Over the next year, I’ll be surveying how we use a range of resources with two objectives in mind: environmental impact and security of supply. To that end, I’m going to focus on four broad categories.
- Electricity.
- Natural gas.
- Transport.
- Water.
I’ve been tracking three of these for sometime, as previously discussed using the Carbon Account, but as a starting point, I’ve had to extract water data from our bills.
I’m hoping to personally read the water meter weekly in the future, as I do the other utilities, but it’s dependent on being able to see my submerged meter… Anglian Water, I’m looking at you.
Energy not CO2.
I prefer to work with energy units (kWh), rather than the now popular kgCO2. Energy is more definitive whilst the mixture of energy supply sources is shifting; some energy is ‘green’, and some is not, but it’s not something I can control.
To make this review process meaningful, I’m going to need an idea of my current energy profile: where I’m spending the energy I consume. That way I can make sound decisions about were to cut back.
Converting meter readings into energy.
Converting from meter units to energy requires a little maths in the case of natural gas, transport, and water. Here’s a brief explanation of how I went about it armed with a little technical data and the information from my bills.
Natural Gas.
The conversion for the gas supply was provided on my bill:
Energy consumed (kWh) = (2.83 x 39.5679 x 1.02264) / (3.6 x 100) x volume of gas used (ft3)
Most of these numbers are volume and energy conversion constants, but the 39.5679 figure is the calorific value of the natural gas: its energy content.
Transport.
In our case, transport can be defined almost exclusively as a 35 mpg car, so the job here is to convert mileage into a mass of fuel burned, and then into the chemical energy released.
I’ve take data from the seventh edition of Technical Data on Fuel, which given a density of 0.75 kg/litre, and a calorific value of 44000 kJ/kg for petrol:
Fuel consumed (kg) = ( miles / mpg ) x 4.54609 x 0.75
Energy consumed (kWh) = ( fuel consumed x 44000 ) / 3600
If you work this out for our car, each mile travelled uses 1.191 kWh of energy.
Water.
I’ve used data from issue 4 of the BRE Water Centre newsletter:
- Energy used in supply = 0.468 kWh/m3
- Energy used in treatment = 0.437 kWh/m3
It states that about 90% of all mains water supply is returned for treatment, which allowed me to estimate a total energy consumption associated with water supply of 0.861 kWh/m3.
These data are from 1998/99, and as such a little old, but I’ve check the results against more recent Government information, and it appears to be accurate enough.
The results.
The data collected over the last year result in the following average energy mix profile.
| Resource Category | Percentage Contribution |
|---|---|
| Electricity | 19.3% |
| Natural Gas | 54.2% |
| Transport | 25.9% |
| Water | 0.6% |
The only thing that surprised me was the insignificance of the energy contribution from our water supply. It would appear that the environmental impact is almost entirely related to the availability of water in a changing climate.
As for reductions… we use Gas for central heating, water heating and some of the cooking, and it looks like the best target for improvement.