Power demand sustainability

(Valeriano Handumon/ITP)

The current electricity generation capacity in the UAE is in excess of 16GW. It has almost doubled since 2000, but in order to meet demands it will have to rise by another 60% to 26GW in 2010. While more than 80% of the electricity produced by UAE utilities firms supplies the residential and commercial segments, electric cooling represents 70% of the peak capacity and over half of the total consumption of these segments.

Electricity utilities consume close to 35% of the country's total gas production and it is no secret that, with the exception of Abu Dhabi, gas production levels are declining in the Emirates. Therefore the use of a more efficient delivery of cooling to the residential and commercial sectors is likely to have a significant impact on the overall energy consumption figures. This result can be achieved through demand-side management, energy efficiency measures, district cooling or non-electrical (including solar) cooling technologies. Moreover, the strain put on the country's generation, transmission and distribution infrastructure by double-digit growth rates can be relieved through the selective implementation of distributed generation at end-user premises.

Managing electricity demand

The most direct - and often also the most effective - way of managing demand is through pricing. Electricity demand is typically responsive to pricing, so by varying the costs, it is possible to exert some level of control on demand. The most extreme application of this principle would consist in passing along, in real-time, the market price of electricity to the end-user. Such so-called ‘real-time pricing' schemes are usually sustained by a wholesale market where electricity is traded on a real-time basis. Most utilities however have not gone beyond the more traditional ‘time-of-use' tariffs, whereby the price of electricity varies as a function of the day-of-week and time-of-day according to predetermined patterns.

Within the UAE electricity is a highly subsidised commodity, particularly for agriculture and nationals, but also to a lesser degree for non-nationals and businesses. Therefore, a price increase is to be expected in the perhaps not-too-distant future. However, trying to control demand through pricing has not proven effective in the past. For instance, the 1994 and 1995 price increases had little impact on the growth of demand. Indeed, the price elasticity of electricity demand in the UAE is very limited. This is mainly due to the fact that air conditioning is an absolute necessity.

Since there is little flexibility in the amount of cooling required, why not try to influence the effectiveness of its delivery to the end-users? There are several avenues that can lead to the more efficient and sustainable cooling of commercial and residential end-user premises. The end-users, developers and financiers all stand to benefit from such initiatives. It is generally assumed that developers and financiers are indifferent to energy efficiency because they either sell the property or, if they retain it, pass along the operations costs to the tenants. This analysis is not entirely accurate because the reduced energy consumption will enable the developer to negotiate a higher rent or sale price.

Reducing the cooling load by limiting heat gains

A major portion of the cooling load of a typical office building in the UAE can be attributed to solar gain. Clearly the highest potential for load reduction is through reduced and/or advanced glazing, but other measures such as window shading, roof insulation, roof wetting and building surface colouring are also effective.

With regards to artificial lighting, which could constitute up to 20% of the cooling load, when possible the combination of low natural or artificial ambient lighting and high efficiency workstation lighting should be the preferred design option for office buildings.

Particular care should be taken in precisely accounting for the impact of such energy efficient design on the heating, ventilation and air conditioning (hvac) system. Proper downsizing of the hvac system will avoid inefficient under-capacity operation. If the measures concern a retrofit, only the chiller and the air handling unit (ahu) can be easily replaced. If, however, the building is not yet built, all hvac system components (including ducts, which represent a major portion of the total system costs) should be downsized, resulting in significant savings. Reducing the cooling load also has a non-negligible impact on operations and maintenance costs.

Improving the hvac system efficiency

The cost of the hvac system design rarely exceeds 1% of the total cost of a new building. The design of a high efficiency hvac system using, for instance, a building simulation software may add a little to that 1%, but payback in terms of energy savings will be realised in no more than a couple of years.

In the case of a new building, the enhanced design initiative should concern all hvac system components, whereas in a retrofit usually only the chiller and ahu are concerned. While the chiller is, rightly, the main focus of many energy efficiency upgrades, the savings potential of the air handling system is sometimes overlooked. This is despite the fact that an average ahu can consume up to 0.6kW/ton ie more than some high efficiency chillers and can be easily rendered more efficient - often by an order of magnitude.

Another hvac component that should be designed in an energy-conscious way is the delivery system. The use of low-friction ducting and high efficiency fans can have a major impact on the overall energy consumption of the hvac system. Finally, the inclusion of a thermal storage device such as ice storage enables a reduction in the capacity of all hvac components, which can be as high as 30%. With such systems, at night the chillers operate to charge the thermal energy storage (TES) system. The stored cooling energy is then released by the TES system during the peak period so that the peak load can be met with a lower chiller capacity.

Alternative cooling technologies

Solar thermal energy or any kind of waste heat, such as the thermal energy released by onsite generation devices as a byproduct of electricity generation, can be used to power absorption chillers. Absorption chillers use a thermochemical refrigeration cycle instead of the traditional vapour-compression refrigeration cycle.

The absorption chiller is powered by heat; the heat delivery medium could be exhaust gas released by an internal combustion engine or a gas turbine, hot water or steam. Solar cooling is particularly attractive in this region given the abundance of solar energy. Other non-electrical approaches to cooling include geothermal cooling, natural ventilation with cool outside air and evaporative cooling.

District cooling is undeniably more energy efficient that the currently widespread air-cooled split units (approximately 1kW/ton compared to 1.7kW/ton). However, the adoption of a fixed-fee pricing schemes by some district cooling companies could potentially cancel part of that efficiency gain since end-users will have little incentive to use the cooling service efficiently.

Combining such fixed-fee schemes with demand-side management measures and programs such as raising awareness and using programmable thermostats could go a long way to addressing this issue. Alternatively, the price of cooling could have a variable consumption-dependent component based on actual usage as measured by thermal energy meters installed at end-user premises.

Distributed generation

Some of today's most efficient combined cycle gas turbine central power generation plants run by electricity utilities firms in this region manage to achieve 45% electrical efficiency. But many of the existing plants have even lower efficiencies. Provided that natural gas is available and can be purchased at reasonable prices up to about $5-$6 per 293kWh it may be economical for large end-users to install modern small to medium-scale gas engines in the 1-30MW capacity range, with electrical efficiencies of 40% or more.

The onsite electricity could be used to power highly efficient centrifugal chillers. Additionally, the waste heat produced as a byproduct of electricity generation can power absorption chillers, further increasing the overall efficiency of the plant. Some end-users may find it more cost-effective to use the waste heat for steam generation to be used in their internal processes. Distributed generation could be equally attractive for district cooling companies.

Print | Email | Discuss this article |

USER COMMENTS (0 COMMENTS)

POST A COMMENT

CLICK HERE TO POST A COMMENT

Add your Comment All posts are sent to the administrator for review and are published only after approval. ArabianBusiness.com reserves the right to remove any comment at any time for any reason. Please keep your responses appropriate and on topic.
Name *
Remember me on this computer
Email *	(Your email address will not be published)
City
Country
Subject *
Comment *
Notify me of further comments
Security Code *
Please click post only once - your comment will not be published immediately.