, so ASHPs have a crankcase heater that may be activated if the OAT is too low.

 

I take it your Legionella cycle is not coming on, or the cylinder is using direct heat at any time.

[Alan Ambrose]

Wow, that’s low - can you give us some tips on how you did that?

[joe90]

8 minutes ago, Alan Ambrose said:

Wow, that’s low - can you give us some tips on how you did that?

Thick jumpers, scarfs and woolly underwear 🥷

[Garald]

1 hour ago, Alan Ambrose said:

But the HP was still used for both heating and hot water on the 25th - so presumably it was cold enough that the ‘frost’ setting kicked in and presumably you didn’t turn off the hot water while you were away. Why not btw?

 

 

 

Because I thought I had done so (from the wifi controller and the controller on the heat-pump itself, by switching to 'travel' mode) but I really succeeded in doing so only from the MelCloud app, after noticing what you just noticed!

[Garald]

36 minutes ago, SteamyTea said:

 

I take it your Legionella cycle is not coming on, or the cylinder is using direct heat at any time.

 

It is coming on (I notice: the shower is pleasantly hot on those days), once every two weeks. No, I have set up DHW to go on auto, not on direct heat all the time. What makes you say otherwise?

[Garald]

The problem is not so much the excess right now (2.5kWh to 5 kWh is not a huge lot for someone with an old, malfunctioning fridge (will replace), as well as a VMC fan I didn't ask for that is always on and that I'm thinking of having uninstalled) as the fact that the excess is much larger when heat-pump consumption is really high.

I don't have day-by-day resolution for the most striking period (I had wifi installed on the heat-pump just a couple of weeks ago) but here is some monthly data.

 

Heat pump (according to itself):

                      energy consumed         energy produced

December                    583 kWh        2122 kWh

January                       883 kWh         2698 kWh

 

Yes, the settings were suboptimal (45C fixed temperature) and the COP improved in February, after I let the heat-pump choose its own temperature (of course temperatures also became milder). That's not the point, however. The point:

 

(data from the energy company)

 

                   total energy consumed

December          709kWh   

January             1783kWh

February             871hWh

 

You can see the issue: non-heat-pump consumption was reasonable in December (709-583 = 126 kWh, i.e., about 4kWh per day) but non-heat-pump consumption was absolutely nasty (and very expensive to me): 1783-883 = 900 kWh, i.e., about 30kWh per day.

 

So, in January, either

(a) the heat-pump was lying and lies about its energy consumption,

(b) some problem in the electrical installation leads to some sort of huge energy sink at times, perhaps especially when the heat-pump is particularly hungry

(c) the malfunctioning fridge is guilty (but what kind of fridge, even an old, large fridge, could ever use that much energy? Is that even the right order of magnitude? What is more, I defrosted it at the end of November, not in January)

(d) the clowns from the electricity-delivery monopoly who came in early January to change the maximal voltage from 6kW to 12kW messed something up temporarily that caused a huge January energy bill (no idea what that would have been)

(e) some other possibility?

 

My January bill was 516 eur; that's not funny.

 

 

 

[John Carroll]

Can you do without the HP for  a 24 hour period?, if so, you see what the remaining consumption is. You might also look at the defrosting cycles.

[HughF]

516eur seems reasonable…. We’re £100/week during the depths of winter. Backstop rate, 28p/kWh and 50p/day standing charge.

 

All electric house, bit of car charging, lots of tumble drier use.

[SteamyTea]

1 hour ago, Garald said:

What makes you say otherwise?

Just making sure it is not a pure resistance load that is being drawn.

 

[marshian]

Our electricity usage is pretty constant (Gas Central Heating/Water not ASHP) 4 bed detached - 2 occupants

 

Our background overnight usage is 250w per hr (2 fridges, 1 freezer, CCTV, skybox, router, signal repeaters, microwave clock and a load of smart items that all consume a little)

 

Daily consumption overall varies from 7.0 kW to 13kW at the weekends (washing days, tumble drier and oven usage are all quite large consumers)

 

Point I'm making is usage overall will mirror ASHP as for most houses the usage is pretty constant and I can see why you would put the case that it seems to be double the declared ASHP usage.

 

Summer time when space heating is not required should give you a good guide to your base line usage?

[Alan Ambrose]

Just to give us an idea of context - what kind of place is this - rough size, kind of insulation, format (flat, town house, country cottage etc)? Also, is this a new HP install, what happened before? Was there anything else re January that was odd or unusual? Are there other high load items e.g. car charging, other electrical heating? What geographical area are you in? e.g. this is not your rooftop snow melt system kicking in?

 

BTW I don't think (a) to (d) are very likely, given that the HP consumption could not very accurate, but I would expect maybe within +- 5-15% of actual.

 

CoP 3.6 in Dec, 3.1 in Jan. Sounds about right given I expect Jan was colder there too?

 

I see your app gives you consumption by hour - it might be interesting to look at that and see whether there are any odd spikes in use - particularly on a high usage day. I've debugged a couple of things that way.

 

My guess - either some other high load item was on at some point or there's something odd in the HP defrost cycle. Also, maybe look out Jan data by day to see if it adds up to 1,783?

 

March looks like, say, 12 on average for a total of maybe 370?

 

 

 

Edited March 29 by Alan Ambrose

[SteamyTea]

5 minutes ago, marshian said:

Our background overnight usage is 250w per hr (2 fridges, 1 freezer, CCTV, skybox, router, signal repeaters, microwave clock and a load of smart items that all consume a little)

 

No it isn't

 

W is power, not w.  But anyway, if you break down 250 W/h, you get 250 J.s^-1.3600 s^-1 which is 0.0964 J, or the force needed to move 10 grams, 1 metre.

 

9 minutes ago, marshian said:

Daily consumption overall varies from 7.0 kW to 13kW at the weekends

Again, not, kW is power, kWh is energy.

 

If your weekend power was 7 kW, your energy usage would be 168 kWh.

[Alan Ambrose]

I knew the Capitalisation Police would be along shortly

[SteamyTea]

11 minutes ago, Alan Ambrose said:

I knew the Capitalisation Police would be along shortly

It is a slow day, everyone is stuck at the A30 roadwork between Carland Cross and Chiverton.

Keep quiet about the £8m from the EU.

Edited March 29 by SteamyTea

[Garald]

1 hour ago, John Carroll said:

Can you do without the HP for  a 24 hour period?, if so, you see what the remaining consumption is. You might also look at the defrosting cycles.

 

Sure - that was yesterday. I'm on a conference trip, returning tonight.

[Garald]

1 hour ago, marshian said:

 

Summer time when space heating is not required should give you a good guide to your base line usage?

 

My consumption in August and September was 233kWh and 216kWh. No doubt one can do better, but that's my baseline. (Or rather, my baseline is at most that: my parents were visiting.)

[Garald]

1 hour ago, Alan Ambrose said:

Just to give us an idea of context - what kind of place is this - rough size, kind of insulation, format (flat, town house, country cottage etc)? Also, is this a new HP install, what happened before? Was there anything else re January that was odd or unusual? Are there other high load items e.g. car charging, other electrical heating? What geographical area are you in? e.g. this is not your rooftop snow melt system kicking in?

 

Most of a small house: 120m^2 loi Carrez (i.e. not counting most of the attic, staircases, bike garage), 180m^2 total. Just got a pretty good interior insulation done (went ftom energy class F to energy class B, by French standards) with 15cm BioFib Trio on some walls and a combination of 5cm BioFib Trio with reflective insulation (with synthetic conventional-insulation backing) on the others. Elsewhere on this site, you can find the pictures I took with a thermal camera.

 

The heat pump was installed a year ago, begore I moved in. No other electric heating. No electric car. No rooftop snow. This is Paris-area weather, i.e., southern English weather except that the six-month autumn is slightly less miserable and the summer can include a couple of weeks of serious heat wave.

 

1 hour ago, Alan Ambrose said:

 

BTW I don't think (a) to (d) are very likely, given that the HP consumption could not very accurate, but I would expect maybe within +- 5-15% of actual.

 

CoP 3.6 in Dec, 3.1 in Jan. Sounds about right given I expect Jan was colder there too?

 

Sure, and also that I made the mistake of setting the operating temperature at 45C rather than let the heat-pump choose. (I wanted to test that 45C would be rnough; of course it was.)

 

The problem is really the difference between total energy consumption and heat-pump consumption in January.

 

1 hour ago, Alan Ambrose said:

 

I see your app gives you consumption by hour - it might be interesting to look at that and see whether there are any odd spikes in use - particularly on a high usage day. I've debugged a couple of things that way.

 

My guess - either some other high load item was on at some point or there's something odd in the HP defrost cycle. Also, maybe look out Jan data by day to see if it adds up to 1,783?

 

March looks like, say, 12 on average for a total of maybe 370?

 

 

 

 

I had the wifi controller installed in the heat pump a couple of weeks ago, so I don't have day-by-day heat-pump statistics before then. 

 

The January data from the energy provided is marked as provisional and estimated, and does *not* add up to 1783 (which is *not* marked as provisional). I wonder whether the energy company thought I would use as much energy as last year in January (workmen with tools and electric heaters in a construction site) and will send me a fat refund check in a while? One can always hope...

 

March is shaping up to be slightly over 500kWh in total. Still a tad more than one might wish for, but nothing suspicious.

Edited March 29 by Garald

[Alan Ambrose]

Ah, I assumed from the green screenshot that the overall consumption was smart meter data, no?

[Garald]

2 minutes ago, Alan Ambrose said:

Ah, I assumed from the green screenshot that the overall consumption was smart meter data, no?

 

Semi-smart maybe? I'm paying a bit extra for it to be as smart as possible (after the January surprise) - for the period before that, daily data seems accessible for some days and not others.

[Alan Ambrose]

So, you can’t look at hourly data for a high demand day?