This summer’s heatwaves across the world have focused minds on how we can keep cool in the face of record high temperatures.
Air conditioning and refrigeration are the obvious solutions to keep ourselves, food and other products such as medicines cool – but they are also a growing environmental concern, one that is often overlooked given it is counterintuitive that cooling could lead to warming.
The United Nations Environment Programme says that “there are an estimated 3.6bn cooling appliances in use globally today, and that number is growing by up to ten devices every second”.
This growth is set to increase the sector’s greenhouse gas emissions dramatically, further warming the planet. Air conditioners are a double burden. Not only do they require significant energy to run – in most cases, they use hydrofluorocarbons (HFCs), extremely potent greenhouse gases that are hundreds of thousands of times more powerful than CO2.
Carbon emissions from space cooling more than tripled from 1990 to 2020 and, without policy intervention, emissions from air conditioning and refrigeration are projected to rise 90% above 2017 levels by 2050, UNEP says.
Demand for cooling can be reduced by simple, non-mechanical measures – from designing buildings to have plenty of shade and ventilation to reflective window coatings and insulation. Smart thermostats can turn cooling off when no-one is in the room and turn it up when more people are present.
The best air conditioners on the market are 50% more efficient than the worst, so there is plenty of room for innovation to make devices use less energy.
It is also possible to use CO2 as a refrigerant instead of HFCs. CO2-based cooling systems work differently to traditional systems, where typical refrigerants cool the air around them because they evaporate at around -15C. In a CO2 system, the gas is compressed and then, when it expands, it absorbs heat.
And when it comes to refrigeration, a number of start-ups are working with food coatings that improve shelf life and reduce the need for refrigeration, as well as AI-based sensors for air conditioning and refrigeration.
While air conditioning is commonplace in the warmer regions of the world, in countries such as the UK, where extremely hot days have been rare, few homes have air conditioning. And although temperatures are set to rise, temperate regions are still unlikely to have enough days hot enough to justify air conditioning in every home. One solution ties in well with the need to decarbonise heating – homeowners can buy heat pumps that are able to provide cooling in the summer as well as warmth in the winter.
Like heating, cooling is more efficient when done at scale and just as places like the Nordic countries have district heating systems, there are district cooling systems, too, in places ranging from Finland and France to India and the UAE.
These systems pipe chilled water from a central point to buildings, where the water is fed into building cooling systems through a heat exchanger, before returning to the cooling plant to be chilled again. District cooling systems can cut energy use for cooling by 50% compared to individual building systems, reducing strains on the grid and emissions from air conditioning use. They also make it easier to ensure that refrigerants do not leak into the atmosphere.
Another approach is to use evaporative cooling, which cools air by extracting water from it, without the need for compressors or refrigerants. Blue Frontier, one of the winners of the 2022 BNEF Pioneers award, uses cheap renewable energy at times of high supply to remove water from a salt solution, then pumps the concentrated solution around buildings when cooling is needed. Contact with the air in the building draws water from the air, cooling it. This process can cut energy use by 40-80%.
Meanwhile, in India, Godrej’s evaporative cooling units are fitted with a small solar panel to further reduce electricity consumption and companies such as Kraton are developing membranes that increase the amount of moisture removed from the air.
Prof Toby Peters, an expert in the “cold economy” at the University of Birmingham in the UK, says that we can also use the large amounts of low-grade waste heat from industry, for example, to enhance cooling with the help of absorption chillers, which refrigerate through a sudden change of pressure, driven by heat.
And he says that the cold used to transport liquefied natural gas (LNG), which is cooled to -162C for shipping before being heated to turn it back into gas, could be transferred to buildings or district cooling systems at its destination rather than being wasted.
In short, while more cooling will be unavoidable in our warming world, but it must be as efficient as possible. Innovation can provide the solutions.