High KW appliances and energy efficiency

Buster_Danog

If you buy an appliance say an oven, fridge or air conditioner that is around 4.7kw would I be right in thinking this could set you back around 50p per hour?

If that is correct what difference would energy efficiency make to that 50p. If an appliance is sold as being A or A+ what does that actually mean in the real world in relation to how much less you pay per hour for an appliance that is still 4.7kw?

tronator

Buster_Danog wrote: »

If you buy an appliance say an oven, fridge or air conditioner that is around 4.7kw would I be right in thinking this could set you back around 50p per hour?

If that is correct what difference would energy efficiency make to that 50p. If an appliance is sold as being A or A+ what does that actually mean in the real world in relation to how much less you pay per hour for an appliance that is still 4.7kw?

An oven or fridge will not continuously draw 4.7kW. I don't know about air conditioner, but 4.7 kW seems quite high too.

Buster_Danog

Which? magazine said that for running a washing machine the difference was hardly anything over a year, according to a post I read elsewhere, but that was only 5 washes a week - I guess for a couple of hours each time.

There is a thread from MSE in 2006 where someone bought a hot tub at 4.7kw and it was costing them £60 a month to run. That is what concerns me about high KW.

At £60 a month any efficiency that would reduce the cost would be important to know about and calculate.

macman

The highest drawing device in modern homes is likely to be an electric shower, some drawing upwards of 10kW. However what you need to remember is that such devices are only used for short periods-you don't run a shower or kettle for an hour.

footyguy

Buster_Danog wrote: »

If you buy an appliance say an oven, fridge or air conditioner that is around 4.7kw would I be right in thinking this could set you back around 50p per hour?

If that is correct what difference would energy efficiency make to that 50p. If an appliance is sold as being A or A+ what does that actually mean in the real world in relation to how much less you pay per hour for an appliance that is still 4.7kw?

A fridge does not use around 4.7kW, and nor does a portable air conditioning unit (although a fixed installation may well do)
They are fitted with a 13A plug.
Some ovens come with a 13A plug too, although an oven & hob does require the special higher capacity cooker point.

The energy efficiency is all about how efficient the energy consumed (the electricity) is transformed into the desired effect, heating, cooling etc.

You can read more about energy efficiency of appliances here:
http://www.energysavingtrust.org.uk/domestic/content/home-appliances

matelodave

As said above most appliances don't continuously consume their rated kw.


Things like oven, fridges, freezers, even washing machines, tumble dryers and heaters have thermostats inside them that turn them on & off to maintain their temperatures.


Efficiency comes into play with certain devices which might be better insulated like fridges & freezers and hot water tanks where more insulation reduces the heat loss (or gain) thus requiring less energy to maintain the internal temperature.


Washing machines, tumble dryers & dishwashers might use less water or be designed to have shorter cycle times or more efficient operation which reduces the amount of energy being consumed.


Even some electric kettles can be slightly more efficient than others if you can just boil the exact amount of water that you need. A flat bottomed element type can boil exactly the right amount of water whereas a coiled exposed element type might need two or three cupfulls of water in it to cover the element.


Lighting efficiency is obtained by producing the same amount of light for less energy so incandescent lights are least efficient and LEDs the most although they are one device that uses the rated kw all the time that they are in use.


So without knowing what device you are using no one can say whether it will use 4.7kw continuously - 13amp sockets will only deliver approx. 3.2kw so anything that requires 4.7kw would need to have a special circuit dedicated for it, like a cooker or dedicated heating unit.


Even ovens & hobs will only use as much power as required to maintain their temperatures so better insulated ovens or hobs with induction rings will be more efficient and therefore use less energy than an older poorly insulated oven or hobs with radiant rings or solid rings even though they might have the same kw rating.

Smiley_Dan

Are you sure about hobs? I've never seen my hob (ceramic) reduce the amount of power it draws. Likewise gas burners don't automatically turn down as a general rule, and for induction plates it seems counter to how they work.

GreenBo

I noticed a few months ago that most new appliances now have an energy rating sticker on them that estimates how much it should use in a year.

More info here: http://www.which.co.uk/energy/saving-money/guides/energy-labels-explained/eu-energy-efficiency-labels/

My energy monitor gives me visibility of the energy cost for most of my existing appliances and breaks them all down into an itemised bill for the home. Although everyone's home and appliances are different I thought I'd list out a few of mine in case it's of any use:

Fridge freezer - £34/year
Oven - £130/year
Microwave - £6/year
Kettle - £55/year
Fridge - £23/year
Dishwasher - £17/year
Combi boiler (pump) - £48/year
Washing machine - £14/year
Toaster - £5/year

There are loads more but I think that should give you an idea of the usual suspects. At least for my house anyway.

matelodave

Smiley_Dan wrote: »

Are you sure about hobs? I've never seen my hob (ceramic) reduce the amount of power it draws. Likewise gas burners don't automatically turn down as a general rule, and for induction plates it seems counter to how they work.

My induction hob has a level control which regulates the amount of energy going to it. If I turn it down it doesn't consume the whole of it's 2kw rating all of the time - in fact you can hear it pulsing. Most electric & gas hobs have a regulator which means they don't use 100% of their rating all of the time unless they are turned full on.

However the induction hob just heats the pan base internally rather than the surrounding air like a conventional hob so virtually all the energy is concentrated into the pan base. None gets wasted around the edges. It also shuts off when the pan is removed which most other hob types don't do.

Likewise a microwave oven could be rated at 700-800 watts but actually takes 1500 watts or so in pulses which get averaged out - if you turn the level down then the pulse on times get shorter and off times get longer thus delivering less energy to the food and consuming less energy from the supply but the peak load is still 1500w during the on times.

Smiley_Dan

matelodave wrote: »

My induction hob has a level control which regulates the amount of energy going to it. If I turn it down it doesn't consume the whole of it's 2kw rating all of the time - in fact you can hear it pulsing. Most electric & gas hobs have a regulator which means they don't use 100% of their rating all of the time unless they are turned full on.

Of course, I realise they have variable control. I was responding to:

Even ovens & hobs will only use as much power as required to maintain their temperatures so better insulated ovens or hobs with induction rings will be more efficient

Likewise a microwave oven could be rated at 700-800 watts but actually takes 1500 watts or so in pulses which get averaged out - if you turn the level down then the pulse on times get shorter and off times get longer thus delivering less energy to the food and consuming less energy from the supply but the peak load is still 1500w during the on times.

Are you sure that's the reason? I thought microwaves were just 50% efficient. When I watch the power on mine it looks to use about the rated power when the pulse is on, and barely anything when off. I'll check that when I remember, it might be me reading it incorrectly.

It seems odd to average a power draw... average energy consumption given a time period yes, but not power.

But I agree the pulse times are just further apart. It's a bit crap really!

AIUI the Panasonic microwaves are the only ones on the market which have inverters and actually change their draw.

Buster_Danog

Thanks for the replies guys. After starting this thread I realise the manufacturers tell you how much energy is actually used by the input value. So an air conditioner for example that has 2.6kw power might only be using 1kw of energy. You would therefore calculate costs and energy use based on the 1kw value. I guess that is the difference between the two is where the efficiency comes in.