Siemens ET 790 Series Información técnica descargar pdf (Pagina 91)

Devices for Special Applications

Lighting

Introduction

5/3

Siemens ET G1 · 10/2008

Energy efficient lighting

Approx. 28 % of all the electrical energy in a building is used for

lighting. Increased demands made on the energy efficiency of

buildings require enhanced optimization of energy supply,

distribution and use. This goal can only be achieved through

automation. Useful automation takes into account the comfort

requirements of room users so that room temperature and the

level of lighting can be optimally adjusted to the current usage

situation. Room users need to be able to adjust their work

environment to suit individual requirements.

Savings potential demonstrated using an office building

To reduce energy costs, the artificial lighting of a room can be

controlled dependent on time, occupancy and daylight. A range

of solutions are available for this purpose, which we shall describe

in the following sections and consider their effectiveness with

regard to reducing energy costs.

By way of an example, we will demonstrate potential energy

savings in an office. In the case of lighting that is not automated,

a user profile can be assumed, which is demonstrated in the

diagram "Options for potential savings". It is assumed that

minimum lighting is switched on at 7 am. From 8 am onwards,

the lighting is switched on fully by room users. The lighting is

then left on all day until the last person leaves the room and

switches off the light. Minimum lighting is typically left running for

cleaning purposes. This lighting is then switched off, either by

the cleaners or by security.

Potential savings - the gray areas of the diagram represent the energy used in

the case of manual light control.

Time-dependent light control

When lighting is switched on by persons entering a room due to

the level of lighting, in many cases they forget to switch it off

again on leaving. A time-dependent light control would take this

into account. Time-dependent light control is either relative in

relation to an event or absolute in relation to a time or date. If the

time-dependent light control is relative to an event, the lighting is

switched off on expiry of a set time or dimmed to a minimum

value. The best known example of this type of light control is

stairwell lighting control.

In the event of time-dependent light control, the lighting is

automatically switched off at a preset time. In order to warn users

of an impending off, the lighting can be set to flash prior to the

action or, depending on the equipment, dimmed to a preset

value. This gives users the opportunity to delay the switch off by

a set time, e.g. 60 minutes, by overriding it manually.

The diagram "Potential savings quantified" shows the effect of

time-dependent light control on energy consumption.

By switching off lighting centrally, energy consumption can be

reduced by 18 %.

Daylight-dependent light control

There are generally two methods for the daylight-dependent

control of the brightness in a room: light control over a brightness

sensor in the room (constant light level control) or light control

over an outdoor brightness sensor in combination with control

devices, which take into account the direction of the window, the

geometry of the window and the possibility of objects that may

throw shadows (buildings, trees).

There are arguments in favor of both methods. While the daylight-

dependent light control requires fewer sensors than other light

controls, commissioning involves considerably higher engineering

costs. The level of lighting can be kept at a preset or user-defined

value by a constant light level control in a way that optimally

utilizes the available daylight and reduces energy costs. In order

to utilize the daylight and offer anti-glare protection, the slats of

the relevant shutter/blinds can be controlled so that these permit

the penetration of available daylight while preventing the glare of

direct sunlight. Preventing direct sunlight from penetrating the

room also prevents the room from becoming too hot.

Presence-dependent light control

Many rooms are only used for part of the day so that a presence-

dependent daylight control system could be usefully implemented

to reduce energy costs.

Using presence detectors, room functions can be automatically

switched from comfort mode to ready-to-run or energy-saving

mode. They can also be used in combination with an access

control or controlled manually or over a preset time. In corridors

the lighting can be switched off outside the main periods of use

and only switched back on when the presence of persons is

detected. Within the main periods of use, the lighting can also be

dimmed to a minimum brightness level if there are no persons

present. This achieves optimum energy savings and extends the

service life of lighting.

If operation of the corridor lighting is presence-dependent, the

right level of lighting is always delivered as and when required.

And energy consumption is in keeping with actual requirements.

This also applies to outdoor and path lighting that switches on

depending on brightness, movement and time - and is therefore

always on when required.

Electrical energy – total

28%

lighting

I2_15424

Conventional

Light

7.00 18.00 21.00

"Presence detector control" –

saves energy on lighting in the case of non-occupancy

"Constant light level control" –

reduces artificial light as soon as sufficient daylight is available

"Central OFF" –

switches off lights that have been forgotten

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