Passives Test 2

Sleeping Porch

a deck or balcony, sometimes screened or otherwise enclosed with screened windows, and furnished for sleeping in warmer months

Arcade

a series of arches carried by columns or piers or a covered walkway that provides access to adjacent shops. They are popular in hot climates to shade both storefronts and pedestrians.

Selective low-e glazing

The low-e coating blocks the short-wave (solar) infrared radiation more than light radiation thereby providing "cool daylight."

Roof radiation trap

The glazing on the roof is tilted to maximize winter collection at any latitude. After passing through the glazing, the solar radiation is absorbed by the black-painted concrete ceiling slab. The building is, thus, heated by radiation from the ceiling.

Radiation traps

The greenhouse gases in the atmosphere act as a one. They allow most of the solar radiation to pass through to reach the earth's surface, which then radiates increased amounts of heat back toward space in the form of long-wave infrared radiation, but the greenhouse gases trap some of this radiation.

a. Orientation b. Plan c. Slope of Glazing d. Shading e. Reflectors f. Conservation

The important Passive Solar Design Considerations

Solar Heat Gain

The increase in thermal energy of a space, object, or structure as it absorbs incident solar radiation. The intensity of solar radiation reaching the surface of the earth combined with its angle

Candlepower

The intensity of a light source in any given direction - measured in Candelas

Direct radiant cooling

A building's roof structure cools by radiation to the night sky. An exposed concrete roof will rapidly lose heat by radiating to the night sky but in the next day, the cool mass of concrete can effectively cool a building by acting as a heat sink.

Eggcrate

A combination of vertical and horizontal elements can be used for shading, when these elements are closely spaced, the system is called an

Wind Exposure Categories

B - Urban, Suburban, Wooded areas (highest) C - Open terrain with scattered obstructions having heights less than 30 feet. D - Flat, unobstructed areas and water surfaces. This category includes smooth mud flats, salt flats, and unbroken ice. (lowest density)

Mesa Verde Cliff Dwellings

A good example of vernacular passive cooling. The dwellings harmonize with the landscape for functional reasons. This allows the summer sun to be blocked, but allows winter light in to warms it

Solar chimney

A passive device for ventilating a building in the summer by using the heat of the sun. Air then rises faster, exhausting more warm air and in turn pulling more cool air into a building at lower levels.

Mashrabiya

A screened bay window popular in the Middle East. It shades, ventilates, and provides evaporative cooling.

"Solar Hemicycle"

A semicircular in-plan structure that features shading from the summer sun and glazing faces for the winter sun. Guaranteeing all residents solar access at one time of day. The Jacobs II house was developed by Frank Lloyd Wright which Wright called a solar hemicycle.

Trombe wall

A thermal storage wall that's usually made of solid material, conducts time lag, and is used to store heat during the day and use it at night

Indirect earth coupling

Air enters the building by way of earth tubes. By the means of tubes buried in the ground. Sloped tubes and a sump are required to catch condensation. An open-loop system is shown, while a closed-loop system would return the air from indoors.

Reason for Air flow

Air flows either because of natural convection currents, caused by differences in temperature, or because of differences in pressure

Transmission of Glazing by Orientation

All orientations except south receive maximum solar radiation in summer. A skylight receives about four times the solar heating that south windows receive on June 21.

Brises Soleil

An architectural feature of a building that reduces heat gain within that building by deflecting sunlight

Direct earth coupling

An earth-sheltered building loses heat directly to the earth. Insulating the soil around an earth-sheltered building created a more desirable earth temperature for the building in both summer and winter. The soil will be warmer in the winter and cooler in the summer.

Water

An excellent heat-storage material not only because it has the highest heat capacity of any material but also because it has a very high heat-absorption rate.

Bernoulli Effect

An increase in the velocity of a fluid decreases its static pressure. Thus, there is negative pressure at areas of increased velocity.

High low pressure

As air hits the windward side of a building, it compresses and creates positive pressure. When air deflects around a building it does not follow the edges exactly. So it pulls air outward from the building, creating negative pressure.

Design Guidelines for South Overhangs

As stated in the rules above, a fixed horizontal overhang is most appropriate when passive solar heating is not desired. The goal, then, is to find the length of overhang that will shade the south windows until the last day of the overheated period.

Orientation Lighting through the roof Form Space planning Color View and daylighting

Basic daylighting strategies

1. Reason 2. Types 3. Inertia 4. Conservation 5. High and Low Pressure 6. Bernoulli Effect 7. Stack Effect

Basic principles of airflow

The shape causes radiant heating to be minimized and radiant cooling maximized. It also has high spaces where stratification will enable the occupants to inhabit the cooler levels.

Benefits of a dome

The uses of vegetation as a shading device

By means of shading and transpiration, plants can significantly reduce air and ground temperatures. They also increase the humidity, whether or not it is already too high.

Shading from trees

Can be a useful natural shading device. Depending on the species, it can provide a great deal of shade during the summer and provide great sun exposure in the winter.

Sunspace

Collects solar radiation and distributes much of the heat to the rest of the building. At night, it must be sealed form the main building to keep it from becoming an energy drain on the main building.

a. Transmitted b. Absorbed c. Reflected

How does glazing work as a shading device?

Promotes the use of large picture windows Least expensive Most efficient Can effectively use clerestories Daylighting and heating can be combined, which makes this system very appropriate for schools, small offices, etc

Direct gain advantages

Possibly too much light, which can cause glare and fading of colors. Concrete floor slabs must not be covered by carpets Overheating can occur if precautions are not taken Fairly large temperature swings must be tolerated (about 10°F)

Direct gain disadvantages

Surface-area-to-volume ratio - High Building form - Spread out Internal heat gain - Low Balances point temperature is 60 degrees F

Envelope-Dominated building form

Indirect Evaporative Cooling

Evaporation cools the incoming air of the building without raising the indoor humidity. The cooling effect from evaporation can also be used to cool the roof of a building, which then becomes a heat sink to cool the interior

Le Corbusier

Famous swiss-french architect most closely linked with an aesthetic based on sun shading.

Overhang Vertical Fin Eggcrate

Fixed shading devices

1. Laminar 2. Separated 3. Turbulent 4. Eddy

Four types of airflow

One

Heat avoidance and shading are part of which tier?

100

How many 60 W incandescent lamps would be required to produce the same amount of light as a 3 × 5 ft window?

Stack effect

If the temperature difference between a low and a high opening is greater indoors than outdoors, natural convection will cause air to rise up and out of the building, creating air movement.

Orientation Plan Slope of Glazing Shading Reflectors Conservation

Important Passive Solar Design Considerations

Reflector

It can increase the solar collection without some of the drawbacks of using larger glazing areas. Both winter heat loss and summer heat gain can be minimized by using these, rather than larger window sizes to increase the solar collection

Jacobs II House

It was designed by architect Frank Lloyd Wright and built in Madison, Wisconsin, circa 1948. This building would in many ways make a fine passive home by present-day standards.

Unite d'Habitation

Le Corbusier came up with an ingenious solution for cross ventilation in his this building at Marseilles

1. Pilotis 2. Free Plan 3. Free Facade 4. Strip Window 5. Roof Garden

Le Corbusier's Five Points of Architecture (Villa Savoye)

Albedo

Number that indicates how much of the solar radiation is reflected from a surface. 0 indicates that no sunlight is reflected or that all sunlight is absorbed, while a measure of 1 indicates that all sunlight is reflected.

Balcomb residence

One of the best-known sunspace houses belonged to J. Douglas Balcomb, the foremost researcher in passive solar systems. Because it is located in historic Santa Fe, New Mexico, adobe is used for the common wall

Wind tower

Passive evaporative coolers that act like reverse chimneys. At the top of the tower, water is sprayed in absorbent pads. As air enters the top of the tower, it is cooled, becomes denser, and sinks. The cool air then enters the building through openings that look much like fireplaces.

Roof vents

Passive roof ventilators are usually used to reduce temperatures in an attic. However, properly sized and placed, these can also be used to ventilate habitable space.

Indirect Radiant Cooling

Radiation to the night sky cools a heat-transfer fluid, which then cools the building. Painted metal radiator cools air at night, which is then blown into the building to cool the indoor mass but the next morning, the fan is turned off and the building is sealed

Efficacy

Ratio of light output to energy input. The higher the number - the more efficacy - the better

For clear glazing, about 90 percent of the incident solar radiation ends up as heat gain. Can be used when winter solar heating is desired.

Result of clear glazing

Reflective glazing effectively blocks solar radiation without color distortion. The amount of solar radiation that is reflected from glazing can be increased significantly by adding a reflective coating. Unfortunately, because it also reflects sunlight almost as much as a mirror, neighbors can end up with unexpected glare and additional solar heating.

Result of reflective glazing

Although tinted glazing reduces the light transmission, it usually does not decrease the heat gain by much because much of the absorbed radiation is then reradiated indoors

Result of tinted glazing

Portico

Roof supported by columns, forming a porch or a covered walk. It is simply a feature to protect against the rain and sun

1. During Summer, introduce just enough light to keep electric lights off. 2. During Winter, introduce as much sunlight as possible into buildings which need heating. 3. Any building that does not need heating should obey Rule 1 year-round. 4. The efficacy of sunlight can be significantly increased with spectrally-selective glazing, aka "Low-E Coatings"

Rules for Daylighting Quantity

Inlets and Outlets size

Should generally be about the same. If not, the outlet should be larger. This creates a pressure differential and maximizes the velocity. The inlet opening determines the velocity and the airflow pattern. The outlet has much less effect.

Inertia

Since air has mass, when moving it tends to go in a straight line. When forced to change direction, air streams will not follow right angles, but will follow a curve instead.

Conservation of air

The amount of air leaving a building must equal the amount approaching. Lines representing airstreams should be drawn as continuous lines.

Hybrid Sunspace

Spaces with balconies or covered porches that effectively shade windows or glass doors in the summer unfortunately also block the much-needed sun in the winter. By enclosing the balconies in glazing during the winter, a valuable sunspace can be created

Very attractive amenity Extra living space Can function as a greenhouse

Sunspace advantages

Most expensive system Least efficient Cannot be occupied when too hot or cold

Sunspaces disadvantages

Internally-Dominated building form

Surface-area-to-volume ratio - Low Building form - Compact Internal heat gain - High Balances point temperature is 50 degrees F

Open stack, turbine, and deflector

The 3 Roof Vents

Direct gain, Trombe wall, and Sunspace

The 3 types of Solar Heat Gain systems

Heat capacity

The amount of heat required to raise the temperature of a material 1°F (1°C) is called the heat capacity of that material. The heat capacity of different materials varies widely, but in general, heavier materials have a higher heat capacity.

Reflectance Factor

The amount of light falling on a surface that is reflected, expressed as a ratio of the amount of light reflected divided by the amount of light hitting the surface (the incident light)

Transmittance Factor

The amount of light falling on a surface that is transmitted through it, expressed as a ratio of the amount of light transmitted divided by the amount of incident light

Overhang

The best choice in shading device for the south facade. Because they are directionally selective in a desirable way, they can block the sun but not the view. Can also be designed to block the high summer sun while allowing the lower winter sun to enter the window.

Daylighting

The controlled admission of natural light into a space is used to reduce or eliminate electric lighting. About half of all that electricity could be saved by this.

Luminance

The detectable light bouncing from a surface measured in Lumens

Thermosiphon

The method of using a heated surface and the resulting convection to move fluid out of a space. The key to success in this system, therefore, is to place the thermal storage at a higher elevation than the collector.

Illuminance

The number of Lumens falling on each square foot of a surface. Measured in Footcandles

Solar Heat Gain Coefficient

The performance of shading devices can be quantified by means of the solar heat gain coefficient (SHGC), which can have values from 0 to 1 where 0 indicates no solar gain (complete shading) and a value of 1 indicates unimpeded solar gain (no shading).

Light

The portion of the electromagnetic spectrum to which our eyes are visually sensitive

Luminous Flux

The rate at which a light source emits light energy - measured in Lumens

Outdoor shading

These shading devices are best at blocking direct solar radiation. It should be designed to let the winter sun enter while rejecting the summer sun

Shading Coefficient

This is counterintuitive because a value of 1 equals no shading, while a value of 0 indicates that not sunlight can enter. Although this coefficient was developed for use in analytical work, we will use it here as a rough way to compare various shading devices.

Moveable shading devices

This type of shading device responses better to the dynamic nature of the environment. Since full shade is needed during the overheated periods and full sun during the underheated periods, a shading device must be in phase with the thermal conditions.

Shading and Light colors

Tier One

Gives a high level of thermal comfort Good in conjunction with direct gain to limit lighting levels Medium cost Good for large heating loads

Trombe wall advantages

More expensive than direct gain Less glazing will be available for views and daylighting No wall hangings or other coverings permitted on Trombe wall

Trombe wall disadvantages

a. Curtain b. Roller Shade c. Shutter d. Venetian Blind e. Light Shelf

Type of interior shading device

1. Clear 2. Reflective 3. Tinted

Types of glazing

Attached, Semiclosed, and Enclosed

Types of sunspaces

Comfort Ventilation

Ventilation during the day and night to increase evaporation from the skin and thereby increase thermal comfort.

Night Flush cooling

Ventilation to precool the building for the next day. This cool night air can be used to flush out the heat from a building's mass. The precooled mass can then act as a heat sink during the following day by absorbing heat.

Direct Evaporative Cooling

Water is sprayed into the air entering a building. This lowers the air's temperature but raises its humidity. When water evaporates in the indoor air, the temperature drops but the humidity goes up. It is not appropriate in humid climates because the cooling effect is low and the humidity is already too high

Orientation. Each orientation requires a different shading strategy

What is critical to shading?

Tier 2

What tier is daylighting?

Window types

casement, awning, and jalousie

Direct gain

it lets the short-wave solar energy enter but blocks the heat from escaping; the thermal mass inside the building then absorbs this heat to prevent daytime overheating and store it for nighttime usage.

Overheated Period

period of the year when the average daily outdoor temperature is greater than 60 degrees F (ex: summer)

Underheated Period

period of the year when the average daily outdoor temperature is under 50 degrees F (ex: winter)

Transition Periods

period of time in which one season transitions into another

Heat Capacity

the number of heat units needed to raise the temperature of a body by one degree

Brightness

the perception by a human observer of the light bouncing from a surface

Convective Loop

the way energy is lost from the living space through the building envelope