Green Roofs - Living Architecture Monitor - Fall 2011 - (Page 32)

GRHC UPDATE RENEWED ENERGY CALCULATOR THIS NEWLY UPDATED, EASY-TO-USE ONLINE TOOL CAN HELP YOU ASSESS THE BUILDING ENERGY USE IMPLICATIONS OF VARIOUS GREEN ROOF DESIGN DECISIONS By David Sailor T he Green Roof Energy Calculator was developed through a collaboration involving researchers at Portland State University, the University of Toronto and Green Roofs for Healthy Cities. The project was funded by the U.S. Green Building Council with the primary goal of developing an easy-to-use online tool to allow developers, engineers and architects to assess the building energy use implications of various green roof design decisions. To develop the calculator, two fundamentally different whole-building energy simulation approaches were pursued simultaneously. The research team in Toronto had developed an empirically based representation of green roofs in the energy simulation software ESP-r. The team in Portland had created a physically-based green roof module as part of the EnergyPlus simulation software. After validating the modeling tools with field and laboratory measurements the two approaches were applied to prototypical buildings across numerous North American climates. The results of the two models were generally consistent with predicted energy savings of green-roofs typically within 20 percent of each other. For the calculator it was decided that the physically based model, with its flexibility to explicitly represent variations in green-roof design characteristics would be used as the foundation for the calculator. A total of 8,000 simulations were conducted for old and new office and multifamily residential buildings in 100 North American cities. Each building was simulated with a control dark membrane and also a light membrane. Then, a total of 18 variations of green roofs were simulated for each building. Irrigation LIVING ARCHITECTURE MONITOR FALL 2011 schedules were provided for half of the green roof simulations. All simulations used representative (TMY3) weather and precipitation files. The calculator interface allows the user to select the location and type of building as well as the roof area and multiple green roof design characteristics (growing media depth, leaf area index, irrigation). Utility pricing schedules are automatically used for all simulations of U.S.based cities. Fixed utility rates can also be specified. The calculator then interpolates within the data base of building simulation results and scales the output based on roof area. It presents green roof energy and energy cost savings relative to a conventional darker roof and also as compared to a highly reflective "white" roof. Because the underlying energy simulation module within EnergyPlus tracks moisture and surface heat fluxes the calculator reports information related to the effect on the urban heat island and the rooftop water balance. While the tool is still being refined, it is available for use at Portland State University's Green Building Research Laboratory's website: The Green Roof Energy Calculator will eventually be integrated into the GreenSave Calculator - a lifecycle-cost analysis tool available from Green Roofs for Healthy Cities at GRHC gratefully acknowledges support (both in-kind and financial) it has received from Environment Canada for the development of the Green Roof Energy Calculator. D David J. Sailor, Ph.D., is professor, Mechanical and Materials Engineering Dept at Portland State University in Portland, Oregon. 32

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Fall 2011

Green Roofs - Living Architecture Monitor - Fall 2011
From the Founder
On the Roof With…
Policy: The Game Changer
Policy: Toronto’s Green Roof by-Law
Policy: Energy Code Break-Through
GRHC: Update
GRHC: Welcome New Members
On Spec

Green Roofs - Living Architecture Monitor - Fall 2011