Many remarkable statistics surround the use of air conditioning (AC) systems. The International Energy Agency (IEA), for example, expects global energy demand from AC systems to triple by 2050, making them one of the leading energy consumers. By then, air conditioners alone will demand electricity capacity equal to the combined current electrical load of the United States, the EU and Japan.
According to the IEA’s report – ‘The Future of Cooling’: “The global stock of air conditioners in buildings will grow to 5.6 billion by 2050, up from 1.6 billion today, which amounts to 10 new air conditioners sold every second for the next 30 years.”
But why this dramatic growth? The irony is that, arguably, higher AC sales are driven by climate change – particularly global warming – which is itself caused, at least in part, by the increasing use of AC; it’s a vicious circle. This begs a fundamental question: are there more environmentally friendly alternatives to air conditioning?
The answer is a qualified ‘yes’ (see box out for some of the main contenders and how they work). Perhaps the most propitious alternative to AC is evaporative cooling, the conversion of liquid water into vapour using the thermal energy in the air, resulting in a lower air temperature.
Evaporative cooling is, according to Sarah Higgs-Clarke, sales manager for UK & Ireland at Seeley International, fast becoming the best option for cooling large industrial and commercial spaces. She says it offers several advantages over traditional air conditioning: “First, running costs of evaporative coolers are fairly low as these units only need water and electricity to run. In a location like Birmingham, running costs are reduced up to 84%, if we consider a comparison with a refrigerated AC unit. That all adds up to very responsible environmental and energy saving characteristics. In the same city, adopting an evaporative cooler can reduce up to 87% carbon emissions.”
Moreover, Higgs-Clarke adds, the air inside the building is never recirculated, as evaporative coolers only draw fresh air from outside. “Stale air needs to be extracted by means of extract fans or keeping doors and windows open. For this reason, evaporative cooling can be a great solution to improve indoor air quality, for example, in production areas where fumes and germs are involved.”
The performance of an evaporative cooler depends on outside temperature and relative humidity so it’s difficult to guarantee a specific indoor temperature set point at all times. For this reason, evaporative coolers are often adopted in commercial or industrial spaces, where comfort cooling is acceptable.
Higgs-Clarke concludes: “No matter how hot it gets outside, evaporative coolers use the same amount of power and still deliver 100% fresh, cool air inside. This is in direct contrast to refrigerated systems, which require increasing amounts of power as outside temperatures rise.”
One alternative approach to standard air conditioning is to take advantage of ‘free cooling’, where the mechanical system runs for as short a time as possible by using naturally occurring cool air.
Josh Emerson, who works on building efficiency and occupant wellbeing at indoor environment company Swegon UK & Ireland, says there are many applications in the UK that could take advantage of naturally low air temperatures (the average ambient temperature in the UK is a miserly 10°C) to dramatically reduce the amount of energy used.
“Any process where there is demand for chilled water on a constant basis throughout the year could potentially benefit from free cooling chillers,” he says. “This type of technology uses the naturally occurring cool air to pre-chill the water before it reaches the refrigeration circuit and so reduces the amount of work the compressors have to do. This has major positive implications for energy consumption and extending the life of the equipment.”
Water supplied at 10°C would normally result in warm water returning to the chiller at about 15°C. Therefore, as soon as the ambient temperature falls below 15°C, the chiller can switch into ‘free cooling’ mode.
Free cooling and AC alternatives are all very well, says James Henley, product development manager at Daikin Applied UK, but those arguing for them may not be fully aware of the progress the AC industry has made in recent years, tackling global warming impact and reducing carbon emissions.
“Technology improvements and the odd breakthrough have played their part, but the ability to introduce incremental changes is, arguably, the most important strategic step towards a net zero future," James Henley, product development manager at Daikin Applied UK
Henley believes the industry has made giant strides towards a ‘circular economy’ approach that will minimise waste and pollution by keeping products and materials in use as much as possible. This includes an ambitious programme to reduce the consumption of new refrigerant gases by tens of thousands of kilograms every year.
Reclaiming gas from installed systems for re-use is a highly sustainable exercise because it makes use of material that has already been produced and reduces carbon footprint because it helps to prolong the life of equipment, he says. “It is also very much in line with the total lifecycle approach that has led to the adoption of energy saving technologies, such as inverters and heat recovery, that are helping to reduce our environmental impact.”
|Box: Cool alternatives to AC|
Solar shading systems – designed to mitigate heat gain from the sun in buildings, these typically comprise fixed brise soleil (sun breaker) or controllable louvres manufactured from aluminium, textile or glass fins in vertical or horizontal configurations. Solar louvres are designed to control airflow in and out of buildings. They can control the entry of air, as well as providing ventilation while protecting against the elements. They can be used as a temperature control device to reduce exposure of occupied spaces in buildings to direct sunlight as either basic static units or with mobile controlled vanes. Although they can help mitigate higher indoor air temperatures, they can’t provide the ventilation air required in occupied buildings, says Peter Dyment, technical manager of filter supplier Camfil: “Careful cost analysis would be needed to justify the decision to install this type of unit.”
Natural ventilation – this involves supplying air to, and removing air from, an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces. As used by nature in structures like termite mounds, the varying temperature of air causes air currents that can be used to ventilate buildings. However, says Dyment: “Although energy efficient, this ventilation method is not effective enough for use in urban locations that suffer from traffic air pollution and other combustion process pollution using fossil fuels. Fine combustion particles (PM1/PM2.5 and nitrogen dioxide) usually need to be reduced in supply air from outside, usually by air filtration, so it can be safely introduced into the building.”
Evaporative cooling – modern evaporative coolers are typically installed in the roof or on the side of a building and work using only water and electricity. A motor pumps hot outside air through water-soaked cellulose pads. As the air blows through the pads, the water is evaporated and the heat in the air is absorbed: this lowers the air temperature. A fan then pushes the cool air through a ducting system, which lets the cool air inside the whole building.
Fans – these can circulate cool air around a building, but this assumes that the cool air it there in the first place. In fact, most air fans don’t actually do much in terms of ‘cooling’ the air. They simply help circulate the air around you, which helps give you the sensation that you are being cooled off.
Other methods – alternative ways to reduce energy consumption but deliver the required level of ventilation using clean healthy outside air can also be devised. Apart from employing free cooling (as discussed in the main article), for example, it is possible to use damper systems to intelligently control air flows based on real-time air pollution levels, building occupancy and ongoing activities. Life cycle costing can be used to evaluate design options. One example system comes from manufacturer Airflow Developments.