Wednesday, December 22, 2010

How much CO2 is this saving?

22 December '10: I have been trying to work out how we calculate CO2 savings, as this is the ultimate judge of success, not kilowatt hours.  KWh are a guide, but they are different for each fuel, as for example, Gas is burnt in your own boiler and turned directly to heat, but electricity from a gas powered station meant that gas had to be burnt elsewhere, converted to electricity in turbines, then posted 20 miles through a series of stepping up and stepping down stations until it gets to us - it is very efficient when it's in our house, but it may only be 1/4 the efficiency of the original gas, which partially explains the 1 to 4 ratio in the gas to electricity price.
  Used well, and generated from renewable sources, electricity is in the long run more efficient once it is in your house.
  The Peveril Solar house (during this coldest December since 1910) is using 27-29 kWh / day to provide space  heating and hot water for this house, and a neighbour with a well insulated house of similar size, but with gas central heating and DHW is using about 120-140 kWh / day of gas to achieve the same comfort.

With regard to Climate Change, what matters finally is the amount of CO2 you emit from heating your house and other activities, such as transport and food purchasing decisions.

Quote 16 Dec: 'A Task Group convened by the Zero Carbon Hub has delivered a report to the Minister for Housing and Local Government setting out its recommendations for carbon compliance levels for new homes from 2016. Carbon Compliance – that is, on-site reductions in emissions – form part of the Government’s overall plan for achieving zero carbon homes; the other part comprises off-site "allowable solutions."'
for the details.

Their recommendations are that the 'built performance' emissions from new homes should not exceed:
  • 10 kg CO2(eq) /m2/year for detached houses
  • 11 kg CO2(eq) /m2/year for other houses
  • 14 kg CO2(eq) /m2/year for low rise apartment blocks
What does this mean? The Carbon Trust site gives some help from a table published in 2009:
Conversion to CO2e (gross CV basis)
  • Grid electricity: 1.0 kWh =0.544 Kg CO2 per unit
  • Natural gas: 1.0 kWh 0.184 Kg CO2 per unit
On this basis from the kWh above for heating and hot water:
  • Peveril house is costing (during these coldest winter days) 27-29 x 0.544= 14.6 - 15.8 kg/day
  • Neighbour's house in the same time period 120-140  x 0.184 = 22 - 26 kg/day
This is in no way a criticism of my neighbour, it's a technical comparison. He has just invested thousands in a south facing PV roof that is doing a lot better than my roof, and he has replaced all his 25yr old central heating radiators with modern efficient ones, with insulated backing and thermostatic valves to reduce heat loss through the wall. We are all trying our best here!

During the year 1 Oct'09 to 1 Oct'10, our House Space Heating requirement was 3,000 kWh = 1632 kg of CO2. For 120 sq metre house, that is 13.6 kg / sqm / year. considering that this is a developer built house with insulation only slightly better than the current building regulations, and not having MVHR (Heat Recovery), that is pretty good!
The Passivhaus requirement is for 15 kWh /sqm/year or 8.16 kg of CO2/sqm/year, so we are still far from that target.
 Our PV roof generated 3,325 kWh in the same time period, which was all either used by us or sent to the Grid for others to enjoy. This is equivalent to reducing CO2 emissions by 1809 kg/year.

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