What uses most power?

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Re: What uses most power?

Postby zzsstt » Thu Apr 28, 2011 1:47 pm

munrre wrote:Our all electric house for 3 is currently (Autumn) using between 6 and 8 Kwh per day.
I'm pretty sure most of that is the fairly new fridge and ludicrously large LCD TV


It's unlikely to be the TV, even the biggest LCD's rarely use much more than 200W, and often less so even if it's on for 10 hours a day that's only 2kWh.... and most now have eco settings, reduced backlight levels etc. that you can use to reduce the consumption.

A new-ish mid-range "family sized" fridge should only use 1.5 to 2kWh a day at maximum.

So if the TV is on from 4pm when the kids come home, to 10pm, that gives 6 hours use and possibly 1.2kWh power. Add an average fridge at about 1.75kWh a day, and those two items use about 2.9kWh, which leaves you looking for the cause of the other 5kWh!!

But if you have a constant load of just 200W (a few clocks, your STB/PVR, internet modem etc.) thats 4.8kWh a day....!

It's very tricky, because we are encouraged to buy a new LED TV to save power, but in reality it's probably only going to save about 50W, which over a 6 hour viewing day is just 0.3kWh. Compare that to what we are all wasting on "standby" power consumption and it is rather insignificant, or at best a lot of money and embedded energy for a small return in ongoing consumption!
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Re: What uses most power?

Postby munrre » Thu Apr 28, 2011 4:49 pm

I agree. It doesn't make economic sense to buy a more efficient TV to save 100 or so watts x 6 hours.
The documentation for the TV quotes 280 watts and 6 hours a day would be average.
I'm just glad I didn't get a Plasma.

Standby on the STB is only 7 watts, which surprised me. 28 watts when on. The wireless modem is on most of the day but only uses 10 watts but I guess it all adds up.

We also have a water pump and I think the inverter has some losses.
I have a Power meter and keep meaning to do a spreadsheet with all the electrical items to try to track down where it is all being used.

It is a bit frustrating not being able to put a figure on how much we use for cooking which in an energy efficient house must account for a greater percentage of overall usage than an average house.
Not enough to make it worthwhile putting gas on though.

I do agree though, that many people are unaware of how much leaving items on standby is costing them.
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Re: What uses most power?

Postby cw nsw » Thu Apr 28, 2011 5:08 pm

munrre

what is your HW source - also what about bathroom lights & gadgets etc?
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Re: What uses most power?

Postby zzsstt » Thu Apr 28, 2011 5:14 pm

munrre wrote:It is a bit frustrating not being able to put a figure on how much we use for cooking which in an energy efficient house must account for a greater percentage of overall usage than an average house.
Not enough to make it worthwhile putting gas on though.


If your "cooker" is on its own circuit (most are) you could use a clamp style meter (a Wattson or similar) to monitor it? Microwaves are all plug-in's so you can monitor them with a PowerMate or similar.

Cooking in an energy efficient home (or any other home really) is interesting. A microwave uses a fair chunk of power for a relatively short period, where an oven uses a large chunk of power and then stops if it's well designed and insulated. The recent Miele ovens have a very fast heat up, and can be set to "power save" as the end of the cooking time approaches - they automatically calculate the cooking time to allow for a fall of temperature at the end to avoid powering the element. A hob/cooktop uses power almost continuously while it's on, because it is effectively heating the room (no insulation!). But on the other hand, all the heat produced by the oven or hob also heats the house - in winter this reduces the heating load for other heat sources, but in summer it may require air-con to remove the addtional heat. An oven (or fridge, computer, TV) are not the most efficient form of heating, but the energy they use IS converted to heat and therefore "used twice" if the building requires heating. However if the building requires cooling, then twice the power is used, one to add it and one to take it away!

You are however quite correct that in an energy efficient home the cooking load will be a greater proportion of the total, but even that is subject to circumstances. We have a wood burning oven that is running 24/7 through the winter and therefore, whilst it still uses "energy" in the form of firewood, our electrical and gas use for cooking is reduced through the winter.....
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