Air conditioning tends to be either associated with individual domestic units installed on the exterior of homes or apartments, or else with the cooling plant that controls the system for an entire building. However, many countries based in tropical Southeast Asia are looking at alternative cooling sources as a way of generating far more energy efficient urban centres. District cooling has emerged in recent times as a possible method to achieve economies of scale in air-conditioning provision, leading to rapid implementation in places such as Singapore, Hong Kong, Indonesia and Malaysia. The following discussion will look at how district cooling operates, and the advantages and disadvantages in comparison to air conditioning use.
District cooling consists of cold water being distributed from one main plant, via a network of pipes, to a multi-block area of homes, offices, commercial centres and public buildings. The cold water is pumped around the district cooling network to specific properties where specially designed units cool the air within each building. Once it has completed its cycle, the same water is fed back to the plant and cooled again. District Cooling can be run on electricity, natural gas, waste heat, renewable energies (such as geothermal energy) or natural cooling from water sources (this occurs mainly in Europe) and can use either regular water or seawater, although the plant's proximity to the ocean needs to be taken into consideration. Many plants also contain an ice storage facility as a way of consistently chilling water so demand during peak times, seasonal highs or even when the plant shuts down, does not put pressure on the system or increase energy output. As district cooling operates from one main plant, the need for individual buildings to operate chillers, cooling towers and pump rooms is instantly eliminated, and the ability for the district cooling plant to gradually expand over time ensures it can meet growing loads in comparison to single-building systems which stagnate. With cooling consuming the majority of energy consumption in hot countries, district cooling has provided a means to conserve energy and maintain comfort, illustrated by the growth rate of the district cooling market in the Middle East and Asia region by up to . There are predictions that it will have a dominant market share globally by 2019.
The advantages listed by district cooling providers include:
- Eco-efficient energy; reduction of power generation infrastructure, ability to use alternative, renewable and cheaper fuels, 50% reduction in power consumption, no need for refrigerants, reduced green house gas emissions, flexibility of cooling load
- Lower life cycle costs; less maintenance on machinery, longer life cycle of plant, ability to expand and distribute to more buildings so less construction of new operational machinery
- Reliable; available 24 hours a day, unaffected by peak loading, back up systems available, operated at external site to building thus can be responded to immediately
- Decreased building costs and architectural flexibility; buildings connected to district cooling do not require energy equipment such as boilers and chillers or storage space for refrigerants, thus reducing cost and making space within the building; the laying of pipes beneath the ground reduces heat transfer within the urban setting, thereby eliminating input into the heat island effect; vibrations and noise problems are removed
District cooling is often marketed as a viable and sustainable option, that is far more cost and energy efficient in the long term than any other cooling option available. However, there are disadvantages also, which include:
- District Cooling uses up to 50-80% more water than other cooling technologies. In places such as the Middle East where 100% of the potable water comes from desalinated sources, this actually could increase energy use during the desalination process
- The use of sea water as the cooling element means heated seawater returns to the ocean, potentially increasing the temperature of the seawater nearest to the discharge location and thereby threatening the marine ecosystem
- District Cooling is only appropriate in highly dense urban areas to ensure the cooling usage bill is equally split and kept at a minimum. For example low-rise villa developments would pay higher prices than large residential towers as there are less people but they are receiving the same amount of cooling
- The front–end investment demands for district cooling are quite substantial and require long-term financial commitment. Initial bills for users of district cooling for this reason are relatively high but gradually reduce over time
- Lastly, the lack of knowledge about district cooling and the availability of skilled operators can inhibit companies in investing and constructing district cooling plants.
Its growing use in Southeast Asia has overshadowed the listed disadvantages and instead is gradually being sold as a feasible, affordable and attractive option for private investors, seeking effective long term efficient cooling solutions. In Singapore, the Marina Bay district cooling system was constructed in 2006 and will ultimately consist of five plants, with proponents claiming that it will reduce the energy use of businesses in the area by 30%. In Malaysia, the Asian Development Bank is promoting the expansion of district cooling services across the country via information sessions for investors and local communities. The Hong Kong Government has also committed to the development of district cooling across the city.