Daylight Harvesting Gains from System Integration

  October 14, 2015

Long-term operation of a green building is mainly based on energy conservation, water efficiency, and indoor environmental quality, all of which are controlled, monitored, and driven by building control systems. Integrating these and other building control systems has significant advantages and can provide some additional building operational support. One benefit is acquiring data from the building systems, normalizing it into a standard data format, creating a database, analyzing the information, identifying correlations and outliers, and creating optimal rules for real time system operations. Another plus is integrating the functionality of two systems to gain functionality that neither system could provide alone. This is the maxim that “the whole of the sum is greater than the parts.” A good example is daylight harvesting.

If a building has motorized exterior shading, typical lighting controls, and a DDC system, there’s a need to integrate the systems and optimize several variables within them. When they are not integrated, each system is operating in a silo, cooling, shading, or lighting without full consideration of overall potential thermal loads or light levels.

It’s really about controlling the penetration of sunlight. The goal is to use daylight to reduce the need to use the electric lighting system, thus saving energy and at the same time maintaining a minimum recommended light level for the space. Too much sunlight may result in heat gain and trigger cooling from the HVAC system, which would require additional energy. Too little sunlight may result in greater use of the electric lighting system.

Integration aims to balance the optimal lighting needs of the occupants with the energy consumption of the lighting or HVAC system. The position of the shades affects thermal loads because it determines the amount of sunlight entering the space as well as the amount of heat coming from the lighting system. Keeping the shades closed would eliminate the thermal load from sunlight entering the space, but of course the reason for having a daylight harvesting system is to let in sunlight. An integrated approach can be used to control active and passive sources of heating, lighting, shading, and ventilation via a preset sequence of operations.

This quick read is from Jim Sinopoli, managing principal, Smart Buildings LLC.

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