Finding the chase and cutting to it

For many, the costs of producing energy efficient good, thermal insulation, or green power consumption, far outweighs the benefits. In the past, Number crunching part 1 has examined how much carbon was used in producing our batteries and solar cells, and whether that effort made a return – is the juice worth the squeeze? – so to speak.

We should look at the same numbers for the replacement windows. Although, can I put a caveat here that the windows were failing, whatever we did to preserve our thermal envelop was necessary. We just took the opportunity to go the full way with triple glazing.

We replaced twelve windows with triple glazing at 110-140 kg CO₂, let’s call that 125 kg CO₂ a pop => 1,500 kg CO₂. And one double glazed window, coming in at 110kg CO₂, so our total is 1,610 kg CO₂ for the windows.

We then have 3 UPVC French doors, two triple glazed and one double glazed. The triple glazed ones are 140 kg CO₂/m², so that’s 5.4 m² * 140 kg CO₂/m² = 768.18 kg CO₂. The double glazed unit is 110 kg CO₂/m², so 301.785 kg CO₂. French doors in total is 1,069.965 kg of CO₂.

The aluminum patio door is harder to judge, because it depends on how the aluminum was sourced, but 140 kg CO₂/m² is probably fair. So, that one cost is 743.4 kg in terms of CO₂. So all the doors contributed 1,813.365 kg of CO₂.

The total for the windows and doors was 1,610+1,813.365 kg CO₂ or 3,423.37 kg CO₂. Or 3.423 Mg CO₂.

In the UK, 124g CO₂ (or 0.124 kg CO₂) is generated per 1 kWh of electricity produced. That means to break even, our windows need to save 27.6 MWh of electricity.

Given our pre-window expenditure of 3.9 MWh on heating, we can expect it to be 3.25 MWh, (an estimated save of 650 kWh over the year), they should break even in their life-time, hopefully within 10½ years.

This is a reasonable estimate, we may do better, it’s hard to tell until we start to see it in action. It also takes into account we had to replace our existing windows either this year or next and took the opportunity to upgrade the performance. If we’d gone for double glazing everywhere and retained our layout, the cost would have been less both in terms of money and CO₂ produced, but the efficiency gains would have been much less too, so the returns would have possibly come in during the life-time of the product.

There’s so much to take into account here, not least because of when we’re doing the replacement. It meant we got a great price on the windows, but losing our thermal envelop in each and every room of the house meant we had to use electricity to restore the thermal levels – the temperature in each and every room.

This means I may have to play about with November’s numbers to get a blended estimate, if I want to do an annual comparision pre- and post- replacement windows. Or I may just exclude November. Both would be reasonable approaches, the later probably being much more meaningful and understandable. In the rooms where the windows had already failed, it is already much easier to get the rooms up to temperature and to maintain them there.

Hopefully, this article gives you the means to work out if it is worth the replacement for you and your carbon footprint!

NB: Stephen Hawking’s editor said Prof Hawking lost sales for every mathematical formula published in his book. Please be forgiving, as this is the easiest way to explain what is happening regarding payback.

Also, Number crunching part two is coming in the first week of January, when the numbers are all in for the year.