Paying by numbers - analysing energy data

12th March 2012

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Collecting and interpreting data effectively is the key to successfully managing energy, says James Patterson

It goes without saying that good data are essential for successful energy management, and yet so often information is not available, incomplete or inaccurate. So, why are good data important? What sort of data is best? How do you analyse it? And how can data streams be improved?

Good data are key to understanding annual energy costs, not only historic, but also current and projected future costs, which is essential for budgeting. Access to data is also important in controlling unnecessary energy spend. Energy-supplying companies are only obligated to read meters every two years, although most will try to read them every six months. In the meantime, they rely on estimated readings. Having ready access to good data enables organisations to check and challenge estimated bills, and to spot any mistakes in meter readings, often saving money and avoiding nasty surprises.

Carbon footprint

Having access to the necessary energy data enables a firm to calculate a carbon footprint using conversion factors published annually by DECC. A carbon footprint may be essential if a company is affected by one of the emissions-based regulatory mechanisms, such as the Carbon Reduction Commitment Energy Efficiency (CRC) scheme.

The CRC is comparatively new and the data requirements are onerous, so many participants will be looking to improve the quality and accuracy of their data, and to use this to calculate the potential cost liabilities from emission allowance purchases. Some may also wish to disclose their carbon footprint data publicly.

Good data are also vital to any programme seeking to cut energy use and its resulting costs and emissions. Data help to quantify potential savings against capital investments, and to verify that these were achieved post-project. Also, when trying to save energy by changing employee behaviour, access to data helps to put the benefits in context by expressing the monetary value of savings, for example, and is key to ensuring buy-in.

Reading meters

For most organisations the main fuels used will be natural gas and electricity, which are supplied from a distribution network and measured by an inline meter. Some users in more remote locations may use other fuels, such as gas oil (red diesel), kerosene or liquefied petroleum gas (LPG). These are generally supplied on a bulk basis and stored in local tanks.

Metered energy sources are read by the supplier and bills are then submitted for the energy used. However, readings, as already noted, may be sporadic or even inaccurate, so it is a good idea to start taking your own readings. Larger electricity and gas users may have automatic meters that the energy supplier can read remotely (see below).

Reading an electricity meter is usually straightforward, but there are some things to be aware of. The key measure on which bills are based is units of kilowatt hours (kWh). Meters may have only a single register, through which electricity is charged at a flat rate. If the site is supplied on a dual-rate tariff with different rates for daytime (07.00 to midnight, sometimes referred to as “normal”) and night-time (midnight to 07.00, sometimes referred to as “low”), you should record both figures.

More complex automatic meters may have several registers recording kWh at different times of day as well as reactive power (sometimes used by electricity firms to charge for inefficient power distribution and measured in kVArh – kilowatt amps reactive hours), instantaneous demand (in kW or kVA – kilowatt amps) and monthly maximum demand. These registers are accessed by pressing buttons on the front of the meter to cycle through the different readings. Check against your bill to see what you are charged for and record the figures.

Gas meters will have a single register on the body of the meter. If the meter is fitted with a device for automatic reading, this will be located nearby and may have its own register. Gas meters record volume, measured either in cubic metres (cu, m or m3) or cubic feet (cu, ft or ft3) or tens or hundreds of cubic feet. The units of measurement will be marked on the face of the meter, and should be stated on the bill.

Meter reading frequency tends to be dictated by size of energy spend. For sites spending around £100,000 a year, monthly readings will suffice. For larger sites, weekly readings may be preferable, while for very big sites, daily readings might be the norm, although these sites are likely to be fitted with automatic meter readers (AMR), giving high-resolution data.

To measure the use of batch or bulk fuels, such as oil or LPG, a meter is fitted between the storage tank and the user and should be read regularly. Oil meters will generally read in litres. LPG will be measured in m3 or ft3, as for natural gas. If no meter is installed, fuel usage can be approximated, calculating the volume consumed by subtracting the stored volume (obtained by gauge or dipstick) from the delivered volume.

Basic data analysis

For all fuels, the aim should be to convert the meter readings back to common units of energy. In most cases this will be kWh.

As electricity is measured in kWh for most small and medium-sized users, this is straightforward. Gas, on the other hand, is measured in volume terms and must be converted to units of energy. This is a slightly complex calculation involving several steps, and is explained on the gas bill.

Meter readings taken in units or cubic feet are first converted to cubic metres and then converted to energy by application of joules per cubic metre (MJ/m3 – this varies between about 38 and 40 in the UK). Finally, the energy is converted into kWh by application of a further conversion factor (1 kWh = 3.6 MJ).

For oil or LPG, the conversion is straightforward, and there are a number of conversion factors to convert volume or mass into kWh for a range of fuels.

Having got the meter readings, set up a simple spreadsheet to record these on a weekly or monthly basis, and use calculation cells to automate the conversion from meter reading units to kWh. Further calculation can be made to convert energy use in kWh into carbon emissions, using standard factors. Add in meter reading, consumption and cost data from bills and use meter readings to compare against what is billed. This alone can produce some surprising savings!

You may wish to include floor area, activity or production data and start to derive some benchmarks, such as kWh per m2 or kWh per tonne by energy source. Use these to measure your performance against published benchmarks, or to compare similar sites to identify best and worst performers.

Benchmark data are also handy for gauging the potential for improvement, for example by comparing site performance against typical and best-practice performers. After having built up a few months’ or years’ worth of data, look at long-term trends and seasonal variations.

There are techniques for normalising or correcting consumption to account for variations in weather, which has a big influence on energy use for space heating or cooling. More advanced techniques include regression analysis, in which energy use and an influencing variable – for example, external temperature (expressed in degrees), days of production or other activity – are plotted against each other in an X-Y chart or scattergraph. This can help to identify poor control and wasteful practice, and is a key tool in effective energy management, used in monitoring and target setting.

Automatic meter readings

Larger sites will have a form of AMR installed on the electricity supplies, known as half-hourly metering. Large gas supplies will operate on a similar basis, with a data logger connected to the meter.

In both cases, the data should be available to the user via the supplier. This type of metering will soon become widespread with the roll-out of the government’s planned smart-metering strategy, but in the meantime users can get ahead of the game by voluntarily installing their own AMR equipment.

AMR is invaluable in identifying inefficiencies and cutting costs. Obvious areas for savings are higher-than-necessary baseload energy use – what is running out of hours that does not need to be? AMR can also help to identify plant and equipment programmed to start unnecessarily early, run after hours or even at weekends.

All of these common errors can be rapidly identified and rectified, generating savings with a value many times more than the cost of installing the metering system.


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