Lighting Controls

Modified on Tue, 18 Jun at 3:06 PM

Modelling individual zones to find optimum improvements

The NCM offers various means of lighting control. These are available in SBEM and DSM. Not all types of control will be effective or appropriate in a particular zone. This article goes through the different types and offers some advice on making choices.

Lighting Controls can be roughly split into 'Daylight Linking' and 'Presence sensing' (Occupancy control)

Daylight linking:

• Constant illuminance Control

• Local Manual Switching

• Photoelectric Control

Presence sensing / Occupancy control

• Occupancy Sensing

Parasitic Power

With the exception of Local Manual Switching, all require sensors which consume 'parasitic power'. The parasitic power operates 24/7 (8760 hours a year) . There are two default settings:

• Stand-alone sensors: the default power is 0.3W/m²: this equates to an energy consumption for the controls of 2.6kWh/m² (0.3 * 8760 / 1000)

• Addressable systems: these use a default of 0.57W/m² this equates to an energy consumption for the controls of 5.0kWh/m² (0.57 * 8760 / 1000).

Note that occupancy control also has a default parasitic power of 0.3W/m². If both lighting controls are used and the parasitic power left at the default value then the zone will consume approximately

5.2kWh/m² ( based on a parasitic power of 0.3W/m² for Daylight control plus a further 0.3W/m² for Occupancy control)

7.6kWh/m² ( based on a parasitic power of 0.57W/m² for Daylight control plus a further 0.3W/m² for Occupancy control)

This additional consumption for the controls can mask the savings provided by reduced light output, sometimes generating a lighting consumption above that achieved without the controls.

It is thus best to identify the actual power consumed by the sensors (fitted or specified) and divide this by the zone area (not the area controlled) to generate the correct W/m².

Note that the Notional Building assumes a total 0.1W/m² for Daylight + Occupancy Control.

Occupancy Sensing

Occupancy sensing has 5 classifications, offering different fixed savings

Activities which don't allow Manual types of control include (list is not exhaustive)

Circulation spaces
Car Parks
Changing Rooms
Sports Halls
Sales
Eating & Drinking
Teaching
Industrial process

Constant Illuminance Control

Lighting Design calculations include an adjustment 'Maintenance Factor' to account for degradation in performance over time. This means that the initial output from a lighting installation will exceed the design requirements. With dimmable luminaires it is possible to control the output so it does not exceed the design illuminance. This is referred to as Constant illuminance Control. In SBEM this is modelled as a 10% reduction in lighting energy though the controls will contribute to an additional parasitic power which will reduce this saving (and potentially increase the consumed electricity).

Constant illuminance Control can be used in any zone but is best used in zones with

higher illuminance requirements
long 7 day schedules
where daylight or occupancy control is inappropriate

Some example activities meeting these requirements:

Food Preparation Area (Commercial and Institutional)
Laboratories: particularly in B2-B7, C2 & D1 Building Classes
Operating Theatres and Post Mortem facilities
Hotel Receptions

Local Manual Switching

This type of lighting control is based on human assessment of the need for lighting in a space. Generally this is made by the first person to enter the space in a day. If there is sufficient daylight when the lighting schedule first operates in a day the lighting will be halved until the daylight available is below that required. It is a manual control and thus does not require sensors/controls that consume additional energy. It is particularly useful for spaces with a low illuminance setting (below 200lux). It is not appropriate for 24/7 activities and there are some activity types that the NCM does not permit its use:

dry sports/fitness
ice rinks
changing rooms
swimming pools
sales areas
baggage reclaim areas
security check areas
eating/drinking areas
Halls
lecture theatres
cold stores
display areas
A&E
industrial process areas
warehouse storage
performance areas (stages)

Unfortunately some of the activity types with the greatest potential are not usually daylit (Plant Rooms, Toilets, Store Rooms).

It is understood (SBEM Technical Manual) that this control can be set automatically in any zone (with appropriate activity) of floor area less than 30m. Otherwise, there should be access throughout the zone to a switch within 6m. If these requirements are met then it can be applied to any space, there is no parasitic control so it can only reduce the lighting energy.

Photoelectric Control

Photoelectric control reduces the lamp output when the daylight available in the space is sufficient to do this. There are two types available in SBEM:

PH Switching
PH Dimming

PH Switching is effectively On/Off control. If the daylight at the rear of the space being controlled is above the Design Illuminance for the space, the lighting is switched off and all light is provided by daylight.
PH Dimming enables the lamp output to be reduced so that the minimum illuminance at the rear of the space is not less that the Design illuminance. Even with low levels of daylight the lamp output (and energy consumed) can be reduced.

The following chart is an illustration of the relative performance of Daylight Dimming and Switching. It considers a rectangular zone (B1_Office) lit from one elevation only. Width of space (10m), Height of space (3.5m) and Depth of space (6m) will all impact the results.

Opening Ratio is impacted by

Lsolar (taken as 1.0)
Frame Fraction (taken as 0.0)
Shading transmission Factor (and other shading settings) (taken as 1.0)

In practice the results shown here for an Opening Ratio of 20% may be more representative of a glazing ratio of 40% taking into account realistic values for the above factors.

Note that:

For low opening / glazing ratios PH Dimming will usually perform much better than PH Switching
For high opening / glazing ratios there is less of a difference in the effectiveness of the two technologies

Note also that:

Unless you select 'different sensor to control back half of the room' only the Front 3m from windows will be controlled.
With a sensor controlling the back half you will include the area 3-6m from the windows.
PH Switching will generally not be successful in the rear of the zone

Whilst SBEM automatically splits a zone into a daylit area (6m deep) and an unlit area it will apply parasitic power to the full zone area. Thus deep spaces are unlikely to benefit from Photoelectric Control if default parasitic power is used.
You can get an increased lighting consumption with photoelectric control, particularly for:
- deep spaces
- low glazing ratios
- activities that predominantly operate in the evening / early morning