Have you considered University of Limerick? I know come of the tutors there, and I've seen the facilities, and I have heard nothing but good things about it.
UCD is currently in a transitional stage at the moment as modularisation has been brutally steam rolled across all faculties, and unfortunately the architecture program has not dealt with it well, what should be a simple admin task has filtered down and is affecting the quality of the student's experience, and is currently causing a lot of frustration. I don't want to put you off, I'm sure they will sort out these issues over the next year or two, and the module system should eventually be very beneficial especially to mature students, so do be aware of the issues.
Finally do question your motives, issues of sustainability, and the environment are admirable concerns, in really its just one of the considerations of the architect, this has been a pet peev of mine for a while. I will not attempt to define architecture, but some of the quailities of great architecture, that I believe most won't argue with are the creation of space, scale and proportion, innovation, respect for history and traditions, craaftsmanship, enjoyment of materials, quality of light, harmony with nature, etc etc, etc. Of course sustainability is inherent to many of these qualities, but it is not enough on its own. If this is your primary concern, then perhaps you would be better applied to building services engineering, or planning as mentioned above. I do not say this in a way that is meant to be demeaning either to you or these professions and I hope I don't sound patronising; they are invaluable, as, lets face it a lot of architects still haven't got the whole green thing: "if Mies can have single glazing then so can I"
Hope this is useful rather than confusing.