Noticing the recent threads about 'What's your electricity usage..?' -
I would appreciate recommendations for monitoring kit for whole-house
(not single-socket) energy monitors - ideally with a wireless link into
a PC for datalogging.
Wondering about getting off-peak electricity metering installed - we
have a 3kw ground-water heatpump for dhw & central heating - but it (and
the house) is currently running on standard daytime tariff -
and I would like an easy way of logging usage over time...
There seems to be a bewildering variety of kit out there -
it'd be nice to have something that showed usage by the hour, so I could
see the effect of playing with the various timers / stats on the heating
Thanks in advance
Before I had smartmeters, my energy company provided a free energy
monitor (the coil around the meter tails variety) the transmitter unit
stayed in the meter cupboard, powered by a D cell, the receiver was
in-range anywhere in the house, and ran from a wall-wart, as well as a
display, it had an RS232 output (they even provided a USB->RS232
soap-on-a-rope with it) which periodically spat out current and previous
It was a re-badged CurrentCost unit, plenty of open source stuff to talk
to them, I gave it to my dad to monitor his kiln's cost when I didn't
need it any more.
I have an Eco-Eye Smart PV. The display includes a special
SD card, from which data can be downloaded when convenient, and
there is an included analysis program.
If you have no PV, they have a slightly cheaper option.
You can also connect via a USB lead to graph the data in
real-time, if you wish, but it is not essential to do this.
Basically it does what is claimed. Like all such devices there is
a degree of error in the readings, but it seems sensitive enough
to changes. There doesn't seem to be a wired option, so you need
the display to be able to receive a reasonable signal from the
Chris J Dixon Nottingham UK
Thanks - that looks interesting. No - we don't have PV -
so that saves a few pennies..
The heat-pump guy I had round a couple of years ago was quite insistent
that running dual-tariff would save me money - but I'm not so sure.
At least, with one of the gizmos, I can see how much electricity we're
using in the (potentially) cheap-rate times and then do some sums..
I have one of these
which records 30 days worth of data at 1 minute intervals (and can be
downloaded to PC at any time) or can record at 6 second intervals when
connected to an operating PC.
Don't think I would recommend it as the supplied software is absolute
rubbish (can only display whole months for example, not 6th Jan to 6th Feb)
Others have recognised the crassness of the software and there is some
open source alternative
but I have never managed to get this to work either.
Ah - thanks! Not entirely 5-stars then ?
I have a monitor that doesn't talk to a PC - but it's very much
1st-generation - and only shows a day's consumption - no way of
identifying peak vs cheap-rate usage..
On Sun, 23 Feb 2014 16:12:13 +0000, Adrian Brentnall wrote:
Hum, E7 probably won't be economic as the off peak use won't really
be high enough to offset the higher day time rate. Generally you need
to use about 60% or more of your power in the 7 hour (29% of the day)
off peak period. I should imagine your use is fairly level compared
to having night storage heaters that apply, in our case, 9 kW for at
least 4 hours before they start to cycle as being "full", after that
there is another 3 hrs averaging about 5 kW. So 50 odd kWHr out of a
total daily consumption of 75 kWHr (ish).
Our E7 tarrif is 16.08 day, 6.02 night and 18p/day standing charge (+
5% VAT) EDF Blue + Price Promise Feb 15 paperless and DD.
On power monitors the CurrenCost unit is probably the easiest to use
in a DIY context. I have the ENVI has worked well for years (I have
logs going back to 2008). It spits out the latest power use every 6
seconds or so in a published XML format, then every hour (I think)
the full historical data it has. The connection for this is an RJ45
but it's a TTL level serial data stream, they have a lead that
converts that to USB.
Mines connected to a linux based server (via the USB lead). The
server runs a little perl script that captures the data and logs the
average, min and max of the previous minute into a file. A bit of PHP
and GNUPlot can read that data file and display a plot on a web page.
The accuaracy is pretty good, even though I haven't actually cross
checked with the bill. Figures from the bills fed to spread sheets
come up with very similar numbers as the web page. I'd say better
than 1 kWHr/day. The CT needs to be square to the tail and with that
into the hinge side of the jaw, also fixed so the jaw/tail can't move
relative to each other if knocked. Just "hung on" will work won't be
best to consistent over time.
There are a number of third party programs out there and the unit can
take up to three current transformers so you could monitor your heat
pump independantly though you might need to do a bit of maths to gete
rest of house consumption depending on the wiring.
OK - we're in Ireland (and they're about to put the 'lekky prices up
but, at the moment, our standard tariff is (cents) 18.50 with a standing
charge of 185 euro per year.
The nightsaver tariff is 20 cents daytime and 10 cents nightime, with a
standing charge of 241 euro / year - so I guess I'd need to use enough
'cheap' electricity to cover the extra 56 euro or annual standing charge
and the extra 1.5 cents of daytime /kwh.
It's possible that our setup with an non-heat-stored heatpump (feeds
radiators directly) may not suit 'economy' tariffs..?
Interesting - and I'd love to have the time to play with such a system...
but, for the time being, it's an 'out of box' solution I'm looking for..
On Mon, 24 Feb 2014 09:03:54 +0000, Adrian Brentnall wrote:
I have a spread sheet... on those figures it says you'll need to use
at least 1.53 night units (every night) to save the extra standing
charge and an additional 0.15 night units for every day unit used
just to break even.
Units Units Total
5 2.28 7.28
10 3.03 13.03
15 3.78 18.78
20 4.53 24.53
25 5.28 30.28
30 6.03 36.03
35 6.78 41.78
40 7.53 47.53
Divide the "Required Night Units) figure by 7 to find what the
average load needs to be during the night period, normally 0100 to
Quite possibly as a night the heat pump isn't likely to come on and
you'll be at the households lowest base load.
Well you don't *have* to do the logging and coding yourself there are
programs already out there. Just get get the unit and data cable,
install and play with the existing programs. I can't comment on them
as I've never used them. The unit holds historical data and squirts
it all out of the data port at intervals so you don't need the PC to
be connected to the ENVI and on all the time. I *think* you can kick
the unit into sending all the historical data so you don't have to
wait for it to send automatically.
The ENVI display unit shows the current demand and cycles through the
last day, 7 and 31 days.
OK. At the moment all water heating is on the 'daytime' rate.
It's done with a mixture of heatpump (up to a certain temperature)
and immersion heater (for the rest).
I've just checked the ac current on the heatpump - it's in the region of
20A, or about 5kw, and the electric immersion heater would be 3kw.
We tend to have 2 x baths in the evening - between 9:30pm and 10:30pm -
but have a small usage of hot water during the day...
however - if we started the day with a tank-full of 'cheap' hot water -
and then used the heatpump or the immersion just for a top-up @ 9pm
then that's used at least the 1.53 night units...
Overnight domestic heating tends to be a very small amount - as the
temperature is set-back to 10c from 10:30 to 7am
Sounds promising - now if I can just find a supplier who doesn't want to
charge me £20 for shipping from the UK to Ireland.... <g>
On Mon, 24 Feb 2014 12:38:42 +0000, Adrian Brentnall wrote:
Is that the ratings plate or actual current?
9 pm won't be night rate, at least not this side of the puddle. Over
here night rate is 7 hours starting somewhere between about 2330 and
0130. The actual start/stop times of any individual E7 supply are
fixed. Unless you have mechanical time switch with bust clockwork, so
when there is a power cut the clock stops...
It's the measured value - with a cheap & cheerful 'Ferm' clamp-on meter.
Ratings plate is round the back of the heat-pump, and not immediately
Understand that - so the top-up water heating would need to be at
'standard' rate electricity - guess it depends on how warm the tank
remains during the day (after it's half-price heating-up in the morning).
I know that additional insulation on the HW tank is always recommended -
but the tank's in the airing cupboard, and there'll be trouble if the
cupboard's not allowed to be warm-ish for clothes airing...
So many 'gotchas'!
I'm thinking that it may be marginal as to whether we'd be better off
with split-rate electricity - might still get hold of a monitor and take
some 'real' readings, though.
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