Bruce—the maths
Home » Magazine » Good, issue 10 » 10:10 » Bruce—the mathsHere’s how Bruce can cut his carbon footprint 10% in 2010.
Bruce’s total annual emissions for electricity, transport and beef are 4,812.45kg CO2e + 1,197 (meat) = 6,010kg = 6 tonnes
10:10 reduction goal = 0.6 tonnes
Assumptions
- average per capita electricity use per year = 2,908 kWh (EECA)
- average beef consumption = 34.2kg per year (Beef NZ)
- lives 8km from work
- regular petrol car
- Subaru Legacy 3.0R Wagon Auto (2004) (5 seats, 2,999cc 180kW petrol engine, 4-gear automatic) = 11.2 litres/km (average NZ mileage)
- drives average 14,000km/year, at 11.2l/100km = 1,568 lires petrol/year
- one 6kg rubbish bag/week
Calculations
Remove roof rack = 0.18
- Drives 14,000km/year, at 11.2l/100km = 1,568 litres petrol/year
- A roof rack, ski box or bike rack attached to your car causes more wind resistance. More of the vehicle’s power is needed to overcome this resistance in order to travel at a given speed = 5% more fuel (via FuelSaver)
- 5% fuel saved = 78.4 litres
- 78.4 litres × 2.33 kg CO2e/litre regular petrol = 183 kg CO2e
Use the sun to dry clothes, rather than a dryer = 0.17
- Median electricity consumption for a dryer 800 kWh, based on 700 kWh average for 3.5kg dryer and 900 kWh average for 5kg dryer, from Consumer NZ Appliance Running Costs report (updated 2 Jul 2009), converted back to kWh using quoted electricity cost of 22 c/kWh; assumes 4 loads a week
- 800 kWh × 0.21 EEF = 168 kg CO2e
Get rid of the second fridge (or just switch it off) = 0.13
- Average electricity consumption for a fridge was stated as 621±30 kWh/yr in BRANZ report EC1208/01 Analysis of Refrigeration Appliances from HEEP
- 621 kWh × 0.21 kg CO2e/kWh electricity emissions factor 2008 (EEF) = 130.4 kg CO2e
Only use your heated towel rail four hours a day (instead of all the time) = 0.11
- Average wattage of a heated towel rail was stated as 70W in BRANZ year 10 HEEP report
- 70W × 20hrs × 365 days/yr = 511 kWh/yr saved
- 511 kWh × 0.21 EEF = 107.3 kg CO2e
Compost all food and garden waste = 0.1
- 52 × 6kg bags rubbish
- CarboNZero calculator = 106kg CO2e
Go beef and dairy-free 2 days a week = 0.34
- 34.2kg beef per year × 35kg CO2e per kilogram beef = 1197kg CO2e
- 1,197 divided by 7 = 171kg per day’s beef consumption
- 171kg × 2 days = 342 kg CO2e
Open car window instead of air con = 0.09
- Assume need air con for half of all journeys (warmer months) = 7,000km
- 0.112 litres/km × 7000 = 784 litres
- Open window/sunroof (at speeds under 80 km/h; the higher the speed, the more wind resistance and therefore the more fuel the car uses) = save 5% fuel (via FuelSaver)
- 5% of 784 litres = 39.2 litres
- 39.2 litres regular petrol × 2.33 kg CO2e/litre = 91 kg CO2e
Replace two 100W bulbs with 20W eco-bulbs = 0.06
- Assume bulbs on for five hours a day
- 100W bulb × 5 hours × 365 = 182,500 = 182.5kWh
- 20W bulb × 5 × 365 = 36,500 = 36.5kWh
- 182.5 – 36.5 = 146 kWh saved per bulb
- 146 × 0.21 EEF = 31 kg CO2e per bulb
- 31 × 2 = 62 kg CO2e
Cycle to work three days a week = 0.61
- Lives 8km from work
- 8km × 2 × 5 days a week × 48 weeks a year = 3,840km/year work commute
- 3,840km × 0.112l/km = 430 litres petrol = 1015kg CO2e
- 1,015kg CO2e / 5 days per week = 203 kg CO2e per weekday/year
- 203 × 3 = 609kg CO2e saved by not driving three days a week
Take the bus to work instead of drive = 0.69
- Lives 8km from work
- 8km × 2 × 5 days a week × 48 weeks a year = 3,840km/year work commute
- 3,840km × 0.112l/km = 430 litres petrol = 1015kg CO2e
- Bus 3,840km = 329kg CO2e (CarboNZero calculator)
- 1,015 – 329 = 686kg CO2e saved
Install 2 kilowatt solar PV panels = 0.49
- Assume capacity factor of 12–15%
- 2kWh × 12–15% × 8,760hrs/yr = 2,100–2,600kWh (EECA supplied info)
- median = 2,350kWh
- 2,350 kWh × 0.21 EEF = 494 kg CO2e
Replace old fridge with a new Energy Star refrigerator = 0.11
- Assume 300kWh/yr for new EnergyStar fridge/freezer
- Assume 800kWh/yr for old fridge/freezer (comparison on fig 48 in year 10 HEEP report)
- 500 kWh saved
- 500 kWh × 0.21 EEF = 105 kg CO2e
Replace your old electric hot water cyclinder with a solar hot water heating system = 0.47
- Based on 50%–75% reduction of energy use for heating water, with a solar hot water system for a 4–5 person household (AS/NZS 4234:2008)
- Based on average savings of between 1,800 kWh and 2,700 kWh a year
- 1,800–2,700kWh = 2,250 kWh median
- 2,250 kWh median × 0.21 EEF = 473 kg CO2e
Install double glazing = 0.19
- Consumer energy use per household: 10,549 kWh/year
- Space heating: 34% of household energy
- 34% × 10,549 kWh/year = 3,587 kWh/yr for space heating
- Assume 25% heat loss reduction (proxy for otherwise fully insulated houses)
- 25% × 3,587 kWh = 900 kWh/yr
- 900kWh saved/year × 0.21 EEF = 189kg CO2e
- NB This is extremely variable due to different climates, house sizes, house thermal efficiencies, heating regimes
Buy a new small car with fuel economy of 6 litres per kilometre, then sell the old one for scrap = 1.7 [a 28% cut, plus Bruce would save $1,142 a year]
- Average mileage 14,000km/year
- Before: Subaru Legacy 3.0R Wagon Auto (2004) (5 seats, 2,999cc 180kW petrol engine, 4-gear automatic) = 11.2 litres/km (average NZ mileage)
- After: Toyoto Corolla 1.5P Wagon 5DR 5M (5 seats, 1496cc 81kW petrol engine, 5-gear manual) = 6 litres/km (average new mileage)
- 0.112 litres/km × 14,000 = 1,568 litres per year
- 0.061 litres/km × 14,000 = 854 litres
- 1,568 − 854 = save 714 litres/year
- 714 litres × 2.33 kg CO2e/litre = 1,664kg
