Future Building as a Shadowing Element

ASHRAE 90.1-2010 Table G3.1-14 should be used to guide the modeling of the surroundings. In terms of your situation I do not think that you would be allowed to model something that was not already in place.

Dear Marcus, Thank you for your comment. Table G3.1-14 of ASHRAE 90.1-2010 does not mention anything about future adjacent structures that could create shading effects. In my opinion, for this particular case, the second tower is planned to be constructed in a short period of time after the first one, so it should be taken into account in the energy modeling, considering the life-time of the buildings and the significant shading effect it will create. Another issue is that the sizing of the HVAC system must be done without considering the second tower, but once it is built then the system will be oversized. Have you heard cases like this one before? Thanks

I think it does not mention it because things that "might" be built in the future cannot be assured of actually being built and logically should not be taken into account. You bring up a good point about the system sizing. If you are sizing the HVAC without the second tower it sounds like the designers are not too sure it will happen or it will be too long between construction to account for it. In general projects receive credit for what they actually do. In some cases they get credit for what they do in response to a preexisting situation. They usually do not get credit for something that might happen in the future.

The second tower is part of the project, there are actually four towers in total in the whole plan within the site. If we would be able to make the client prove that it will be built within a short period of time, do you think we could include it? About the system sizing I think that it has to be done without considering the 2nd tower even if is 100% sure it will be built, otherwise during the construction of it there will be a lot of thermal comfort problems. Thanks

My previous response was based on what I think the ASHARE Appendix G reason would be for including the second tower or not. I do not think that under Appendix G it should be included. In my opinion it will not make much difference for LEED if you model it. If you did include it you would have to do so for the baseline as well, so the effect on the savings is minimal. If you did include it in both models I think the reviewer would probably not make you take it out.