Lighting control

Lighting tab in model data

You can control the electric lights according to the availability of natural daylight. When Lighting control is switched on, illuminance levels are calculated at every time step during Simulations and Cooling design calculations and then used to determine how much the electric lighting can be reduced. The daylight illuminance level in a zone depends on many factors, including sky condition, sun position, photocell sensor positions, location, size, and glass transmittance of windows, window shades and reflectance of interior surfaces. Reduction of electric lighting depends on daylight illuminance level, illuminance set point, fraction of zone controlled and type of lighting control.

Tip: When running Cooling design calculations you may prefer to size without lighting control, in which case you should switch the option off at building level and clear to default to ensure it is off in all zones.

Note: You should not use daylight control in zones without any windows - this will generate errors preventing calculations from running. You should therefore use the building and block level lighting control setting with care, checking for any zones without windows and switching off lighting control at the zone level.

Lighting control is available for General lighting but not for Task and display lighting. If no general lighting is specified then lighting control won't be applied.

See also the Lighting data and daylight controls tutorial

Lighting areas

When lighting control is switched on, by default all of the lights in the zone are controlled by the first (main) lighting sensor and % Zone Controlled by Lighting Area 1 has value 100%. Some larger spaces may have 2 Lighting Areas, each area having its own lighting sensor and covering its own area of the zone. The area is not defined geometrically in DesignBuilder - it simply reflects the fraction of the total General overhead electric lighting that can be dimmed by its lighting sensor.

You may wish to use 2 Lighting Areas for these situations:

1. A large zone may need more than one sensor if the output from main sensor does not represent the daylight available in other parts of the zone. For example a zone having facades in both South and East directions would need 2 sensors (and 2 Lighting Areas), one on each facade.
2. The zone has 2 different activity areas which have been lumped into a single zone for convenience. The 2 activities have different visual illuminance requirements and the Lighting Areas for both can benefit from daylighting through daylighting control. An example would be a zone having both office and recreational space. The office space may have a lighting requirement of 500 lux and the recreational space may need 300 lux.

Note 1: if the zone has a different sensor for the back half (for example) you should check the Second light sensor option.

Note 2: if the zone has perimeter and core areas, perimeter lights having daylight control and core lights not, then you only need to use a single lighting sensor. The fact that the core lights are not controlled can be modelled using % Zone Controlled by Lighting Area 1. If 60% of the lights in the zone are located in the core zone and do not have daylight control then set % Zone Controlled by Lighting Area 1 to 40.

Perimeter Area

Daylight illuminance on the 'working plane' is calculated for up to two locations in each zone during the simulation and illuminance setpoints are maintained where necessary by electric lighting.  The sensor is always located in the working plane which, by default, is 0.8m above the floor. By default, when lighting control is switched on, a single photo sensor monitors the daylight illuminance at the first sensor location and controls the lights for the whole of the zone. You can however set up 2 Lighting Areas in each zone, by checking the Second lighting area check box. In this case you can set a target illuminance for the second lighting area separately and also define the percentage of the zone covered by Lighting Area 2.

Note 1: the floor area covered by the 2 sensors does not need to add to 100%. The lights in the remaining floor area operate without daylight control.

Note 2: the target illuminance for Lighting Area 1 is set on the Activity tab under Environmental Control.

If there is only one lighting area then a percentage equal to

100 - (%Zone covered by Lighting Area 1)

is assumed to have no lighting control..

% Zone Controlled by Lighting Area 2

The fraction of the zone floor-area whose electric lighting is controlled by the daylight illuminance on the second sensor. This data is required if Lighting Area 2 is being used. A percentage equal to

100 – [%Zone Controlled by Lighting Area 1] - [%Zone Controlled by Lighting Area 2]

is assumed to have no lighting control (i.e. in this uncontrolled area of the space, the lights operate purely according to the schedule without any dimming/switching).

Procedure

The procedure for introducing the lighting control is:

1. Check the Lighting Control On checkbox (at building level if all zones are to have lighting control).
2. Enter the working plane height which should normally be the height of the lighting control sensor above the top of the floor surface of the zone.
3. Select the type of control as described below.
4. Position the first sensor in each zone having lighting control. The z-position is set by the Working plane height on the Advanced tab of the Model options dialog.
5. Set the % Zone covered by Lighting Area 1. If all the lights in the zone are in Lighting Area 1 (i.e. they are controlled by the 1st (main) lighting sensor then enter 100%.
6. If there are two lighting areas then position the second sensor.
7. Set the % Zone covered by Lighting Area 2. If all the lights in the zone are in Lighting Area 2 (i.e. they are controlled by the 2nd lighting sensor) then enter 100 - %Zone covered by Lighting Area 1.

Note: by default the main lighting sensor is positioned in the geometric centre of the zone. It is important that you check the position of all lighting sensors to obtain accurate results. For example, if the lighting sensor is positioned right next to a window receiving large amounts of daylight, the lighting sensor will signal 'enough daylight' even if the rest of the zone is only dimly lit and electric lighting energy will be under-estimated (daylight savings over-estimated).

Linear Control

With Linear control, the overhead lights dim continuously and linearly from maximum electric power, maximum light output to minimum electric power, minimum light output as the daylight illuminance increases.  The lights stay at the minimum point with further increase in the daylight illuminance.

The Minimum input power fraction for Linear control type is the lowest power the lighting system can dim down to, expressed as a fraction of maximum input power.  For Linear/off lighting control, this is the power fraction reached just before the lights switch off completely.

The Minimum output fraction for Linear control type, is the lowest lighting output the lighting system can dim down to, expressed as a fraction of maximum light output.  This is the fractional light output that the system produces at minimum input power.  For Linear/off lighting control, this is the light output fraction reached just before the lights switch off completely.

Note: Linear control provides an idealised lighting control mechanism which can be useful for calculating upper limits on the potential for savings when using natural daylight to offset electric lighting.

Linear/Off Control

Linear/off control is the same as Linear control except that the lights switch off completely when the minimum dimming point is reached.

Stepped Control

Stepped control allows you to switch lighting on/off according to the availability of natural daylight in discrete steps.  Whereas the Linear control described above provides precisely controlled illuminance by dimming the lights, the stepped control models blocks of lights switching on/off according to the electric lighting requirement.

The electric power input and light output vary in discreet, equally spaced steps. The number of steps can be set.

Example of a Stepped Lighting Control System with 3 Steps:

Daylight illuminance	Fraction of lights that are on
0-200	1.0
200-400	2/3
400-600	1/3
600 and above	0.0

Graphical representation of above example:

See also EnergyPlus Daylight Calculations.

Glare

Maximum allowable glare index

If a daylit zone has windows with Window shading devices, the shades will be deployed if the daylight glare at sensor 1 exceeds the value of Maximum allowable glare index. To get this type of glare control you have to specify Shading control type as 5-Glare for one or more windows in the zone (see Window Shading Control).

Recommended Values of Maximum Allowable Discomfort Glare Index:

     *Source EnergyPlus documentation

View angle relative to y-axis

Daylight glare from a window depends on occupant view direction. It is highest when you look directly at a window and decreases as you look away from a window. This field specifies the view direction for calculating glare. It is the angle, measured clockwise in the horizontal plane, between the positive y-axis and the occupant view direction, i.e. it is the bearing of the persons line of sight. For example, with Site orientation = 0, in the Northern Hemisphere, 90 = Facing East, 180 = Facing South etc).

Algorithms

By default, DesignBuilder uses the EnergyPlus Daylighting:Detailed object to model the control of electric lighting according to daylight illumination levels. You can find more information on the algorithms used in the EnergyPlus Daylight Calculations sectionRelated TopicsRelated Topics.

Output

For any zone simulated with daylighting controls, an illuminance map can be output with a 10 x 10 grid of additional daylighting reference points. The resulting map is output as a comma delimited text file called eplusmap.csv in the EnergyPlus folder. This file can be imported into a spreadsheet program for rapid visualisation of the daylighting illuminance patterns in a zone. To generate this file, at least one zone must have daylight control and the Daylight map output selection on the Output tab of the Simulation output options dialog must be made.

Setting the position of daylight sensors

Working plane height

You can set the height of the working plane (otherwise known as desk height) to define the z-position of the lighting sensor. The x-y coordinate is set by moving the lighting sensor marker(s) at zone level.

The Working plane height is used for EnergyPlus daylighting simulations only and is not used in Radiance daylighting where a separate value is defined on the Daylighting calculation options dialog.

Horizontal Position

To calculate the default position of the first and second daylight sensors DesignBuilder follows these steps:

1. For zones that are non-convex (zones where some surfaces cannot see all of the other surfaces in the zone, e.g. L-shaped zone) the floor plan is broken down into the smallest possible number of convex areas.
2. The geometric centre of the largest of the convex areas derived in step 1 is used as the basis for the position of the lighting sensors.
3. The specific position of the first and second sensors are 0.5m to the "left" and "right" of the geometric centre position derived in step 2.

You can move the sensor by following these steps:

1. Move to the zone level on the layout tab.
2. Select the sensor you wish to move. This enables the Move toolbar icon. You will only see the daylight sensor if lighting control is active in the current zone.
3. Click on the Move toolbar icon to start the move process.
4. Click once to define the reference or 'handle' position and click again to define the new position for the sensor.

If the second sensor is enabled in the zone then you will be able to position that in the same way.

See also: Placing Light Sensors