Making a case for zero-energy district cooling plants in Qatar to meet the air conditioning demands of the 2022 FIFA World Cup, Salah Nezar plots the path ahead by weighing the pros and cons.

In simple terms, net-zero energy implies that a solution involves producing as much energy as it consumes. Net-zero site energy use can be ascertained by exporting an equal amount of received energy measured over the course of one year. The equation for net-zero source energy use is that one energy unit produced on-site could offset three imported units produced off-site. Net-zero energy emissions offset the amount of produced carbon emissions through the energy source powering a building.

Natural resources – the state of affairs in the GCC

Before a case can be made for any energy source, it is important to gauge the ground reality. Looking at the present scenario, it is evident that the GCC countries will have the dubious distinction of emerging as world leaders in electricity consumption, as per capita consumption is expected to increase at annual rates of 2.5%. By the same token, power requirement in Qatar is expected to rise to 10 GW by 2020, compared to 7.6 GW today. Water demand in Qatar is also envisaged to double from 1.1 million m3/day in 2011 to 2.1 million m3/day by 2020. A large part of this increase can be attributed to the needs of a growing population and a significant 47% of energy consumption being diverted for residential use. It is interesting to note that the GCC countries put to use only 10.5% of their electricity in the industrial sector, as opposed to 37.7% globally.

The graphs on Figure 1 and 2 depict the water consumption in the GCC states in 2010 and water production in Qatar, respectively. From the two graphs, one can say that Qatar is, at present, the highest consumer of water among the GCC states and that there is a steady and steep increase in total water production in Qatar in the last five years. The average annual increase from 2006 to 2010 is an alarming 13.2%.

The map on Figure 3 indicates the limitation of seawater desalination, which is an eloquent comment on the heavy dependence on seawater in the region to meet its ever-increasing water demands and the pressure the region in general, and Qatar in particular, puts on its desalination plants.

Challenges and solutions

Given the data, it is not difficult to realise that there are several challenges to be overcome in the path to achieving net-zero. The challenges become even more daunting in the light of the fact that Qatar is getting ready to host the 2022 FIFA World Cup.

The country’s resources and infrastructure will be tested to their limits during the preparation stage, to the run up to the event, and during the mega event itself in the coming decade. Viewed from this prism, a few of the parameters and challenges to be kept in mind are:

1. Climatic conditions
2. Water scarcity
3. An open-air experience
4. Evening matches in summer
5. Safety of athletes
6. Comfort of spectators
7. State of technology
8. Integration and flexibility
9. Infrastructure

One way of combating the challenges is to press into service solar-assisted refrigeration solution. The specific areas which need special attention are:

• Source of the solution
• Systems of the solution
• Current system solution
• Alternatives at a larger scale
• Alternatives at a smaller scale
• Alternatives at the air side

Absorption chillers

Absorption chillers offer a solution. The following are the advantages of absorption chillers:

• Reliable, durable and mature technology
• Significant reduction of electrical consumption
• Reduced operating costs
• Reduced CO2 emissions
• Non-flammable and non-toxic
• Ecologically benign
• Ozone-friendly working medium LiBr
• Vacuum and LiBr solutions charged in factory (“plug & play”)
• Water as refrigerant
• Available for outdoor installations

However, absorption chiller technology is not without its drawbacks. In a nutshell, they are:

• High sensitivity towards high condenser water temperature
• High make-up water rates (evaporation, blow-down and drift loss)
• Relatively high chilled water temperature (7°C to 8°C)
• Temperature level of the heat medium, provokes aggressive corrosion
• Large area for solar collectors
• Assisting rather than driving
• When we compare steam-driven centrifugal chillers against absorption chillers, we notice the following:
• Applicable to large tonnage from 100 to 5,000 TR with free source of steam
• Machine COP = 1.8
• Steam-driven centrifugal chiller at capacities more than 1,000 TR is more cost effective than two-stage absorption chiller

The sun as a solution – pros and cons

Now, going back to the use of solar energy in the light of the 2022 World Cup, it can be seen that the use of solar energy and infrastructure have been favourable in major competitive and non-competitive venues. A few of them which can be cited as examples are: the 2022-bid Showcase Stadium, Doha; Masdar City, Abu Dhabi, UAE; ESAB Head Office, UAE; and UEFA HQ, Nyon, Switzerland.

Masdar City Solar Cooling Plant Solution Pilot has the following features:

• A Sopogy micro-parabolic trough collector with uniaxial tracking and a total mirror aperture area of 334 m2
• Synthetic oil as thermal media
• Heat is transferred to the system’s pressurised water circuit through a heat exchanger
• A Mirroxx linear fresnel collector with uniaxial tracking and a total mirror aperture area of 132 m2 heats the pressurised water directly
• The two solar thermal collector systems have been in successful test operation already for more than three months
• Schneider Electric provided the control system components for the pilot plant
• Fraunhofer Institute of Solar Energy to analyse the monitored data and assess system performance
• Collector’s thermal energy has been driving the broad 50 refrigeration-tonne double-effect absorption chiller cooling 1,700 m2 of office building
• Air delivery system uses chilled beams coupled with fresh air energy recovery units
• Water consumption data not available

The 2022-bid Showcase Stadium, Doha, has the following features:

• A 500-seats model stadium with retractable roof
• A Mirroxx linear fresnel collector with uniaxial tracking and a total mirror aperture area of 1,040 m2 heats the pressurised water directly
• Thermal storage PV arrays for electricity generation with a monitoring system and not connected to the local electrical grid
• Double-Effect 150 TR Thermax absorption chiller with dual fuel source and underground chilled water storage tank
• Displacement ventilation for air delivery system for the pitch coupled with UFAD for spectator stands
• Water consumption data not available

ESAB Head Office, Jafza, UAE, has the following features:

• 6,500 m2 built to achieve LEED Platinum
• USD 1 million solar thermal cooling system, one of the large-scale applications in the region
• Solar system use 1,500 solar vacuum tubes
• 70% energy reduction compared to a “As-Usual Building” by using solar thermal and efficient lighting systems
• Six packaged absorption units (climate well) to serve roof-mounted AHUs handling latent loads
• Radiant cooling system using thermo-deck approach (hollow-core ceiling slab) handling sensible loads

UEFA HQ, Nyon, Switzerland has the following features:

• Design intent: must be a sustainable and energy-efficient building operating in 2010
• Building’s cooling load: 100 TR
• Renewable energy source: geothermal, thermal solar and PV (200 m2)
• Thermal array: 90 vacuum tubes over 110 m2 area generating 55 KW used for heating and domestic water in winter and cooling in summer to cover 10% only of the loads
• Water temperature: hot at 88°C for generator and chilled water at 7°C.
• Storage tank: 3,000 litres
• Refrigeration machine: absorption chiller with cooling capacity of 10 TR

Delivering on promises

Despite the examples cited, it needs to be noted that delivering on promises of net-zero comes with its own set of attendant conditions, like context integration, systems selection justification, cost effectiveness, infrastructure integration and controls integration. Let us examine a few of them.

Context integration

Integration with other aspects:

• Event, accommodation, medical, mobility and education
• The location of district cooling plants
• Chilled water reticulation optimisation
• Location of solar fields
• Relationship with other utilities
• Use of recycled water for heat rejection
• Used cooling tower blow-down water for irrigation

[table here] – Systems selection justification

Systems integration

• At present, most solar cooling systems are assemblies of single components and don’t provide a fully integrated system.
• These components, in many cases, have their own control units.
• The performance of the solar cooling solution depends a lot on the availability of a single-source centralised control.
• The industry will follow the market momentum in embracing a fully integrated solution for solar cooling system.

Cost effectiveness

• Thermal absorption solar refrigeration system costs almost three to four times the cost of a conventional vapour compression system.
• Double effect direct-fired/steam absorption chiller costs between 1.8 to two times the cost of a vapour compression chiller.
• The cost of reduced scale cooling system using adsorption machine costs almost four times compared to a non-solar assisted system.
• The cost of a direct-fired and steam absorption chiller is 35% higher than the direct-fired chiller.
• The cost of a direct-fired and hot water absorption chiller is 35% higher than the direct-fired chiller.
• A square metre of a thermal solar flat collector costs between QR 1,700 to QR 3,400.
• A square metre of solar evacuated tube costs between QR 3,400 to QR 3,970.

Conclusion

The main aim of conducting this study was to demonstrate the feasibility of a carbon-neutral (solar) solution for a cooling plant at a different scale vis-à-vis the 2022 World Cup. To begin with, the entire operation needs a vast area for the solar field (15 to 20 times the football pitch size). It also requires a single-source control system for all the systems’ components. It also needs to be pointed out that cooling system efficiency is sensitive to high condenser water temperature. The adverse impact of dust and humidity on system’s efficiency also needs to be taken into account. Other aspects that have to be factored in are high rates of water depletion and pollution (evaporation and bleed-off) and higher costs. The cooling plant reticulation needs be integrated into the city’s infrastructure for its effective and efficient functioning.

Finally, an “opportunity document” needs to be developed for each venue to grasp more accurately the pros and cons before the project is implemented.

The article is based on a presentation made by Salah Nezar at an ASHRAE Oryx Chapter seminar on September 24, 2012. The presenter’s disclaimer: This is an unscientific presentation with scientific overtones.

The author is a LEED AP, GSAS GCP, Sustainability Director, QPM. He can be contacted at s.nezar@qpm.com.qa