Modeling DES

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Hello all,

I am working on a project that needs some guidance from you all!

The project consists of 3 office buildings and 1 dining hall/auditorium building in a corporate campus environment. The buildings are being designed and constructed via 3 phased stages with Phase 1 containing 1 office building and the dining hall/auditorium building, Phase 2 with 1 office building, and Phase 3 for the final office building. The dining hall/auditorium building contains a campus chilled water system that is to serve air handling units for each of the office buildings as well as the amenities building itself.

We plan on submitting each phase's buildings as separate projects under an umbrella of a master site since it is a corporate campus environment. Because the District Energy System (DES) is within one of the Phase 1 buildings, we referred to page 7 of USGBC's "Treatment of District or Campus Thermal Energy in LEED V2 and LEED 2009 - Design & Construction" for guidance:

Downstream equipment - all heating or cooling systems, equipment, and controls located within the LEED project building and/or on the project site associated with transporting the thermal energy of the DES into heated or cooled spaces. This includes the thermal connection or interface with the DES, secondary distribution systems in the building, and terminal units.

Exception: When the building housing the thermal energy plant is itself seeking LEED certification, then the project shall treat the DES equipment as "downstream equipment" for the following prerequisites and credits:

* EA prerequisite 1

* EA prerequisite 2

o Mandatory Measures: The district energy equipment shall comply with all mandatory measures from ASHRAE 90.1-2004.

o Prescriptive Method: The district energy equipment shall comply with any applicable prescriptive requirements

o Performance Method: The district energy equipment shall be modeled as upstream equipment, NOT downstream equipment. USGBC recommends that such projects use modeling Option 2 (described below).

* EA prerequisite 3

* EA credit 3

* EA credit 4

* EA credit 5

Unfortunately, the statements contradict each other. If the equipment is to be treated as "downstream equipment", then I have to include all the chillers, boilers, pumps, etc. However, if the equipment is to be treated as "upstream equipment", I just create virtual chillers/boilers with some efficiencies based on Table 4 on page 12:

Table 4: Energy Source for Option 2 District heating

Baseline

On-site heating plant or fossil fuel furnaces as defined in ASHRAE 90.1 Appx. G, tables G3.1.1A and G3.1.1B, representing code minimum efficiency2

Proposed

Virtual on-site hot water or steam boiler representing upstream DH system

District cooling

Baseline

On-site cooling plant or packaged cooling as defined in ASHRAE 90.1 Appx. G, tables G3.1.1A and G3.1.1B, representing code minimum efficiency3

Proposed

Virtual on-site chiller representing upstream DC system

Phase 2 and 3 buildings will be straight forward on the energy modeling because we will have to model virtual systems to simulate the DES since it is physically outside of the LEED project. How have you interpreted this before with the DES within the LEED building that is attempting LEED certification and which approach would you use in modeling using eQuest?

William Mak

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I agree, that doesn?t make any sense.

Bottom line, you want to do a full accounting of the DES, therefore you have
to use option 2.

Having worked on 4 of these under the DES v2.0 guidance, that?s what I would
do. For what it?s worth, it?s far better than v1.0 and they openly say it?s
a work in progress (see para 4 sec 1.2). I think the confusion results from
GBCI defining a DES as being located offsite (read the introduction
paragraph), so to be consistent in Table 4, they have to say model a virtual
onsite DES.

Anthony Hardman, PE

Anthony Hardman, PE

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I agree, Option 2 is definitely the better method to do a full accounting of the DES.

However, does it make more sense to model the virtual plants or the actual proposed design in the proposed model?

William Mak, LEED Green Associate

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If you?re referring to modeling a virtual plant with constant efficiency
curves as opposed to the actual design with mfgr performance curves, then I
think the latter is more appropriate for the first building.

Anthony Hardman, PE

Anthony Hardman, PE

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