The air-conditioning conundrum

Published:  07 May, 2007

MBS 07-05 comment target is 20 to 22 cm

Adapting to the climate change in countries like the UK where some buildings require air conditioning and some areas require air conditioning more than others implies that more air conditioning — or, at least, some approach to reducing overheating in buildings — will be required in the future.

On the other hand, mitigating climate change by reducing emissions of carbon dioxide into the atmosphere equally clearly implies not adding to the burden by installing more air conditioning.

Adapting and mitigation are just two responses to climate change. The third is behaviour, which can also have a significant effect on carbon emissions by accepting or tolerating different levels of comfort and through simple actions such as not using energy unnecessarily. Simple changes in fashion are also possibilities, such as breaking away from the suit-and-tie culture whatever the weather. Walk round any town or city to see the proof.

But does air conditioning deserve its image as a serious contributor to global warming? The use of air conditioning is scorned by many environmentalists, but the simple fact is that its performance has improved by over 50% in the last five years or so with developments in vapour-compression air conditioning. That means being able to double the installed air-conditioning base without adding to carbon emissions. However, we are looking to reduce carbon emissions... .

Integrated thinking provides the key to maintaining comfort in buildings and reducing carbon emissions. Tucked away in the latest Building Regulations, for example, is an explanation of the potential of absorption chillers for reducing carbon emissions. Driven by waste heat from CHP plant (trigeneration), absorption chillers have over 85% lower carbon emissions than vapour-compression air conditioning using electricity. The trick is to design developments to enable the benefits of CHP for generating electricity to be added to their benefits for providing heating and cooling. That, indeed, is what Woking Borough Council started to do in the late 1990s and what now forms a fundamental plank of the London Climate Change Agency.

‘Conventional’ air conditioning using heat-pump technology also has the capability to reduce carbon emissions if an holistic view is taken of servicing a building. For space heating, heat-pump technology is 500% more efficient than traditional boiler plant. That level of saving leaves headroom for using the same equipment to cool the same building in summer.

While designing buildings to use less energy is vital to reducing carbon-dioxide emissions, there will remain the need to use energy to trim the internal environment — which is what building-services engineering is really about.

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