I am so thankful I don’t have to work all the time in an air-conditioned office building. Especially since Covid-19, our entire Close Comfort team works part of the time at home. We’re happier and feel healthier too.
Of course, I have a Close Comfort personal air conditioner with me. Our team members each have at least one at home as well.
Lee Kuan Yew, honoured as Singapore’s founding father, loved to tell everyone how air conditioning enabled today’s Singapore by providing a comfortable working and sleeping environment. However, there’s a dark side that comes with 20th-century air conditioning systems.
It is well established that people who live most of the time in constant temperature air-conditioned buildings lose their natural thermal acclimatization. As a result, they only feel comfortable at about 23 °C.
Recently I hailed a Singapore cab and climbed into the shiny black refrigerator on wheels, feeling so glad I remembered to bring a cardigan tied around my shoulders. The driver exclaimed, “Ah, it’s so hot today, la!”
“What’s the temperature?” I asked.
“33, it’s really hot, la”.
“But, yesterday it was 32”.
“Yeah, 33, it’s so hot today, la!”

Studies on thermal comfort in naturally ventilated buildings reveal that people adapt to local temperature, for example, by wearing appropriate clothing. Most people living in these buildings feel comfortable in a wide range of indoor temperatures, from as low as 10 °C to 33 °C. A recent study in China provides a good example: people acclimatized to hot and humid conditions felt comfortable at 33 °C and 70% humidity, and only mildly uncomfortable at 37 °C.
However, people who live in mechanical ventilated buildings soon lose their natural adaptation and prefer a constant temperature, all year round.
Now we know the consequences only too well: the sick building syndrome is no joke. Many people experience acute discomfort with headaches; eye, nose, or throat irritation; dry cough; dry or itchy skin; dizziness and nausea; difficulty in concentrating; and fatigue, according to the US Environmental Protection Authority.
Worse, the advent of mechanical heating and air conditioning has enormously increased the construction and running costs of modern buildings and now accounts for a huge proportion of energy consumption.
How did we get to this point?
Well, it turns out that air conditioning, even for engineers, is never simple.
I should know. I have been developing Close Comfort personal air conditioners for 14 years. From time to time I would think of improvements, only to find from experiments that they made the performance worse. I have learned that air conditioning technology is often counter-intuitive. For example, one of my students thought we needed to replace a cross-flow fan drawing a gentle stream of air through a heat exchanger. He set up four powerful computer ventilation fans blowing air directly onto the heat exchanger, thinking this would improve the performance. Instead, measurements showed a 20% reduction in performance!
To help make air conditioning practical, engineering specialists formed the American Society of Heating, Refrigeration and Air-Conditioning Engineers, ASHRAE. Through the society publications, they shared knowledge in the form of standards to help engineers design reliable air conditioning systems more easily, reducing the cost. Unfortunately, ASHRAE based their standards on American 1960s business executives’ notions of comfort while wearing suits. By the 1970’s, the air conditioning industry was positioning ‘comfort’ as a product to be provided by their machines, regardless of building design. Architects, freed from the constraints to design buildings that were naturally comfortable, created concrete and glass towers that relied on air conditioning to be habitable.
In the early 2000s, ASHRAE committees started to recognise the global influence of their institution and revised their standards to allow for climatic differences. A new edition of their standard, ASHRAE 55, recommended slightly warmer temperature settings for buildings in hot climates. However, the Singapore air conditioning standard still advocates only a slightly warmer fixed indoor temperature range 23 – 25 °C with a maximum of 65% relative humidity. American businessmen wearing shirts rather than suits!
With the benefit of research, we now know that a more appropriate Singaporean setting would be higher. People who allow themselves to adapt naturally to the local environment feel comfortable at 26 – 28 °C, even higher during the day.
However, many Singaporeans live cocooned in air-conditioned homes, cars, trains, buses, shopping malls and offices, and so have lost their natural acclimatization to heat. Building air conditioning systems are tricky enough to fine-tune to their designed temperature setting: changing the temperature is an expensive and risky undertaking. In addition, everyone has their personal preference, especially women who seem to have more variation in comfort perception than men. Also, air emerging from supply ducts in the building has to be colder than the desired temperature so if you’re sitting in the inlet air stream you will likely feel too cold.
The new Design and Environment building at the National University of Singapore demonstrates a new design paradigm for large public buildings in tropical climates. The air conditioning system delivers warmer air than prescribed by the local standard and uses overhead ceiling fans to create enough comfort, even for chill-adapted Singaporeans. This saves 30-40% of the cooling energy requirement, enabling roof-top solar electricity to provide more than enough energy to run the building, with large running cost savings. However, a different approach is needed for residential apartment buildings with relatively small roofs.
Fortunately, for homes, there is a new idea enabling us to take more control over our environment, health, and the household budget: personal air conditioning.
I originally developed Close Comfort as a cost-effective way to keep cool in Pakistan and other countries. The summer heat there is far fiercer than Singapore. My bedroom where I stay in Islamabad remains at about 40 °C indoors, day and night, for months at a time through the summer. Electric power is often unreliable or intermittent, so I designed Close Comfort to run on battery backup power when needed.
A personal air conditioner is extremely simple: a tiny fridge with a fan that blows cool air at one or more people nearby. The idea is to cool people, not buildings. Bricks and concrete don’t need cooling: only people (and perhaps pets). 300 Watts is enough to keep two or three people cool as cucumbers, especially at night with a spacious bed tent that also keeps out mosquitos.
Now the personal air conditioner is emerging as a far more affordable, comfortable, convenient and healthy alternative to traditional building air conditioning.
Traditional building air conditioning requires everyone to put up with having to live with the same temperature. Doors and windows to be closed so stale room air is constantly recycled, especially with split air conditioners.
With a personal air conditioner, it’s possible to enjoy living in healthy fresh air with a cool micro-climate to suit our individual preferences.
It is the cooling equivalent of a camp fire: move it closer to feel cooler.
One advantage of personal air conditioning is that people are exposed to warmer air when they move from time to time. This may be promoting natural physiological adaptation to heat.
Already some of our users are reporting that they feel less discomfort with heat than before. They seem to be rebuilding their natural adaptation so they need less air conditioning to keep cool. Other people have told us how their eye and throat irritations, itchy skin conditions and fatigue they felt with traditional room air conditioners has faded or disappeared with their personal air conditioner. We don’t yet have the kind of research budget that would enable us to conduct systematic trials, but these observations fit in with the available science. For example, physiological research on heat acclimatization is showing significant health benefits from moderate heat exposure, improving cardio-vascular health.
While there is still debate among the scientific community, we have seen how traditional air conditioning can promote the spread of Covid-19 in buildings. Airborne virus transmission is now thought to be a major infection risk. Fresh air living is back in fashion, and is healthier for everyone.
Developing Close Comfort has been a fascinating journey for me, personally. Apart from cooling technology, I have had to extend my learning into psychology, physiology, architecture, marketing and online commerce. Every time I write articles like this, I find I have to learn a little more, and understand new aspects of the ways that people experience life and happiness. Reading enthusiastic product reviews brings a smile to my face, however witnessing the smiling faces of grateful users brings the greatest satisfaction.
I had little idea when I first created Close Comfort what the future might hold. Whatever the differences in the ways that individuals perceive comfort and their ability to adapt naturally, we know that human mortality increases exponentially above about 35 °C. I learned recently that many cities are warming at up to three times the rate of climate change, thanks in part to proliferation of traditional room air conditioners. Personal air conditioners might just be one of the solutions that enables people to be healthy and comfortable while helping to keep our growing cities cooler.