Hi,
We are studying a building in Saudi Arabia that has a fully glazed facade shaded with an exterior facade system made of ultra high performance concrete. The shading decreases the direct irradiation on the façade and thus the cooling demand of the building.
Would it be valid to compare the proposed building (with the façade/shading system) to a baseline building that does not have the shading but it has, for example, 5% of the cooling demand? (if the cooling demand that we save, only because we implement the shading system, is 5%)
Besides the façade, the rest of the building’s u-values and energy performance is the same, and the baseline building meets the minimum energy requirements. It is just that with the implementation of the facade, the cooling demand is further reduced.
This way we basically compare the environmental impacts of the façade/shading material to the environmental impacts of the extra energy production that would be needed for cooling if there was no shading. Although, it is stated that the baseline building and the proposed building should have the same energy performance, this approach coincides with the “Behind the intent” section in the LEED guide:
“An LCA also allows the design team to understand the trade-offs of material selection and energy performance and find an appropriate balance between the two. For example, high thermal mass can reduce a building’s peak energy demands; an LCA can quantify the environmental damage associated with the additional materials used so that the team can compare those effects with the benefits for energy performance and then make more informed design decisions.”
Paula Melton
Editorial DirectorBuildingGreen, Inc.
LEEDuser Expert
183 thumbs up
November 11, 2015 - 11:09 am
No. The intent is one thing, and the actual rules are another. The Reference Guide states that the following must remain the same between the baseline and design:
You will get credit for the shading in the energy model, so you don't get to double-count it in the LCA model. I suspect it would simply be too easy to game the system if they allowed exceptions like this. (It's already pretty game-able, but that's another topic!)
Charalampos Giannikopoulos
Senior Sustainability ConsultantDCarbon
84 thumbs up
November 12, 2015 - 4:19 am
Just to clarify that operating energy performance does not mean operating energy, since this is an issue analysed in the EA prerequisite Minimum Energy Performance. The energy consumption of the project should be irrelevant. The baseline and proposed buildings must serve the same programmatic function, and must meet EA prerequisite Minimum Energy Performance by adhering to the requirements of ASHRAE 90.1-2010, Appendix G, Opaque Assemblies, Vertical Fenestration, Skylights, and Roof Solar Reflectance and Thermal Emittance sections.
Paula Melton
Editorial DirectorBuildingGreen, Inc.
LEEDuser Expert
183 thumbs up
November 12, 2015 - 7:12 am
I'm not sure I understand your comment, Charalampos. Are you replying to me or to Jody? Are you saying that the reference guide means something different by "operating energy performance" than it does by "operating energy"?
Charalampos Giannikopoulos
Senior Sustainability ConsultantDCarbon
84 thumbs up
November 12, 2015 - 7:35 am
Hi Paula. What I intended to mean that during a conversation with the GBCI we got a reply that the energy consumption of the project should be irrelevant with the LCA model. Hence, the question still is whether the result of the energy model in terms of kWh would be an input to the LCA model or just the materials used to achieve the specific energy usage of the model. If the latter is the case, then the reference guide should clearly clarify that by "operating energy performance" it is meant that "the baseline and proposed buildings must serve the same programmatic function, and must meet EA prerequisite Minimum Energy Performance by adhering to the requirements of ASHRAE 90.1-2010, Appendix G."
To give you an example: Imagine an energy-intensive building (e.g. a data center) which needed increased amount of energy 40% less than its baseline. This building, although energy efficient (compared to its baseline), if its energy consumption (kWh) was entered in the LCA model (and keeping it the same for baseline and proposed case), then by definition the reduction required in the LCA impact indicators would not be possible because the impact of the tremendous energy usage would neutralize the improvement in the impact indicators.
In other words, entering kWh in the LCA models would make sense only if the baseline and proposed cases were allowed to use their corresponding baseline and proposed energy usages and not the same one.