Final Report: An Integrated Ecoroof Energy Analysis Model

EPA Contract Number: EPD06054
Title: An Integrated Ecoroof Energy Analysis Model
Investigators: Lee, Allen
Small Business: Quantec, LLC.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: March 1, 2006 through August 31, 2006
Project Amount: $69,856
RFA: Small Business Innovation Research (SBIR) - Phase I (2006) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , SBIR - Green Buildings , Small Business Innovation Research (SBIR)


In recent years there has been a steady increase in the use of energy-efficient and environmentally friendly building technologies. This growth is driven by increasing energy prices, environmental concerns, and the availability of green building rating tools such as Leadership in Energy and Environmental Design (LEED). Vegetated roofs (ecoroofs or green roofs) are used increasingly in green buildings and offer diverse benefits, including energy savings and stormwater runoff reductions.

Adding an ecoroof to a conventional roofing system modifies the roof energy balance in a complex way. Existing building energy analysis tools, however, lack the ability to model the complex effects of ecoroofs on building energy use. In addition, using such tools requires specialized expertise that only experienced professionals can provide to designers, architects, and developers; these tools require significant time to set up and run. Furthermore, values of the physical properties of ecoroofs that affect energy consumption are not readily available. The general inability to accurately model and validate the energy and environmental performance of ecoroofs, the lack of measured property data, and the lack of simplified tools for doing these analyses will continue to hinder use of ecoroofs until an authoritative and peer-reviewed methodology is available for building energy modelers and designers to apply.

To develop accurate estimates of the energy effects of ecoroofs, Quantec, LLC, in association with Portland State University, conducted this Small Business Innovation Research (SBIR) Phase I project.

The research project objectives were to: (1) develop, implement, and validate an ecoroof module accessible by the U.S. Department of Energy’s (DOE) primary building energy simulation model EnergyPlus (the module combined with EnergyPlus is the “integrated model”); (2) conduct integrated-model simulations as the basis for a prototype of an easy-to-use Web-based analysis tool that would replicate the results of the integrated model; (3) determine initial requirements for the Web-based tool; (4) identify potential markets for the integrated model, Web-based tool, and ecoroof analysis consulting services; and (5) lay the groundwork for an SBIR Phase II project, which will include conducting experiments to measure ecoroof properties, completing development of the integrated model, and developing a functional Web-based ecoroof assessment tool.

The Phase I project was conducted through a series of research tasks. The first task was to develop a stand-alone ecoroof energy analysis module and integrate it with DOE’s EnergyPlus simulation model to produce an integrated model. The ecoroof module incorporated a series of equations to calculate the energy flow between the environment and a building, when an ecoroof was present. As with traditional roofs, the energy balance of ecoroofs is dominated by radiative forcing from the sun. This solar radiation is balanced by sensible (convection) and latent (evaporative) heat flux from soil and plant surfaces combined with conduction of heat into the soil substrate. The energy budget analysis follows the Fast All-Season Soil STrength (FASST) model developed by Frankenstein and Koenig for the U.S. Army Corps of Engineers.

The next research task was compiling literature values for ecoroof material properties. To supplement these data, Quantec conducted experiments with various ecoroof soils to measure several properties.

The third task was to design a series of integrated-model runs to validate the performance of the model and examine the sensitivity of estimated space heating and cooling loads to the model inputs. Several hundred runs of the integrated model were conducted to verify functionality and examine sensitivity of the results to inputs. Quantec next developed an initial interface and requirements for a Web-based analysis tool; a focus group was held to obtain feedback from possible users. Potential market opportunities were assessed through discussions with industry experts and from an assessment provided by a contractor who conducted a Technology Niche Analysis funded by the U.S. Environmental Protection Agency.

Summary/Accomplishments (Outputs/Outcomes):

The experiments provided estimates of density, thermal conductivity, and specific heat for eight different ecoroof soil mixtures; they were conducted under two different moisture conditions to estimate the effect of moisture on these characteristics.

An initial, functional ecoroof energy analysis module was developed and integrated with EnergyPlus. Initial runs were used to identify and resolve errors in the model. Several hundred runs were conducted with the final model, and they produced reasonable estimates of heating and cooling energy savings for a range of building configurations, climates, and ecoroof characteristics. Approximately 200 runs were performed to examine the sensitivity of the savings estimates to input parameters.

An initial set of requirements and a user interface were developed for the Web-based analysis tool. The interface was demonstrated to a focus group of potential users and, based on their feedback, a revised interface was developed. The overall feedback from the reviewers on the interface was positive, and they suggested adding the capability to model stormwater effects and the economics of ecoroofs in the final Web-based tool.

Responses from focus group participants and other potential users, and the results of the Technology Niche Analysis, verified that there is an existing and growing market for the integrated model, the Web-based tool, and consulting services to analyze ecoroofs.


This research project succeeded in meeting its objectives. Based on the project findings, the team is convinced that it is feasible to develop and validate an integrated ecoroof model and create a Web-based tool that will use the outputs from a suite of runs of the integrated-model to develop simplified calculations for estimating the energy effects of ecoroofs. The team also concluded that the value of the Web-based tool will be enhanced greatly by including the capability to conduct simplified stormwater and life cycle economic impact analyses of ecoroofs.

Supplemental Keywords:

small business, SBIR, green roof, energy analysis, ecoroofs, vegetated roofs, EnergyPlus, Penman-Monteith, energy, energy consumption, vegetation heat transfer, LEED green building rating, EPA, pollution prevention, green building design, energy conservation, energy efficiency, alternative building technology, ecological design, ecoroof energy analysis model, environmental conscious construction, green building design,, RFA, Scientific Discipline, Sustainable Industry/Business, POLLUTION PREVENTION, Sustainable Environment, Energy, Technology for Sustainable Environment, Environmental Engineering, energy conservation, alternative building technology, ecological design, environmental conscious construction, green building design, vegetated roofs, concrete , energy efficiency