Daylighting

• Daylighting is the controlled admission of natural light into a space through windows to reduce or eliminate electric lighting.

• By providing a direct link to the dynamic and perpetually evolving patterns of outdoor illumination, daylighting helps create a visually stimulating and productive environment for building occupants, while reducing as much as one-third of total building energy costs.

Benefits of Daylighting

• Daylighting has the potential to significantly improve life-cycle cost, increase user productivity, reduce emissions, and reduce operating costs:

• Improved Life-Cycle Cost: Increased User Productivity: Daylight enlivens spaces and has been shown to increase user satisfaction and visual comfort leading to improved performance.

• Reduced Emissions: By reducing the need for electric consumption for lighting and cooling, the use of daylight reduces greenhouse gases and slows fossil fuel depletion.

• Reduced Operating Costs: Electric lighting accounts for 35 to 50 percent of the total electrical energy consumption in commercial buildings. By generating waste heat, lighting also adds to the loads imposed on a building's mechanical cooling equipment.

• The energy savings from reduced electric lighting through the use of daylighting strategies can directly reduce building cooling energy usage an additional 10 to 20 percent.

• Consequently, for many institutional and commercial buildings, total energy costs can be reduced by as much as one third through the optimal integration of daylighting strategies.

The light entering a room is a result of • direct (from the sun) or • indirect (reflected and diffuse) radiation. • In an average room the light will be strong near

the windows, where the component of direct light is high,

• and weaker further inside the room, where most of the light is a result of reflection from surfaces within the room itself

Location of windows on the planEfficient utilization and uniformity of light improve if the window is located close to a side wall in the room, because of reflection from the wall. Columns between the windows reduce light uniformity. A higher placement of the window in the room (in section) will give a lower level of light at the level of work surfaces but greater uniformity of light because of reflection from the window.

• A nearly uniform lighting level within the building space may be achieved by adding sources of light far from the window. This can be done either by artificial lighting or by natural light from a parallel wall or the ceiling.

Combining artificial and natural lighting

• Bringing the window closer to the ceiling causes higher average light intensity and more uniform lighting in the room.

Daylight designs techniques:

A number of design strategies should be understood and explored during the design process. These strategies are briefly described below.

• Increase perimeter daylight zones—extend the perimeter footprint to maximize the usable day lighting area.

• Allow daylight penetration high in a space. Windows located high in a wall or in roof monitors and clerestories will result in deeper light penetration and reduce the likelihood of excessive brightness.

• Slope ceilings to direct more light into a space. Sloping the ceiling away form the fenestration area will help increase the surface brightness of the ceiling further into a space.

• Avoid direct beam daylight on critical visual tasks. Poor visibility and discomfort will result if excessive brightness differences occur in the vicinity of critical visual tasks.

• Filter daylight. The harshness of direct light can be filtered with vegetation, curtains, louvers, or the like, and will help distribute light.

• Reflect daylight within a space to increase room brightness. A light shelf, if properly designed, has the potential to increase room brightness and decrease window brightness.

Understand that different building orientations will benefit from different daylighting strategies; for example light shelves which are effective on south façades are often ineffective on the east or west elevations of buildings.

Materials and Methods of Construction

• Exterior Shading and Control Devices: In hot climates, exterior shading devices often work well to both reduce heat gain and diffuse natural light before entering the work space. Examples of such devices include light shelves, overhangs, horizontal louvers, vertical louvers, and dynamic tracking or reflecting systems.

• Glazing Materials: The simplest method to maximize daylight within a space is to increase the glazing area. However, three glass characteristics need to be understood in order to optimize a fenestration system: U-value, Shading Coefficient, and Visible Transmittance.– U-value represents the rate of heat transfer due to temperature

difference through a particular glazing material. – Shading Coefficient (SC) is a ratio of solar heat gain of a given

glazing assembly compared to double-strength, single glazing. [NB: A related term, Solar Heat Gain Factor (SHGF), is beginning to replace the term Shading Coefficient.]

– Visible Transmittance (Tvis) is a measure of how much visible light is transmitted through a given glazing material.

• Aperture Location: Simple side lighting strategies allow daylight to enter a space and can also serve to facilitate views and ventilation. A rule-of-thumb is that the depth of daylight penetration is about two and one-half times the distance between the top of a window and the sill.

• Reflectance of Room Surfaces: Reflectance values for room surfaces will significantly impact daylight performance and should be kept as high as possible.

• It is desirable to keep ceiling reflectances over 80%, walls over 50%, and floors around 20%.

• Of the various room surfaces, floor reflectance has the least impact on daylighting penetration.

Integration with Electric Lighting Controls: A successful daylighting design not only optimizes architectural features, but is also integrated with the electric lighting system. With advanced lighting controls, it is now possible to adjust the level of electric light when sufficient daylight is available. Three types of controls are commercially available:

• Switching controls—on/off controls simply turn the electric lights off when there is ample daylight.

• Stepped controls—provide intermediate levels of electric lighting by controlling individual lamps within a luminaire.

• Dimming controls—continuously adjust electric lighting by modulating the power input to lamps to complement the illumination level provided by daylight.

Daylight designs

Windows

• 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

Light shelves

• Special light shelves in the windows ensure energy efficiency and comfort by deflecting natural light into the rooms and reflecting it off the ceiling to light the room and reduce the heat of direct sunlight. Interior lights include motion sensors that automatically turn lights on and off as people enter and exit a room.

• Reflectors placed on the outside of a building absorb and reflect the sun's rays. By adjusting the angle of the panel, the brightness and direction of the sun's light can be controlled.

skylight• Skylights are often used for

daylighting. • Skylights admit more light per

unit area than windows, and distribute it more evenly over a space.

• The optimum number of skylights (usually quantified as "effective aperture") varies according to climate, latitude, and the characteristics of the skylight, but is usually 1-10% of floor area.

• The thermal performance of skylights is affected by stratification, i.e. the tendency of warm air to collect in the skylight wells, which in cool climates increases the rate of heat loss.

Light tubes• Light tubes or light pipes are

used for transporting or distributing natural or artificial light. In their application to day lighting, they are also called solar pipes, daylight pipes, or solar light pipes.

• Generally speaking, a light pipe or light tube may refer to:

• a tube or pipe for transport of light to another location, minimizing the loss of light;

• a transparent tube or pipe for distribution of light over its length, either for equidistribution along the entire length

• A round tube lined with highly reflective material leads the light rays through a building, starting from an entrance-point located on its roof or one of its outer walls.

• The entrance point usually comprises a dome (cupola), which has the function of collecting and reflecting as much sunlight as possible into the tube.

• Light transmission efficiency is greatest if the tube is short and straight. In longer, angled, or flexible tubes, part of the light intensity is lost

• Solar energy is the utilization of the radiant energy from the Sun.

• Solar energy and shading are important considerations in building design.

• Thermal mass is used to conserve the heat that sunshine delivers to all buildings.

• Daylighting techniques optimize the use of light in buildings.

• Solar water heaters heat swimming pools and provide domestic hot water.

• Solar technologies such as photovoltaics and water heaters increase the supply of energy and may be characterized as supply side technologies

• Sunlight has influenced building design since the beginning of architectural history.

Solar water heaters

• Why should one go for solar water heating?

• Because-- Solar water heaters save electricity

• they are clean and green

How do they work?

• A typical domestic solar water heater consists of a hot water storage tank and one or more flat plate collectors.

• The collectors are glazed on the sun facing side to allow solar radiation to come in.

• A black absorbing surface (absorber) inside the flat plate collectors absorbs solar radiation and transfers the energy to water flowing through it.

• Heated water is collected in the tank which is insulated to prevent heat loss.

• Circulation of water from the tank through the collectors and back to the tank continues automatically due to density difference between hot and cold water

Flat plate collectors

Flat Plate Collector based Solar Water Heaters

Solar water heaters based on Flat plate Collectors (FPC based SWH)

• Here the solar radiation is absorbed by  flat plate collectors which consist of an insulated outer metallic box covered on the top with glass sheet.

• Inside there are blackened metallic absorber (selectively coated) sheets with built in channels or riser tubes to carry water.

• The absorber absorbs the solar radiation and transfers the heat to the flowing water.

Evacuated Tube Collector based Solar Water Heater

• Here the collector is made of double layer borosilicate glass tubes evacuated for providing insulation.

• The outer wall of the inner tube is coated with selective absorbing material.

• This helps absorption of solar radiation and transfers the heat to the water  which flows through the inner tube.

• Hot water storage tank• The hot water storage tank in domestic solar water heating systems is

typically a double walled tank. • The space between the inner and the outer tanks is filled with insulation to

prevent heat losses. • The inner tank is generally made of copper or stainless steel to ensure long

life. • The outer tank could be made of stainless steel sheet, painted steel sheet

or aluminum. • Electrical heating elements controlled by thermostats can be provided as an

option in the tank itself to take care of those days when sun is not there or demand of water has gone up.

• The capacity of the tank should be in proportion to the collector area used in the system.

• A commonly used thumb rule is to provide 50 litres of storage for every sq. m of collector area. Too large or too small tanks are both detrimental to efficiency.

• Photovoltaics is the direct conversion of light into electricity at the atomic level. Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons. When these free electrons are captured, an electric current results that can be used as electricity.

• Solar cells are made of the same kinds of semiconductor materials, such as silicon, used in the microelectronics industry.

• For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other.

• When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material.

• If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current -- that is, electricity. This electricity can then be used to power a load, such as a light or a tool.

• Photovoltaic Module or Array

• A number of solar cells electrically connected to each other and mounted in a support structure or frame is called a photovoltaic module.

• Modules are designed to supply electricity at a certain voltage, such as a common 12 volts system.

• The current produced is directly dependent on how much light strikes the module.