Beating urban heat at scale

Twenty-five metres underground, the chillers hum loudly. Gauges and control panels line winding passageways. A few workers mill about with earplugs and helmets.

This facility under the bay area in Singapore runs round the clock, chilling some 15,000 litres of water to near freezing point, and pumping it through five kilometres of pipes.

Video: Eco-Business/ Liang Lei.

On the other end of the pipes, at ground level, are about two dozen office buildings and luxury malls.

In one of them, the iconic Marina Bay Sands integrated resort, it is cool enough for sweaters.

Inside Marina Bay Sands. Image: Eco-Business/ Liang Lei.
Inside Marina Bay Sands. Image: Eco-Business/ Liang Lei.

The cold piped water powers the air conditioning systems in these properties, before being sent back underground to be chilled again.

This system of centralised cooling is called district cooling. Rather than individual air-conditioning systems for each building, these are bigger cooling systems that serve multiple properties and benefit from economies of scale.

This is because one big condenser, a machine that provides cooling power, uses less energy than multiple small ones. Running one condenser constantly at near maximum capacity is more efficient than running several which have to respond to changes in demand for air-conditioning.

SP Group senior engineer Tan Wee Bing on the benefits of district cooling systems. Video: Eco-Business/ Liang Lei.

District cooling achieves greater energy efficiency on a large scale, and such large energy-slashing innovations are essential in the pathway to net-zero emissions.

In tropical Singapore, where cooling on a large scale is essential but energy-intensive, district cooling is emerging as an especially promising technology in the country’s climate action.

Air conditioning accounts for a third of total electricity consumption in Singapore. Cost and inefficiency aside, the electrical consumption might also hamper the country’s climate goals, as it aims to reach net-zero by 2050.

The district cooling system at Singapore’s Marina Bay area helps to avoid over 19,000 tonnes of carbon emissions a year, according to local utility firm SP group, which designed and operates the facilities.

Although this district cooling system is the largest one built underground in the world, it was “designed to be invisible”, said SP group senior engineer Tan Wee Bing, who works on the Marina Bay plant.

“Nobody will know there is an industrial grade system underneath the Marina Bay district.”

Only the cooling towers of the Marina Bay district cooling system can be seen above ground, and they have been designed to fit in with the surrounding architecture. Images: Eco-Business/ Liang Lei.
Only the cooling towers of the Marina Bay district cooling system can be seen above ground, and they have been designed to fit in with the surrounding architecture. Images: Eco-Business/ Liang Lei.

SP Group is aiming to expand this project even further. In April, it announced that five new properties in Marina Bay, two new and three redeveloped, will be plugged into the network.

The new additions will bring the plant’s cooling capacity from about 55,000 to about 70,000 Refrigeration Tons (RT), which is equivalent to using about 250 megawatts of power, or the output of a small power plant.

The underground facility at Marina Bay, Singapore, has space for more chiller units for future expansion. Image: Eco-Business/ Liang Lei.
The underground facility at Marina Bay, Singapore, has space for more chiller units for future expansion. Image: Eco-Business/ Liang Lei.

Even so, the system is utilising only three-quarters of its maximum capacity, rated at about 340 megawatts.

This maximum capacity can be further expanded. The underground plant has space allocated for more chiller units.

“District cooling is the future of cooling,” Tan said.

Asia's urgent cooling challenge

Air conditioning is a double-edged sword for the fossil-fueled region.

Air conditioners lining a building in Kuala Lumpur, Malaysia. Image: Wikimedia Commons/ Tinou Bao.

The demand for air conditioning in Asia is skyrocketing as its population grows and moves into cities.

According to the World Bank, East Asia, along with Pacific countries, is the world’s most rapidly urbanising region with an annual growth rate of 3 per cent. Over 1.2 billion people, or half of the population in these areas, are already living in cities.

Economic opportunities congregate in urban areas, but so does heat. Concrete traps heat better than earth and tree cover, so city apartments in summer get hot in the day and stay warm at night – a phenomenon known as the “urban heat island” effect.

The issue is getting worse with climate change. Last August, a report by the United Nation’s Intergovernmental Panel on Climate Change found that Asian cities are among the worst victims of the urban heat island.

For example, India’s eastern metropolis Kolkata, home to 15 million people, has warmed by 2.6°C more than its surroundings between 1950 and 2018. Vietnam’s Ho Chi Minh area is 0.4°C hotter than its vicinity.

Places already prone to heat waves may get up to four more days per year of daytime temperatures high enough to limit outdoor work, which is measured at 32°C on a wet-bulb thermometer.

As cities warm up, many Asians, especially those in the middle class and with high disposable incomes, are buying air conditioning to keep cool. In Southeast Asia, electricity use for cooling increased over seven times between 1990 to 2017. In India, there could be a billion air conditioners in 2050, up from 30 million today.

Air-conditioning may prove to be more crucial with more extreme heat expected in the coming decades. But its prevalence also makes it much harder to tackle the root problem of climate change and high power consumption in the fossil fuel-powered region.

Data: World Bank.

A general urban heat island profile. Image: Adapted from Wikimedia Commons/ TheNewPhobia.

An office block in Hong Kong. Image: Wikimedia Commons/ Underwaterbuffalo.

Finding the spark

Garnering support for huge infrastructure projects isn't easy. Not with the steep upfront costs and technological know-how required.

Water pipes in the Marina Bay district cooling plant. Image: Eco-Business/ Liang Lei.

Using giant chillers to cool multiple buildings uses anywhere from 20 to 80 per cent less power than conventional cooling systems, according to accountancy firm PwC, making district cooling a potentially climate-friendly solution.

The spread of district cooling systems lagged behind a similar technology, district heating, by a few years, as by and large it had been more crucial to have heat in winter than cooling in summer.

The concept has its roots in the United States back in the 1880s, when refrigerant was shared among different cold rooms for storing food. Larger air conditioning systems using piped cold water in the 1960s formed the basis of the modern set-ups today, which quickly popped up across European and American cities. Middle Eastern cities, which face searing summers, have some of the biggest installations.

Further east, Japan was an early adopter, having installed a system at the Osaka World Expo site in the summer of 1970. Today, such systems are found in many of its major cities like Tokyo, Osaka and Sapporo.

South Korea had its first district cooling project in the 1990s, the same time Singapore started exploring the technology. South Korea now has 27 projects, while Singapore has five, with five more in development across the city-state.

The uptake of district cooling has been slower in many other parts of Asia, in part because of the price tag, which often goes into tens to hundreds of millions of dollars.

The initial few years will be “painful”, said Dr Chen Zhuolun, a senior adviser at the Copenhagen Climate Centre of the United Nations Environment Programme (UNEP). That’s because the cooling plants are usually built in tandem with the new buildings they service, which means that whatever has been shelled out for chillers and pipes will not be recuperated until the buildings are occupied and their owners start paying for air conditioning many years later.

Chen is part of a UNEP programme, ‘District Energy in Cities Initiative’, which facilitates the development of district cooling systems in developing markets. In his experience, interest in such projects can be sparked in a few ways.

In India, international organisations helped to kickstart the development of such systems. In 2015, UNEP had conducted studies to identify US$600 million worth of district cooling projects in the country. The International Finance Corporation (IFC) later participated in one of the pilot projects in 2017.

IFC inked another US$400 million deal with UAE-based district cooling firm Tabreed last year to develop projects in India. India now has a national cooling plan that prioritises district-scale projects and has at least 10 such projects running or under construction.

In China, district cooling started appearing in urban development plans largely due to chronic power shortages in the 2010s. The energy shortages were caused by rising coal prices that caused some power plants to opt to idle their turbines in the early 2010s. There was also a drought in 2011 that affected the supply of hydropower, and major cities like Shanghai had to ration electricity in summer.

“The government found out that if they continued developments in a business-as-usual way, in the next five years, there was no way they could get sufficient electricity without paying a lot of money for additional electricity supply,” Chen said.

In response to these challenges, energy-efficient district cooling projects were started in cities like Qianhai, in the southern Guangdong province.

“In China, when you have one successful business case or technical trial, then a lot of other cities will start emulating the efforts.” Chen said. Today, there are about 100 district cooling projects across the country.

Singapore’s SP Group is in the Chinese market too. It runs the district cooling plant at Raffles City Chongqing, a series of tower blocks housing malls, offices and homes built by another Singapore firm CapitaLand.

Foo Yang Kwang, SP Group's chief engineer, said that the Chongqing project was a "beachhead" from which to launch more district cooling developments.

"When people visit our district cooling plant, they are impressed with what we have done in China," Foo said.

There are about 35 district cooling projects in Southeast Asia, according to a 2021 tally by the Asia Pacific Urban Energy Association (APUEA), an industry group. Over 20 of them are in Malaysia, mostly clustered around its commercial hubs Kuala Lumpur, Putrajaya and surrounding Selangor state.

“In countries like Indonesia, Vietnam and Thailand, private developers and governments are interested but hesitant on district cooling,” Chen said. APUEA also identified other issues such as scepticism and lack of regulatory frameworks.

Moreover, not every Asian city has the technical know-how and capabilities.

“Like on most other continents, technical readiness levels between cities vary greatly. The two most important components that determine whether a city is ready to adopt district cooling are a high quality of underground civil engineering, and a high reliability of its electrical system,” said Mathias Niffeler, an energy systems engineer at the Singapore-ETH Centre, a research centre based in Singapore.

For countries just starting out, Foo said a successful demonstrator project is needed to build market confidence for district cooling, as many property owners still prefer sticking with individual building cooling systems as these options seem "real and credible".

Equally important is the ability to collect good data to demonstrate the long-term benefits of switching to district cooling systems, Foo added.

How much control governments have over urban planning could be a key factor too. In cities like Japan and Singapore, authorities can and have mandated that new developments need to connect to district cooling projects, thus helping to overcome the buy-in barrier.

Singapore's Marina Bay district cooling project was aided by state intervention and urban planning. The district cooling apparatus was developed alongside a government-built 'common service tunnel' running under the bay area, which had room for both water pipes and electricity cables, simplifying the process of getting cold water pumped from chiller to tenants.

Stretching the concept

New climate-friendly developments reduce our impact on the environment, but innovations are also needed to help existing buildings decarbonise.

Aerial view of Shanghai, China, home to some 26 million people. Image: Wikimedia Commons/ Jiaqian AirplaneFan.

In general, district cooling is more easily installed in greenfield projects. This is because existing buildings that do not have centralised air-conditioning cannot hook up to an off-site chiller. In crowded cities, it can also be hard to find room for new pipes.

SP Group is trying to prove that such projects are not impossible. In a white paper last year, the firm argued that it was possible to convince existing tenants to conduct major revamps on their cooling systems with promises of carbon and cost savings.

This April, it committed up to S$60 million (US$42 million) to bring district cooling to a town centre in Tampines, eastern Singapore. The project involves seven blocks, including shopping malls, office buildings and a community centre that doubles as a sports hub.

Instead of building a brand new chiller plant, existing ones in some of the buildings will be used, with new pipes connecting the properties.

When completed in 2025, the project will slash emissions equivalent to what over 900 average-sized government housing units would use in a year, and provide the properties economic benefits of over S$50 million over three decades, SP Group said. But implementation won’t be easy.

“Every building owner, developer, customer, has different ambitions, different goals, different ideas in terms of where they want to be from a sustainability perspective,” said Harsha Sundararaman, managing director of sustainable energy solutions at SP Group.

Foo said that brownfield district cooling projects need to be taken seriously for the technology to benefit the environment, pointing to how existing buildings vastly outnumber new developments in cities.

Another district cooling project SP Group is helming in Singapore is in Tengah, a 700-hectare residential development in the west that is expected to house up to 42,000 families when fully built-up.

Concept art of the future housing development in Tengah. Image: SP Group.
Concept art of the future housing development in Tengah. Image: SP Group.

Prospective buyers of government housing units are told of 20 per cent reductions in upfront costs, and 30 per cent in the long run, if they sign up to the district cooling system. SP Group said that it will eventually offer the service to 18,000 Tengah households, and that nine of 10 households that have already been offered district cooling have signed up.

SP Group added that new chillers with variable speed drives are used to tackle fluctuations in demand patterns. They can be tuned to be most efficient at about 60 per cent load, which allows for more flexibility compared to traditional systems that run best at maximum capacity.

Shopping malls and community centres, with more constant cooling demand, will also be connected to the Tengah project to mitigate the fluxes expected with the residential blocks.

No silver bullet

For maximum climate impact, district cooling should go hand in hand with sustainable building design and be powered by clean energy.

A walkway along the Marina Bay district cooling plant. Image: Eco-Business/Liang Lei.

The narrative from climate scientists in recent times have been fairly constant: not every problem needs a big technical fix, and nor can one solution address the multifaceted, cascading issues brought about by global warming.

As such, the energy savings from urban cooling will be most effective if it works in tandem with other climate-friendly solutions.

“District cooling is a very complex solution, it is not suitable for every area,” Chen said, adding that urban planners should also weigh up solutions like ensuring better wind flow through new urban spaces, and minimising the use of large untinted windows to cut indoor heat.

“To make cooling systems truly sustainable, the energy that is used to operate cooling systems also needs to become more sustainable,” Niffeler said. Clean energy is a huge challenge for Asia Pacific, with the region accounting for over three-quarters of the global coal power generation capacity. This figure is set to rise, against an expected gradual decline in the West.

The Intergovernmental Panel on Climate Change, a global network of climate researchers, recommended in its latest report on climate adaptation that cities also prioritise nature-based solutions, such as street trees and green roofs to cool urban spaces.

Social services and early warning against heat waves need to be beefed up too, according to the United Nation’s Sustainable Energy for All initiative.

Still, district cooling, with its promises of energy savings at scale, could play an important role in decarbonising cooling as Asia grows – and its impact would be boosted with the right support structures in place.