Looking backwards to help move forwards

Monodraught, natural ventilation
Natural ventilation using devices such as Monodraught’s Windcatcher can deliver low-energy ventilation and cooling with minimal maintenance requirements.

Benjamin Jones finds lessons in looking at historic buildings to discover effective ways to meet carbon-reduction targets.

The Climate Change Act of 2008 commits the UK to reducing its annual net carbon emissions to 80% lower than the 1990 baseline by the year 2050. Make no mistake, this is a tough target to meet, but to do it we must acknowledge that emissions are directly related to the consumption of energy.

The Digest of UK Energy Statistics shows that the fuels used to produce our energy are, overwhelmingly, from fossil-based sources. Earlier this decade, it became clear that the 160 million buildings within the EU use over 40% of its energy and create over 40% of its carbon-dioxide emissions. In 2003, the European Parliament & Council responded by publishing the Energy Performance of Buildings Directive (EPBD), which was designed to affect the awareness of energy consumption in buildings.

The EPBD is now enshrined into UK law, the use of the national calculation methodology is standard, energy certificates are issued, minimum energy performance requirements are encapsulated within the Building Regulations (part L), and the inspection of boilers and air conditioning systems is mandatory.

There are many products that are claimed to be the correct low-energy solution for any number of building-services problems. However, the eminent Egyptian architect Hassan Fathy has suggested: ‘Before investing or proposing new mechanical solutions, traditional solutions in vernacular architecture should be evaluated and then adopted or modified and developed to make them compatible with modern requirements.’ Therefore, for lessons in how to achieve low energy consumption in a changing climate, it may be helpful to look backwards to help us move forwards. After all, these buildings have developed over time through trial and error to produce generic designs that are efficient and a function of their environment.

Vernacular Middle Eastern buildings are thermally massive to mitigate against high diurnal temperature differences, are often naturally ventilated and carefully regulate daylight. But, how are these ancient principles reapplied to a modern building to reduce its energy consumption?

Naturally ventilated buildings rely on two forces to drive air flow: those created by action of the wind, and the buoyancy of hot air. There is plenty of wind in the UK, and its mean speed is at least 3.5 m/s for all UK locations, so natural-ventilation strategies can use simple windows or more advanced openings such as stacks or wind-catchers to generate air movement through a building.

These principles are widely used in UK buildings such as schools and hospitals where the occupants are particularly vulnerable, thus demonstrating their capability.

Monodraught, natural ventilation
The city of Yazd in Iran is almost exclusively vernacular architecture, with features such as this wind tower to ventilate and cool buildings.

Contrary to Middle Eastern buildings, many modern non-domestic buildings in the UK are built from lightweight materials because of costs and material scarcity; consequently they contain little thermal mass. However, it can be retrofitted using phase-change materials (PCM) that change state at room temperature so heat energy can be stored during the day and dissipated when the internal temperature drops at night. They come in readily available panels that can be attached to internal walls, as part of low-energy cooling systems, or even in clothing.

Occupants of a building have a preference for daylight over electric lighting, yet lighting can account for up to 25% of emissions from commercial buildings. Using daylight represents a real opportunity to reduce energy consumption and associated carbon emissions by installing windows, light pipes, light wells, atria, or any other daylight facilitators.

There are mechanical equivalents to these low- or zero-energy solutions; their energy consumption is explicitly clear, which makes comparison simple. However, the consequences of differing approaches to their maintenance are often not considered. If no maintenance is undertaken, preventative activities are not performed, which can result in frequent and long breakdowns, high levels of unplanned work and lost production and output. Conversely, too much maintenance performs preventative activities at a frequency that is greater than the optimum so that they add little or no value to the output of the product and squander precious maintenance resources.

Consider an air-conditioning system with a cooling capacity of more than 12 kW. Maintenance is mandatory under the EPBD yet the Chartered Institution of Building Services Engineers (CIBSE) has pointed out in its ‘Compliance costs’ campaign the process is not working as it should. CIBSE estimates that fewer than 5% of systems that requiring inspecting have been inspected. A poorly maintained AC system could be wasting a lot of electricity and money, and contributing unnecessary carbon emissions.

This is just one example of many and suggests that a maintenance risk assessment should be considered before a product is chosen. The consequences of poorly maintained products include a reduction in performance and safety, and an increase in costs and carbon emissions. If we are to meet our national carbon-reduction commitments then modern building services have to perform as efficiently as possible for as long as possible, and this approach must favour more traditional approaches to building services that utilise natural ventilation, daylight, and thermal storage.

Dr Benjamin Jones is a research engineer with Monodraught.

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