The chill factor

District cooling is the most viable cooling solution in the region

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ANALYSIS, MEP
A district cooling piping network.
A district cooling piping network.
A cogeneration plant, which produces electricity and heat used for cooling purposes.
A cogeneration plant, which produces electricity and heat used for cooling purposes.

District cooling is the most viable cooling solution in the Middle East. But the impact of the global economic crisis on the construction industry in the UAE has forced developers to look more closely at the costs involved of keeping cool.

In a region where the temperature tops 45°C at the height of summer, and air-conditioning consumes 70% of peak power, governments have increasingly turned to district cooling as a cheaper and more efficient alternative. However, district cooling not only stands to mitigate the power-supply crisis in the GCC, but can also help to reduce its carbon footprint through increased energy efficiency and lower carbon dioxide emissions.

Ganesh Krishnamurthy, head of the mechanical department at Cansult Maunsell, argues that ‘green’ building can boost the efficiency and cost-effectiveness of district cooling. “Tightly-sealed buildings with better insulation and high-efficiency glazing mean that the actual cooling load comes down. Thus plant and piping size will be reduced drastically,” he argues.

Arup director John Roberts concurs: “Research has indicated that 50% to 60% of energy consumption in buildings is sensitive to building design. Designing buildings to conserve energy is not just about the fabric, but encompasses all its systems and equipment.” Roberts says this will produce a ‘low-carbon’ cooling load as opposed to the ‘business as usual’ model where energy conservation is ignored. “This design approach helps to enhance the economic case already presented by district cooling.”

In a 2009 report entitled ‘Analysis of the District Cooling Market in the Middle East Region’, Frost & Sullivan predicts that the district cooling market will “become more organised, populated and competitive.

Multinational companies will be attracted to this market due to the prospects presented by the investor-friendly laws, improved standards of living, and high disposable income, which has set off a retail boom in the region.

Distinct need

“With the GCC becoming home to the biggest shopping malls in the world, there is a distinct need for district cooling in not only the residential sector, but also the commercial sector. The UAE alone is expecting to have 80 million square feet of office space by 2010, widening the scope for district cooling companies.” Frost & Sullivan state that, among all Middle Eastern countries, Saudi Arabia is perceived to have the most untapped potential, with more than US$100 billion worth construction projects underway. Its rapidly-expanding industrial base and population have increased the demand for power.

The report states that, by 2013, the Middle East district cooling market is expected to have an additional capacity of 4,5 million tonnage of refrigeration (TR), contributed largely by Saudi Arabia and Qatar.

“Although there is a continuous rise in the demand for power in almost all GCC member countries, power is still provided at subsidised rates for the residential sector. This puts a huge drain on the region’s utilities, as power costs account for around 50% to 60% of the district cooling production cost,” it points out.

District cooling production also requires copious water, which is a limited resource like electricity, and therefore costly in the GCC. District cooling plants use potable water at present, but the search is on for a technology that will allow them to use non-desalinated seawater. Even though a few plants are already using seawater, the corrosion-resistant equipment needed will increase their equipment cost – and the prevailing credit crunch is curtailing such investment.

Could it be possible that such issues are taking the shine from district cooling as the best-possible cooling solution for the region? Not at all, according to Roberts, who argues that the additional problems posed by the global financial crisis present a unique opportunity for district cooling providers and designers, who have a critical role to play, he maintains.

Low-hanging fruit

“What can the designer do? A lot really. The low-hanging fruit is always to reduce your demand. Those who supply chiller plant might not like this, but energy has to be supplied efficiently. Energy-demand reduction, and not renewable energy, is the real saviour of the world.

“The real implication is for developers. There is a global paradigm shift as developers are becoming utility providers. The private sector is increasingly taking over this role. As designers, we have to convince developers of the business case presented by district cooling,” says Roberts.

BS Prashanth, senior development manager at Rakeen, calls for a new perspective on district cooling in light of the global financial crisis. “Where is the district cooling industry at present in terms of the current economic situation? How does district cooling form part of a wider developmental strategy in such a changed context, and what influences its business decisions?” he asks. He explains that a developer is mandated by various regulations as being responsible for assorted infrastructure – and district cooling is fast becoming part of this obligation.

A developer has to look at infrastructure like water, power, roads, wastewater and telecommunications in a holistic manner, which presents an opportunity for various synergies and cost-savings. “For example, a district cooling provider will come in and lay a cable, followed by a telecommunications provider that will lay its own cable. We can cut costs easily by integrating such requirements,” says Prashanth.

Ken Currie, business development manager at TAS ME, says that district cooling providers have to resort to technology in order to survive the global downturn. “The prevailing uncertainty has meant that district cooling plants have been built with only a third or even a quarter of the actual load connected. This is a nightmare scenario. However, some developers are still building, so you are still required to provide chilled water.” Additional problems are that concession agreements are not finalised, financial models no longer work, billing has to be cut back, and future load forecasts are weak.

Mitigate risks

What can the industry do to mitigate such a plethora of risks? “There are technological solutions to limit the capital outlay and the cost of distributing chilled water. If you can cut down the cost of both, and keep the lenders happy, then you will be on a much better wicket.” Currie says this approach calls for a close examination of the actual cost of providing your first tonnage of refrigeration. “The question is how much it will cost you before you can turn on the switch and produce your first chilled water,” he says.

One such solution is packaged or modular district cooling. “This requires a smaller footprint. Plant can be located at ground level, with no need for a basement, and hence no major excavation or dewatering. You can throw down rough foundations, bring in one or two self-contained modules, and start to produce chilled water straightaway. This can be a temporary solution, or you can place the units in a fixed position right at the beginning and then add modules as needed,” is Currie’s succinct explanation.

In the present economic climate where funding is a problem, modular district cooling plants help to mitigate the financial risk posed by investment as they are movable assets and can be transported to wherever they will be needed the most. Another option is a distributed cooling system, which utilises a common piping and pumping network. “The benefit of such a system is that it is infinitely extendable, while it can also use dead or wasted space such as internal wells and multi-storey car parks. You can even have supplementary thermal storage systems on roundabouts, all tied together with small-diameter piping.”

Khalil Atieh, vice-president: UAE at Jain & Partners, says cogeneration is gaining favour as a technological option. “We all agree that district cooling is a good solution to provide chilled water for big developments. It is more energy-efficient and is very well designed from a maintenance and operational point of view. It is sustainable, functional and reliable – and hence appeals to master planners and developers alike.”

Atieh says the main stumbling block faced by the district cooling industry at present is the power and water-supply supply crisis looming in the GCC. “We have seen too many developments that have been completed, but which have no power.

“Why? It is because infrastructure development has not been aligned with urban development, making for a serious shortfall. It is imperative we find a solution for this, as water and power shortages are perhaps the biggest problems faced by the district cooling industry.”

Krishnamurthy gives his assessment of the various technological options and combinations available to the district cooling industry at present:

Electric-driven
• Conventional system used extensively at present;
• Efficiencies in the range of 0,85 kW/TR to 1,1 kW/TR;
• Places a high demand on electrical utilities and incurs increased infrastructure costs;
• However, thermal energy storage can reduce the installed equipment and the power demand.

Electric + absorption system
• Only feasible when piped gas is available;
• Features reduced power demand;
• However, poor overall energy efficiency as the COP of absorption systems is quite low (0,8 to 1) as compared with vapour compression systems (3,6 to 4,2);
• A combination of electric and absorption can give a reasonable COP;
• The main benefit is reduced grid demand.

Gas Turbine + electric
• Feasible when piped gas is available and grid power is in short supply;
• The efficiency of gas turbines without heat recovery is quite low – in the range of 0,33 to 0,38;
• High capital cost;
• Feasible when captive power plants are required.

Gas turbine with heat recovery + steam-driven chiller
• Feasible when piped gas and grid power is available, but the latter is in short supply;
• The efficiency of gas turbines with heat recovery is acceptable, being in the range of 0,55 to 0,60;
• The captive power is used for base load operations and grid power for incremental loads, as local authorities do not allow electricity to be exported.

Gas turbine with heat recovery steam generator and electric + absorption chillers
• Combination of steam driven absorption chillers and electric driven chillers;
• The capital cost is less.

Gas turbine with heat recovery steam generator and electric + absorption chillers with thermal energy storage
• Added benefit of thermal storage;
• Reduced capital cost and increased efficiency.

Solar heating system with absorption machine + electric chiller
• The availability of space for the solar panels is a limiting factor, as about one square metre is required for each kW of heat. A 1 000 TR chiller with a COP of 0,8 will require 4 375 square metres of flat solar panels.
• Solar heat used to generate hot water used in absorption machine;
• Electric chiller used as downstream chiller;
• Capital cost can be high;
• Can be considered as an add-on for optimisation, but not for full load requirements. This option may be more appropriate for distributed loads in buildings.

Heat Rejection Systems
Air-Cooled
Direct refrigerant cooling in condensers for smaller systems and radiators, with closed-circuit water-to-air exchangers and water-cooled condensers in larger systems.
• Saving on water consumption;
• Penalty on power consumption of the chillers;
• Possible to use evaporative system to reduce condensing temperature in summer and use air-cooled only at lower ambient temperatures.

Water-Cooled
Domestic water used in cooling towers as make up
• High water consumption/high utility costs;
• The availability of the water needed is an issue.

Treated sewage effluent or grey water used in cooling towers as make up
• Lower utility costs;
• Increased water treatment cost;
• Higher bleed-off, plus the seweage connection;
• Water recycling means less fresh water used.

Once-through system with seawater
• The district cooling plant is located right next to the seawater source;
• High temperature of seawater in summer;
• High capital costs;
• High chemical treatment/maintenance costs;
• High capital cost due to corrosion-resistant materials used;
• Environmental impacts due to large quantities of water discharged back to the sea, containing added chemicals, especially close to the shore.

Seawater used in cooling tower as make up
• Reduced intake of seawater;
• Lower water temperature to condenser;
• Lower chemical treatment costs.

Seawater desalinated and used as make up in cooling tower
• Higher capital cost;
• Higher operating and maintenance costs;
• Reduced demand on utilities for water.

Chilled Water Distribution System
Primary/secondary distribution used normally
• Higher installed power;
• More equipment and piping, which equates to a higher capital cost;
• Easier to control and operate;
• Efficiency penalties at part loads of chillers.

Primary-only distribution
• Variable flow through the chillers possible due to current control technology available’
• Lesser installed equipment/piping;
• Better able to cope with part loads and maintain higher efficiencies;
• Minimum base load required;
• Commissioning/start-up needs to be well thought-out.

Higher delta T systems
• Currently 9°C delta T used;
• Possible to use higher delta T, which has multiple benefits;
• Lower pumping cost (the power is proportional to the flow, with a 1°C increase in delta T above 9°C reducing the pumping power by 11%;
• Lower pipe sizes, leading to reduced space demand on service corridors and reduced capital cost for piping;
• Increased efficiency when combined with thermal energy storage.

Thermal Energy Storage

Reduces the peak load, the maximum demand and the installed equipment, plus plant can be optimised to run at full load. There are two types of storage media:

Chilled water
• Very large storage tanks required (90 gallons per ton hour);
• Availability of space is critical;
• Simple to operate and maintain;
• No additional chillers/equipment required;
• Capital cost increase is negligible;
• Increased returns possible with differential tariffs for peak and off-peak hours.

Ice storage
• Much smaller storage tanks required compared to chilled water;
• Additional equipment required;
• Reduced COP for the ice-making chillers;
• Increased capital cost;
• Increased returns possible with differential tariffs for peak and off peak hours;
• Possible to use a higher delta T, reducing the pumping costs even further.

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