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 the simulation 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: Daylight control set in zones without any windows will generate errors preventing calculations from running.
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.
If the zone has a different sensor for the back half (for example) you should check the Second light sensor option.
You may wish to use 2 Lighting Areas for these situations:
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.
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.
Important note: 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 uncontrolled core lights 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
A typical perimeter area would be the areas of the zone that are close to a window. By convention, perimeter areas are defined as the area within a fixed distance from a normal to the perimeter. In the UK NCM the fixed distance is 6m.
If you wish to create a separate thermal zone to model the different lighting and solar conditions in the perimeter area, you can use the Offset snap option to draw Virtual partitions.
Daylight illuminance on the 'working plane' is calculated for 1 or 2 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. Also 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).
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).
Continuous Control
With Continuous 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 Continuous control type is the lowest power the lighting system can dim down to, expressed as a fraction of maximum input power. For Continuous/off lighting control, this is the power fraction reached just before the lights switch off completely.
The Minimum output fraction for Continuous 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 Continuous/off lighting control, this is the power fraction reached just before the lights switch off completely.
Note: Continuous control provides an idealised lighting control mechanism which can be useful for calculating upper limits on the potential for savings using natural
daylight.
Continuous/Off Control
Continuous/off control is the same as continuous 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 Continuous 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.
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).
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
DesignBuilder offers a choice of EnergyPlus daylighting algorithms:
1-Detailed is the default option and the most practical for most purposes.
2-DELight does a full radiosity lighting calculation, i.e. it bounces light beams around each zone to calculate daylight distribution. It has some limitations though.
These can be selected on the Model options dialog on the Advanced tab under Lighting.
Daylight control procedure
The procedure for introducing the lighting control is:
Check the Lighting Control On checkbox (at building level if all zones are to
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%.
If there are two lighting areas then position the second sensor.
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.
Check for zones with lighting control specified but having no natural daylight.
Check hourly results and make sure they make sense!
Exercise – Daylighting calculations To test the various daylighting settings:
Following on from the last exercise, at building level go to the Lighting tab and switch on Lighting Control.
Note that the default control method is 1-Linear.With this method you can also define the minimum output fraction of the lights when fully dimmed and the corresponding power fraction. These these in their default states.
Now go to the Layout tab and notice that the sensor position is shown.
By default the sensor is placed in the middle of the zone. You can move it to a specific location by selecting it then moving it using the move toolbar icon.
Also keep the default the Detailed daylighting method and 0.8 m working plane height (Model options > Advanced tab > Lighting header).
Click on the Simulation tab and run a simulation for 6 December only. Select Sub-hourly results and set the Time steps per hour to 4.
Go to Ground floor > Zone 1, select the sub-hourly interval and show 4-Internal gains data. Open the Detailed Display options tab and switch off the display of the Zone/Sys sensible heating system under the Internal gains header and save the selection as a template for later use by pressing the Save Display options toolbar button. The results should look like:
Now go back to the edit screen (press F7), go to building level and change the light control settings.
Use the 2-Linear/off Lighting control type this time and run a simulation choosing the same calculation and display options as before, you should see:
Now test the Stepped control method using 3 steps.
Optional Exercise - DElight
Use the EnergyPlus tab of the Program options dialog to change the version of
EnergyPlus used. If you have been able to get the exe version, go to the Advanced tab of the model options dialog, open the Lighting header and change the Daylighting method to 2-DELight. This will use the advanced DElight calculation method using ray-tracing to calculate the daylight illuminance.
The DElight method of analysing daylighting in buildings is very similar to that used in the Detailed method. For each point in time, DElight calculates the interior
daylighting illuminance at specified reference points and then determines how much the electric lighting can be reduced while still achieving a combined daylighting and electric lighting illuminance target. The daylight illuminance level in a zone depends on many factors, including exterior light sources; location, size, and visible light transmittance of simple and complex fenestration systems; reflectance of interior surfaces; and location of calculation reference points. The subsequent reduction of electric lighting depends on daylight illuminance level, illuminance set point, fraction of zone controlled, and type of lighting control.
There are two primary differences between the Detailed and DElight methods of calculating interior illuminance levels:
The first is that DElight includes the capability of analysing complex
fenestration systems that include geometrically complicated shading systems (e.g., roof monitors) and/or optically complicated glazing systems (e.g., prismatic or holographic glass).
The second key difference is that DElight uses a radiosity method to calculate the effects of light reflection inside a zone. These methods are discussed in more detail in the engineering documentation.
There are other important differences between the two methods:
One is the inability of DElight to perform the type of dynamic shading controls possible using the Detailed method at each point in time during the thermal simulation (e.g., changes in electrochromic glazing transmittances and blind slat angles).
Another is the DElight ability to include > 2 reference points in its interior illuminance and electric lighting reduction calculations. A third is the current lack of visual quality (e.g., glare) calculations performed by DElight.
Fourth, the modelling of interior obstructions is different in the two methods.
In the DElight method, interior obstructions block inter-reflections but do not block the initial direct illuminance. In the Detailed method, interior
obstructions block the initial direct illuminance but do not block inter-reflections.
Compare the results using DElight with those calculated using the Detailed daylighting method.