Sustainable design requires awareness of ventilation patterns when designing. In residences, comfort is more easily addressed with a few operable windows. The effect of airspeed on comfort has been studied as part of HVAC system design, but it is less well understood in mixed-mode systems where HVAC systems and natural ventilation are both used to provide comfort.

The natural air change rate within a building depends on several factors:

• Speed and direction of winds at the building site
• External geometry of the building and adjacent surroundings
• Window type, size, location, and geometry
• The building’s internal partition layout

Each of these factors may have an overriding influence on the air change rate of a given building.

NATURAL VENTILATION TYPOLOGIES

There are two main types of natural ventilation: cross ventilation and stack ventilation.

Cross Ventilation

Cross ventilation is a type of wind ventilation and among the easiest and cheapest forms of natural, passive ventilation. Simply put, cross ventilation is the placing of openings or windows to strategically allow for natural breezes to pass through the space. This can be done with windows on opposing walls, neighboring walls, or even two openings within a single wall.

According to sustainabilityworkshop.com, having two openings directly opposite each other is not always optimal, as it can cause parts of the building not directly in that path to end up with stagnant air. “Placing openings across from, but not directly opposite, each other causes the room’s air to mix, better distributing the cooling and fresh air.” Larger openings on the leeward side and smaller ones on the windward side can also help.

Stack Ventilation

Meanwhile, stack ventilation makes use of differences in temperature to cause air to move around. Most people know that warm air rises, and when it does, fresh, cooler, moving air flows in to replace it.

A related concept is a solar chimney, a device that uses the sun to warm columns of air, which then rise and facilitate stack ventilation. In their simplest form, solar chimneys are simply pipes that have been painted black, maximizing the solar energy that is absorbed and heating the air inside. Per sustainabilityworkshop.com, “[s]olar chimneys need their exhaust higher than roof level, and need generous sun exposure. They are generally most effective for climates with a lot of sun and little wind; climates with more wind on hot days can usually get more ventilation using the wind itself.

ASHRAE STANDARDS FOR VENTILATION

ASHRAE (American Society of Heating, Refrigerating, and Air‐Conditioning Engineers) standards and guidelines dominate the design of HVAC systems. AHRI (Air‐Conditioning, Heating, and Refrigeration Institute) standards dominate equipment certifications. Federal requirements establish minimum equipment efficiency thresholds. A series of Advanced Energy Design Guides (available through ASHRAE) provides recommendations for designing a variety of building types to substantially exceed code‐mandated energy performance. HVAC systems will play a key role in achieving green building certification under LEED or Green Globes. Key standards affecting the design of most commercial/institutional projects include:

• ASHRAE Standard 90.1, “Energy Standard for Buildings Except Low‐Rise Residential Buildings”
• ASHRAE Standard 55, “Thermal Environmental Conditions for Human Occupancy”
• ASHRAE Standard 62.1, “Ventilation for Acceptable Indoor Air Quality”
• ASHRAE Guideline 0, “The Commissioning Process”

ASHRAE Standard 62.1 is, in particular, relevant to ventilation. ANSI/ASHRAE Standards 62.1 and 62.2 are the recognized standards for ventilation system design and acceptable IAQ. First published in 1973 as Standard 62, Standard 62.1 specifies minimum ventilation rates and other measures for new and existing buildings that are intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects. More information is available here.

In AGS Online, “Ventilation—An Integral Part of Sustainable Design,” the basic principles of ventilation are studied. The illustrations presented in this discussion are based on both isolated buildings and neighborhoods, as well as the effects of vegetation. Additional material pertaining to ventilation change rate, external effects, effect of wind incidence angle on airflow rates, and rule-of-thumb examples are included. It’s a good introduction to the basic principles of ventilation.

 

 

In the practice of architecture, daylighting refers to the use of natural light, be it brilliant sunlight or muted overcast light, to support the visual demands of building occupants. Research supports daylighting’s positive effect on building performance and human health. Along with happier workers, substantial financial and human-performance benefits have been associated with increased daylight.

To be successful, daylighting requires the integration of all major building systems. Daylighting issues should be well-defined in the programmatic or schematic phases of design and monitored through construction to occupancy. Early planning is essential because it may be difficult and costly to add features later in design development. Many architects and lighting designers are skilled in resolving daylighting design issues and trade-offs. However, in designs that push the state-of-the-art, present unusual conditions, or designs that have quantitative performance expectations that must be met, it may be appropriate to use a daylighting consultant with expertise in many of the computer-based tools now available.

DAYLIGHTING: A DEFINITION

Architects understand design of space and light as a central principle of form making. The term daylighting requires clear definition, as it represents multiple design intentions, often at cross‐purposes. Daylighting design incorporates strategies for controlling the way light enters a building while also considering energy, lighting design, operable shades, and controls. Daylighting design uses scientific tools, but it is ultimately an art, concerned with comfort, quality of light, and space, as well as more measurable attributes such as footcandle levels and energy savings.

DAYLIGHTING OPPORTUNITIES

An atrium with the predominant function to provide natural lighting takes its shape from the predominant sky condition. In cool, cloudy climates, ideally, the atrium cross-section would be stepped outward as it gets higher to increase overhead lighting. In hot sunny locations with clear sunny skies, the cross-section is like a large lighting fixture designed to reflect, diffuse, and make usable the light from above. Daylighting design is complicated by the movement of the sun as it changes position with respect to the building throughout the day and the year.

Use skylighting for daylighting with proper solar controls. Skylighting that is properly sized and oriented is an efficient and cost‐effective source of lighting. Consider that for most office buildings, sunlight is available for nearly the entire period of occupancy and that the lighting requirement for interior lighting is only about 1 percent of the amount of light available outside. Electric lighting costs, peak demand charges, and work interruptions during power brownouts can be greatly reduced by using daylight. Cost‐effective, energy‐efficient skylights can be small and spaced widely, with “splayed” interior light wells that help reflect and diffuse the light. White‐painted ceilings and walls further improve the efficiency of daylighting (by as much as 300 percent, when compared with dark interior finishes). Skylights should include some means to control undesired solar gain by one or more of the following means: (1) Face the skylight to the polar orientation; (2) provide exterior light‐reflecting sun shading; and (3) provide movable sunshades on the inside, with a means to vent the heat above the sunshade.

MANAGING GLARE WITH NATURAL LIGHTING

According to a post on the Buildings Buzz blog on buildings.com, the greatest challenge to daylight design is managing glare, which can cause a handful of physical problems. Per the post:

“Vast amounts of daylight may save energy, but uncontrolled glare can cause headaches, eyestrain, decreased productivity, and increased absenteeism, quickly offsetting achieved energy savings. Smart shading devices know when to close for glare mitigation, as well as open when glare is no longer present to maximize views and daylight autonomy.”

One solution to the challenge of managing glare is dynamic fenestration. For example, tinting reduces glare, though at the cost of reduced daylight. Conversely, increasing window size can then improve daylight—at the expense of increased glare. Dynamic fenestration, which allows for automated shading, is one solution to this and can be installed for only a few hundred dollars for each window, according to buildings.com.

Another option is light shelves, which reflect direct sunlight onto the ceiling into a space. A light shelf can be located inside or outside the building. Light shelves are not exterior shades by definition, but an exterior sun shade with a reflective top surface can be a light shelf. Other exterior shading elements such as overhangs and awnings can limit direct‐beam penetration into a space, though such elements also cut down on daylight. The best solution in any particular situation involves consideration of the planning and use of the space, climate, and expectations related to use and comfort.

AGS Online, “Daylighting” offers an introduction and graphic illustrations for the young architect looking for daylighting options to incorporate into his next-generation building design. New types of light-redirecting systems, such as prismatic glazings, provide shading at a task location by redirecting the sunlight to the ceiling. This and other systems are discussed and explored.

Fundamental design principles related to orientation, massing, and openings can have a greater overall effect than the application of advanced technology. The best architecture can function in an “unplugged” state in good weather and then take advantage of climate control only when needed. This approach, using shading devices,  provides “energy security,” allowing buildings to remain occupied without outside energy.

By overlaying a shading mask in the proper orientation on the sun-path diagram, you can read off the times when the sun rays will be intercepted. Masks can be drawn for full shade (100 percent mask) when the observation point is at the lowest point of the surface needing shading, or for 50 percent shading when the observation point is placed at the halfway mark on the surface. It is customary to design a shading device in such a way that, as soon as shading is needed on a surface, the masking angle should exceed 50 percent.

WHAT IS A SHADING MASK?

According to the U.S. Green Building Council, a shading mask is “a representation of the sky as viewed from a reference point, indicating the portion of sky that is visible and obstructed.” This tool is part of the passive solar design process that helps determine solar access, along with a sun-path diagram. Software is available that can be used to create a shading mask.

SHADING DEVICES AND SHADING COEFFICIENT

Each individual fenestration system, consisting of glazing and shading devices, has a unique capability to admit solar heat. This property is evaluated in terms of its shading coefficient (SC), which is the ratio of the amount of solar heat admitted by the system under consideration to the solar heat gain factor for the same conditions. In equation form, this becomes:

Solar heat gain(Btu/sq.ft.*hr)=SC×SHGF

Values of the shading coefficient also are given in the ASHRAE Handbook of Fundamentals (1981), Chapter 27, for the most widely used glazing materials alone and in combination with internal and external shading devices. Selected values for single and double glazing are given below:

SHADING COEFFICIENT FOR SELECTED GLAZING SYSTEMS

TYPE OF GLASS	SOLAR TRANSMISSION	SHADING COEFFICIENT
Clear
1/8″	0.86	1.00
1/4″	0.78	0.94
Heat‐absorbing
1/8″	0.64	0.83
1/4″	0.46	0.69
Insulating glass: clear both lights
1/8″ + 1/8″	0.71	0.88
1/4″ + 1/4″	0.61	0.81
Heat‐absorbing out
Clear in, 1/4″	0.36	0.55

For combinations of glazing and shading devices, also refer to the ASHRAE Handbook of Fundamentals, Chapter 27.

TYPES OF SHADING DEVICES

Vertical Rolling Shutters

Rolling shutters provide sun control not only by shading windows from direct sun rays but also by way of two dead airspaces—one between the shutter and window, the other within the shutter extrusions to serve as insulation. The dead airspaces work as well in winter to prevent the escape of heat from the interior. In addition, shutters are useful as privacy and security measures. They can be installed in new or existing construction and are manufactured in standard window sizes. They are also effective for storm protection. They are composed of vertical rolling shutters with head box, metal angle brace, shutter slats PVC or extruded aluminum, guide rail, and rod or cord control.

External Venetian Blinds

External blinds protect the building interior from solar gain and glare and can be raised partially or fully to the head when not needed. Manual or electric control is from inside the building. They are composed of aluminum slats, side guide or wires, and rod control for tilting or lifting.

Horizontal Rolling Shutters

These miniature external louvers shade windows from direct sunlight and glare, while allowing a high degree of visibility, light ventilation, insect protection, and daytime privacy. The solar screen is installed in aluminum frames and can be adapted to suit most applications. They are composed of a head and sill with fixed and side-hinged horizontal sliding and aluminum frames positioned in different angles—45ᴼ, 30ᴼ, 15ᴼ, and 0ᴼ.

Architects are graphically oriented professionals and need quick access to potential shading device options with components that will adapt to a variety of overall floor plans. For more than 85 years, Architectural Graphic Standards (AGS) has sought to provide architects with graphic illustrations of the most current design practices and standards. Now, AGS Online provides these graphic illustrations for “Shading Masks and Shading Devices” in a downloadable format.

Climate control systems (solar heating/cooling systems) may be classified as either active or passive in nature. Passive systems use no purchased energy resources; normally are assembled of “architectural” building elements doing double duty, such as glazings, walls, floors, and finishes; and require design coordination. Cooling, for example, can include induced air precooled from the earth’s mass using air-to-earth heat exchangers (“coolth” tubes) or cooling ponds. Systems can be combined depending on thermal needs. Active climate control systems use purchased energy resources and employ task-specific, single-purpose elements, such as pumps, fans, ducts, and diffusers. Although mechanical engineers usually design HVAC systems, they must coordinate with the entire project.

Passive Solar Heating

A passive solar heating system can displace all, a substantial part of, or some portion of annual heating demands—depending upon system design and project climate. Even where a passive heating system cannot reasonably handle all heating needs—necessitating installation of a backup active heating system—the passive system can contribute to efforts to reach net‐zero energy status without the installation of a larger‐than‐necessary PV or wind system and, perhaps more importantly, reduce carbon emissions related to building heating. There are three basic passive heating system configurations: direct gain, indirect gain (see image below), and isolated gain. A direct gain system is essentially south‐facing glazing coupled with interior thermal mass and with appropriate solar and heat loss control mechanisms. There are three distinct forms of indirect gain systems: Trombe walls, water walls, and roof ponds. Isolated gain systems typically take the form of a sunspace.

Passive Solar Cooling

A passive cooling system uses an exterior condition (such as dry‐bulb air temperature, soil temperature, or night sky temperature) as a heat sink where heat from a building interior can be dumped. As opposed to a passive heating system that obtains substantial heat flow from one source—solar radiation—passive cooling systems typically seek appropriate heat sinks in the face of challenging exterior conditions. The capacity of most heat sinks is inversely proportional to cooling demands—the greater the need for cooling, usually the lower the capacity of passive cooling systems. Nevertheless, a passive cooling system can reduce climate control energy consumption and carbon emissions associated with space cooling.

Passive vs. Active Climate Control Systems

Climate control systems are fundamentally either active or passive. Passive systems use no purchased energy resources, normally are assembled of “architectural” building elements doing double duty (such as glazings, walls, floors, finishes), and require design coordination. Active climate control (HVAC) systems use purchased energy resources and employ task‐specific, single‐purpose elements (such as pumps, fans, ducts, and diffusers).

Thermal Storage Walls, Ground-Source Hat Pumps, and Other Passive Elements

Thermal Storage Walls

A thermal storage wall is a mass wall, usually masonry, located directly behind solar glazing (facing the equator), according to 2030 Palette. The wall and solar glazing area should be sized as a percentage of the floor area to be heated, based on the latitude and corresponding climate. The color of the wall may also be different based on the usable space and the presence of a convective connection.

Ground-Source Heat Pumps

Also called a geothermal heat pump (GHP), GeoExchange, earth-coupled heat pump, or heat source, ground-source heat pumps have been in use since the late 1940s, per the U.S. Department of Energy. They use the constant temperature of the earth as the exchange medium instead of the outside air temperature.

There are several types of ground-source heat pumps: closed-loop, horizontal, vertical, pond/lake, open-loop, and hybrid, but all of them work off the same basic premise:

“Although many parts of the country experience seasonal temperature extremes—from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth’s surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45 °F (7 °C) to 75 °F (21 °C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger.”

As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water.

Thermosiphon

Natural convection systems rely on the rise and fall of heated and cooled elements such as air. As temperatures change, air moves without mechanical assistance. When the sun warms a collector surface, warm air rises. Simultaneously, cooler air is pulled from the storage bottom, causing a natural convection loop. Heat is convected into the space or stored in the thermal mass until needed.

Coolth Tubes

Coolth tubes are a component of isolated systems in passive solar design. Heat gain or loss occurs away from the weatherskin in these systems, and cooling can include air precooled from the earth’s mass using air to earth heat exchanges such as coolth tubes or cooling ponds.

These and other considerations are now explored with AGS Online, “Passive Solar Heating and Cooling Systems.” The online update provides a good introduction into the alternative system options for passive energy systems. Additionally, this topic includes design limitations, components of passive solar systems, and conceptual graphic illustrations for the architect to consider.

Sustainable design is not a new concept but rather at the heart of sound, place-based design, from the vernacular traditions of Vitruvius to the modern era. Basic elements of bioclimatic design are passive solar systems that are incorporated onto buildings and utilize environmental sources (i.e. sun, air, wind, vegetation, water, soil, sky) for heating, cooling, and lighting buildings. Passive systems can and should be incorporated with advanced technology in building design. Fundamental design principles related to orientation, massing, and openings can have greater overall effect than the application of advanced technology. The best architecture can function in an “unplugged” state in good weather and then take advantage of climate control only when needed.

Bioclimatic Design

According to Greece’s Center for Renewable Energy Sources and Saving (CRES), bioclimatic design is:

“the design of buildings and spaces (interior—exterior—outdoor) based on local climate, aimed at providing thermal and visual comfort, making use of solar energy and other environmental sources.”

One of the keys of bioclimatic design is taking into account the environment in which the building is located, from sun and wind to soil and vegetation on the ground. Per the CRES, some ways this can be done include:

• Heat protection of the building
• Use of solar energy
• Removal of heat

Climate Implications for Bioclimatic Design

Although classified as arid and overheated, severe desert climates in the United States typically have four distinct periods for determining comfort strategies, which can be categorized as the hot dry season, the hot humid season, the winter season, and the transitional or thermal sailing season.

The hot dry season covers most of the warm half of the year, ranging from the late spring to the early fall, as well as the early summer. It has dry, clear atmospheres that provide high insulation levels and daytime air temperatures and large thermal radiation losses at night. It is distinct from the hot humid season of July and August, which has high dew point temperatures and a reduced usefulness of evaporative cooling for comfort conditioning. The daily temperature range is 20 °F or less, compared to 30 ° to 40 °F in the hot dry season, thanks in large part to less nighttime thermal re-radiation. As a result, the humid season requires refrigeration or dehumidification even in the night, unlike the dry season.

The winter season, conversely, has clear skies, cold nights, very low dew point temperatures, a daily range of nearly 40 °F, and the opportunity for passively meeting all heating requirements from isolation. Buffering this season from the hot dry season is the transitional season and requires no intervention by environmental control systems.

• The hot dry season, occurring in late spring, early summer, and early fall, has dry, clear atmospheres that provide high insulation levels, high daytime air temperatures, very high sol‐air temperatures, and large thermal radiation losses at night, producing a daily range of 30 ° to 40 °F. Nighttime temperatures may fall below the comfort limits and are useful for cooling. Low humidity allows effective evaporative cooling.
• The hot humid seasonoccurs in July and August. In addition to high insulation, it is characterized by high dew point temperatures (above 55 °F), reducing the usefulness of evaporative cooling for comfort conditioning. Cloudiness and haze prevent nighttime thermal re‐radiation, resulting in a daily range of only a 20 °F or less. The lowest nighttime temperatures are frequently higher than the comfort limits. Thus, refrigeration or dehumidification may be needed to meet comfort standards.
• The winter seasontypically has clear skies, cold nights, very low dew point temperatures, a daily range of nearly 40 °F, and the opportunity for passively meeting all heating requirements from isolation.
• The transitionalor thermal sailing season occurs before and after the winter season and requires no intervention by environmental control systems. This season can be extended by the passive features of the building. Other desert climates have similar seasons but in different proportions and at cooler scales.

Bioclimatic Design for Cold Climates

Unlike in the severe desert climates covered above, design considerations in very cold climates in North America (general north of the 40th parallel) are dominated by considerations for foundations and the permafrost on which they are built.

Foundations in these climates are extremely important and technically challenging to design. The danger for foundations in these climates is that the soil around and under the foundation might thaw and lose strength. There are several strategies for designing in these areas. Both self‐contained convection (passive) and mechanically refrigerated (active) systems are used for new construction and stabilization of existing foundations, either directly as pipe piles or in smaller pipes (probes) that can be placed beside a pile or under a slab or foundation.

For cold and underheated climates, such as in the northern half of the United States and its mountainous regions, designing foundations is treated in a more typical manner, such as providing a foundation below the frost depth, including a basement, and providing insulation on the exterior to reduce the cold ground temperatures from reaching the structure.

Energy Conservation in Building Design

Capitalize on climatic conditions by incorporating construction practices that respond in beneficial ways to the environment, including:

• Insulate coolant and refrigerant pipes from remote evaporative towers and condensers for their entire length.
• In hot locations, use roof construction similar to the cold climate roof detail.
• Do not use exposed wood (especially in small cross-sections) and many plastics, as they deteriorate from excessive heat and high ultraviolet exposure.
• Although vapor retarders may not be critical to control condensation, implement them as a building wrap or wind shield, both to control dust penetration and to avoid convective leaks from high temperature differentials.
• Avoid thermal bridges such as extensive cantilevered slabs.
• Radiant barriers and details appropriate to humid overheated climates are at least as effective as vapor retarders, but avoid holes in assembly where convection would leak their thermal advantage.
• Ventilate building skin (attic or roof, walls) to relieve sol‐air heat transfer.

Suggestions and diagrams pertaining to bioclimatic design are now available with AGS Online. For more than 85 years, Architectural Graphic Standards (AGS) has sought to provide architects with the most current design practices and standards. With the power of electronic online publishing, AGS Online is able to continuously update technical and design knowledge in an industry that can’t wait on traditional book publishing. “Bioclimatic Design” is one of many AGS Online series that addresses the needs of a changing world and reflects the current standard of care in building design. It includes a step-by-step design process and figures showing what is current best practice.