Extreme summer temperatures have sent demand for air conditioning soaring, yet building-systems expert Arno Schlüter regards it as a solution only in special cases – and worse, it can exacerbate the problem. For the majority of workplaces, warehouses and residences, other measures are already effective and more sustainable.

In recent years, the debate about air conditioning (AC) has flared up on cue every summer. Given that heatwaves are becoming longer and more frequent, that is hardly a surprise. In Switzerland, heat already claims more lives than road traffic. Yet these discussions often miss the bigger picture. There is much we can do to avoid the widespread rollout of air conditioning – and plenty of good reasons for doing so. Modern AC units have become considerably more efficient, but they are still noisy and consume a great deal of electricity. Manufacturing them is energy-intensive, and the refrigerants they use are usually harmful to the climate. Portable air conditioners, which have sold in huge numbers this summer, are particularly inefficient.

AC systems also have a side effect that is often underestimated: they expel heat from indoor spaces into the surrounding environment, intensifying the very urban heat islands they are meant to mitigate. In Singapore, where I also conduct research for 15 years, narrow alleyways tend to become unbearably hot as a result. Even if all AC units ran on renewable electricity, this problem would remain unresolved.

Rethinking comfort without air conditioning

In our climate, much can already be achieved with simple yet effective measures such as shading, night-time ventilation and using fans to move the air. Often, the demand for lower air temperatures through air conditioning is based on a limited perspective on human comfort in buildings. In fact, direct sunlight, temperatures of the surfaces and the movement of air in a room are equally important factors. As research demonstrates, a fan, for instance, can help people feel comfortable even at an air temperature of 28 degrees Celsius.

In addition to building-level measures such as systematic shading, night-time ventilation, adjusting our daily routines – at work and at home – and wearing clothing suitable for hot weather can increase comfort. That is why the conversation should not primarily be about air conditioning, but how we achieve human comfort in buildings. This requires some rethinking. Time and again, I see windows being thrown open in the middle of the day, even though by that point it is almost impossible to get heat out of the building. And many people are still wary of fans because they fear catching a cold due to the moving air.

Efficient cooling for new and existing buildings

Although passive measures such as the ones mentioned above should be at the forefront, for new buildings, efficient building systems such as ground-coupled heat pumps that use the ground as a heat sink allow for efficient cooling. Heat removed through cooling can be stored in the ground and used again for heating in winter. Also possible is what is known as free cooling: in Zurich, this principle is used to draw cold water from the lake to cool large office buildings along the shore, without significantly warming the lake. The challenge is greater with existing buildings, particularly rented spaces, where comprehensive retrofits are generally not feasible at short notice and for tenants. Here, shading, night-time ventilation and fans allow for higher levels of comfort using little energy.

A coordinated approach to heat protection

Heat protection, however, is a broader societal challenge that calls for a coordinated approach centered around climate-responsive urban design, infrastructure and green spaces. Long-term infrastructure such as district cooling and urban design measures are important, but will come too late to help this summer or the next. Tried and tested measures such as the ones mentioned above can provide immediate relief for many. Alongside these, we need well-communicated heat plans that identify public amenities and facilities where people can go to cool down in their vicinity and free of charge during a heatwave.

Air conditioning will nevertheless become more important. Used selectively, it makes sense wherever lower air temperatures are essential: in hospitals, care homes and schools, for example, and to protect the vulnerable part of the population. But a future in which every home, office and warehouse is air-conditioned is not the direction we should be taking. To make increasingly hot summers bearable for all without jeopardizing our climate targets we need coordinated, selective and targeted measures.

This article was originally published by ETH Zürich and is reprinted here with permission. Read the original version at ethz.ch.

Portrait image credit: Kilian Kessler / ETH Zurich