How cities can stay cool on a warming Earth

Date: 20 August 2019

Presentation: Air conditioning, a necessity of modern life, is unique because it perpetuates the very problem it solves. As the planet warms and as it prospers, more people demand air conditioning. Traditional systems consume a lot of energy, which requires burning fossil fuels. That leads to greater carbon dioxide emissions, further warming the planet and intensifying the demand for air conditioning.

Traditional air conditioning systems are inefficient by design. They are designed to meet peak loads, such as a fully occupied building on the afternoon of the hottest day of the year — even though that load rarely occurs. Most residential buildings are empty during working hours, and most office buildings are vacant at night. Fortunately, a more effective alternative for areas of high-density demand exists: district cooling. District cooling, which is the flip side of the district heating systems in use in the Nordic countries, is not a technology but rather an approach. It treats the provision of cooling as a utility and uses a single networked system to cool multiple buildings, such as an apartment tower, an office building, and a shopping center.

District cooling has many virtues. It is far more energy efficient than traditional systems and more cost-effective for customers. District cooling reduces peak power capacity requirements, because it does not need to meet large spikes in demand. Nor does it require radical advances in the underlying technology, because it is already in use today, primarily in the countries of the Gulf Cooperation Council (GCC), which comprises Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates (UAE). In fact, in countries such as Qatar and the UAE, district cooling already accounts for between 15 and 25 percent of cooling capacity. Most importantly, the district cooling approach holds the potential for significant savings. Our analysis shows that using district cooling where appropriate to meet future additional cooling demand could reduce the total energy required for cooling by 16 percent, leading to more than US$1 trillion in energy savings worldwide through 2035.

Growing demand
A recent report by the International Energy Agency (IEA) projected that global demand for air conditioning will triple over the next 30 years because of growing populations and rising prosperity. The world’s population will increase by about 1 billion, reaching a total world population of 8.7 billion by 2035. Most of that growth will occur in places with hot and humid climates. A burgeoning middle class and rising living standards in large developing markets such as China, India, and Indonesia mean that more people will want air conditioning, and they will have the means to pay for it. Urbanization increases demand. Appliances and machinery generate heat and increase the local temperature, creating urban “heat islands” that are much warmer than the surrounding rural areas. These factors are compounded by global warming.

Using district cooling where appropriate to meet future additional cooling demand could reduce the total energy required for cooling by 16 percent, leading to more than US$1 trillion in energy savings worldwide through 2035.

In all, these trends will push the total number of cooling units to rise by approximately 57 percent, from 4.4 billion in 2019 to 6.9 billion in 2035. More than half of this increase will come from lower-efficiency residential split air conditioners, which involve an external component that chills water and an internal component that blows cool air. However, the power capacity required for cooling will increase faster than the number of units, rising by 78 percent by 2035. This means that if current systems remain the dominant means of providing cooling, the global energy used for cooling will nearly double.

Given these challenges, the IEA has called for increasing the efficiency of traditional air conditioning systems through interim measures such as minimum energy performance standards, better building designs, and stricter building codes. Although improved energy efficiency is necessary, it likely will not be sufficient on its own. This approach is akin to focusing on the fuel efficiency of gas-powered cars, rather than considering newer options such as electric cars.

District cooling offers a smarter and more effective approach. In district cooling, a single centralized plant pushes chilled water through a distribution network to multiple buildings, which can tap into it according to their needs (see “Cool design: How district cooling works”). Each building has its own heat/cooling exchanger and uses the chilled water to provide cooling, as needed, to different types of occupants with different demand schedules: offices during the day, restaurants in the evening, apartments in the early morning. This design leads to reductions in power consumption of 60 to 80 percent compared with the average conventional cooling system. District cooling also offers other benefits, including reduced carbon dioxide emissions, more reliable cooling for occupants, and increased real estate values (because buildings can use their rooftops for purposes other than housing air-conditioning equipment).

by George Sarraf, Christopher Decker, and Jad Moussalli, Strategy and Business