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  • Tropical architecture in the humid zone
    Tropical architecture in the humid zone
    by Maxwell Fry
  • Manual of Tropical Housing and Building Design
    Manual of Tropical Housing and Building Design
    by O. H. Koenigsberger
  • Off The Grid Homes: Case Studies for Sunstainable Living
    Off The Grid Homes: Case Studies for Sunstainable Living
    by Lori Ryker
  • The Green Studio Handbook: Environmental Strategies for Schematic Design
    The Green Studio Handbook: Environmental Strategies for Schematic Design
    by Alison Kwok, Walter Grondzik
  • Climate Responsive Design: A Study of Buildings in Moderate and Hot Humid Climates
    Climate Responsive Design: A Study of Buildings in Moderate and Hot Humid Climates
    by Richard Hyde
  • Bioclimatic Housing: Innovative Designs for Warmer Climates
    Bioclimatic Housing: Innovative Designs for Warmer Climates
    Earthscan Publications Ltd.
  • Design-Tech: Building Science for Architects
    Design-Tech: Building Science for Architects
    by Jason Alread, Thomas Leslie
  • Fundamentals of Building Energy Dynamics (Solar Heat Technologies)
    Fundamentals of Building Energy Dynamics (Solar Heat Technologies)
    The MIT Press
  • Sun, Wind & Light: Architectural Design Strategies, 2nd Edition
    Sun, Wind & Light: Architectural Design Strategies, 2nd Edition
    by G. Z. Brown, Mark DeKay
  • Passive and Active Environmental Controls: Informing the Schematic Designing of Buildings
    Passive and Active Environmental Controls: Informing the Schematic Designing of Buildings
    by Dean Heerwagen, Dean Heerwagen
  • The Climatic Dwelling: An Introduction to Climate-Responsive Residential Architecture (Eur (Series), 16615 En.)
    The Climatic Dwelling: An Introduction to Climate-Responsive Residential Architecture (Eur (Series), 16615 En.)
    by E. O'Cofaigh, J. A. Olley, J. O. Lewis

 

Elements of Intelligent Design - Location, Location, Location

"In houses with a southern aspect the sun's rays penetrate into the porticos in winter, but in summer the path of the sun is right over our heads and above the roofs, so that there is shade. If, then this is the best arrangement, we should build the south side loftier to get winter sun, and the north side lower to keep out the cold winds."

- Socrates, circa 300 BC, Greece

Where We Are...

Initial steps in the design process include identifying the regional climate zone, local area climatic conditions, and site-specific conditions. Based on the climate information, properly locating the building on the site, defining appropriate building shape and orientation, and satisfying sun, shade, and breeze objectives, are the priorities. Basic, yet specific, design solutions that are based on criteria discussed in the preceding sections for major climatic regions include:

Cold Regions

  • Use dense windbreaks to protect homes from cold winter winds
  • Maximize south-facing windows and allow winter sun to reach them
  • Shade south and west windows from direct summer sun
  • Maximize multi-layered and nested interior spaces help keep the heat inside and the cold outside

Temperate Regions

  • Orient buildings slightly east of south
  • Deflect winter winds away from the home
  • Funnel summer winds toward the home
  • Select and arrange landscaping to maximize warming from the sun in the winter and maximize shading in the summer

Hot + Arid (Dry) Regions:

  • Orient the home's long axis east-west, to minimize surface area exposed to the hot morning (east) and afternoon (west) sun
  • Minimize summer solar heat gain by providing shade to cool roofs, walls, and windows
  • Provide maximum shading for any windows on the east and west sides
  • Maximize opportunities for ventilation
  • Allow summer winds to access homes, but block cold winter winds
  • Choose and locate trees to maximize summer shade and still allow penetration of low-angle winter sun

Warm/Hot + Humid (Wet) Regions (Sub-Tropical/Tropical)

  • Situate the home to maximize exposure to breezes
  • Orient the home's long axis east-west, to minimize surface area exposed to the hot morning (east) and afternoon (west) sun
  • Minimize summer solar heat gain by providing shade to cool roofs, walls, and windows
  • Provide maximum shading for any windows on the east and west sides
  • Maximize opportunities for ventilation
  • Orient walls and landscaping to channel breezes toward the home
  • Choose and locate trees to maximize summer shade and still allow penetration of low-angle winter sun

 

What to do...

This project focuses on the approaches to take for single family residential design in Florida, which is considered a Warm/Hot + Humid (Wet) Region (Sub-Tropical/Tropical). Even though the temperature in the shade rarely exceeds 90 F (32.2 C), the atmosphere has a high vapor pressure (i.e., the summer season's humidity level is consistently high, sometimes reaching 100%), which results in unpleasant, natural living conditions.

Beginning design with passive concepts improves the standard of living within a home by providing a structure that is more energy efficient, comfortable, and healthy than one that ignores them. Optimum results can be achieved if the design is holistic and uses integrated approaches.

Each project and site will have a unique set of opportunities and constraints, and shall be considered on a case-by-case basis. Common characteristics of houses in Warm/Hot + Humid (Wet) regions is their openness. Homes are designed to catch every breeze, as air currents provide the best relief in humid climates. Protection from the sun - deep verandas, shade from trees - enhances the effect of cooling breezes. The most important design considerations for homes in Florida and other sub-tropical and tropical regions include:

 

Building Placement and Orientation

  • Axial orientation E-W (i.e., southern exposure) to 10 degrees east of south is desirable, with 5 degrees east of south representing an optimum balance
  • Maximize the distance between the home and other buildings on the north side (the preferred spacing is a minimun of five building heights between adjacent buildings)
  • Avoid solid enclosure walls or fences that may block wind

 

Programmatic Elements

  • Maximize the amount of daytime living spaces that face north
  • Arrange living spaces so that rooms used at night are on the east side and rooms used in the morning are on the west side
  • Locate utility rooms such as garages and storage sheds on the south side
  • Locate heat, humidity, or odor-producing spaces such as bathrooms, laundry rooms on the lee side of the building
  • Separately ventilate heat, humidity, or odor-producing spaces
  • Separate (and ventilate) heat- and moisture-producing areas from other habitable spaces
  • Provide ceiling fans in major occupied spaces for use when outside wind speeds are too low
  • Maximize combined indoor-outdoor spaces

 

Building Characteristics

  • Minimize radiation effects with plans of up to 1:3 on east-west axis
  • Create plans with one-room depth to maximize cross-ventilation
  • Connect interior spaces with adjacent exterior patio spaces
  • Minimize solid interior partitions

 

Construction

  • Use lightweight (low mass) construction
  • Choose light colored, reflective roof and wall materials
  • Choose materials and finishes that are easiest to keep clean, as dirt increases solar radiation absorption
  • Avoid adjacent exterior surfaces that reflect radiation upon walls
  • Provide insulation (index = 35) relative to South at: E=1.4; W=1.5; N=1.1; Roof=2.3
  • Design for tropical weather (hurricanes/cyclones) structurally, as well as providing removable shutters for openings

 

Shade (non-landscaping)

  • Maximize shading of the entire building - consider using a double (fly) roof arrangement
  • Include generous overhangs to avoid sun and shed rain
  • Provide screened, shaded outdoor living areas
  • Provide shading devices for south-facing windows, if any, to minimize solar gain
  • Maximize north facing windows to increase daylighting without solar heat gain
  • Install shading devices on the outside of windows rather than inside

 

Ventilation

  • Elevate the building to provide airflow below floors
  • Incorporate changes in levels to enhance air movement
  • Ventilate roof spaces
  • Utilize high or raked ceilings
  • Minimize the distinction between walls and openings by creating movable (rollable, foldable), multi-purpose partitions
  • Maximize use of screening, louvers, jalousies, and grills in lieu of solid partitions
  • Consider outdoor sleeping areas
  • Locate large openings in south and north walls
  • Provide relatively smaller windows on the south side for cross ventilation
  • Locate windows other than on the north side high to protect from ground radiation
  • Promote air movement through the use of properly placed windows and wing walls
  • Install insect screens on balconies and/or verandas/porches in lieu of placing them directly on windows

 

Landscaping

  • Place trees and hedges to shade the ground, building surfaces, open outdoor areas, and paved areas
  • Select shade trees that have high branching canopies so that they do not interfere with breezes
  • Keep low vegetation away from walls to avoid blocking air movement
  • Create ground-covered spaces adjacent to interior spaces that receive breezes

 

DESIGN PREMISE

Intelligent Design of modern homes in a Warm/Hot + Humid (Wet) (Sub-Tropical/Tropical) region incorporates natural ventilation with a Heating-Ventilation and Air Conditioning (HVAC) system, creating a fully integrated, zoned and/or seasonally-adjusted, 'hybrid' system. The design process should consider and incorporate zoned and/or seasonally-adjustable elements during the earliest stages in order to maximize their effectiveness.

 

Zoned System

The zoning approach can involve migration of occupants by providing a variety of thermal zones, each of which is comfortable under a different set of of climatic conditions. Because each thermal stage is tuned to a limited set of environmental conditions, its design is simpler. The zone approach may exploit a particular site characteristic such as orientation or placement near, a particular material characteristic such as thermal capacity, a particular climate characteristic such as nighttime downslope winds, or a particular cultural or social pattern such as sleeping outdoors. Traditional examples of such zones are the verandas/porches of the southern U.S. and the rooftop sleeping areas of home in the Middle East.

 

Seasonally Adjustable Buildings

Suitable for natural ventilation for only part of the year, seasonably adjustable buildings aim to balance differing requirements of the various seasons. The characteristics of the building envelope and siting will vary depending upon the length and severity of the seasons. They commonly employ seasonally adjustable features such as storm windows, insulated shutters, and solar shading devices such as awnings and vegetated trellises.

 

Analysis and Testing of Design

A climate analysis should be the first step in determining the percentage of time that natural ventilation will provide comfort and the air velocity required to achieve comfort in the given climate (see ...). This process will also determine possible seasonal variations which may affect design.

Evaluation of quality of ventilation from a human comfort standpoint should include analysis of interior air distribution as well as the amount of airflow. Performing an analytical window sizing procedure (as described in ...) and/or the ASHRAE process (see ...) for determining interior air movement rates for the two worst naturally ventilated months should provide sufficient information to determine the overall effectiveness of the design.

 

Getting with the flow...

The flow of air around buildings is complex and highly dependent on wind direction and building geometry. Features such as eaves, canopies, parapets, wingwalls, and neighboring buildings and landscaping may change the flow pattern around a building significantly.

 

AIRFLOW AROUND A SINGLE BUILDING

When moving air encounters an obstruction such as a building, a portion of the air movement is stopped or slowed. The deceleration converts the kinetic energy of the flow to potential energy in the form of positive pressure. If the obstruction is very streamlined, the region over which this positive pressure exists is very small (e.g., an airplane wing). On the other hand, if the obstruction is large and unstreamlined, such as the face of a building, the region of positive pressure is roughly as large as the face of the building.

As the air is squeezed around, above, or below the building, the velocity accelerates and the potential energy of the positive pressure build-up is converted back into kinetic energy. When the velocity exceeds that of the approach flow, the potential energy will be lower than that of the ambient flow, resulting in negative pressures, or suctions.

As the wind approaches a sharp corner of the building, it tries to follow the geometry around the corner, but cannot due to the momentum of the flow. The wind separates from the building, defining an upstream limit of the wake. Within the wake, the pressure is negative, and there is relatively little air movement. At the boundary between the wake and the free stream there is substantial turbulence. Momentum transfer across the wake boundary tends to blur the position of the boundary. The free-stream airflow curves in toward the wake from all sides until it rejoins the ground or the opposite streamline downstream of the obstacle. The point at which the free-stream airflows rejoin defines the end of the wake cavity. FIG A-8

 

Airflow Pressure Zones

In order for the free-stream airflows to be drawn back together ti rejoin downstream of the obstacle, the pressures must be negative withing the entire wake. The greater the suction, the faster the free-stream airflows are drawn together. Diagrammatically, the highest suctions occur where the radius of curvature of the wake boundary is smallest. At the end of the wake, where the wake suction approaches zero (i.e., the ambient pressure), the radius of curvature of the wake cavity approaches infinity. Since flows within the wake are small, structures placed and fully engulfed in the wake will not significantly alter the shape of the wake. [FIG A-9 to come]

 

Wake Geometry

The geometry of the wake is important because it defines the limits of significant air movement. Outside the wake, the air movement is similar to that of the free-stream, but the area within the wake may be considered as a cavity of relatively still air, where the pressure differences needed for building ventilation are unlikely to occur.

 

 

AIRFLOW AROUND MULTIPLE BUILDINGS

Airflow around groups of buildings or other obstructions is very complex. The diagram shows the general airflow patterns that are commonly found to produce strong winds. These patterns may be used to benefit the ventilation of buildings in their path, but they might also adversely affect the comfort of pedestrians outside the buildings or in semi enclosed courtyards, hallways, or balconies.

 

Downwash

Some of the strongest winds around buildings are found at the windward side and edges of tall buildings protruding above the surrounding general level of development. This effect occurs because winds aloft are stronger than at ground level, causing higher pressures at the top od a building's windward face than st its base. This pressure difference creates a strong downward flow on the windward face. [FIG A-10 to come]

 

Corner Effect

Strong winds occur at building corners as the airflows from the higher pressure zone on a building's windward side to the low pressure zone on the leeward side. Accelerated wind is generally restricted to an area with radius no longer than the building's width. The taller and wider the building, the more intense the effect. If two towers of 30 stories or more are placed less than two building widths apart, an acceleration will fill the entire space between them. [FIG A-11 to come]

 

Gap Effect

When a building of five stories or more is elevated on columns or has an open passageway through it, air forced through the opening(s) creates a channel of intensified wind in the opening and on its downwind side. [FIG A-12 to come]

 

Pressure Connection Effect

Pressure connection effects develop as the wind approaches parallel rows of offset buildings, creating suctions between them that draw in downdrafts from exposed windward faces and create transverse flows along the ground into the wake regions. The intensity of the effect varies with building height, with taller buildings producing more intense effects. The effects intensify further if the crossflow channel is narrow and regular. [FIG A-13 to come]

 

Channel Effect

A street or other open space lined with tightly grouped sets of buildings can tend to channel the wind if the space is long and narrow (less than three heights) in relation to the heights of the buildings which bound it. [FIG A-14 to come]

 

Venturi Effect

the venturi effect occurs when two large buildings are placed at an angle to each other creating a funnel with a narrow opening that is no more than two or three times the building height. winds channeling through the opening are accelerated to high speeds. This effect occurs only when the buildings are at least five stories high, have a combined length of 300 feet, and when the areas in front of and behind the venturi are relatively open.

 

Pyramid Effect

Pyramidal structures offer little resistance to the wind, and generally seem to disperse the wind energy in all directions. One application of the pyramid principle is the use of tiered configurations in the design of tall buildings as a way of reducing airflow, wake, and corner effects.

 

In the sections that follow ... It is important to understand that none of the sections is independent of the others. Each section must be considered in conjunction with all of the others as a successful design will only be realized by incorporating all parameters.

It is interesting to note that some of the most comprehensive and informative discussion of building techniques apropos of tropical climates comes from the U.S. military. This is logical though, as the various organizations are required to create comfortable living conditions, in every climate, using minimal resources, in an efficient and effective manner. Accordingly, much of the following is derived from a DOD document entitled Cooling Buildings By Natural Ventilation, (UFC 3-440-06N / 16 January 2004, Approved for Public Release). As additional pertinent information is 'discovered' through research and investigation it has been and will continue to be added in the following sections.