Your car air-con is consuming half your fuel in heavy traffic

Asian traffic!

After a recent visit to Jakarta, where I experienced serious developing city traffic congestion, I thought I would explore the fuel consumption impacts of this congestion using the transport calculator I developed for the EPA Victoria Greenhouse Calculator. I assumed a ‘small’ car (Corolla size), 10 km/h average speed, with stops every 50 metres and a Darwin climate.

The results are only approximate, as the model is fairly basic and changes in environmental and traffic conditions and driving techniques can affect the outcomes significantly.

The big message was that air conditioner usage was almost half of total fuel use under these conditions. Fuel consumption for movement was, surprisingly, not very different from typical Australian usage.

It seems that the reduction in aerodynamic drag from slower speeds may offset the long periods of idling and inertia effects of frequent stops and starts from low speed.

A well-designed hybrid (e.g. a Prius) used half as much fuel overall and saved two-thirds of fuel used for movement. The large savings reflect the potential to recover and reuse a lot of braking energy from the stop-start driving, and the higher efficiency of the Prius engine.

A focus on optimum car air conditioner efficiency and the thermal performance of the car body could save a lot of fuel! High efficiency air conditioners and refrigerants with evaporative cooling of the condenser— which could be retrofitted—could help a lot. So could a light colour or ‘cool roof’,

or insulation of roof, shading (e.g. the old ‘tropical‘ roof used on 4WDs) and effective heat-reflective coatings or shading of windows. Some of these options could increase aerodynamic drag when a car finally escapes the congestion, though, so careful design is needed.

This looks like fertile ground for research into new cars and their air conditioners, and retrofit measures.

Of course, improved urban planning, effective public transport and electric bikes would reduce the time wasted (and productivity lost) trapped in traffic and cut air pollution too.

Alan Pears, AM, is one of Australia’s best- regarded sustainability experts. He is a Senior Industry Fellow at RMIT University, advises a number of industry and community organisations and works as a consultant. This story was first published in Renew magazine. Reproduced with permission of the author.