Hong Kong is iconic for its unique subtropical high rise, high density urban built environment, with a strong demand of air conditioning for its enormous indoor spaces in skyscrapers across the city. To reduce the overall energy consumption by air-conditioning of the 320 hectares new urban development following the relocation of the Kai Tak airport in the city centre, the Hong Kong government has taken the lead in planning the first-of-its-kind seawater district cooling system (DCS). Arup has worked with the Electrical and Mechanical Services Department (EMSD), from concept to implementation, for 20 years to bring one of the most important sustainable infrastructures to the city and realise Hong Kong government’s sustainability vision.
284MW designed refrigeration capacity
1.73 millionm²air-conditioned floor areas covered
35%reduction in electricity consumption and carbon emission annually
Ground-breaking climate resilient initiative
In 1998, the Hong Kong International Airport was relocated from Kai Tak to Chek Lap Kok. The Hong Kong government then planned for urban development on the old airport site and the surrounding older district, covering about 323 hectares. Apart from providing a large piece of available land for a new central business district and home to a population of more than 110,000, this Kai Tak development (KTD) also aims to play a pivotal role in promoting sustainable development and fostering a green environment for future generations. As such, the government has taken the opportunity to implement the first-ever DCS in Hong Kong.
Why air-conditioning a key for Hong Kong’s ‘cool’ ambition?
Buildings account for some 90% of Hong Kong’s total electricity consumption, compared to a global average of 40%. This high level of energy consumption by buildings accounts for 60% of the city’s greenhouse gas emissions, while air-conditioning systems in buildings like offices and malls contribute to the highest portion. In planning a mega-size urban development project like the KTD, a DCS is considered to be the most energy-efficient system as it consumes about 35% less electricity than traditional air-cooled air-conditioning systems, and is therefore playing a key role to decarbonise Hong Kong.
Realising the sustainability vision
Arup’s involvement in this DCS project started in 1999. Our sustainability, building services and civil engineers initially looked at the benefits that can be achieved through a DCS. We were then involved in the installation of electrical and mechanical equipment at the plant rooms, seawater pump house and DCS substation of the user buildings. This also included the laying of underground DCS pipes, seawater pipes and associated interface connection so as to provide chilled water to the whole development. We have provided further electrical and mechanical engineering services as well as contract administration and construction supervision of the contracts for the final phase.
District cooling in action
The DCS utilises seawater to produce chilled water at the central plants and distributes to consumer buildings in the area through 40km-long underground water piping network. The cooling capacity is about 284 megawatt of refrigeration (MWr) for serving the non-domestic air-conditioned floor area of about 1.73 million m2, equivalent to a cooling supply for 40 nos. of 30-storey high commercial buildings. Upon completion of the project, there would be around 50 buildings in KTD connected to the DCS.
The system has been in operation since 2013 and the whole project is expected to be completed by 2022, with an expected annual saving of electricity to be about 85 million kWh, equivalent to HK$96.2 million on electricity bills and a reduction of 59,500 tonnes of carbon dioxide emission from the development.
Benefits over conventional system
The DCS offers economic advantages over the conventional systems as the total installed cooling capacity at the centralised plant is smaller than the sum of individual conventional plants at the individual buildings. It is estimated that savings of at about 15-20% on overall installed capacity can be achieved, which will also reduce the material use and plant space in individual buildings.
By using seawater for heat rejection, there is further energy saving and also more open space released to the public through removal of cooling towers. With the intake of nearby seawater to produce chilled water, the water flow circulation and thus the water quality of the Kai Tak Approach Channel are enhanced as well. The DCS also helps mitigate the heat island effect by eliminating the heat rejection of separate air conditioning systems from individual buildings.
With significant benefits in terms of environment, comfort, operational efficiency, energy conservation, flexibility in planning and superior system reliability, DCS is not only efficient but also a vital city-level solution to address carbon emission reduction and climate change.
This project has become a role model for wider applications of DCS in Hong Kong, and the government has made DCS a key initiative for all new development areas in the coming years. ” Vincent Cheng Arup Fellow, Director of Building Sustainability, East Asia