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Models and Meters Make the Difference

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For many years, UK electric utilities and policy-makers were content with their view on residential energy use. Lighting use, for instance, was not metered directly. Instead, it was estimated as the difference between total household electricity consumption and the roughly measured consumption of some large household appliances.

In early 1994, the Environmental Change Unit (ECU) at Oxford University started the Decade program, sponsored by the European Commission and the UK Department of the Environment. Instead of simply estimating consumption based on uncertain data, Decade did a detailed analysis of national sales data for all appliances and light sources over a long period of years. Since the average energy use of each appliance model and light source sold over the period was known, and the life of each product could be estimated fairly well, each type of residential energy end-use in the past, present, and future could be calculated.

Meanwhile, up in the North, the Lothian-Edinburgh Environmental Partnership (LEEP) began metering the lighting consumption of 200 households varying in size and income. The metering technology was not very sophisticated, but since much of the lighting in UK homes is connected to a single dedicated circuit, lighting energy use could be calculated fairly accurately. The data supported the Decade model very well. By 1996, a completely new picture had emerged. Lighting now is believed to account for an average of 720-730 kWh/year and household, almost exactly twice that of the previous estimate of 365 kWh/year.

During the course of time, it also became more and more obvious to the UK Electricity Association that residential lighting was not well understood. Metering technology also had become more sophisticated, and a meter could now be placed on the lighting circuit as well as in the plug of every separate portable luminaire. Data from the meters are transferred to a central recording unit in the house over the mains wires. The recording unit uses a modem to send data on energy use and bi-weekly load characteristics to a central computer. Using this metering technology, 100 households are presently being surveyed by the Electricity Association Load Research Project. Although final results are not yet available, the preliminary data appear to confirm that the accuracy of the latest estimate of lighting energy consumption, according to Jane Palmer at ECU.

Increasing lighting energy use for each household from 1 to 2 kWh a day may not seem like much. But numbers add up, and the UK residential lighting energy use estimates suddenly doubled from 8 to 16 TWh/year or the equivalent of two nuclear reactors - or 8 million tons of CO_2 emissions. Why does this matter? Total energy use for UK homes has not changed because of detailed metering, of course, but now we know much more about how electricity is used. And this has far-reaching implications for how the government and other actors should allocate funding for efficiency programs. The new data also help UK utilities control their peak loads.

LOGGERS GIVE DIFFERENT DATA
There is also increasing interest in detailed measurements of household energy use in other countries. Again, it appears that the driving forces are the need for data upon which policy decisions can be based, combined with advances in measurement technology.

In Sweden, the world's second largest lighting logger metering project has been running since early 1997. Here, lighting loggers have been placed on each single luminaire in ~40 households. Each household will be metered for a whole year in order to cover large seasonal variations in available daylight. The lighting loggers are small, simple devices that are placed close to the light source within the luminaire. The logger, which has a small light sensor, simply records the total time that the lamp is in use. If the luminaire is too small to house the logger, a fiber optic cable is led from the "eye" of the logger into the light source. The total energy use for each luminaire can easily be established by multiplying operating hours by the lamp wattage. Load profiles cannot be measured, but more advanced loggers can keep track of the number of lighting hours for peak and off-peak hours. Plug-in kWh-meters are used in cases where loggers are unsuitable.

The Swedish logger project was originally developed to support the "Future Bulb" technology procurement project, and it is run by the municipal utilities of Gothenburg and Borlänge. Based on the data obtained, advice will be given on where to place various lamps. The data will also be used by the European Delight project .

In 1994-96, a group of utilities in the US Northwest also used more than 1200 lighting loggers to establish similar data for several hundred households. (Also see IAEEL No. 2/94)

French metering project
In France, the national energy and environmental agency Ademe recently completed a detailed metering and demonstration project in 120 French households. There, the energy consumption of every single household appliance and luminaire was metered using a plug-in device that also could also record load data every five minutes. Lighting use was found to be ~500 kWh per year and household, and halogen torchieres alone represented about 60 percent of total lighting energy use. 20 of the households were metered for a full year. After that, all appliances and as many light sources as possible were changed to the most efficient alternative. Analysis of another year's worth of metering data indicated that average energy use as a whole had been cut by 45%, and lighting by almost 70%.

Nils Borg

Contacts:
UK:Jane Palmer, ECU
Tel: +44 1865 281 209,
Fax: +44 1865 281 202
E-mail: jane.palmer@ecu.ox.ac.uk

Loggers:Calle Lindroth, Borlänge Energi
Tel +46 243 73 018,
Fax: +46 243 86 304
Email: c.lindroth@borlange.mail.telia.com

France: Olivier Sidler
Tel/fax: +33 4 75 90 18 54
Email: sidler@club-internet.fr



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