Incorporate lighting controls with BAS to save energy

09/23/2013


Controls and sensors 

Figure 2: The southwest view of the Dicke Hall lobby from the second floor shows daylight harvesting through the large windows. Courtesy: Metro CD EngineeringProper selection and calibration of the photocontrol sensor is critical in maximizing the energy savings with daylighting harvesting. Some manufacturers have multiple sensors for different space functions. For example, an indoor photocontrol sensor is a sensor specifically designed and calibrated for interior spaces with windows. An atrium photocontrol sensor is for atriums with higher natural daylight levels. A skylight photocontrol sensor is for areas with direct sunlight exposure.

A lighting controller can automate the lowering and raising of window shades to optimize daylight and minimize glare based on the sun’s position. Daylight harvesting should also be included with this shading control strategy. The BAS can determine energy savings by monitoring the energy usage for the lighting circuits affected by the shading devices. 

Occupancy sensors and photocontrol sensors can counterbalance each other. For example, an occupancy sensor can detect a person entering a private office with windows during a sunny day. If the photocontrol sensor detects that adequate daylight exists, the lighting controller can ensure that the artificial lighting in the room remains off. 

If the room did not have a photocontrol sensor, the lighting controller would have turned on the artificial lighting even though there was adequate daylight. This is a good example of how an integrated daylighting and lighting control strategy can save energy. 

Another benefit of integrating lighting controls with a BAS is space use. For example, a BAS that incorporates occupancy sensors can be used to determine how often certain rooms and areas are occupied. Having access to this data allows facility managers to determine if an adjustment is needed to optimize use. An example of using this data is adjusting the time-of-day lighting shutoff for a certain floor or area based on actual usage. 

Consideration should be given by the designer when incorporating more complexity in a lighting strategy. The facility’s management and maintenance capabilities and associated cost to maintain the system should be included in the analysis.

Load shedding 

A BAS can also save energy and money by load shedding. The BAS through the lighting controller can dim or turn off lighting to lower a building’s load during periods of high electric utility demand. Load shedding helps utility companies avoid blackouts and brownouts, and can result in utility credits or rebates for the customer. 

The designer should ensure that dimmable ballasts are specified and installed when a lighting controller is programmed to dim lighting. Severe ballast damage can result if non-dimmable ballasts are used in dimming scenarios. The designer also should consider dimming or turning off lighting with load shedding in certain areas or with a certain percentage of the lighting fixtures. Communication with the facility’s operations personnel is critical in ensuring operations are maintained with the lower lighting levels in certain key areas.

Smart Grid and smart metering systems help automate load shedding. A typical scenario involves the local utility company sending an automated signal prior to an anticipated high demand period to a facility’s smart meter. The smart meter then sends a command to the facility’s BAS. The BAS through its programming can then reduce the lighting levels and lower the energy usage by the facility. 

Load shedding typically has minimal impact to the building occupants when effective daylight harvesting strategies are used. Most load shedding is done during the summer months when there is sufficient daylighting, thereby minimizing the impact of reduced artificial lighting loads. This is particularly effective when a facility does not have photocontrol sensors.

Many utility companies also offer energy efficiency incentives when lighting controls and/or daylight harvesting are incorporated into a new or retrofit installation. There may be other local and state incentives as well.



CARLOS , TX, United States, 09/27/13 09:47 AM:

I found the article to be very useful on the subject of lighting control and interface with BAS.