Guide To Natural Ventilation in High Rise Office Buildings

Antony Wood, Antony Wood, Ruba Salib, Antony Wood, Ruba Salib

• Publisher: Routledge
• Year: 2012
• Print ISBN:
  9780415509589
  9781138408692
• eBook ISBN:
  9781135872113
• Edition: 1
• Topic: Architecture
• Subtopic: Architecture General

Tall buildings are not the only solution for achieving sustainability through increased density in cities but, given the scale of current population shifts, the vertical city is increasingly being seen as the most viable solution for many urban centers. However, the full implications of concentrating more people on smaller plots of land by building vertically - whether for work, residential or leisure functions - needs to be better researched and understood.

It is generally accepted that we need to reduce the energy equation – in both operating and embodied terms – of every component and system in the building as an essential element in making it more sustainable. Mechanical HVAC systems (Heating, Ventilation and Air-Conditioning) in tall office buildings typically account for 30-40 percent of overall building energy consumption. The increased efficiency (or possibly even elimination) of these mechanical systems – through the provision of natural ventilation – could thus be argued to be the most important single step we could make in making tall buildings more sustainable.

This guide sets out recommendations for every phase of the planning, construction and operation of natural ventilation systems in these buildings, including local climatic factors that need to be taken into account, how to plan for seasonal variations in weather, and the risks in adopting different implementation strategies. All of the recommendations are based on analysis of the research findings from richly-illustrated international case studies.

Tried and tested solutions to real-life problems make this an essential guide for anyone working on the design and operation of tall buildings anywhere in the world. This is the first technical guide from the Council on Tall Buildings and Urban Habitat's Tall Buildings & Sustainability Working Group looking in depth at a key element in the creation of tall buildings with a much-reduced environmental impact, while taking the industry closer to an appreciation of what constitutes a sustainable tall building, and what factors affect the sustainability threshold for tall.

1.0 Introduction and Background

1.0 Introduction and Background

1.1 Historical Overview of Natural Ventilation in High-Rise Office Buildings

The 19th century marked the emergence of the office building typology as we know it today. Controlling the indoor environment in these early office buildings was achieved by passive means. In most US and European cities, operable windows were used for natural ventilation and for keeping cool, while stoves and radiators were the main sources of heat energy when it was cold. The high cost of electricity and the need to conduct tasks under natural lighting conditions had a profound impact on the design of office buildings. The need to provide adequate daylight limited the depth of office floor plans, and consequently enabled natural ventilation by means of operable windows.

Although keeping cool was not a major concern for architects at the time, natural ventilation was considered necessary for sanitary purposes and for the elimination of excessive humidity. Furthermore, many of the large office buildings during that period were influenced by the classical styles of architecture, which involved the use of central open courts, or light-wells, that limited plan depths to allow natural light and air into the interior.

This building type became particularly common in Chicago during the office building boom that followed the Great Fire of 1871. The building type was referred to as the “Chicago Quarter Block” because it employed open courts and occupied the plot of the entire city block between streets. This building type was also exported to many other US cities, where it was used as a model for emerging office buildings.

Light courts were integrated into the buildings in E, H, and U-shaped plan arrangements (Arnold 1999a, pp. 40–54). Louis Sullivan’s Wainwright Building in St. Louis, which was completed in 1891, is a good example of the adoption of this classical style (based on the Uffizi in Florence) through the use of a U-shaped plan to provide light and air to every office (see Figure 1.1). It is also worth noting that external sunshades were integrated into the design of the Wainwright Building as a passive means of controlling solar gains and providing thermal comfort.

Figure 1.1: View of the 1891 Wainwright Building, St. Louis (top); and typical floor plan (bottom). © Antony Wood/CTBUH

Built in 1924, the Straus Building in Chicago (a 21-story building with a nine-story tower) set another example of how the classical style was adopted through the use of a large central light court (see Figure 1.2).

Figure 1.2: View of the 1924 Straus Building, Chicago (top); and typical floor plan (bottom). © Marshall Gerometta/CTBUH

At the beginning of the 20th century, architects started to design many of the most prominent skyscrapers in New York on the same basis. Iconic buildings such as the Chrysler Building (1930), and the Empire State Building (1931) reached unprecedented heights while still relying on natural ventilation and lighting. The form of these skyscrapers and the depth of their plans (see Figure 1.3) were still driven by the need to provide natural light for office interiors, with no particular emphasis given to the development of a natural ventilation strategy.

Figure 1.3: View of the 1930 Chrysler Building, New York (top); and typical floor plan (bottom). © Steven Henry/CTBUH

By the 1950s, the availability of cheap energy and the widespread use of air-conditioning had a profound impact on the form and planning of office buildings. The ability to control indoor temperature and humidity by mechanical means eliminated the restrictions architects faced with regards to plan form, plan depth, and window fenestrations. In other words, the consideration of passive measures to provide comfortable indoor environments were no longer a central concern for architects and engineers at that time. The dependence on air-conditioning allowed the emergence of deep-planned, transparent office buildings with curtain-walled windows. The heavyweight stone or brick-clad skyscrapers of the early 1900s were replaced by the light, fully-glazed office buildings of the 1950s and 1960s. Renowned architect Mies van der Rohe’s work in high-rise buildings exemplifies this era of the all-glass-box style of architecture, from his 1958 Seagram Building in New York (see Figure 1.4), to his 1972 IBM Building in Chicago. The increased transparency and lightness of the structure, as well as the lack of solar shading devices, placed a higher load on air-conditioning systems to cool down buildings during the summer and to heat them during the winter (in temperate climates).

Figure 1.4: View of the 1958 Seagram Building, New York (top); and typical floor plan (bottom). © Antony Wood/CTBUH

The oil crisis of 1973 marked another turning point in the development of office buildings. As a result of this crisis, western countries aimed to reduce global energy consumption – mainly by reducing the energy used in buildings for heating, cooling, and ventilation. The proposed solutions mainly focused on increasing the insulation level of building envelopes and reducing the air infiltration level by sealing the building. In other words, the main goal was to reduce the consumption of fuel by reducing heat loss through ventilation. The introduction of these increasingly sealed office buildings impacted negatively the comfort and health of the occupants. This resulted in the deterioration of indoor air quality and the spread of diseases due to humidity condensation and the growth of mold (e.g., “sick building syndrome”). The lack of fresh air and the overheating problems in summer affected the productivity and performance of office workers.

As a response to the oil crisis and the development of building-related illnesses, designers started to consider energy conservation measures that provided healthier and more comfortable working environments. The 1980s and 1990s thus marked the start of greater building energy efficiency and a return to considering the benefits of natural ventilation in buildings, as well as passive heating and cooling strategies in office building designs. This report will focus on the most advanced strategies adopted to naturally ventilate high-rise office buildings during the late 20th and early 21st centuries.

1.2 The Principles of Natural Ventilation in a High-Rise Building

The driving forces for natural ventilation in a tall building are of course the same as those for other buildings. The physical mechanisms for natural ventilation rely on the pressure differences generated across the envelope openings of a building. The pressure differences are generated by:

(I) the effects of wind,

(II) temperature differences (gravity acting on density) between inlet and outlet of air, or

(III) a combination of both.

Natural ventilation can therefore be categorized into “wind-induced” and “buoyancy-induced” ventilation according to the physical mechanism driving the air. Wind-induced ventilation occurs when wind creates a pressure distribution around a building with respect to the atmospheric pressure (see Figure 1.5). The pressure differences drive air into the building’s envelope on the windward side (positive pressure zone) and out of the building through the openings on the leeward side (negative pressure zone). The pressure effect of the wind on a building is primarily dominated by the building’s shape, the wind direction and velocity, and the influence of the surroundings, which are all factors that influence the pressure coefficient. In addition to the value of the pressure coefficient, the mean pressure difference across a building’s envelope is dependent upon the mean wind velocity at upwind building height, and the indoor air density as a function of atmospheric pressure, temperature, and humidity.

Figure 1.5: Pressure distribution around a building due to wind flow.

Buoyancy-induced ventilation (also known as “stack effect” or the “chimney effect”) occurs due to density differences caused by variations in temperature and height between the inside and the outside or between certain zones within a building. The pressure differences generated by buoyancy are mainly dependant on the stack height (the height difference between air intake and extract openings) and the air density difference as a function of temperature and moisture content in the air. To guarantee inward airflow in the absence of wind, it is important to ensure that outdoor temperatures are lower than indoor temperatures to achieve buoyancy-induced ventilation. When the indoor air temperature exceeds the outdoor temperature, an under-pressure is formed in the lower part of a building, pulling air inwards through the openings in the envelope (although, if outdoor temperatures are equal to indoor temperatures, buoyancy can still occur due to internal loadings). As the air travels through the building, it is heated by the internal gains and building occupants.

The density difference caused by the indoor/outdoor temperature difference results in a different pressure gradient in the building. The over-pressured zones at the top of the building drive air out of the openings in the building (since air flows from areas of high pressure to areas of low pressure). At a certain height of the building, however, the indoor pressure and the outdoor pressure are equal to each other. This level is referred to as the “neutral plane” or “neutral pressure level” (see Figure 1.6). In order to achieve effective buoyancy-induced ventilation, there has to be a significant temperature differential between the inlet and outlet of air, and minimal internal resistance to air movement within the interior spaces (e.g., on most buildings where floor plates cover ...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Contents
• About the CTBUH
• About the Authors
• Preface
• 1.0 Introduction and Background
• 2.0 Case Studies
• 3.0 Design Considerations, Risks, and Limitations
• 4.0 Recommendations and Future Research
• 5.0 References