District cooling (DC) is bogged down by various obstacles. A few of them are the lack of demand or timeline guarantee by the master developer, the issue of retrofitting within existing buildings, high upfront cost by the DC plant operator requiring long-term usage agreement, adopting building design to suit district cooling requirement, etc. All of these observations are made by Arvind Bhatnagar, general manager at TTE (Technical & Trading).
Although Bhatnagar says that rapid urbanisation along with growing infrastructure spending across GCC countries is driving the Middle East district cooling market. He says: “In 2016, the government of the UAE had set a budget of $4.62bn towards infrastructure development till 2020. Growing adoption of sustainable cooling technologies to fulfil energy conservation targets will foster the district cooling market share. Shifting trends toward optimisation of energy-efficient air conditioning will further boost the product demand.”
By specifying the percentage of district cooling in the energy mix, the government is taking initiatives to increase the share of district cooling. Certain areas are mandated for DC, such as in commercial towers for energy conservation. He says that such stringent government norms toward development of sustainable energy will embellish the UAE district cooling market. The government of Dubai has set its goal to achieve 40% of the cooling demand through DC systems by 2030. The target aims to reduce the power consumption of the city’s air conditioning by 50% through various initiatives.
In 2014, the government of Dubai setup a target to reduce building energy consumption by 20% by 2030. The government of Abu Dhabi in line with its vision 2030 formulated a programme named Estidama, which regulates construction, design, operation, and performance of buildings, villas, and communities, says Bhatnagar.
However, the use of treated sewage effluent (TSE) water is still a challenge. He says: “TSE can be used in agriculture and district cooling sector. The price of TSE water in Dubai is one tenth of potable water. So when used in district cooling, it reduces the cost of operation by 8 to 10%. As TSE is supplied to both agriculture and DC, the challenge is to get sufficient supply in summer when the demand is high by reducing supply to the agriculture sector.”
George Berbari, CEO, DC PRO Engineering, in an earlier interview, had suggested that since there is a shortage of TSE water in summer and excess in winter and agriculture is better in winter, than in summer, it is therefore better for agriculture to be supplied with TSE water during the winter, while district cooling should be supplied with TSE water in the summer.
A case of Legionella
Then there is another bacterial challenge. According to a report by the European Centre for Disease Prevention and Control, an increase in cases of Legionnaires’ disease − compared with previous years − is reported in EU travellers returning from Dubai. As per the report, cooling towers, evaporative condensers, humidifiers, decorative fountains, whirlpools, showers, etc. are examples of installations with identified risks. Bhatnagar observes by saying: “Legionella bacteria can infect humans through multiple sources and HVAC, fountains, etc., may not be the major cause even if the incidence is higher than previous years.
“Hotels and crowded swimming pools are severely regulated and constant health checks of public facilities takes place in Dubai. The bacteria can grow on any wet surface not limited to cooling towers, evaporative condensers (cooling plant) and scrubbers. Also, poorly positioned air intakes for air conditioning units can also capture the bacterial plume and draw it into buildings.”
He says that the industry takes the following control measures as cooling towers are susceptible to such bacterial growth:
• Use processes that restrict bacterial growth (for example, a hot water unit with mixing valves instead of a warm water storage system)
• Have parts that avoid sludge build-up. Legionella grow better in sludge
• Avoid dead legs in pipe work so bacteria cannot grow in them
• Use well-designed drift eliminators for effective capture of aerosols
• Have easy access for maintenance and cleaning
• Use a continuously-operating disinfection process to kill bacteria
• Use a closed-circuit system instead of an open circuit – this removes bacteria growth surface
While no water treatment or maintenance system can completely and permanently eradicate the organism, merely being aware of the bacteria and working with HVAC professionals on a solid preventive maintenance schedule, as listed down by Bhatnagar, can help circumvent an outbreak.