Analysis of Architectural Design Sustainability Issues of Office Towers in Hot Climates: UAE Case

Abstract

The UAE has been spending billions of dollars to construct new urban developments in order to satisfy the country’s fast development, which started since the country was founded in 2 December 1971. The architecture in the major cities such as Abu Dhabi, Dubai, and Sharjah has been shifting into large-scale projects or the so-called mega projects. Such projects typically involve tower architecture. These huge developments are manifested by the continuous vibrant change of the cities’ skylines, which sometimes could be noticed easily within a few weeks.

Appendices

8 Appendix A: Guidelines for Sustainable Tower Architectural Design

A. Built form configuration
A1. Orientation
The long axis of the built form should be oriented east–west so that the long side of the building faces north and south
This allows to design the majority of the windows into the north and south walls and accordingly to reduce solar heat gain
A2. Aspect ratio
As a general rule of thumb, the optimum aspect ratio of the built form should be as 1:2–1:3 for climatic zones nearer to the equatorial zone and lesser at the higher latitudes

B. Arrangement of the building masses
In arid and tropical regions, the service cores of the building should be located on the east and west sides of the building, so as to help shade its form from the low angles of the sun during the major part of the day
Studies show that double-core configuration, with window openings running north and south and cores on the east and west, can achieve significant savings in air-conditioning
The advantage of using this placement is to reduce solar heat gain into the internal user spaces and provides a thermal buffer zone to the hot sides, while at the same time maximizing heat loss away from user spaces

C. Floor-plate design
C1. Position on the site and relation to sun and wind
The floor-plate strategy is about the relationship of the building’s floor plate shape, its position on the site, and its orientation to the sun’s path and wind direction
C2. Floor-plate shape
In hot arid and tropical climates, the optimum shape is a rectangle that minimizes the length of east and west sides while maximizes that of north and south sides, to reduce solar insolation on wider sides
The internal spaces arrangement should be planned to reduce solar gain into high occupancy spaces while service spaces can be used as solar buffers

D. Building skin design
The green approach does not recommend using hermetically sealed skins. The ideal building skin is the one that is environmentally responsive filter, which has to be multi-functional:
• Reduces solar heat gain to the internal space through external shading
• Maximizes the use of daylighting, provides fresh air ventilation
• Serves as acoustic barrier, and contributes to the building’s esthetics
Its permeability to light, heat, and air and its visual transparency must be controlled with flexibility of modification, so that the building can react to changing local climatic conditions

E. Shading devices
Solar shading is needed on east, west, and south sides of the building, especially during the overheated period. Shading by light shelves can help to reduce glare and direct sunlight into deeper reaches of the floor-plate
Fixed shading devices are effective and not costly. Movable devices are more expensive, but provide high flexibility and control to suit outside conditions. Depending upon the season and time of the day, the angle control achieves optimal daylight incidence in combination with minimal heat gain
Intelligent façades operate with automated angle control, regulated by incident radiation and outside air temperature

F. Glazing
Clear glass is often preferred as it gives a more natural light into the inside. Tinted glass has two negative effects: it conducts heat (approx. 80 %) to inside space after it absorbs it and it reduces daylight significantly
Low-e glass reduces direct heat gain by transmitting a greater proportion of light than heat. It has the appearance of clear glass and is useful in situations where daylight is desired, while solar heat gain should be minimized. It allows the use of larger glazing area for admitting daylight, without necessarily incurring an energy penalty. The green approach encourages the use of clear or low emissivity glass
Other new intelligent glazing systems are currently being researched and some are available today such as photo-chromatics, phase-change materials, holographic, and electrically responsive glass

G. Natural and artificial lighting systems
Objective: to enhance the quality of indoor spaces and cut energy consumption through optimizing the use of daylighting and minimizing the need for artificial lighting
Adequate daylight can easily be introduced up to 4.6 m (15 ft) with conventional height window. New technologies can passively redirect sunlight to larger depths (4.6–9.1 m, 15–30 ft); i.e., holographic optical elements, articulated light shelves, and light pipes
Narrowing the width of floor plate to approx. 14 m can help to reduce artificial lighting and optimize natural lighting

9 Appendix B: Case Studies Data (Based on Data Collection and Survey)

	Dubai World Trade Center (DWTC)	Emirates Towers Office Building (ETOB)	National Bank of Abu Dhabi Headquarter (NBAD)
Basic information
Client/owner	Dubai Government	HH Sheikh Mohammed bin Rashid Al Makhtoum	NBAD
Location	Sheikh Zayed Road, Dubai	Sheikh Zayed Road, Dubai	Khalifa Street, Abu Dhabi
Architect	John R. Harns	Hazel Wong	Carlos Ott
Other consultants		NORR, Hyder, DSSR	APG
Date completed	1979	Opened April 2000	Feb. 2003
Gross area	46,567 m2	64,000 m2	37,000 m2
Construction cost	N/A	N/A	200,000,000 AED
Energy performance
Total energy consumption	278 KwH/m2/year	560 KwH/m2/year	N/A
Artificial lighting	40 %	N/A	N/A
Refrigeration cooling	1600 tons	N/A	1500 tons
Mechanical ventilation	20 %	N/A	N/A
Total estimated CO2 output	700 ppm	Not known	Not known
Energy features
Natural vent. (% of floor area)	20 %	Nil	Nil
Thermal transmission of building envelope	Not known	Not known	Above standard
Night-time ventilation provision	Forced, through BMS ventilation is provided as per the enthalpy reading	Forced	Forced
Utilization of building mass for thermal storage	No	No	Yes
Solar control systems	External eggcrate shading devices	Only internal blinds	Only internal blinds
Building designed to maximize use of daylight	Yes	No	No
Net floor area %, needing artificial lighting	60 %	100 %	100 %
Energy-saving controls for artificial lighting	Building management system	Computer-based centralized lighting control system	Lighting control system, access control system
Use of energy-efficient lighting fixtures	Reflective type diffusers	Modular and compact fluorescent luminaries, each light fixture is attached to a lighting control module which supplies power and enables independent or group dimming and on/off switching	Task-oriented fluorescent fixtures with electronic transformer starters saving energy consump. up to 20 % and expand tube life up to 30 %