Problem Description

Part 1: Informal Requirements

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This part contains the needs for a new light control system for the fourth floor of building 32 of the University of Kaiserslautern.

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The main motivation for the development of a new light control system are the disadvan tages of the currently existing system. Since all lights are controlled manually, electrical energy is wasted by lighting rooms which are not occupied and by little possibilities to adjust light sources relative to need and daylight.

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Paragraphs are numbered for easier reference.

1 Needs

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In this section, the needs for the new light control system are presented. In 1.1, functional needs are listed and in 1.2 non-functional needs.

1.1 Functional Needs

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The functional needs are split into two groups, user needs and facility manager needs, depending on the person who has expressed them.

1.1.1 User Needs

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The user needs are numbered by U<number>.

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At first, general user needs are listed, which are demanded for each kind of room:

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If a person occupies a room, the light has to be sufficient to move safely, if nothing else is desired by a chosen light scene.

Need	U2

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As long as the room is occupied, the actual chosen light scene has to be maintained.

Need	U3

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If the room is reoccupied within T1 minutes after the last person has left the room, the last chosen light scene has to be reestablished.

Need	U4

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If the room is reoccupied after more than T1 minutes since the last person has left the room, the standard light scene has to be established.

Need	U5

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The wall switches for the window- and the wall-ceiling light group in a room should show the following behavior: if the corresponding ceiling light is completely on, then the light will be switched off otherwise the ceiling light will be switched on completely

Need	U6

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The light scenes can be determined by using the control panel.

Need	U7

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For each room, the actual ambient light level can be set by the user using the control panel.

Need	U8

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For each room, a default light scene can be set (not by using the control panel).

Need	U9

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For each room, a default ambient light level can be set (not by using the control panel).

Need	U10

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The value T1 can be set for each room separately (not by using the control panel).

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If the outdoor light sensor or the motion detector of a room does not work correctly, the user has to be informed.

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The user needs concerning the offices are:

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The ceiling lights and the task light should be maintained by the control system depending on different light scenes.

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The control panel should be movable in the offices, like a telephone.

Need	U14

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The control panel should contain at least: a switch to set the task light (on/off) a switch to set the ceiling lights (on/off/ambient) a possibility to set the actual ambient light level

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The user needs concerning the remaining rooms are:

Need	U15

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In all other rooms the control panel should be installed near a door to the hallway.

Need	U16

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The control panel should contain at least: a switch to set the ceiling lights (on/off/ambient) a possibility to set the actual ambient light level

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The user needs for the hallway sections are:

Need	U17

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When a hallway section is occupied by a person, the light in this hallway section has to be sufficient to move safely.

Need	U18

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Before a person enters one hallway section from another one, the light in the section being entered is turned on if necessary.

Need	U19

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The wall switches for lights in the hallway section have to show the following behavior: if the light is on, then the light will be switched off otherwise the light will be switched on.

1.1.2 Facility Manager Needs

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The facility manager needs are numbered by FM<number>.

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Use daylight to achieve the desired light whenever possible.

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Lights in a hallway section have to be switched off when the section has been unoccupied for T2 min.

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If a room is unoccupied for more than T3 minutes, all lights must be switched off.

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The value T2 can be set for each hallway section separately.

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The value T3 can be set for each room separately.

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The facility manager can turn off any light in a room or hallway section that is not occupied.

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If a malfunction occurs, the facility manager has to be informed.

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If a malfunction occurs, the control system supports the facility manager by finding the reason.

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The system provides reports on current and past energy consumption.

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All malfunctions and unusual conditions are stored and reported on request.

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Malfunctions that the system cannot detect can be entered manually.

1.2 Non-Functional Needs

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The non-functional needs are split into several groups depending on the aspect they are dealing with. They are numbered by NF<number>.

1.2.1 Fault Tolerance

In any case of failure the system shall provide a stepwise degradation of functionality down to manual operability.

Needs in the case of a malfunction of the outdoor light sensor:

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In any case of failure the system shall provide a stepwise degradation of functionality down to manual operability.

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Needs in the case of a malfunction of the outdoor light sensor:

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If the outdoor light sensor does not work correctly, the control system for rooms should behave as if the outdoor light sensor had been submitting the last correct measurement of the outdoor light constantly.

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If the outdoor light sensor does not work correctly, the standard light scene for all rooms is that all ceiling lights are on.

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If the outdoor light sensor does not work correctly and a hallway section is occupied, the lights in this hallway section has to be on.

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Needs in the case of a malfunction of the motion detector:

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If the motion detector of a room or a hallway section does not work correctly, the control system should behave as if the room or the hallway section mere occupied.

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Needs in a worst case failure of the control system:

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If the lights in a hallway section are neither controllable automatically nor manually, the lights have to be on.

1.2.1 Safety and Legal Aspects

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All hardware connections have to be made according to DIN standards.

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No hazardous conditions for persons, inventory, or building are allowed.

1.2.1 User Interface

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The control panel should be easy and intuitive to use.

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The system issues warnings on unreasonable inputs.