How Big is Your Carbon Footprint?

  • Building Design Expert
  • 6 years ago

Once you have committed to add the words ‘Carbon Footprint’  to your project priority list, your next step is to decide how near the top they are going to appear?

How much you feel the pressure to go the extra mile to lighten the pressure, or reduce the size of your carbon footprint, beyond the statutory minimum laid down by the regulatory bodies is a feeling that is entirely yours. The distance, of course, is dictated by how much of your budget you wish to make available for the purpose.

Is it just money that governs what we do? – Largely yes. But the design integration is fairly crucial too. So the decision of how far to go, and in what vehicle ideally needs to be made early in the design process.

What vehicle!?
Really amounts to the choices available for carbon reduction:

  • Increased Insulation
  • Increased Air-tightness
  • Renewables
  • Energy Efficiencies

Increased Insulation –
Arguably the best, cheapest and easiest way to reduce energy use is to increase the building insulation envelope – Thermal Insulation – You can’t go wrong, can you?
But as we know it has to be carefully designed, and not just thrown in. Industry knowledge tells us that millimetre for millimetre all insulation is not the same. So if we choose mineral fibre insulation over a high density foam board we must be prepared to give up the internal space required for the increased wall thickness. OR, the offset on insulation material savings, against the cost of longer cavity wall ties and a wider foundation / sub-structure. So every apparent saving has it’s price.

Increased Air-tightness –
Mainly through enforcement, this is now becoming accepted as major source of heat loss. We have all heard about draft proofing our windows and doors, but this takes the philosophy a little further and looks to draft proof your building walls, roof and floor. You can relatively easily retro-fit draft proofing measures to windows and doors. Not so easy with the hidden building fabric: If the open textured block inner leaf behind a dot and dabbed plasterboard wall lining has not been thoroughly slurried and sealed as part of the construction, no amount of perimeter mastic will alter the air loss through that wall. Because of course the air has been heated and is more than happy to take the heat with it when it leaves. “You are the weakest link – Good-bye!”

So it is difficult, if not impossible to ‘retro-fit air-tightness’. However, we know on ‘new build’ it’s worth doing, and it’s worth doing well. It has taken a long time but Passivhaus has demonstrated that reducing air loss to less than 1/10th the level demanded by current Building Regulations is one of the biggest keys to unlocking the door to significant energy conservation.

Renewables –
Photo-voltaic panels – Still languish behind in terms of ‘bang for buck’, but getting better all the time in terms of efficicency. There was a time when you needed a building with a roof the size of a football field and full of panels, to power your train set. Now a 4Kw system, although still taking a significant area, has become eminently more practical, and will make a significant impact on the energy needs of a typical family home.

Solar-thermal panels – This is a ‘no-brainer’. As long as you have a pitched roof facing somewhere south of east-west – It just works. At around £3k to convert an existing family house, or less for new build . It’s worth every penny, in not only reducing energy costs, but a constant supply of hot water.

Air-source Heat pumps (ASHP) – Up to 4 times energy out from energy in. That’s for every penny spent on power to the unit, it gives up to four pennies worth back. It gives a new meaning to having your four-penneth worth. But it’s the “up to” bit you need be wary of, as this can be infinitely variable dependent on the prevailing climate and ambient air temperatures. Chances are with our ever worsening winters your average ASHP will almost certainly require a supplemental heat source.

Ground-source Heat pumps (GSHP) – These are great. Up to, and reasonably reliable, 6 x energy out from energy in. But ohhh the cost of installation can be the most effective wallet contraception: Excavation of hundreds of metres of trench (about 1.0m deep), or, deep bore hole(s) dependent on local ground conditions is not the cheapest exercise to undertake. Although, if you must build using piled foundations, a useful solution can be to incorporate your latent heat collection coils within those bore holes at a significant saving. – A limited range solution – yes. But if the cap fits…….

As good as ‘Heat Pump’ systems are; to get the best from them you need a low temperature heating system – underfloor heating is perfect, – preferably coupled with a highly insulated building envelope. As with any energy related installation, it always tracks back to how well your building is insulated. You can couple that too, to the air tightness as was explained above.

Wind turbines – Talking of limited range. I have yet to come across a man from the top deck of a Clapham omni-bus, who is able to express any satisfaction what-so-ever with a wind turbine installation. Mainly due to the suburban winds in Clapham being lacking in their built in energy charge. Not just Clapham either. In fact unless you reside on a windy Pennine moor, or are a Scottish crofter. The reported pay-back for wind power will generally not come close to justifying the outlay. Remember these are one off domestic / small business installations we are talking about, and not huge multi-unit wind farms which are sited hopefully where the wind doth blow most of the time.

Bio-mass boilers – The jury has not returned with a verdict on Bio-mass. The capital outlay is around 5 x that of the most modern fuel efficient gas boiler. They don’t ‘give away’ the fuel pellets and you need a significant amount of physical space for the boiler unit, which can occupy 4 – 6 times the volume of a standard gas fired unit, and of course you will need somewhere to put your fuel. So Bio-mass is not for everyone. In fact as far as the domestic market goes, it’s for very few.

Even the humble wood burning stove counts under the ‘renewables’ heading. You can use this to provide supplemental heating, not only as a localised room source, but also heat water for storage in a thermal store  for use as domestic hot water. Incidentally, if you have room for one, and are designing a new system for a new build or refurbishment project – a ‘thermal store’ is a must have option.

Energy Efficiencies –
These are measures pretty much anyone can put in place at relatively little cost:

  • If there is a fixed budget ensure that the building insulation is as good as it can be, before anything else.
  • Draft proof doors and windows
  • Use LED (Light Emitting Diode) lighting – this is still relatively expensive, but costs are coming down. LED is to fluorescent lighting, what fluorescent was to tungsten filament ten years ago. Look out for OLED  (Organic Light Emitting Diode) lighting beyond this as well. Once this takes hold we will still need to think about when we turn the lights on, but it will be much less of a contributory issue.
  • An underfloor heating system will provide the most effective and efficient heating, utilising low temperature hot water within a concealed grid of heating pipes installed below the finished floor level.
  • A+++ rating for new electrical equipment
  • Last but not least – Cook two pies instead of one!!!

We all have much still to learn to effectively realise How big our Domestic and Business  ‘Carbon Footprints’ are – and take the necessary steps to reduce them.

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