Personal air conditioning: A low energy option for keeping your cool

‘Air conditioners alone could account for up to 40% of the world’s remaining global carbon budget by 2050’
We’re now at the end of yet another hot summer. In recent weeks I have met quite a few people who have decided now is the time to install an air-conditioner. They have found this summer has been so hot that fans can no longer keep them comfortable in their homes.
This story is likely to be replicated millions of times over the coming decades as the world’s population adjusts to living on an increasingly warmer planet.
We are all aware of the strains household air conditioning puts on the National Electricity Market (NEM) on hot summer days in Australia, but this is just one element of a global problem.
Alarm bells are beginning to ring about the global climate change impacts of air conditioning – the quote at the beginning of the article indicates the magnitude of the problem.
Late last year a broad-based international grouping of Government and Non-Government parties established the Global Cooling Prize in an effort to stimulate significant improvements in the efficiency of air conditioners.
The Global Cooling Prize is focused on producing more efficient air conditioners for space cooling. This is a very laudable goal, but I believe this should not be pursued at the expense of other viable options. In particular, I am interested in exploring the enormous energy reductions that can be gained if we use personal, rather than space, cooling.
Personal Cooling
I have been a keen supporter of personal heating and cooling for a few years now. The energy savings when you heat/cool people, rather than spaces, can be quite startling. Why do we conventionally heat or cool all the air in a house simply to provide thermal comfort for often only one or two people?
I started my new low energy life by testing a range of personal heating devices in our home over one cold Canberra winter. Personal heating, especially using heated clothing, is now enabling us to make some quite amazing savings in our household heating energy use.
I have written about some of my early work in this area in a previous One Step off the Grid article. Can we replicate these energy savings for cooling?
Clearly personal cooling is much more of a challenge than personal heating. With current technology I can’t practically walk around my house with a mechanical cooling system integrated into my clothing.
Nevertheless, this past summer I determined that I would trial some personal cooling devices to see how they work. In particular, I wanted to see whether personal cooling devices provide good thermal comfort and I also wanted to understand the potential energy/carbon benefits. I tested two quite different personal air conditioners.
Ultra-low energy coolers – 10W devices
The first personal cooler I bought was an evaLIGHT USB personal air cooler (see photo). You can find quite a number of devices on the internet which look like this, but they vary quite markedly both in capabilities and cost (the price range appears to be roughly $40 – $300).

The one thing in common is that they are all USB devices and therefore operate at a maximum power of around 10W.  All these devices are evaporative coolers and therefore they are really only effective in dry climates (say a relative humidity <50%).
One feature that I really like about our model is the variable speed fan – the device has a great user interface and it is possible to micro-adjust the fan speed.
When I ordered this I had no great expectations – how can you cool someone with 10W? I have been very surprised! It is a subtle appliance but in the right circumstances it delivers a beautiful cooling effect. We have mainly used our device to keep us cool when we are sleeping.
As illustrated in the photo, we have been placing it on one of our bedside cabinets and set it up to give us a very gentle cool breeze across our heads all night. We normally set the fan speed at about 25% full power – at this setting it is very quiet and uses less than 5W. This is seriously low energy cooling!
We have found that we can easily move the cooler around the house (using a standard USB power bank) and it has also proved very useful in giving one person a nice breeze when they are sitting at a table say eating a meal or doing homework. In this mode, to be effective the unit needs to be placed right next to the person being cooled.
Low energy refrigerated air conditioners
The second device, called the Close Comfort, is very different (see photo). This is a portable refrigerated personal air conditioner but it has a revolutionary design that challenges established thinking. Instead of expelling its warm air outside like a conventional air conditioner, it releases this into the same room as the person being cooled.

It can do this because it is designed as a personal device which generates a cool zone around an individual – it is not designed to cool a whole room.
This device works very well. If you sit in front of it, the cool air feels the same as if it were coming from a conventional air conditioner. While the Close Comfort exhausts a very noticeable stream of warm air at the back of the machine, this does not appear to heat up a room to any perceptible extent provided it operates in a well-ventilated space.
At the settings we’ve been using, it consumes about 255W of electricity. The amount of heat it is emitting into a room is therefore not dissimilar to that emitted by other commonly used domestic electrical appliances.
The big advantage of this type of portable AC is that its rated power capacity is about 1/5 of that of a conventional portable device (300W cf 1,500W). There is also no need to use the very cumbersome flexible exhaust pipes which restrict where the conventional portable space cooling devices are able to be located.
The Close Comfort was invented by an Australian engineer, James Trevelyan, from Perth. Professor Trevelyan developed the concept over some years based on his experience of working, and having trouble sleeping, in the heat of Pakistan.
The air conditioner is now being marketed in four countries in Asia, in addition to Australia. The published feedback suggests it works really well in very hot climates.
The Future
For certain applications space cooling will continue to be the best solution, but in many cases personal cooling provides more than sufficient cooling (and indeed can be more thermally comfortable). The energy savings of adopting widespread personal cooling could be massive.
Professor Trevelyan has indicated that he will be entering the Close Comfort in the Global Cooling Prize. I hope this alerts the world to the benefits of cooling targeted on the person.
Dave Southgate retired from the public service in July 2012 after a 31 year career as an environmental specialist in the Australian Government Transport Department and then as the Australian Government representative on the United Nations International Civil Aviation Organization (ICAO) Committee on Aviation Environmental Protection (CAEP). Since his retirement he has expanded his climate change interests and has become fascinated with renewable energy.

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