Passive cooling techniques

Includes:

a. Through orientation

b. Site layout

c. Solar control device

d. Passive daylight concept

e. Passive cooling by wind and ventilation

PASSIVE COOLING TECHNIQUES:

Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or nil energy consumption. This approach works either by preventing heat from entering the interior (heat gain prevention) or by removing heat from the building (natural cooling). Natural cooling utilizes on-site energy, available from the natural environment, combined with the architectural

design of building components (e.g. building envelope), rather than mechanical systems to dissipate heat. Therefore, natural cooling depends not only on the architectural design of the building but how it uses the local site natural resources as heat sinks (i.e. everything that absorbs or dissipates heat). Examples of on-site heat sinks are the upper atmosphere (night sky), the outdoor air (wind), and the earth/soil.

Passive cooling covers all natural processes and techniques of heat dissipation and modulation without the use of energy.[1] Some authors consider that minor and simple mechanical systems (e.g. pumps and economizers) can be integrated in passive cooling techniques, as long they are used to enhance the effectiveness of the natural cooling process.[4] Such applications are also called ‘hybrid cooling systems’. [1] The techniques for passive cooling can be grouped in two main categories:

Preventative techniques: that aims to provide protection and/or prevention of external and internal heat gains.

Modulation and heat dissipation techniques: allow the building to store and dissipate heat gain through the transfer of heat from heat sinks to the climate. This technique can be the result of thermal mass or natural cooling.

Preventative techniques:

Protection from or prevention of heat gains encompasses all the design techniques that minimizes the impact of solar heat gains through the building’s envelope and of internal heat gains that is generated inside the building due occupancy and equipment. It includes the following design techniques:

Microclimate and site design - By taking into account the local climate and the site context, specific cooling strategies can be selected to apply which are the most appropriate for preventing overheating through the envelope of the building. The microclimate can play a huge role in determining the most favorable building location by analyzing the combined availability of sun and wind. The bioclimatic chart, the solar diagram and the wind rose are relevant analysis tools in the application of this technique.

Solar control - A properly designed shading system can effectively contribute to minimizing the solar heat gains. Shading both transparent and opaque surfaces of the building envelope will minimize the amount of solar radiation that induces overheating in both indoor spaces and building’s structure. By shading the building structure, the heat gain captured through the windows and envelope will be reduced.

Building form and layout - Building orientation and an optimized distribution of interior spaces can prevent overheating. Rooms can be zoned within the buildings in order to reject sources of internal heat gain and/or allocating heat gains where they can be useful, considering the different activities of the building. For example, creating a flat, horizontal plan will increase the effectiveness of cross-ventilation across the plan. Locating the zones vertically can take advantage of temperature stratification. Typically, building zones in the upper levels are warmer than the lower zones due to stratification. Vertical zoning of spaces and activities uses this temperature stratification to accommodate zone uses according to their temperature requirements.[5] Form factor (i.e. the ratio between volume and surface) also plays a major role in the building’s energy and thermal profile. This ratio can be used to shape the building form to the specific local climate. For example, more compact forms tend to preserve more heat than less compact forms because the ratio of the internal loads to envelope area is significant.

Thermal insulation - Insulation in the building’s envelope will decrease the amount of heat transferred by radiation through the facades. This principle applies both to the opaque (walls and roof) and transparent

surfaces (windows) of the envelope. Since roofs could be a larger contributor to the interior heat load, especially in lighter constructions (e.g. building and workshops with roof made out of metal structures), providing thermal insulation can effectively decrease heat transfer from the roof.

Behavioral and occupancy patterns - Some building management policies such as limiting the amount of people in a given area of the building can also contribute effectively to the minimization of heat gains inside a building. Building occupants can also contribute to indoor overheating prevention by: shutting off the lights and equipment of unoccupied spaces, operating shading when necessary to reduce solar heat gains through windows, or dress lighter in order to adapt better to the indoor environment by increasing their thermal comfort tolerance.

Internal gain control - More energy-efficient lighting and electronic equipment tend to release less energy thus contributing to less internal heat loads inside the space.

Modulation and heat dissipation techniques:

The modulation and heat dissipation techniques rely on natural heat sinks to store and remove the internal heat gains. Examples of natural

sinks are night sky, earth soil, and building mass.[8] Therefore passive cooling techniques that use heat sinks can act to either modulate heat gain with thermal mass or dissipate heat through natural cooling strategies.

Thermal mass - Heat gain modulation of an indoor space can be achieved by the proper use of the building’s thermal mass as a heat sink. The thermal mass will absorb and store heat during daytime hours and return it to the space at a later time.[1] Thermal mass can be coupled with night ventilation natural cooling strategy if the stored heat that will be delivered to the space during the evening/night is not desirable.

Natural cooling - Natural cooling refers to the use of ventilation or natural heat sinks for heat dissipation from indoor spaces. Natural cooling can be separated into four different categories: cooling and ventilation, radiative cooling, evaporative cooling, and earth coupling.

Ventilation:

Ventilation as a natural cooling strategy uses the physical properties of air to remove heat or provide cooling to occupants. In select cases, ventilation can

be used to cool the building structure, which subsequently may serve as a heat sink.

Cross ventilation - The strategy of cross ventilation relies on wind to pass through the building for the purpose of cooling the occupants. Cross ventilation requires openings on two sides of the space, called the inlet and outlet. The sizing and placement of the ventilation inlets and outlets will determine the direction and velocity of cross ventilation through the building. Generally, an equal (or greater) area of outlet openings must also be provided to provide adequate cross ventilation.

Stack ventilation - Cross ventilation is an effective cooling strategy, however, wind is an unreliable resource. Stack ventilation is an alternative design strategy that relies on the buoyancy of warm air to rise and exit through openings located at ceiling height. Cooler outside area replaces the rising warm air through carefully designed inlets placed near the floor.

Night flush cooling – The building structure acts as a sink through the day and absorbs internal heat gains and solar radiation. Heat can be dissipated from the structure by convective heat loss by allowing cooler air to pass through the building at night. The flow of outdoor air can be induced naturally or mechanically. The next day, the building will perform as a heat sink, maintaining indoor temperatures below the outdoor temperature. This strategy is most effective in climates with a large diurnal swing so the typical maximum indoor temperature is below the outdoor maximum temperature during the hottest months. Thermal mass is a necessary component to dissipate heat at night.

Radiative cooling:

All objects constantly emit and absorb radiant energy. An object will cool by radiation if the net flow is outward, which is the case during the night. At night, the long-wave radiation from the clear sky is less than the long-wave infrared radiation emitted from a building, thus there is a net flow to the sky. Since the roof provides the greatest surface visible to the night sky,

designing the roof to act as a radiator is an effective strategy. There are two types of radiative cooling strategies that utilize the roof surface: direct and indirect.

Direct radiant cooling - In a building designed to optimize direct radiation cooling, the building roof acts as a heat sink to absorb the daily internal loads. The roof acts as the best heat sink because it is the greatest surface exposed to the night sky. Radiate heat transfer with the night sky will remove heat from the building roof, thus cooling the building structure. Roof ponds are an example of this strategy. The roof pond design became popular with the development of the Sky thermal system designed by Harold Hay in 1977. There are various designs and configurations for the roof pond system but the concept is the same for all designs. The roof uses water, either plastic bags filled with water or an open pond, as the heat sink while a system of movable insulation panels regulate the mode of heating or cooling. During daytime in the summer, the water on the roof is protected from the solar radiation and ambient air temperature by movable insulation, which allows it to serve as a heat sink and absorb, though the ceiling, the heat generated inside. At night, the panels are retracted to allow nocturnal radiation between the roof pond and the night sky, thus removing the stored heat from the day’s internal loads. In winter, the process is reversed so that the roof pond is allowed to absorb solar radiation during the day and release it during the night into the space below.

Indirect radiant cooling - A heat transfer fluid removes heat from the building structure through radiate heat transfer with the night sky. A common design for this strategy involves a plenum between the building roof and the radiator surface. Air is drawn into the building through the plenum, cooled from the radiator, and cools the mass of the building structure. During the day, the building mass acts as a heat sink.

Evaporative cooling:

Evaporative cooling. The design relies on the evaporative process of water to cool the incoming air while simultaneously increasing the relative humidity. A saturated filter is placed at the supply inlet so the natural process of evaporation can cool the supply air. Apart from the energy to drive the fans, water is the only other resource required to provide conditioning to indoor spaces. The effectiveness of evaporative cooling is largely dependent on the humidity of the outside air; dryer air produces more cooling. A study of field

performance results in Kuwait revealed that power requirements for an evaporative cooler are approximately 75% less than the power requirements for a conventional packaged unit air-conditioner.[11] As for interior comfort, a study found that evaporative cooling reduced inside air temperature by 9.6°C compared to outdoor temperature.

Earth coupling:

Earth coupling uses the moderate and consistent temperature of the soil to act as a heat sink to cool a building through conduction. This passive cooling strategy is most effective when earth temperatures are cooler than ambient air temperature, such as hot climates.

Direct coupling - Direct coupling, or earth sheltering, occurs when a building uses earth as a buffer for the walls. The earth is an endless heat sink and can effectively mitigate temperature extremes. Earth sheltering improves the performance of building envelope assemblies by reducing the magnitude of conductive and convective heat loss and gains by reducing infiltration.

Indirect coupling. A building can be indirectly coupled with the earth by means of earth ducts. An earth duct is a buried tube that acts as avenue for supply air to travel through before entering the building. Supply air is cooled by way of conductive heat transfer between the concrete tubes and soil. Therefore, earth ducts will not perform well as a source of cooling unless the soil temperature is lower than the desired room air temperature.[13] Earth ducts typically require long tubes to cool the supply air to an appropriate temperature before entering the building. A fan is required to draw the cool air from the earth duct into the building. Some of the factors that affect the performance of an earth duct are: duct length, number of bends, thickness of duct, depth of duct, diameter of the duct, and air velocity.

Passive Cooling:

A cooling system using a building’s design and construction to maintain a comfortable temperature within the building.

Passive design is essentially low-energy design achieved by the building’s particular morphological organization rather than electro-mechanical means.

Passive Cooling Techniques:

1. BUILDING CONFIGURATION, SITE LAYOUT and SITE PLANNING

Example : A building can be protected from direct sunlight by placing it on a location within the site that utilizes existing features such as trees, terrain etc.

2. BUILDING ORIENTATION:

Example : In tropical countries such as the Philippines, it is best to place service areas in the west and east facing sides of the building because these sides are exposed to direct sunlight.

3. FACADE DESIGN:

Use of Double-layered façadeUse Low-emissivity glass (Low-E glass)Use of Insulation

4. CROSS VENTILATION:

The circulation of fresh air through open windows, doors or other openings on opposite sides of a room

STACK EFFECT / CHIMNEY EFFECT:

The tendency of air or gas in a shaft or other vertical space to rise when heated, creating a draft that draws in cooler air or gas from below

5. SUNSHADING DEVICES:

VERTICAL TYPESVertical Sun Shades are generally used on the East-Facing and West- Facing Sidesof a buildingEGGCRATE TYPESCombination of Horizontal and Vertical ShadesWIND ANALYSIS:

Wind direction: Desirable and undesirable winds in each of the climatic zones depend largely on local conditions. Any breeze in the lower latitude (tropical and arid climates) is beneficial for most of the year.

Cross ventilation: Cross ventilation is far more important in the tropics than in temperate zones. The theoretical strategy for blocking or inducing wind

flow into a building is based on local prevailing wind conditions. Generally, for the tropical zones as much ventilation as possible is desired.

Influences on Built Form:

1. Zoning for transitional spaces - the traditional spaces used for lobbies, stairs, utility spaces, circulation, balconies and any other areas where movement take place. These areas do not require total climatic control and natural ventilation is sufficient. For the tropical and arid zones, the transitional spaces are located on the north and south sides of the building where the sun's penetration is not as great. An atrium can also be used a transitional space.

2. Use of atrium - In the tropical zone the atrium should be located so as to provide ventilation within the built form. In the arid zone the atrium should be located at the centre of the building for cooling and shading purposes.

Influences on Built Form:

1. Form - Optimum building form for each climatic zone. Research has shown that the preferred length of the sides of the building, where the sides are of length x:y, are: tropical zone - 1:3. Analysis of these ratios shows that an elongated form to minimize east and west exposure is needed at the lower latitudes.

2. Orientation - Orientation as well as directional emphasis changes with latitude in response to solar angle. Building's main orientation for tropical countries would have a directional emphasis on an axis 5deg north of east

3. Vertical cores and structure - The arrangement of primary mass can be used as a factor in climatic design as its position can help to shade or retain heat within the building form.

P.C.T. - Through orientation:

Orientation, layout and location on site will all influence the amount of sun a building receives and therefore its year-round temperatures and comfort.

Other considerations include access to views and cooling breezes.

Orientation and layout will also be influenced by topography, wind speed and direction, the site’s relationship with the street, the location of shade elements such as trees and neighboring buildings, and vehicle access and parking.

Orientation for passive heating and cooling:

For maximum solar gain, a building will be located, oriented and designed to maximize window area facing north (or within 20 degrees of north) – for example, a shallow east-west floor plan. However, this will depend on the site’s shape, orientation and topography. For example, an east-west floor plan will not be possible on a narrow north-south site.

Orientation for solar gain will also depend on other factors such as proximity to neighboring buildings and trees that shade the site.

For solar gain, as well as considering location, orientation and window size and placement, it is also important to consider the thermal performance and solar heat gain efficiency of the glazing unit itself (see glazing and glazing units for more information).

While solar gain for passive heating is important, other considerations include noise, day lighting, protection from prevailing winds, access to breezes for ventilation, shade to prevent summer overheating and glare, views, privacy, access, indoor/outdoor flow, owners’ preferences, and covenants and planning restrictions.Where passive cooling is more of a priority than passive heating, the building should be oriented to take advantage of prevailing breezes.Orientation, location and layout should be considered from the beginning of the design process – ideally, from the time the site is being selected. Once a building has been completed, it is impractical and expensive to reorient later.

If optimal orientation can be achieved, it will reduce some of the heating requirement, reduce energy costs and reduce greenhouse gas emissions.

Effective solar orientation requires a good understanding of sun paths at the site at different times of the year.

p.c.t. - site layout:

Choosing a site:

Selecting a site is the first and perhaps most important step in the passive design process. If a site is not suitable for passive design, some elements of the passive design ethos may not work in favor of efficiency and comfort.

The most important factor is the amount of sun the site receives, as a site that receives little or no sunlight can be used for passive solar design.

A flat site will generally have good sunlight access anywhere in New Zealand, but a south-facing slope or a site adjacent to a tall building or substantial planting on the northern side, will not receive good solar access.

An ideal site for passive solar design will:

be flat or north-sloping

be free of obstructions to the north (and be unlikely to be built out in future)

be able to accommodate a building with a relatively large north-facing wall or walls for maximum solar gain (as well as north-facing outdoor areas if those are wanted).

A site with north-south alignment is likely to receive midday sun and with minimal overshadowing, but may have limited morning or evening sun. A site with east-west alignment is more likely to be overshadowed to the north. Be wary of covenants that may prevent good orientation, shading to the north from trees or buildings, south-facing slopes or views.

Building location:

For maximum solar gain, a building should in general be located near the site’s southern boundary. In most cases, this is likely to reduce the risk of shading from neighboring properties, and also provide sunny outdoor space.

However, the best location for solar access will vary from site to site depending on site shape, orientation and topography; and shading from trees and neighboring buildings (or future buildings).

As noted above, other factors such as views, wind, topography, and the location of trees and neighboring buildings will also influence a building’s location on the site.

In areas where cooling is more of a priority than heating, factors such as access to breezes might be more important than solar access.

Layout:

Rooms and outdoor spaces should be located to maximize comfort during use. In general, this means living areas and outdoor spaces facing north, and service areas such as garages, laundries and bathrooms to the south. See Room layout for more detail on suitable uses for north, south, west and east-facing spaces.

Overcoming obstacles:

It is often not possible to obtain the ideal building orientation on a site (particularly in urban areas) and compromise will be necessary – for example, where the view is to the south, the site has a south-facing slope, there is a source of noise on the north side, or the view and sun face into strong prevailing winds.

p.c.t. - solar control devices:

There are many different reasons to want to control the amount of sunlight that is admitted into a building. In warm, sunny climates excess solar gain may result in high cooling energy consumption; in cold and temperate climates winter sun entering south-facing windows can positively contribute to passive solar heating; and in nearly all climates controlling and diffusing natural illumination will improve day lighting.

Well-designed sun control and shading devices can dramatically reduce building peak heat gain and cooling requirements and improve the natural lighting quality of building interiors. Depending on the amount and location of fenestration, reductions in annual cooling energy consumption of 5% to 15% have been reported. Sun control and shading devices can also improve user visual comfort by controlling

glare and reducing contrast ratios. This often leads to increased satisfaction and productivity. Shading devices offer the opportunity of differentiating one building facade from another. This can provide interest and human scale to an otherwise undistinguished design.

The use of sun control and shading devices is an important aspect of many energy-efficient building design strategies. In particular, buildings that employ passive solar heating or day lighting often depend on well-designed sun control and shading devices.

During cooling seasons, external window shading is an excellent way to prevent unwanted solar heat gain from entering a conditioned space. Shading can be provided by natural landscaping or by building elements such as awnings, overhangs, and trellises. Some shading devices can also function as reflectors, called light shelves, which bounce natural light for day lighting deep into building interiors.

The design of effective shading devices will depend on the solar orientation of a particular building facade. For example, simple fixed overhangs are very effective at shading south-facing windows in the summer when sun angles are high. However, the same horizontal device is ineffective at blocking low afternoon sun from entering west-facing windows during peak heat gain periods in the summer.Exterior shading devices are particularly effective in conjunction with clear glass facades. However, high-performance glazings are now available that have very low shading coefficients (SC). When specified, these new glass products reduce the need for exterior shading devices.

Thus, solar control and shading can be provided by a wide range of building components including:

Landscape features such as mature trees or hedge rows.

Exterior elements such as overhangs or vertical fins.

Horizontal reflecting surfaces called light shelves Low shading coefficient (SC) glass and, Interior glare control devices such as Venetian blinds or adjustable louvers.

Fixed exterior shading devices such as overhangs are generally most practical for small commercial buildings. The optimal length of an overhang depends on the size of the window and the relative importance of heating and cooling in the building.

In the summer, peak sun angles occur at the solstice on June 21, but peak temperature and humidity are more likely to occur in August. Remember

that an overhang sized to fully shade a south-facing window in August will also shade the window in April when some solar heat may be desirable.

To properly design shading devices it is necessary to understand the position of the sun in the sky during the cooling season. The position of the sun is expressed in terms of altitude and azimuth angles.

The altitude angle is the angle of the sun above the horizon, achieving its maximum on a given day at solar noon.

The azimuth angle, also known as the bearing angle, is the angle of the sun's projection onto the ground plane relative to south.

An easily accessed source of information on sun angles and solar path diagrams is Architectural Graphic Standards, 11th Edition, available from John Wiley & Sons, Inc. Publishers. Shading devices can have a dramatic impact on building appearance this impact can be for the better or for the worse. The earlier in the design process that shading devices are considered they more likely they are to be attractive and well-integrated in the overall architecture of a project.

Designing Shading Systems:

Given the wide variety of buildings and the range of climates in which they can be found, it is difficult to make sweeping generalizations about the design of shading devices. However, the following design recommendations generally hold true:

Use fixed overhangs on south-facing glass to control direct beam solar radiation. Indirect (diffuse) radiation should be controlled by other measures, such as low-e glazing.

To the greatest extent possible, limit the amount of east and west glass since it is harder to shade than south glass. Consider the use of landscaping to shade east and west exposures.

Do not worry about shading north-facing glass in the continental United States latitudes since it receives very little direct solar gain. In the tropics, disregard this rule-of-thumb since the north side of a building will receive more direct solar gain. Also, in the tropics consider shading the roof even if there are no skylights since the roof is a major source of transmitted solar gain into the building.

Remember that shading effects day lighting; consider both simultaneously. For example, a light shelf bounces natural light deeply into a room through high windows while shading lower windows.

Do not expect interior shading devices such as Venetian blinds or vertical louvers to reduce cooling loads since the solar gain has already been admitted into the work space. However, these interior devices do offer glare control and can contribute to visual acuity and visual comfort in the work place.

Study sun angles. An understanding of sun angles is critical to various aspects of design including determining basic building orientation, selecting shading devices, and placing Building Integrated Photovoltaic (BIPV) panels or solar collectors.

Carefully consider the durability of shading devices. Over time, operable shading devices can require a considerable amount of maintenance and repair.

When relying on landscape elements for shading, be sure to consider the cost of landscape maintenance and upkeep on life-cycle cost.

Shading strategies that work well at one latitude, may be completely inappropriate for other sites at different latitudes. Be careful when applying shading ideas from one project to another.

Materials and Methods of Construction:

In recent years, there has been a dramatic increase in the variety of shading devices and glazing available for use in buildings. A wide range of adjustable shading products is commercially available from canvas awnings to solar screens, roll-down blinds, shutters, and vertical louvers. While they often perform well,

their practicality is limited by the need for manual or mechanical manipulation. Durability and maintenance issues are also a concern.

Require A&E professionals to fully specify all glass. They should be prepared to specify glass U-value, SC, and Tvis and net window U-value for all fenestration systems. The shading coefficient (SC) of a glazing indicates the amount of solar heat gain that is admitted into a building relative to a single-glazed reference glass. Thus, a lower shading coefficient means less solar heat gain. The visible transmittance (Tvis) of a glazing material indicates the percentage of the light available in the visible portion of the spectrum admitted into a building. See also WBDG Windows and Glazing.

When designing shading devices, carefully evaluate all operations and maintenance (O&M) and safety implications. In some locations, hazards such as nesting birds or earthquakes may reduce the viability of incorporating exterior shading devices in the design.

p.c.t. - passive daylight concept:

Day lighting is the use of natural light from the sky as a supplement for electric lighting in buildings. Traditional day lighting systems differ in one major respect from passive heating systems: they use the sky as a source of light and avoid letting direct sunlight into a building. Since light from the sky is used in lieu of direct sunlight, day lighting systems function quite well on overcast, partly cloudy, or clear days.

Day lighting:

Day lighting is an instantaneous use of the light from the sky. Therefore, day lighting systems consist of collection and distribution components and do not include a storage component like passive heating systems. However, much like solar thermal strategies, day lighting systems are categorized according to the type of collection system used. Thus, there are three basic types of day lighting systems:

Side lighting

Top lighting

core day lighting

Day lighting is the most effective passive solar strategy in almost all commercial building types because it reduces two major energy uses in these buildings: electric lighting and cooling.

Day lighting - is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides effective internal lighting.

Particular attention is given to day lighting while designing a building when the aim is to maximize visual comfort or to reduce energy use. Energy savings can be achieved from the reduced use of artificial (electric) lighting or from passive solar heating or cooling.

Artificial lighting energy use can be reduced by simply installing fewer electric lights because daylight is present, or by dimming/switching electric lights automatically in response to the presence of daylight, a process known as daylight harvesting.

Day lighting is a technical term given to a common centuries-old, geography and culture independent design basic when "rediscovered" by 20th century architects. The amount of daylight received in an internal space can be analyzed by undertaking a daylight factor calculation. Today, the use of computers and proprietary industry software such as Radiance can allow an Architect or Engineer to quickly undertake complex calculations to review the benefit of a particular design.

There is no direct sunlight on the polar-side wall of a building from the autumnal equinox to the spring equinox [citation needed]. Traditionally, houses were designed with minimal windows on the polar side but more and larger windows on the equatorial-side. Equatorial-side windows receive at least some direct sunlight on any sunny day of the year (except in tropical

latitudes in summertime) so they are effective at day lighting areas of the house adjacent to the windows.

Even so, during mid-winter, light incidence is highly directional and casts deep shadows. This may be partially ameliorated through light diffusion, light pipes or tubes, and through somewhat reflective internal surfaces. In fairly low latitudes in summertime, windows that face east and west and sometimes those that face toward the pole receive more sunlight than windows facing toward the equator.

Windows - are the most common way to admit daylight into a space. Their vertical orientation means that they selectively admit sunlight and diffuse daylight at different times of the day and year. Therefore windows on multiple orientations must usually be combined to produce the right mix of light for the building, depending on the climate and latitude. There are three ways to improve the amount of light available from a window:

Placing the window close to a light colored wall.

Slanting the sides of window openings so the inner

opening is larger than the outer opening.

Using a large light colored window-sill to project light into the room.

Different types and grades of glass and different window treatments can also affect the amount of light transmission through the windows.

Roof-angle glass / Skylights:

Skylights admit harsh direct overhead sunlight and glare[25] either horizontally (a flat roof) or pitched at the same angle as the roof slope. In some cases, horizontal skylights are used with reflectors to increase the intensity of solar radiation (and harsh glare), depending on the roof angle of incidence. When the winter sun is low on the horizon, most solar radiation reflects off of roof angled glass ( the angle of incidence is nearly parallel to roof-angled glass morning and afternoon ). When the summer sun is high, it is nearly perpendicular to roof-angled glass, which maximizes solar gain at the wrong time of year, and acts like a solar furnace. Skylights should be covered and well-insulated to reduce natural convection ( warm air rising ) heat loss on cold winter nights, and intense solar heat gain during hot spring/summer/fall days.

The equator-facing side of a building is south in the northern hemisphere, and north in the southern hemisphere. Skylights on roofs that face away from the equator provide mostly indirect illumination, except for summer days when the sun rises on the non-equator side of the building (depending on latitude). Skylights on east-facing roofs provide maximum direct light and solar heat gain in the summer morning. West-facing skylights provide afternoon sunlight and heat gain during the hottest part of the day.

Some skylights have expensive glazing that partially reduces summer solar heat gain, while still allowing some visible light transmission. However, if

visible light can pass through it, so can some radiant heat gain (they are both electromagnetic radiation waves).

You can partially reduce some of the unwanted roof-angled-glazing summer solar heat gain by installing a skylight in the shade of deciduous (leaf-shedding) trees, or by adding a movable insulated opaque window covering on the inside or outside of the skylight. This would eliminate the daylight benefit in the summer. If tree limbs hang over a roof, they will increase problems with leaves in rain gutters, possibly cause roof-damaging ice dams, shorten roof life, and provide an easier path for pests to enter your attic. Leaves and twigs on skylights are unappealing, difficult to clean, and can increase the glazing breakage risk in wind storms.

Skylights provide daylight. The only view they provide is essentially straight up in most applications. Well-insulated light tubes can bring daylight into northern rooms, without using a skylight. A passive-solar greenhouse provides abundant daylight for the equator-side of the building."Sawtooth roof glazing" with vertical-glass-only can bring some of the passive solar building design benefits into the core of a commercial or industrial building, without the need for any roof-angled glass or skylights.

p.c.t. - wind and ventilation:

Wind ventilation is a kind of passive ventilation that uses the force of the wind to pull air through the building. Wind ventilation is the easiest, most common,

and often least expensive form of passive cooling and ventilation. Successful wind ventilation is determined by having high thermal comfort and adequate fresh air for the ventilated spaces, while having little or no energy use for active HVAC cooling and ventilation. Strategies for wind ventilation include operable windows, ventilation louvers, and rooftop vents, as well as structures to aim or funnel breezes.

Windows are the most common tool. Advanced systems can have automated windows or louvers actuated by thermostats. If air moves through openings that are intentional as a result of wind ventilation, then the building has natural ventilation.

If air moves through openings that are not intentional as a result of wind ventilation, then the building has infiltration, or unwanted ventilation (air leaking in).

The greatest pressure on the windward side of the building is generated when the elevation is at right angles to the wind direction, so it seems to be obvious that the greatest indoor air velocity will be achieved in this case.

A wind incidence of 45◦ would reduce pressure by 50% Thus the designer must ascertain the prevailing wind direction from wind frequency charts of wind roses and must orientate the building in such a way that the largest openings are facings the wind direction It has, however, been found by Givoni that a wind incidence at 45◦ would increase the average indoor air velocity and would provide a better distribution of indoor air movement.

Tall buildings improve natural ventilation, and in lower latitudes reduce sun exposure.

While thin and tall buildings can improve the effectiveness of natural ventilation to cool buildings, they also increase the exposed area for heat transfer through the building envelope. When planning urban centers, specifically in heating dominated climates, having the buildings gradually increase in height will minimize high speed winds at the pedestrian level which can influence thermal comfort.

The height difference between neighboring buildings should not exceed 100%

Orientation for maximum passive ventilationThe effectiveness of this strategy and aperture placement can be estimated. Here are some rules of thumb for two scenarios in which windows are facing the direction of the prevailing wind:

For spaces with windows on only one side, natural ventilation will not reach farther than two times the floor to ceiling height into the building.

For spaces with windows on opposite sides, the natural ventilation effectiveness limit will be less than five times the floor to ceiling height into the building.

However, buildings do not have to face directly into the wind to achieve good cross-ventilation. Internal spaces and structural elements can be designed to channel air through the building in different directions. In addition, the prevailing wind directions listed by weather data may not be the actual prevailing wind directions, depending on local site obstructions, such as trees or other buildings. For buildings that feature a courtyard and are located in climates where cooling is desired, orienting the courtyard 45 degrees from the prevailing wind maximizes wind in the courtyard and cross ventilation through the building. Natural ventilation is the process of supplying and removing air through an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure or temperature differences. There are two types of natural ventilation occurring in buildings: wind driven ventilation and buoyancy-driven ventilation. While wind is the main mechanism of wind driven ventilation, buoyancy-driven ventilation occurs as a result of the directional buoyancy force that results from temperature differences between the interior and exterior.

The impact of wind on the building form creates areas of positive pressure on the windward side of a building and negative pressure on the leeward and sides of the building. Thus building shape and local wind patterns are crucial in creating the wind pressures that will drive air flow through its apertures. In practical terms wind pressure will vary considerably creating complex air flows and turbulence by its interaction with elements of the natural environment (trees, hills) and urban context (buildings, structures). Vernacular and traditional buildings in different climatic regions rely heavily

on natural ventilation for maintaining thermal comfort conditions in the enclosed spaces.

Natural ventilation, also called passive ventilation, uses natural outside air movement and pressure differences to both passively cool and ventilate a building. It can include design strategies like wind ventilation, the stack effect, and night purge ventilation.

Active concepts/cooling techniques

Includes:

a. Day lighting sensors

b. automatic blinds

c. rain sensors

d. motion detectors

e. integrated lighting control system

COOLING TECHNIQUES:

As the cooling demand is always a result of the climatic conditions on the building site, cooling strategies have to be adapted to regional climate characteristics. Nevertheless measures and strategies for the reduction of cooling energy mentioned in this document are unique principles to be applied to almost all European climate zones. In general there are two strategies to reduce the cooling demand in buildings:

Passive cooling strategies (on which will be the main focus of this report)

Active cooling strategies (like solar cooling)

Passive cooling strategies

The first step towards the reduction of energy consumption has to be done on the demand side. A comprehensive reduction of the cooling load can be realized by following measures:

Building design

Reduction of solar gains – Size and orientation of transparent building elements (applicable mainly for new buildings)

Orientation and size of transparent building elements (windows) have an important influence on the cooling demand. North orientation of offices will generate best results for the cooling energy demand, but worst results for the heating energy demand, so in the Middle European climate pure south orientation is the best orientation for the reduction of the heating and the cooling energy demand, whereby east and west orientation lead to worst results for the cooling energy demand.

Daylighting sensors:

Daylight sensors in conjunction with well-designed lighting systems can maximize the qualities of daylight. The highest efficiency can be reached in environments with ample daylight coming through windows. The intensity of artificial lighting is constantly adjusted to reflect the incoming natural luminous flux. At noon all or most of the illumination can be provided by sun while early or late in the day this function is taken over by the artificial lighting system.

Saves energy:

• Reduces energy consumption by dimming or turning off electric lights based on the natural daylight entering the space

• Can deliver up to 60% lighting energy savings in some areas Provides comfort and convenience

• Helps maintain the proper light level for a space, so a space is never too dark or too bright

• Continuously adjusts lights automatically so occupants don’t have to manually adjust them as daylight levels change.

Meets codes and standards:

• Meets the mandatory requirements set for building construction and renovation

Automatic blinds:

Automatic blind is a type of window covering. There are many different kinds of window blinds which use a variety of control systems. A typical window blind is made up of several long horizontal or vertical slats of various types of fabric, wood, plastic or metal which are held together by cords that run through the blind slats. Window blinds can be adjusted by rotating them from an open position to a closed position with either a manual or remote control which allows the

slats to overlap and block out most of the light. There are also several types of window blinds that use a single piece of material instead of slats.

A window blind is also known as a window shade.

The term window blinds is also sometimes used to describe window coverings generically—in this context window blinds include almost every type of window covering, i.e. shutters, roller blinds, honeycomb shades, wood blinds, roman blinds and of course, standard vertical and horizontal blinds. In the United Kingdom awnings are sometimes called blinds or shades.

Blinds can be made in a variety of materials, some expensive, and some less so. Cheaper blinds are usually made in vinyl, polyester, aluminum, or PVC. These are inexpensive materials that are all easily accessible and durable at the same time.

Roller blinds:

These are usually stiffened polyester, mounted on a metal pole and operated with a side chain or spring mechanism. Lower cost and ready-made blinds often come with a PVC pole.

Rain sensor:

A rain sensor or rain switch is a switching device activated by rainfall. There are two main applications for rain sensors. The first is a water conservation device connected to an automatic irrigation system that causes the system to shut down in the event of rainfall. The second is a device used to protect the interior of an automobile from rain and to support the automatic mode of windscreen wipers.

An additional application in professional satellite communications antennas is to trigger a rain blower on the aperture of the antenna feed, to remove water droplets from the mylar cover that keeps pressurized and dry air inside the wave-guides.

Irrigation sensors:

Rain sensors for irrigation systems are available in both wireless and hard-wired versions, most employing hygroscopic disks that swell in the presence of rain and shrink back down again as they dry out — an electrical switch is in turn depressed or released by the hygroscopic disk stack, and the rate of drying is typically adjusted by controlling the ventilation reaching the stack.

However, some electrical type sensors are also marketed that use tipping bucket or conductance type probes to measure rainfall. Wireless and wired versions both use similar mechanisms to temporarily suspend watering by the irrigation controller — specifically they are connected to the irrigation controller's sensor terminals, or are installed in series with the solenoid valve common circuit such that they prevent the opening of any valves when rain has been sensed.

Motion detectors:

A motion detector is a device that detects moving objects, particularly people. A motion detector is often integrated as a component of a system that automatically performs a task or alerts a user of motion in an area. Motion detectors form a vital component of security, automated lighting control, home control, energy efficiency, and other useful systems.

An electronic motion detector contains an optical, microwave, or acoustic sensor, and in many cases a transmitter for illumination. However a passive sensor only senses a signal emitted by the moving object itself.

Changes in the optical, microwave, or acoustic field in the device's proximity are interpreted by the electronics based on one of the technologies listed below.

Most inexpensive motion detectors can detect up to distances of at least 15 feet (5 meters). Specialized systems are more expensive but have much longer ranges.

Tomographic motion detection systems can cover much larger areas because the radio waves are at frequencies which penetrate most walls and obstructions, and are detected in multiple locations, not just at the location of the transmitter.

Tomographic motion detector:

Tomographic motion detection systems sense disturbances to radio waves as they pass from node to node of a mesh network. They have the ability to detect over complete areas because they can sense through walls and obstructions.

Integrated lighting control system:

Integrated lighting control systems is are intelligent network based lighting control solution that incorporates communication between various system inputs and outputs related to lighting control with the use of one or more central computing devices. Lighting control systems are widely used on both indoor and outdoor lighting of commercial, industrial, and residential spaces. Lighting control systems serve to provide the right amount of light where and when it is needed.

Lighting control systems are employed to maximize the energy savings from the lighting system, satisfy building codes, or comply with green building and

energy conservation programs. Lighting control systems are often referred to under the term Smart Lighting.

Advantage:

The major advantage of a lighting control system over stand-alone lighting controls or conventional manual switching is the ability to control individual lights or groups of lights from a single user interface device. This ability to control multiple light sources from a user device allows complex lighting scenes to be created. A room may have multiple scenes pre-set, each one created for different activities in the room. A major benefit of lighting control systems is reduced energy consumption. Longer lamp life is also gained when dimming and switching off lights when not in use.

Wireless lighting control systems provide additional benefits including reduced installation costs and increased flexibility over where switches and sensors may be placed.