Consulting-Specifying Engineer - August 2007 - (Page 31)

At a late stage in the design of the Burj Lofts and Burj View buildings in Dubai, DEWA insisted on the addition of a low-voltage main isolation room at the ground level. This change required close cooperation between the engineer and architect to accommodate the room with the least impact on the design and loss of leasable space. A similar situation occurred during the construction of the Emaar Residential Towers in Dubai. In this case, DEWA changed its high voltage regulations during construction, so that a ground floor ring main unit (RMU) room had to be added, with a significant impact on the construction process and, once again, loss of leasable space. The medium-voltage supply must be transformed down to the utilization voltage (480 volts in the United States, 600 volts in Canada, and 400 volts or 380 volts in much of Europe and Asia). In standard buildings, the transformers are located at or below ground level. In extra tall buildings, transformers at low levels are insufficient. At some height, the voltage drop caused by the impedance of the supply conductors will become significant and the supply voltage will fall below acceptable values. The architect’s design must therefore accommodate service levels in the upper parts of the building, in which additional transformers are located. Selecting the location of the service level requires cooperation between the engineer and the architect. The engineer will require the service levels to be located where they can adequately service selected floors. The architect will consider issues such as the impact on the esthetics of the façade, the space requirements and space constraints, the impact of the service space on adjacent spaces and the transportation of equipment to and from the service room. In the Emirates Towers, the transformer rooms at the upper level are located close to the elevator shafts, so that transformers can be transported through the elevator shaft in the event that one must be replaced. Medium-voltage cables must be fed to the transformers on the upper levels. Frequently, the owner or LEUC will demand that the medium-voltage cables be kept completely Lighting tall buildings In high-end tall buildings, the design of the lighting treatment is usually undertaken by a lighting design specialist who will develop a design that enhances the architectural features of the building. The electrical engineer must work closely with this designer when developing the power and control systems for the lighting. Frequently, the electrical engineer is responsible for coordinating with the other design professionals with respect to the lighting design. For example, the structural engineer may be required to ensure that the structure can adequately support large chandeliers and the mechanical engineer must ensure that the cooling system accounts for the heat generated by the lighting. separate from any low voltage equipment and routed up the building in separate accessible spaces. The access is necessary so that the cables can be secured and supported at regular intervals so as to relieve stress on the cables, and to limit their movement under short circuit conditions. But what about emergency power? To ensure safety in the event of a normal power outage, emergency power generation is required. The emergency generators also may be used to provide a reduced level of service to non-critical items. When selecting the generation system, the electrical engineer must decide between low-voltage or medium-voltage generators. Selecting medium-voltage generators allows for the use of fewer, larger generating units, all of which can be located at a low level. However, a medium-voltage emergency system will require a sophisticated transfer scheme—more costly than lowvoltage equipment. In addition, some LEUCs will not permit the use of such an arrangement. Conversely, selecting low-voltage generators will require more generator units. And due to voltage drop, they will have to be distributed throughout the building on service floors. Moreover, electrical and mechanical engineers must coordinate their work to ensure that sufficient combustion air and ventilation is provided to the generator rooms, and to ensure that the exhaust, fuel and cooling systems are correctly designed. E Consulting-Specifying Engineer • AUGUST, 2007 31

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - August 2007

Contents M/E Roundtable Giants 100 Pullout Poster Giants Stand Tall: CSE Giants 100 Report Electrical Design for Tall Buildings HVAC and Fire Safety for Elevator Systems How to Beat the Codes GAS Technology Supplement Recovering Waste Heat from Boilers New Applications for Tankless Water Heating Systmes Techniques Improve for Powder Coating MDF New Tools Available for Heat Treating Steel Direct Drive Engines

Consulting-Specifying Engineer - August 2007

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