Presentation on theme: "16469 Lighting and Daylighting Design. Energy Efficient Lighting Lighting accounts for a significant portion of energy use in commercial buildings We."— Presentation transcript:
Energy Efficient Lighting Lighting accounts for a significant portion of energy use in commercial buildings We can significantly reduce this energy use by -using energy efficient lighting -substituting artificial light with daylight (when available) [this requires the use of light sensitive lighting control] -minimise the use of lighting when not required [requires the use of occupancy sensing controls]
Lighting Objectives The prime objectives behind the design of a lighting system are the safety and comfort of occupants – the nature of a task or process performed in a space will dictate the illuminance level which must be provided by the lighting system (lx or lm/m 2 ). Tasks involving high degrees of visual acuity will require higher lighting levels. the minimisation of energy consumption –involves the development of the most energy efficient lighting systems which is suitable for the task, this can be achieved by selecting high efficiency equipment and making use of available daylight. colour rendering or the creation of a specific atmosphere – the colour characteristics of a lighting scheme will affects tasks performed when the lighting system is on. Tasks which require the accurate representation of colour require a light with the spectral characteristics of daylight. Alternatively, to create a “warm atmosphere” in a restaurant requires the selection of lights skewed to the red end of the spectrum.
Design Stages A lighting design has several stages. These are as follows: Identification of the requirements for the lighting system, illuminance levels, colour requirements, available space, etc; Selection of equipment, lamps, luminaires: lighting systems consist of numerous components, the two most important of which are: lamps, which influence the lighting level, colour characteristics and efficiency of the lighting system; luminaires affect the efficiency with which the light is distributed and so affect lighting efficiency and uniformity. Design of the lighting system: lighting systems are designed to achieve a reasonably uniform distribution of light on a particular plane (usually horizontal), avoidance of glare with a minimum expenditure of energy. The most rudimentary form of lighting design is done using a manual calculation - the lumen method. However, lighting design is increasingly done using computers. System control: once a lighting system has been designed it can be controlled in such a way as to make maximum use of available daylight, through selection of appropriate switching mechanisms and daylight responsive controls.
Selection of Components Lamps are selected based on those which are compatible (lamp type, dimensions, frequency of operation, etc) with the selected luminaire and which have the appropriate colour-rendering index. reflector lamp casing
Selection of Components Selection of components follows from the identification of systems requirements. The luminaires are normally chosen first: lighting catalogues usually describe the uses for particular types of luminaire, these also come with different types of reflectors for different applications e.g. low glare reflectors for computer rooms. Reflectors govern the light output characteristic of a luminaire.
Direct Illumination Consider a lamp hanging above a point A The illuminance E (Lux) is a function of the intensity of the lamp I(cd) and the distance of A from the source d The light from the source is perpendicular to A I d A
Direct Illumination Now consider point B The illuminance E (Lux) is still a function of the intensity of the lamp I(cd) and the distance of B from the source d’ However the light beams no are no longer perpendicular to B (they illuminate a greater area) I d A B θ d’
Direct Illumination CB B’ Considering a small area around B The light from the source illuminates area CB The component of I intensity I falling on CB – I’ is θ I Icos
Direct Illumination B The illuminance on plane CB’ can be calculated using substituting for I’
The cosine 3 law allows us to calculate direct illuminance from single of multiple sources However in reality illumination is a combination of direct and indirect illumination (e.g. reflections from other surfaces) With reflection, accurate illumination calculations become exceptionally complex (requires computer) However simplified methods exist to allow us to calculate the luminance on a working plane Direct Illumination
Lumen Method A simple means of calculating illuminance is achieved by means of the lumen method; this is a simplified design approach to enable the designer to achieve an even light distribution in spaces of reasonably simple geometry (i.e. rectangular). N - is the number of luminaires required; E - is the required illuminance (lux); A - is the area to be lit; n - is the number of lamps per luminaire; F - is the lamp lumen output (lumens); MF - is known as the maintenance factor, which is a combination of three factors; UF - is the utilisation and is a function of the luminaire properties and room geometry.
Utilisation Factor The room geometry is a crucial factor in determining the utilisation factor term in the lumen equation. Several parameters are important. –In the lumen method of design the room geometry is characterised by a room index (K) –The reflectances (ρ s ) of surfaces
Manufacturer’s Data The utilisation factor can be obtained once the surface reflectances (or effective reflectances) are known along with the room index (K) each luminaire produced by a manufacturer has a lookup table for UF (UF values in bold):
Maintenance Factors The maintenance factor is a value designed to account for the reduction in light output from a lighting system due to: the ageing of the lamps and the accumulation of dirt and dust on the light fittings and room surfaces. The MF is therefore time varying and is the product of 4 factors: Lamp lumen maintenance factor (LLMF) – a value between 0 and 1 which accounts for the degradation of lamp output over time Lamp survival factor (LSF) – this accounts for the failure of lamps over time, if failed lamps are replaced immediately this factor can be ignored. Luminaire maintenance factor (LMF) – a value between 0 and 1 that accounts for dirt and dust accumulation on the luminaire. Causes LMF to decrease. The room surface maintenance factor (RSMF) - again this is a value between 0 and 1 and accounts for the build up of dirt on room surfaces over time. The build up of dirt over time causes the RSMF to decrease. The overall maintenance factor is the product of the four maintenance factors: MF = LLMF × LLF × LMF × RSMF
Lamp Output Lamp output decreases over time (typically use 2000hr value in design calc)
Cleaning Cleaning and the cleanliness of the environment also affects lamp output
Grids The output from the Lumen Method is a number of lights needed to achieve the desired illuminance level These must be arranged in a grid, the spacing of which is a key parameter in the design axial spacing transverse spacing
Spacing to Height The utilisation factors used in the lumen method are based on a maximum spacing to height ratio. The spacing to height ratio is as follows: If the lighting system arrived at has a grid spacing (fitting to fitting spacing) greater than the maximum (SHR MAX ) then the design process must be iterated as the illuminance (lux) on the working plane will not be acceptable i.e. uneven “patchy” illumination).
Spacing to Height Linear luminaires have two spacing to height ratios an axial (SHR AX ) and transverse ratio (SHR TR ). The axial spacing to height ratio must not exceed the maximum spacing to height ratio. The transverse spacing must not exceed the maximum transverse spacing (SHR MAX TR ). Additionally the product of the two spacings should not exceed (SHR MAX ) 2. SHR AX SHR TR ≤ (SHR MAX ) 2 Also check that the spacing is close to SHR NOM (SHR AX SHR TR ) 0.5 = (SHR NOM ) +/- 0.5 –If the spacing to height ratio is not acceptable then the lighting design process must be iterated.
Daylighting The power consumption of a lighting system can be made responsive if the control (switching) of the lighting system takes account of the fact that daylight can make a contribution to the lighting of a room. A key variable in the determination of daylight contribution to a room is the limiting depth of the daylight into the room.
Daylighting This depth determines the depth to which daylight can penetrate into a room and make a contribution to lighting levels. The formula for limiting depth, D (m), is as follows: D is the limiting depth; H is the height of the window header above floor level; W is the width of the room parallel to the window; ρ s is the average surface reflectance of surfaces in the half of the room remote from the window.
Lighting Control The penetration depth can be used to decide the design of the switching system for a lighting system. manual switching bank w/ timer control photo sensor D occupancy sensor
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