I have this up because this little G3.1.1 throws a lot of people off. It's just this ruling and the problem was that in LEED 2.2 they did it to find this, and so it gave people the option to make up their own rules almost. They just had to come up with something. But what can happen-- let's just say (so that we don't confuse everyone) we don't want to have thermal blocks and we have a 60 story building.
So one system per floor would mean 60 systems, and subsequently, that would mean 60 cooling plants. But here's the catch-- TRACE can only model 20 cooling plants and 20 heating plants. We can't even model that. Therefore, what you could do is make an assumption..
This goes back to probably the most important table, table G3.1, which you'll reference the most. It's the very last thing here. It's “Modeling Limitations to the Stimulation Program.” If it cannot model the component in the proposed explicitly, though this would carry over to the Baseline, you could substitute a thermodynamically similar method.
Thermodynamically Similar Clause and Thermal Blocks 2:10
In such a case, you'd end up making 20 systems for your 60 floors and trying to group them in a way such that the most similar floors are grouped together. Typically, they would probably be adjacent. That's really your only choice, is to model something thermodynamically similar.
In this case actually it makes things easier, as well, because you have less systems and less plants. As you can see, if it were thermal blocks and we required single zone systems, that happens almost every time, and so if we had 100 rooms and it was a smaller building and we didn't create thermal blocks, we end up having 100 systems because we have one system per thermal block which would be, by default, a room. Then we would have to have 100 plants which of course is impossible. So that is just another reason to have thermal blocks, and then if you still can't get around it, you'd have to use that thermodynamically similar clause. The way to word that is just, in your little paragraph where you get to submit and make your statement about the modeling technique, basically say that the modeling limitation to TRACE only allows 20 plants, however G311 would require that we have 60 plants so we model 20 and this is thermodynamically similar. You can see what they say. Every file gets comments. I've never heard of one going through the first time. You're going to get comments. The fact of the matter is that you want as few comments as possible. A comment on something like that would probably just be something like, “Either switch your efficiencies so that you're not modeling it for large blocks,” but I doubt that you'd even get that. They might question you or they might just want further explanation on your thermodynamically similar method. I wouldn't worry about trying that because you have no other choice.