Authors and contributors
IEA (2019), "Tracking Buildings", IEA, Paris https://www.iea.org/reports/tracking-buildings
2018 was an exceptionally hot year in many parts of the world, and energy used for space cooling was an estimated 5% higher globally than in 2017. More than 1.6 billion air conditioning units are now in operation around the world, making space cooling the leading driver of new electricity demand in buildings.
Global AC sales rose an estimated 15% between 2017 and 2018 as a result of rapid growth in AC ownership in emerging economies as well as extreme heat events in 2018.
In China, AC ownership and cooling demand grew substantially in the last decade, and China is now home to more than one in three ACs worldwide. There were nearly 350 million more units in use in China in 2017 than in 2007, and summer heat waves across China in 2018 pushed that number up further.
Other emerging economies are mirroring this rapid growth, particularly Brazil, India, Indonesia and Mexico, which together represented a market of around 100 million AC units in 2018.
Growing cooling demand is impacting power generation and distribution capacity, especially during peak demand periods and extreme heat events. Space cooling in buildings is responsible for 50% or more of residential peak electricity demand, as demonstrated by the daily peaks in Beijing during the summer heat wave of 2017.
CO2 emissions from space cooling are also expanding rapidly – tripling between 1990 and 2018 to 1 130 million tonnes – despite improvements in average AC performance and power sector carbon intensity. Local air pollutant emissions related to higher cooling demand are also on the rise.
High-performance ACs already available on the market today could cut cooling demand in half, reducing power sector impacts.
The average seasonal energy efficiency ratio (SEER) of air conditioners installed globally increased from 3.5 in 2010 to around 4 in 2018, yet data from product registries indicate that this is still far behind the performance of more efficient options available in the market. The typical efficiency of units being sold in major cooling markets is not much better than the available product minimum.
The average SEER of AC units sold in the fastest-growing markets, such as China and India, is typically under 3.5. Yet products available in those same markets – often at comparable prices – can have SEERs that are 50‑70% better. Best available technologies are often twice as efficient, if not more.
Recent market trends suggest that substantial energy efficiency gains could be tapped into quickly. For instance, Carrier launched a new AC unit in early 2018 with a SEER of 12.3 – three times the market average efficiency of residential AC units bought in the United States in 2017. While this level of efficiency is still unlikely to reach the market in most countries, it illustrates the performance potential for cooling equipment.
Without major efficiency improvements to cooling equipment, electricity demand for cooling in buildings could increase by as much as 60% globally by 2030 – 40% higher than in the SDS.
To be in line with the SDS, the average efficiency of new ACs sold would need to jump from a SEER of around 4 today to 7 or higher in 2030 – a target that is not impossible but would require strong market signals and greater country collaboration.
Nearly 59 countries have proposed or already have minimum energy performance standards (MEPS) for ACs.
Morocco adopted AC MEPS in June 2018 and Kenya proposed them in October 2018, while in Rwanda new MEPS using United for Efficiency (U4E) model regulations are pending finalisation.
MEPS vary considerably across countries, however, and are generally weakest or absent in hot and humid countries where rapid AC demand growth is expected.
The Kigali Cooling Efficiency Programme (K-CEP) was launched in 2017 to raise the energy efficiency of cooling, and the Kigali Amendment to the Montreal Protocol came into force in January 2019. K‑CEP is working closely with partners in many countries to promote major energy efficiency improvements and sustainable cooling solutions, uniting philanthropic foundations, technical experts, international organisations and other partners.
In 2018 the IEA also launched the Kigali tracker under its Global Exchange Platform to work with countries and K‑CEP partners to track information on energy efficiency, refrigerants, investments and policies.
The deployment of solar cooling systems started around 2005, and the fastest-growing segment is distributed solar PV systems with storage (through chilled water or ice), particularly for small-scale applications.
Solar cooling is still a niche market, however, with less than 2 000 units deployed globally as of 2018. The Mediterranean region is the main market, although sales in the Middle East and Australia are expanding.
The first solar AC units able to adjust cooling capacity to the availability of electricity produced from solar panels were also commercialised in 2018.
With this technology, users can operate the AC units in renewable-only mode to adjust the cooling output relative to solar PV-produced electricity. Cold (thermal) storage with ice or chilled water can be used as well to meet cooling demand outside of solar production hours.
Governments can reduce the impact of rising space cooling demand by supporting building envelope technologies such as low-emissivity windows, and building-integrated solutions such as solar cooling systems to reduce the overall need for space cooling and to increase the share of renewable energy in space cooling production.
Energy-efficient AC units can dampen the impact of rapidly growing cooling demand. Greater effort is needed to expand and strengthen MEPS, with targets and requirements that progressively move AC energy performance towards the current best-available-technology level and set a course for continual improvement.
Countries can also support R&D efforts to foster innovative AC technologies, including those that use refrigerants with low global-warming potential. Incentives and support for market-based measures can also create economy-of-scale benefits to reduce upfront costs of energy-efficient products.
While efficient ACs will reduce the impact of cooling on electricity systems, more flexibility is needed to distribute electricity demand intelligently.
Governments can promote innovative business models and demand-response incentives to encourage the use of digital technologies such as smart thermostats and other improved controls that optimise the load distribution of energy demand for cooling.
Governments can also support industry in manufacturing smarter and more responsive AC options, including by helping small manufacturers gain access to digital solutions (e.g. smart chips for AC units).
Solar cooling could be instrumental to meet growing cooling demand, as integrated renewable and energy storage solutions (e.g. solar PV with ice-makers) could be used to meet cooling needs and be paired with demand-side management tools to reduce the impact of peak demand on electricity systems.
Governments can work with industry to deliver renewable cooling solutions, particularly to reduce the installed cost of these technology packages.
Improving AC energy efficiency will be critical to weaken cooling demand growth. While improving the efficiency of vapour compression technology is a priority, other high-efficiency solutions can also reduce the energy and environmental footprint of cooling.
Among the potential technologies, liquid desiccant evaporative cooling is an option that requires additional R&D to better understand its performance and the design requirements needed to support deployment.
Until recently, solar energy was too expensive to be used in most cases to directly drive air conditioning units. This is why solar cooling has not been developed beyond the R&D and demonstration levels; solar PV is especially rarely used for vapor compression devices. With the arrival of competitive solar distributed PV electricity, however, integrated solar PV cooling solutions are needed to take advantage of local electricity production.
Solar thermal cooling systems typically combine heat-driven ad/absorption chillers, desiccant evaporative cooling, solar thermal collectors and thermal storage (hot water tank, phase-change material [PCM] or ice storage). The temperature of the solar thermal system depends on system composition, ranging from 40‑70°C for traditional flat plate collectors with desiccant evaporative cooling, to 250°C for Fresnel collectors (a linear concentrating solar thermal collector) with absorption chillers.
In conventional AC systems, the sensible load reduces the temperature of the air until it reaches 100% relative humidity. The latent load then removes the moisture from the air, but this usually results in the air being too cold for thermal comfort, so it must be reheated using additional energy. Humidity (or rather the latent heat that humidity contains) is responsible for a large share of the cooling demand in many countries.
Solar thermal cooling systems with one solid/liquid desiccant wheel could reduce cooling demand significantly, as they do not require extra energy for reheating.
This technology, particularly suitable for hot and humid areas, cools and dries air using a liquid desiccant to simultaneously dehumidify and cool. Liquid desiccant cooling systems typically use liquid water-lithium as the sorption material and can operate on low-grade solar energy (i.e. lower temperatures), allowing for high density and less energy storage in the concentrated desiccant. Desiccants can dry the air without first cooling it to the dew point: when the desiccant is saturated with moisture from the air, solar thermal energy is applied to dehumidify it, ultimately providing air conditioning.
- Birmingham Energy Institute (2015), "Doing cold smarter", University of Birmingham, https://www.birmingham.ac.uk/Documents/college-eps/energy/policy/Doing-Cold-Smarter-Report.pdf.
- Weiss, W. and M. Spork-Dur (2018), Solar Heat Worldwide: Global Market Development and Trends in 2017, IEA Solar Heating and Cooling Programme, https://www.iea-shc.org/Data/Sites/1/publications/Solar-Heat-Worldwide-2018.pdf.