Sunday, 22 February 2015

Which are the big consuming appliances in your home?

Suppose you want to keep an eye on electricity use in your home but you only have a limited number of plug monitors - which appliances would you include? Which ones are most likely to be big energy hogs? This relates to a project I am involved in to plan a very large monitoring program. Using data from the Household Electricity Survey (HES) I have selected the most likely candidates. As ever, with household energy use, there are no hard and fast rules. The table below lists appliances that used over 365 kWh/year - i.e. 1 unit a day on average, costing about £50/year (at 14p/kWh). This is a bit less than 10% of the average total electricity bill.



Energy hog appliances - where at least 10% consume 365 kWh/year or more (about £50/year)

Type of Appliance
Number of energy hogs (in 250 households)
Proportion of appliances that are hogs
Lighting12148%
Fridge freezer8152%
TV6114%
Freezer5336%
Electric cooker4332%
Tumble Dryer3935%
Dishwasher3027%
Shower2928%
Oven1427%
Desktop computer1413%
Audiovisual1220%
Computer site919%
Plasma TV457%
Aquarium427%
Washer/Dryer314%
Dehumidifier266%
Wine cooler267%
Hot tub1100%
Immersion heater150%

Notes: This table is derived from data captured for the HES during 2010/2011. I have excluded appliances to do with room heating. Since most lights aren't on plugs and can't be measured separately I have merged them all together into one 'appliance' per home. Computer site means several items of computer equipment on one plug, similarly Audiovisual means several audiovisual appliances on one plug.

Lighting (all lights counted together) is the most common energy hog. Every household has some lighting and in about half of cases, it's a hog.

Freezers and fridge freezers are also likely to be energy hogs, especially fridge freezers. Not everyone has one but for those that did, about half were hogs. By the way, an A+ fridge freezer bought today is unlikely to be such a hog - according to the John Lewis website the 3 most popular fridge freezers consume at most 268 kWh/year. Of course that estimate won't be exact but the HES found that the energy consumption of freezers and fridge freezers was generally quite close to what it said on the energy certificate - the same was not true of washing machines and tumble dryers.

Only about one in seven TVs were energy hogs, but over half of plasma TVs. For TVs it depends on how much you use them as much as well as how big they are. Also there were several other unusual appliances that were very likely to be hogs: hot tub (only one in the sample), dehumidifier (two out of three), wine cooler (two out of three) and an immersion heater (if regularly used). I guess if you have a wine cooler or a hot tub you probably aren't worried about their running costs. If you keep tropical fish you should be aware that aquariums can take a lot of power for keeping the water warm.

About a third of tumble dryers are energy hogs - some people use them more than others. However washing machines don't appear in the table because less than 10% were hogs, probably because most people run low temperature washes these days.

Adding up the energy hog energy use and dividing by total electricity use for each home, it seems that the hogs consume on average half the total. In a quarter of homes the hogs accounted for less than 38%. Even if you track these appliances, you still don't know where most of it is going. If you reduce the cutoff to 200 kWh/year - about 5% of the average electricity bill, or £28/year - then there are on average 6 hogs per home consuming 72% of the total. Additional appliances that qualified as hogs at this level included kettles (31%), washing machines (27%) and a massage bed. Also the appliances listed above were much more likely to be hogs, including 94% of fridge freezers, 32% of TVs and 47% of aquaria.

There are a number of companies working on ways to analyse your total electricity use to see how much goes on different appliances. That way you don't have to monitor each appliance individually. You just monitor the mains cable and the software sorts it out. However, this is a very hard problem. One of the companies looking at this is Informetis - a spin out from Sony. They are using the high frequency approach - they measure your electricity use many times per second and look for appliance signatures. For example, when a fridge or freezer comes on it generally has a surge of power for a few seconds and then it settles down for a bit. Also you can learn a lot from the difference between real power and reactive power - where the voltage and current cycles are out of phase. Informetis is developing algorithms that can learn to recognise the shapes for different appliances. However, they still don't expect to be able to identify all the appliances, so they will concentrate on the energy hogs. Informetis reckons that not only will they be able to tell you how much your fridge or freezer is using, they will also tell you when it is about to go wrong. That could be useful if it saves you a freezer full of spoiled food!

Other companies working on itemising your electricity bill include High Energy Audits, PlotWatt, Bidgely, and Navetas. One day soon, hopefully, they will get it to work and do a deal with our electricity suppliers to offer the service to people like us. In the meantime, if we really want to know where our electricity is going we will have to buy a lot of plug monitors.



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