Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Regarding validation of the Green Roof Model, I would point you to the EcoroofOrlando.idf example file, which demonstrates the use of the Material:RoofVegetation object. The roof construction (ASHRAE 90.1-2004_Sec 5.5-2_Roof) has the BaseEco material as the outside Layer. Running this model with and without this BaseEco material in the roof construction demonstrates the impact of that material on the zone loads, particularly the top floor zones which are most impacted by changes to roof construction. Looking at the htm output file, there is a table called "Zone Sizing Information" which shows the calculated Design Loads {Watts} for each zone. Design loads are a much better indicator than annual energy consumption to assess the performance of envelope constructions. To see the material's impact on the roof construction's thermal performance (i.e. u-factor and reflectance), look at the Envelope Summary table which summarizes the performance of all the constructions used in the model.
The results show that this green roof reduces heating loads on the top floor zones between 4-11%, and cooling loads from 11% to 29%. Repeating this exercise on the SchoolSecondary model in Buffalo should yield somewhat similar results, but keep in mind that zone cooling/heating loads are impacted by many components other than just envelope performance (e.g. internal loads, roof-area-to-zone-volume ratio, ventilation requirements, ambient weather conditions, space setpoints etc.), so your results may vary widely depending on the specifics of your model, in addition to any differences you may be assuming in your base roof performance and your Material:RoofVegetation definition.
| | 2 | No.2 Revision |
Regarding validation of the Green Roof Model, I would point you to the EcoroofOrlando.idf example file, which demonstrates the use of the Material:RoofVegetation object. The roof construction (ASHRAE 90.1-2004_Sec 5.5-2_Roof) has the BaseEco material as the outside Layer. Running this model with and without this BaseEco material in the roof construction demonstrates the impact of that material on the zone loads, particularly the top floor zones which are most impacted by changes to roof construction. Looking at the htm output file, there is a table called "Zone Sizing Information" which shows the calculated Design Loads {Watts} for each zone. Design loads are a much better indicator than annual energy consumption to assess the performance impacts of envelope constructions. To see the material's impact on the roof construction's thermal performance (i.e. u-factor and reflectance), look at the Envelope Summary table which summarizes the performance of all the constructions used in the model.
The results show that this green roof reduces heating loads on the top floor zones between 4-11%, and cooling loads from 11% to 29%. Repeating this exercise on the SchoolSecondary model in Buffalo should yield somewhat similar results, but keep in mind that zone cooling/heating loads are impacted by many components other than just envelope performance (e.g. internal loads, roof-area-to-zone-volume ratio, ventilation requirements, ambient weather conditions, space setpoints etc.), so your results may vary widely depending on the specifics of your model, in addition to any differences you may be assuming in your base roof performance and your Material:RoofVegetation definition.
