May,
- the energy accounting should be based on the annual efficiency of the entire plant as it will be operated
But also that:
- the energy accounting does not need to include the energy consumption of the entire plant
- the energy modeling does not need to include discrete modeling of every component in the plant

Notice that while Appendix G dictates number, size, type, and efficiency of baseline equipment, this document offers defaults that are simple system level efficiency values.

While the document anticipates refinement and invites feedback to leedinfo at usgbc.org, my emails have received only administrative acknowledgments after 8 weeks.

So if you cannot confidently decide how to apply this document to your project, you probably need to do a CIR. They are not free but neither is time spent responding to the reviewers, remodeling, or both.

Good luck,

Paul Riemer

Dear Bldg-Sim Community,

Keep in mind that "Price" and "Cost" always include non-energy items like
maintenance, overhead, profit, etc. That means using those values does not
often give an apples-apples comparison with energy efficiency. For that
reason, the new USGBC guideline seems to be clear that you may not mix the
two.

James V. Dirkes II, P.E., LEED AP

All;
As I understand it, under the new rules, you should never be comparing district CHW or steam to utility elec and gas. Correct me if I'm wrong.

Either:
District Vs. district, (inc all costs as given by provider) with only changed bldg systems (BUT baseline DX/furnace systems become CHW/HW types), envelope, lighting
Or:
District plant(s) modeled to get elec & gas Vs. un-modified PRM baselines (elec & gas).
Fred

Yes, agreed, the new rules seem to imply that maintenance costs, overhead, profit etc do not need to be included in the analysis (in contrast some old CIRs). These costs would typcially be included in a commercial or municipal district system. However, local campus central plants may or may not have those costs figured in. Either way, it's worth inquiring about with the chw/hw provider. If they have information regarding their maintenance costs etc it would be good to extract those from the cost. It would certainly work in you proposed building's favor and be more of an apples to apples comparison with the baseline building.

----- Original Message ----

It seems that the intention here is that if a credit is taken for an exemplary LEED building for energy efficiency, it will have to overcome district energy system (DES) inefficiencies if they are present. But at the same time, you are able to get the minimum two EAC1 credits, to some degree regardless of how bad the DES performs - so not excluding most projects, but limiting the options for those projects with inefficient infrastructures. This recognizes some of the constraints that a campus project might encounter.

Likewise an efficient DES that may have efficient equipment, cogeneration, heat recovery or other efficiencies will benefit the LEED project and the team is rewarded for having built onto this type of system.

Step 1: Building stand-alone scenario - for EAP2 compliance as well as documenting up to two EAC1 credits. In both cases will be purchased from district energy systems for heating and cooling as appropriate. This I think was the discrepancy between Fred and Julia's posts - the USGBC document states on page 8 that the actual prices are to be used, so it would include the overhead and profit components for a commercial DES. For campus situations without a "price" you must calculate the equivalent value and it isn't specified if this includes the overhead components.

If your building used DES for only one source, then the other source would be modeled as proposed with the baseline equipment per App G.

So as Fred mentioned, it will be DES vs DES, chiller vs chiller, or boiler vs boiler, etc.

If only pursuing EAP2 and two or fewer EAC1 credits (and achieving them?), stop here.

Step 2: Aggregate building - for pursuit of additional EAC1 credits - here the DES will be modeled for electricity and fuel usage, and compared to a building with baseline heating and cooling equipment per App G.

The key point of the text is "virtual on-site equipment representing upstream" systems. So not exactly that system, but representing the LEED project's share of that system.

Putting some numbers to a cooling plant for example purposes, the intention is not for you to model a 500 ton load building being served by a plant with four 5,000 ton chillers. Neither is the intention that you should model the other buildings making up the 19,500 ton difference.

The simulation programs are generally able to use efficiency calculations based on the total plant, but imposed on a theoretical smaller "virtual" plant serving the load of the new project. This is a reasonable approximation to the share of the plant energy for the new project assuming the cooling/heating loads are following the profile of the DES in general. The virtual 500 ton chiller will have capacity specified to match the LEED project's demand, but with the efficiency curves and EIR of the existing 5,000 ton chillers.

Obviously the capacity of everything in the plant would have to be adjusted, not just the chillers and boilers - include pumps, cooling towers, etc.

There is a statement about Step 2 only providing up to four additional EAC1 credits over Step 1, up to a maximum total of ten credits (like normal). But my interpretation of the document is that even if you documented six EAC1 credits in step 1, you can only claim two of them unless you unlocked that potential by proceeding to Step 2. Is this everyone else's interpretation also?

Hope this helps!

David