One small step to reduce your carbon footprint

21 February 2008

Home energy is responsible for 27% of UK C02 emissions according to information published

Home energy is responsible for 27% of UK C02 emissions according to information published in ‘Energy efficient ventilation in dwellings – a guide for specifiers’ publication, ref GPG268, issued by the Energy Saving Trust. In the same document energy loss due to ventilation is said to account for approximately one fifth of space heating energy demand in an older poorly insulated dwelling. The EST adds that by following its best practice guides new build and refurbished housing will be more energy efficient.

Quite rightly industry experts argue that products and systems that contribute to a reduction in a dwelling’s carbon footprint should be used wherever possible. However, the issue of wind effect, which can render some ventilation systems completely ineffective, is generally ignored. Fitting a ventilation grille specially designed to stop air from entering a dwelling will dramatically reduce the problem of wind effect. Such devices do not use energy; they improve the efficiency of ventilation systems and so reduce a dwelling’s carbon footprint. It’s as simple as that.

So why not use them as standard? The problem is one of specification. Although various papers have been written and projects funded to determine ventilator test procedures with a view to seeking British Standards approval, as far as we know there are no European testing standards for ‘wind effect’ in preparation, let alone in place.

This is surprising given the compelling evidence published in independent studies examining the effect of wind on the performance of ventilation devices in housing.

For many years the passive through-the-wall vent, basically a hole in a wall with a grille over the end to keep out draughts, rain ingress and insects, has provided trickle ventilation by allowing fresh air in and stale and damp air out of dwellings. These vents are also used to supply fresh air for combustion in open-flue, gas, oil and solid fuel boilers and fire. However, many ventilators of this type create unnecessary discomfort: when the weather outside increases to beyond a light wind the trickle becomes a stiff breeze inside.

Several ventilation grilles have been developed to reduce the airflow while preserving the statutory requirements for ventilation. The problem is they have been designed to meet the specifications of the standard test to determine ‘Effective or Equivalent Free Area of 100cm2’ and this performed in still air conditions.

When tested for their ‘Effective Area’ open bottomed cowls or grilles designed to combat head-on winds scoop up the air and exacerbate the problem. This is because when wind meets a building it is forced to go over it and so changes to an upward direction. When wind approaches from the side of a building the ‘Discharge Coefficient’ (the ratio of Effective Area with a cross-flow to that in still air) of a conventional hooded vent can be reduced by up to 50%.

Two independent tests, one funded by the HSE and the other undertaken by Betaflow, confirm that design of cowls is critical to optimising ventilation performance. Clearly there is a need for a test procedure that takes account of the detrimental impact external wind has on the performance of domestic ventilation systems.

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One small step to reduce your carbon footprint

21 February 2008

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