Paper Conference

Proceedings of SimBuild Conference 2010: 4th conference of IBPSA-USA


Daylight Nomographs Revisited

Rohit Manudhane, Christoph F. Reinhart
Harvard University, Graduate School of Design, Cambridge MA 02138, USA

Abstract: This study presents a critical review and extension of a classic 1984 paper titled “LBL Daylighting Nomographs” written by Selkowitz and Gabel using RADIANCE/DAYSIM simulations combined with the LIGHTSWITCH occupant behavior model. The nomographs were originally derived from DOE2.1B simulations to allow designers to estimate the energy savings from photocell controlled dimming systems. As an initial step, the DOE2 simulations were successfully reproduced using the RADIANCE-based DAYSIM program for a series of sidelit spaces in Boston using the same simulation assumptions as the original nomographs, i.e. no blinds and lights always switched on during office hours. In a second step the DAYSIM simulation were redone taking occupant use of venetian blinds and light switches into account. For an example office building the new, more realistic nomographs predict about 30% to 50% lower electric lighting energy savings due to photocell controlled dimming than the old nomographs. The new nomographs can be used in combination with a recently developed rule-of-thumb based design sequence for daylighting.