This option will set the automatic control function to PHOTOCELL CONTROL and will be based on the EFFICACY calculation method.
To use this lighting function you will need to have calculated a DAYLIGHT FACTOR within the zone for which the lighting function will be referencing (the 'control zone').
To use the function, under the Control Logic area on the dialog, set the Control Type to "Photocell Control" on the drop-down list. Then choose "Efficacy Method" from the Calculation Method drop-down options. Under the Parameters area, choose whether the applied zone will act as the control zone. The applied zone will be the zone to which the internal condition is applied. Otherwise you will need to specify which zone in the model will act as the control zone. If you select another zone from the drop-down list to be the control zone, its illuminance levels will determine when and how the lights will be operated within the applied zone.
The calculated lighting gains will be a function of the target room illuminance, the minimum illuminance level, and the efficacy value in lm/W. You will need to input the illuminance level at which the lighting gain will be at its minimum value, this will be the target room illuminance. You will then input the minimum illuminance level, this is the level at which the lighting gain will be at its highest value. You will also specify the lighting efficacy. The efficacy will then be used to back-calculate the maximum lighting gain. You will need to enter a minimum percentage gain as well. The minimum percentage gain is defined as the percentage of the maximum lighting gain that will be used when the natural room illuminance exceeds the target room illuminance.
The lights will operate as follows, in the first occupied hour the function will look to see what the illuminance level is, and if it is at or below the target room illuminance. If the illuminance level is at (or above) the target illuminance then the lighting gain will be set to the minimum value, and you will have already specified the percentage of the maximum lighting gain that will apply when the illuminance level is at or above the target room illuminance. Although you haven't entered a maximum lighting gain into the software, this value will be derived from the efficacy value. In the second occupied hour, the function will look to see if the illuminance level has changed. If the illuminance level is still at or above the target illuminance then the lighting gain will not be changed from the value that was used in the first hour, but the function will always look to see if the lighting gain needs to be updated at each hour. If the illuminance level has dropped below the target room illuminance, meaning that the room will have reduced access to daylight than it did during the previous hour, the lighting gain will be increased. The lighting gain will be increased linearly as illuminance levels decrease linearly, until the minimum percentage gain is reached, at which point the lighting gain will be set to the maximum value, as determined by the efficacy.
The defining characteristic of the photocell control function is this, during the occupied period, if the illuminance increases at any hour, the lighting gain will be reduced. The lighting gain will decrease linearly as illuminance level increases linearly, until the target room illuminance level is reached, at which point the lighting gain will be at its lowest value. Note that this is not how the manual control function operates.
Example - plcle,0,0.95,30,6.67,500,10,0.3,1,2.5
The function string begins with a '0', which indicates that the control zone is the applied zone.
The next number is '0.95', which means the lighting gain will be multiplied by a PIR factor of 0.95.
This is followed by the number '30', which represents the efficacy value in lm/W.
The next number is '6.67', giving the percentage of the maximum lighting gain that will apply when the illuminance level is at or above the target room illuminance.
The '500' value is the target room illuminance.
The '10' means the minimum illuminance is 10W/m^2, and this will be the illuminance level when the lighting gain is at its maximum value, as determined by the efficacy.
The '0.3' value is the parasitic power. During all hours a parasitic power gain will be added. The parasitic power represents the amount of energy consumed by the photocell sensor. The parasitic power will not benefit from the PIR sensor.
The next number is '1' which means there will be a timer clock which determines when the photocell sensor is on. A timer clock means that the photocell sensor will be on during the occupied period.
The last number is '2.5' which is the display lighting gain, during hours with sensible occupancy gain a display lighting gain will be added. The display lighting gain will not benefit from the PIR sensor.
Let's look at a worked example, based on this function string. As the timer clock is on, the photocell sensor will only be on during the occupied period, otherwise the parasitic power gain will apply outside of the occupied period. Suppose the illuminance level in the first hour is 500lx, which is the target room illuminance. This means that the lighting gain will be at its minimum value. The minimum value will be determined by the minimum percentage gain value, which in this instance is 6.67%. So the lighting gain at hour 1 will be 6.67% of the maximum lighting gain. At hour 2, the illuminance then falls to 300lx, so the lighting gain will be increased and will scale linearly with the illuminance. At hour 3 the illuminance level increases to 400lx, and so the lighting gain will be reduced, again it will scale linearly. At hour 4 the illuminance level has fallen to 200lx and so the lighting gain will be increased. When the illuminance level has fallen to the minimum lux level, which in this case will be 10lx, the lighting gain will be increased to its maximum value. A PIR factor of 0.95 will be used as a multiplication factor to reduce the calculated gain, this is done in order to model automatic presence detection. Finally, the display lighting gain of 2.5W/m^2 and the parasitic power gain of 0.3W/m^2 will be added on.