Monitoring Efficiency
This section is intended to help you calculate you Energy Costs per annum, how efficient it s and how to improve it by investment cost. If you have any questions on the calculation below or are interested in improving the energy efficiency of your home, office or any other building you can contact us for a free consult and professional advice.
How to Calculate the Cost of your Energy Consumption
Collect your last six two-monthly ESB bills, covering a one-year period. Calculate your electrical energy use by subtracting the “Previous” reading on the first bill from the “Present” reading on the sixth bill. This gives you the total number of “units” of electricity used in the year. These units stand for kilowatt-hours (sometimes shortened to kWh), which are used for measuring energy use. To calculate your electrical energy costs multiply cost per kWh, or “unit”, i.e. the tariff you pay, by the number of kWh used. This is the cost of your electricity. Add the two monthly standing charges x 6 and then the VAT to get the total cost of electricity.
Energy Rating
Your house’s “energy rating” is a figure that compares your annual energy usage to the internal floor area of your home. In other words, it measures your annual energy consumption per square metre of floor area in a particular year. It is quoted as kWh per m2 per year.
Calculate your Rating
To calculate your “energy rating”, first estimate the approximate floor area of all the rooms in the house which are heated.Do not include garages or outhouses unless they are heated or have high electrical loads – perhaps a tumble dryer or washing machine. The annual total number of kWh (or units) used for electricity and heating, calculated previously, are added together. This figure is then divided by the floor area.This will give you the energy rating for your home, for a particular year. For example, a house of 120 m2 area,which uses 7,002 kWh of electricity and 27,456 kWh of heating energy in a year, has an energy rating of 287 kWh / m2 per year. Similarly, having spent €890 on electricity and €985* on heating oil this home will have a cost rating of €15.61/ m2. If gas is the source of home heating an expenditure of m686* will result in a lower cost rating of €13.45/m2. The values you arrive at will depend on how many people occupy your home and your specific heating patterns. The same is true for the savings you will be able to make. For example, poorly insulated older houses will benefit substantially more from additional insulation than newer highly insulated ones. But whatever type of house you live in, it should be possible to improve your home energy-rating year on year. For a more detailed calculation of your homes ‘Heat Energy Rating’ visit www.sei.ie (‘Energy and You’ section).
To summarise the various costs involved in making your home more energy efficient, we have divided the numerous opportunities under four headings. Whatever your budget there are energy saving measures you can undertake.
Zero- cost Energy Saving Measures
• Turn down thermostats
• Use timers for hot water or space heating
• Switch off lights/appliances when not in use
• Shower rather than bathe
• Close curtains at night
• Fix leaking taps
• Position fridges and freezers in a cool place away from direct sunlight and heat
• Always wash full loads in your washing machine and dishwasher
• Maintain your hot water boiler
Low-cost Energy Saving Measures (up to m150)
These measures typically recoup their cost in 1-2 years
• Insulate your hot water cylinder
• Draught seal doors, windows and other gaps
• Improve heating and water controls
• Replace ordinary light bulbs with with energy saving CFLs
• Use lined curtains
Medium-cost Energy Saving Measures (m150-m450)
These measures typically recoup their cost in 3-4 years
• Insulate your attic
• Consider ground floor insulation options
• Central heating controls
• Buy energy efficient appliances
Long-term Energy Saving Measures (>m450)
These measures are ideally considered when doing renovation/replacement work
• Cavity wall insulation
• Internal wall insulation
• External wall insulation
• Low-emissivity double-glazing
• Solar water heating systems
Calculating the amount of energy used for heating will vary depending on the type of fuel you use to heat your home.If you use natural gas or electricity the procedure is very similar to the one shown for electricity. The number of kWh, or “units”, and costs are simply totalled for a one-year period and added to the standing charges and VAT.
The procedure for other fuels is also simple. List all the fuels that you use for heating – perhaps these include coal or oil – and estimate how much you use in a year. Now use the Energy Content of Fuels table below to covert the fuel amount purchased into energy consumed in kWh
Here’s an example of how to calculate the energy consumption and costs for oil fired central heating:
Average for one year: 2600 litres of oil
Conversion Factor: (From table) 1 litre = 10.56 kWh
Total Energy used : 2600 x 10.56 = 27,456 kWh
Now add up the amount and cost of heating energy used across all fuels in the house for a one-year period.
