Another enlightening session of AIA Pittsburgh’s AIA+2030 Educational Series took place in November: Session VI – Illuminating Savings: Daylighting and Integrated Lighting Strategies. As promised, the night featured a series of experts defining good daylighting. They offered resources for useful design tools and demonstrated how these strategies improve the design while reducing energy consumption.
The evening began with the Astorino team of Director of Digital Practice, Brian Skripac, Assoc. AIA, LEED AP BD+C, and Sustainable Design Manager, Rudy Marnich, MArch, LEED AP BD+C. Brian talked about the difference between sunlight and daylight. While sunlight is just the rays of the sun, daylight is actually a manipulation of that light. Quality daylight, Skripac says, is a layered illumination plan that provides a constant standard of light throughout the day. It balances natural light, solar gain, and energy use.
Lighting comprises 24% of the average building energy consumption. Good daylighting design can reduce the lighting energy use 50-80%. The key is controlling heat gain and glare. In addition to the energy benefits of daylighting, a number of Heschong Mahone Group studies have shown the human comfort effects of natural light, such as improved well-being and productivity. CMU’s eBIDS website features further quantifiable effects of daylighting.
Marnich and Skripac shared Astorino’s iterative and integrative design process. Marnich reminded us that the AIA has published a useful primer on this topic: An Architect’s Guide to Integrating Energy Modeling in the Design Process. BIM and energy modeling are at the core of successful daylighting design and a variety of BIM tools assist in validation of sustainable outcomes. The BIM-enabled workflow presented by Skripac and Marnich involves an evaluation of climate metrics, daylighting opportunities, solar control, and energy use. Continuous discussion amongst team members regarding the sharing of the energy model in its various forms is essential. Timing of the model hand-off and methods for keeping the model lightweight should be included in the discussion. A lightweight model expedites the process.
Astorino’s “green team” concluded their presentation with a daylighting case study. The project was in the hot, humid desert of Abu Dhabi. Solar gain was just as important as daylighting. Therefore, studies included various combinations of louvers, fins, and skylights. Building simulation allowed energy use and solar gain to be simultaneously analyzed to balance exterior shading features with daylighting to minimize the energy use burden.
Paul Petrelli, PE, CPMP, LEED AP BD+C, principal at HF Lenz was the next expert to present. He started by providing references to the most relevant energy-efficient codes and design guides. There are two ASHRAE documents worth mentioning. ASHRAE 90.1-2013 has just been released with even lower lighting power density allowances. Also important is ASHRAE 189.1-2011 – Standard for the Design of High Performance Green Buildings. This document was developed in collaboration with the USGBC and had been approved as an ANSI standard. Therefore, it is a bonafide legal document. Petrelli predicts this document will become the basis for future editions of LEED.
After the code review, Petrelli shared the results of a study he had conducted. The study started with the question, “Is daylight really the answer?” and ended with the statement, “Integrated Design is Climate Responsive Design!” The study modeled a multi-phased overlay of energy-efficiency strategies: ASHRAE 90.1 2010 compliance, building massing, window/wall ratio, solar control devices, and building orientation. In comparing EUIs of the various design alternatives, the building incorporating all of the above strategies resulted in the best EUI.
Petrelli concluded his presentation with a few tips for designers. First, watch the room surface reflectance. Hue and color value affect reflectance. Second, the IES Lighting Handbook provides a number of tables useful in daylighting design.
John Northern of Repco II introduced the last expert of the night, Joe McGrath of Wattstopper. McGrath pointed out that the IECC 2012 requires daylighting harvesting. Also, ASHRAE is committed to reaching net zero design by 2030. Therefore, understanding how to utilize daylight is no longer just an option, it is a necessity.
The distinction between passive and active daylighting were described. Passive daylighting is about the architectural elements allowing daylight to enter the building. Side and top lighting along with various accessories, such as light shelves and shades, are the tools of passive daylighting. Active daylighting is about a system of controls that adjust artificial lighting levels in reaction to the daylight amount. Photocells, switches, dimmers, and circuits are the tools of active daylighting. The optimal daylighting system combines passive and active.
The goal of an active system is to make the interplay of natural light manipulation and artificial light accompaniment nearly imperceptible to the occupants. Daylighting systems often fail because the switching on and off of the lights is distracting or inappropriate for the room. That’s when you have people taping over the photocells or constantly overriding the switch.
McGrath shared several helpful tips to keep in mind when designing a daylighting system. First, establish the proper zones for controls. Consider the zones concentrically from the perimeter inward. Second, evaluate whether you want continuous dimming or on/off switching; with multiple zones, on/off switching can be too abrupt. Third, chose wisely between a closed or open loop feedback system. With a closed loop, the lights adjust to the sensor reading, then the sensor reads again, and lights adjust again. This works well for single zone daylighting. With closed loop feedback, the sensor only reads the natural light. The open loop works better for multi-zone systems and spaces with skylights. In spaces with really high ceilings with skylights, such as big box stores and warehouses, the dual-loop system is ideal. It features a back-to-back photocell in the skylight picking up on light levels above and below.
After a short break in December, the AIA+2030 educational series will resume on January 16, 2014 with Session XII – Right Sized: Equipment and Controls for Super-Efficient Building Systems.