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Blog Archive

Saturday, April 2, 2011

Trying to save energy: measure first

A common theme across this blog is reducing my household energy consumption. You will see this in my threads on lighting, computers, gadgets etc.

As I see it there are 3 reasons to do this :

1) to save money - lower bills

2) to reduce my impact on the environment - CO2

3) to reduce my impact on non-renewable energy sources (gas, oil, coal, nuclear - they all have to be mined in some form or other.

While I have Green interests, I also use a lot of energy in my household, through gas & electricity consumption, and I sometimes feel I am the environmental equivalent of a Champagne Socialist. I have computers, TV's and all the modern trappings which I'm reluctant to give up. My house is part old and part new. It's a long way from a super insulated eco-home, so I have to be pragmatic. I will never get my consumption down to super low levels, but I want to try and reduce it as much as possible.

Measure it

How much energy brings me to the first issue in saving energy which is how to measure it. If you don't measure how much you use, how do you know if you are making things better or worse through changes in behaviour or technology ?

You could look at the amount you pay on your bills, but this is misleading. Bills vary with tarrifs and are often estimated. It's common practice in the UK for energy companies to estimate bills and have a single reading to reconcile actual with predicted. Energy prices vary, mostly up, so you could be using less but paying more than you were.You have to look at consumption rather than cost.

There are a number of ways of measuring your consumption. The simplest and cheapest is probably to read your meters (gas, electricity, oil) once a week. Record the number and subtract it from the following weeks reading to see the weekly consumption. If you divide by 7 you have an approximate daily consumption. You can chart this over time. You could refine it with other factors, for example external temperature - there will probably be a correlation between consumption and colder weather.

You could take this further and record the readings daily. This might be excessive BUT it also might show trends which, in turn, might suggest the main causes . In my house, Sunday and Monday tend to be the days of highest electrical consumption. This is due to heavy use of oven and washing machine on Sunday , and more washing on Monday. Electric ovens and washing machines are both heavy users of electricity.

As you employ strategies for reducing your energy consumption i.e low energy lighting, you should see a decrease. You can do this on paper or build a simple spreadsheet.

It's a a good thing to do. You need to read the meter at the same time each week (or day) to make a fair comparison week by week.

All units being equal

A further refinement is to convert everything to the same units so you can see the total energy consumption across gas, electricity or oil, assuming your household uses a combination. If you are all electricity for heating, hot water and lighting, then you can ignore the next bit - your life is simpler. Electricity is measured in kilowatt hours, gas in cubic meters or cubic feet, oil in gallons or litres

Now you could ask why does this matter ? If I can see the rate of use of each, and see if consumption goes up or down, why does it matter if this is expressed in different units.

A fair point. I think it's easier to understand your consumption as a whole by establishing a total figure. While you may take measures that reduce your consumption of electricity i.e turn down the stat on an electric heater, there is no real saving if this increases the amount of other fuels you consume. Other fuels may be cleaner or cheaper or impact the environment less, but my objective is a total reduction first and foremost.

An example of this might be the replacement of conventional filament 100 watt bulbs with low energy equivalents. Pretty simple stuff , swap a 100 watt bulb for a 12 watt equivalent. I've saved 88 watts or 0.088 units every hour they are on. However filament bulbs are inefficient because much of that 88 watts went out as heat. If my house heating has to work harder because of this, it's not as bigger a saving as I thought. Perhaps a too simplistic example, and we could discuss the relative merits of gas Vs electricity as a fuel and it's relative environmental impact. This has been done elsewhere , my objective is to measure what I use , and converting everything to the same units can only help to clarify.

While electricity is conveniently measured in Kilowatt Hours at the meter - the standard unit of energy consumption , gas and oil are measured and metered in units of volume. To compare the amount of energy you are using from electricity with the amount from gas or oil, you have to convert the latter into units Kilowatt Hours. This is a bit more complex as a unit of gas or oil may give out different amounts of energy when burnt, depending on it's calorific value. Just like food, gas has a a calorific value i.e the amount of energy given off if burned, and this varies slightly depending on where it came from and differences in the processing.

You can convert the volume units from the gas meter to kWh using fairly simply process :
  1. Take the units used as reported by the meter
  2. Multiply by the metric conversion factor (2.83)
  3. Multiply by the volume conversion factor (1.02264)
  4. Multiply by the calorific value (specified on your bill, something like 39.47333 , but will vary across regions )
  5. Divide by the kilowatt hour conversion factor (3.6)

For houses that use oil, it's even harder. I have not found a formula, and again , I can see that the calorific value of a type of oil will affect the energy produced. I found this on a web site as a very rough guide

heating Oil is 10 kWh/ltr

A simpler solution

If all of this conversion seems too hard then fear not. There are plenty of resources on the web which can do the conversion for you. I use imeasure , which is a site run by Oxford University. You just type in your meter readings and it does all the conversion, subtraction and charting for you. Once a week I enter my readings into their site. I can also see how my type of house compares with similar properties. I even get an Energy rating, which I'm ashamed to say wobbles between an E and an F - remember I said I was interested, I didn't necessarily say I was good at energy reduction. But I am trying.

The next blog will be on interpreting the measurements

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