Mei—the maths
Home » Magazine » Good, issue 10 » 10:10 » Mei—the mathsHere’s how Mei can cut her carbon footprint 10% in 2010.
Mei’s total annual emissions for electricity and transport are 2,774.12 kg CO2e = 2.77 tonnes
10:10 reduction goal = 0.28 tonnes
Assumptions
- average amount electricity per year = 2,908 kWh (EECA)
- lives 12km from work
- lives 5km from farmer’s market
- Toyoto Corolla 1.5P Wagon 5DR 5M (5 seats, 1,496cc 81kW petrol engine, 5-gear manual) = 6 litres/km
- drives just 2,500km/year, at 6l/100km = 150 litres petrol/year
- 2 × return flight Akl to Wgtn (282.66 kg CO2e per flight, CarboNZero calculator)
- 2 × return flight Akl to Chch (432.54 kg CO2e per flight, CarboNZero calculator)
Calculations
Stop over in Wellington on the way to Christchurch = 0.27
- AK–Chch return = 432.5 kg CO2e per flight (CarboNZero calculator)
- AK–Wlg return = 282.5 kg CO2e per flight (CarboNZero calculator)
- 432.5 + 282.5 = 715 kg CO2e for both return flights
- Akl–Wgtn–Chch–Akl flight = 444 kg CO2e (CarboNZero calculator)
- 715 – 444 = 271 kg CO2e saved
Reduce daily shower time by one minute = 0.02
- 1 shower per day, shower flow rate 10.6 l/min (HEEP average for mains pressure systems), electric resistive water heating
- Savings per minute = 114 kWh/yr per person (EECA supplied)
- 114kWh × 0.21 EEF = 24 kg CO2e saved per person reducing daily shower time by one minute
Cut one Wellington flight = 0.28
- Akl–Wgtn return = 282.5 kg CO2e per flight (CarboNZero calculator)
Work from home one day a week rather than commute by bus = 0.1
- City bus commuting 12 km × 2/day × 5 days/week × 48 weeks/year = 5,760 km
- City bus commuting 12 km × 2/day × 4 days/week × 48 weeks/year = 4,608 km
- 5,760 – 4,608 = 1,152 fewer passenger kilometres
- 1152 passenger kilometres in city bus = 99 kg CO2e (CarboNZero calculator)
Walk or cycle for 25% of weekend car journeys = 0.09
- drives 2,500km/year, at 6l/100km = 150 litres petrol/year
- 150 × 25% = 37.5 litres petrol
- 37.5 litres × 2.33 = 87 kg CO2e saved
Install an efficient shower head = 0.06
- Assume before shower flow rate of 12l/min, afterwards 9l/min
- Assume 3 showers per day of 9 minutes each (NB extremely variable)
- Assume electric water heating
- 830 kWh × 0.21 EEF = 174 kg CO2e (EECA supplied)
- divided by 3 showers = 58 kg CO2e per person
- Doesn’t include CO2e emissions of treating water supply and wastewater
Visit farmer’s market fortnightly instead of weekly = 0.04
- 5km × 2 (return trip) = 10km
- 10km × 0.06 litres/km = 0.6 litres per trip to farmers market
- 0.6 × 52 = = 31.2 litres weekly trips
- 0.6 × 26 = 15.6 litres saved going fortnightly
- 15.6 litres × 2.33 kg CO2e = 36 kg CO2e
Replace old electric hot water cyclinder with a solar hot water heating system = 0.12
- 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
- divided by 4 people in house = 118 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
Install double glazing = 0.07
- Consumer energy use per average household: 10,549 kWh/year
- Divide by 2.7 people in average household = 3,907 kWh/year per person
- Space heating: 34% of household energy
- 34% × 3,907 kWh/year = 1,328.4 kWh/yr for space heating
- Assume 25% heat loss reduction (proxy for otherwise fully insulated houses)
- 25% × 1,328.4 kWh = 332 kWh/yr saved per person
- 332 kWh × 0.21 EEF = 70 kg CO2e
- NB This is extremely variable due to different climates, house sizes, house thermal efficiencies, heating regimes
Replace old fridge with a new Energy Star refrigerator = 0.03
- 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
- Divide by 4 people in house = 26 kg CO2e
Buy a wood- or pellet-burner = 0.28
- Consumer energy use per household: 10,549 kWh/year
- Divide by 2.7 people in average household = 3,907 kWh/year per person
- Space heating: 34% of household energy
- 34% × 3907 kWh/year = 1328.4 kWh/yr for space heating
- 1,328.4 kWh/yr × 0.21 EEF = 279kg CO2e
- NB this is extremely variable due to different climates, house sizes, house thermal efficiencies, heating regimes
