Making power consumption spreadsheet, need help. :)

RowaN

I'm attempting to make a spreadsheet of all the electrical appliances in my house so I can clearly see what is using what. Am I wasting my time, does a similar template exist somewhere else I wonder? Anyway, here it is:

https://docs.google.com/spreadsheets/d/16YX76MIDGsN8MiecwEyMQtyhidX9nsSC2xpO8nseIIY/edit?usp=sharing

Comments welcome.

I've purchased an "Energenie" power monitor but I'm not sure the best way to use it for my calculations. The instructions are a bit thin.
https://energenie4u.co.uk/index.php/catalogue/product/ENER007

e.g. Is knowing your supplier's cost and the wattage that an item draws enough to calculate the cost of running it? I guess that becomes tricky with items like Fridges as their draw different watts at different times (more when actively cooling). But for appliances with a constant draw (when on) (e.g. plasma TV) is it just a case of multiplying the energy cost by (hours of use X kilowatts)?

Something else I don't understand: kWh. I thought this was Kilowatts per hour, but on my energy monitor it seems to increase the longer I leave something running in.

Also, in my spreadsheet I have a static column "kWh in 1h", which is a value I took from the Energenie after 1 hour operation on each particular device. Should I be using that value or simply calculating it from watts/hours calculation?

Lots of questions I know! Thanks in advance to anyone who can help advise me on any of these points. :beer:

Cardew

I am afraid IMO it really is a waste of time; or at least a large amount of effort for very little information.

There is a website http://www.sust-it.net/ that gives comparisons of various appliances.

Something else I don't understand: kWh. I thought this was Kilowatts per hour, but on my energy monitor it seems to increase the longer I leave something running in.

The consumption of all electrical items is measured in watts with a kW being 1,000 watts. Thus if you run a 1kW appliance for one hour it will use 1kWh; for two hours it will use 2kWh.

This assumes that the 1kW appliance uses a constant 1kW. In practice very few appliances in a house do use constant power; they have a thermostat switching the power on and off(fridge, freezer, heaters, ovens etc) or a cycle that switches in different parts of the appliance(washing machine, dryer, dishwasher etc)

For instance my washing machine can use 3kW when the heater is on, and a complete cycle can take 1.5 hours. However instead of the 4.5kWh(3kW x 1.5) you might expect, it can use as little as 0.4kWh.

matelodave

A 50watt light will consume 50 watts in one hour so it would have to be on for 1000/50 = 20hrs to consume 1kwh. If a Kwh cost you 15 pence then your 50watt light would cost you 15/20 = 0.75p in one hour or 15p in 20 hours.

A 3kw electric kettle will use 3000 watts in one hour = 3kw but normally it's only on for five minutes so it will consume 3000/60 watts in one minute = 50 watts multiply that by 5 minutes = 50*5 = 250 watts (0.25kwh) so it will cost you 15p x 0.25kwh = 3.75pence. The same with something like a vacuum cleaner 1500watts for 30 minutes = 750watts = 15 x .75 = 11.25p.
A 250 watt plasma TV on for four hours will consume 1kwh = 15p

Most appliances are similar so you jut have to work out how much power they take in watts (usually on a rating plate somewhere) and multiply it by the amount of time that they are on.

Fridges & freezers are slightly different as they automatically switch on and off, however you can assume that they are on for about 25-30% of the time and off for 70-75%. So a 200watt fridge on for 25% of the time will consume about 50 watts in an hour and so would take about 20 hours to use a kwh. If it's on for 50% of the time then it would use 100w in an hour and use one kwh in 10hours. Your energy monitor should be able to measure it.

Irons, washing machines, dishwashers, tumble dryers, cookers, microwaves and immersion heaters have thermostats in them so they again aren't on all the time so you'd have to use your monitor to see how many watts they use in one cycle or in one hour and do similar sums.

RowaN

Let me see if I have this right then..

My kettle is rated at "2500-3000W". Lets call it 3000W for the sake of argument,
So it would take 1 hour to use 3Kw.
On my 11p per kWh tariff, that would use 33p per hour if constantly boiling.
Thats 1p per boil (2 mins).
Right?

I'd read elsewhere that it normally costs 2.5p to boil a kettle.

Cardew

RowaN wrote: »

Let me see if I have this right then..

My kettle is rated at "2500-3000W". Lets call it 3000W for the sake of argument,
So it would take 1 hour to use 3Kw.
On my 11p per kWh tariff, that would use 33p per hour if constantly boiling.
Thats 1p per boil (2 mins).
Right?

I'd read elsewhere that it normally costs 2.5p to boil a kettle.

Your calculation is correct. i.e. 1p for a 2min boil.


The 2.5p could be a bigger kettle; and/or boiling colder water!!

RowaN

Cardew wrote: »

Your calculation is correct. i.e. 1p for a 2min boil.


The 2.5p could be a bigger kettle; and/or boiling colder water!!

OK. So when my monitor says something is "using" 3000W (like the kettle), it really means thats what it will use in an hour?

matelodave

Effectively yes - it has to be using 3000w for one hour to equate to 3kwh. If it's only on for 20 minutes then it will use 1kwh. The number you see on your monitor is the power that's actually being used at that moment.
Think of it like a car speedometer, it shows the speed you are doing at that particular time. If you maintain it at 70mph then you will drive 70miles in one hour. If you only drive for half an hour then even though you are doing 70 you'll only manage 35miles. If you only drive at 35mph then you'll only do 35 miles in one hour or 70 in two hours.


The reason your kettle is rated at 2500-3000w is because it will also be rated at 230-250v. The kettle element doesn't vary but the power used is proportional to the voltage across it and the current flowing through it. eg at 230v it will use approx. 2500w whereas at 250v it will use approx. 3000w. That's why a lot of clip on energy monitors are so inaccurate as they only detect the current and can't take into account any variations in the voltage. Plug-in ones actually measure the voltage and the current and so are a bit more accurate

Idiophreak

RowaN wrote: »

I'm attempting to make a spreadsheet of all the electrical appliances in my house so I can clearly see what is using what..... I took from the Energenie after 1 hour operation on each particular device.

Sorry, but it sounds like you've already achieved your goal, so I really don't see what the point of the spreadsheet is? You've successfully identified the things that use most / least energy in your house, that should be enough to effectively change your behaviour going forward.

Tracking every penny in and out isn't going to be a good use of your time...just remember the things that use most energy and turn them on less...at the end of a month, if you've used less energy, you know you're in the right direction. Even quite significant changes in routine are unlikely to save you more than a couple of quid per month, though...

RowaN

Idiophreak wrote: »

You've successfully identified the things that use most / least energy in your house, that should be enough to effectively change your behaviour going forward.

Have I? No I haven't. I've tested a handful of devices so far. Theres loads of devices I haven't even added to the spreadsheet yet, let alone taken readings from. But I am touched that you care so much about what is and isn't a good use of my precious, precious time.

matelodave - good analogy re speedometer. However, a speedo gives "Miles Per Hour", so why do appliances not state "Watts per hour". Just saying Watts.. it doesn't read as intuitive to me.

matelodave

Continuing with the speedo analogy think of a watt as a mile - it's just a unit of measurement which changes depending on your instantaneous consumption (or speed) so the dial indicates the rate (or speed) at which you are using not the total.
It's the number of these watts (or miles) that you are using in a hour that you are interested in. That's what your electricity meter (or car odometer) does, it counts the total number of watts (or miles) that you've used.

Cardew

RowaN wrote: »

matelodave - good analogy re speedometer. However, a speedo gives "Miles Per Hour", so why do appliances not state "Watts per hour". Just saying Watts.. it doesn't read as intuitive to me.

Because no appliance consumes a fixed amount of watts.


As explained above, even a 50 watt bulb or 3kW kettle element(that we consider as 'fixed') can have variable consumption depending of the house voltage.


My washing machine is rated(on the plate) as 3,000 watts(3kW) but it only uses that power when the heater is on(for perhaps 7 minutes!), at other times in the washing cycle the consumption varies from 0 watts to say 100 watts(for motor) to say 50 watts for pump. All that is important from a consumption pov is how many kWh it uses in a cycle.


So to be 'intuitive' how would you like the washing machine rated? 3000watts per hour? zero watts per hour? 100 watts per hour? etc


The real purpose of a rating plate on appliance is to let electricians/occupants know the maximum power(watts) that it could consume. From this the current can be calculated and thus the electrical load on the circuit - both wiring and RCD/Fuses) - can be designed. For instance an electric shower or electric cooker might be 10kW and would need heavier duty house wiring and fuses(RCD)


If you put a 3 amp fuse in the plug for your kettle, it will blow. Plug loads of kettles/electric fires in '13 amp' sockets(on the same ring main) and the main fuse will trip out - etc etc.