How do I model a building that has a Central Plant that serves my building and others under LEED?

LEED refers to this as a District Energy System (DES).  You should begin by reading the DES Guidance from USGBC.

Once you have decided which option from the guidelines you will use, follow these instructions:

Option 1 – This approach requires you to treat the plant chilled water and hot water as purchased commodities thus removing any efficiency associated with the central plant from the model.  You will model your HVAC systems as normal and input whatever central plant is appropriate for the chillers, boilers, towers and pumps (you will be discarding all of these numbers so it is not important).  When running the calculations, under the Calculation Options, check the box for CSV reporting (covered in another FAQ) and uncheck Delete Temporary Files.  Now you can run the calculations.

After the calculations are complete, you will open the CSV file in Excel and you will find hourly data for the various end uses (note the units of each column).  The columns for Heating, Cooling, Heat Rejection and Pumps* can be discarded.  On the far right you will find columns for Chilled Water and Hot Water demand for the building.  These are the purchased commodities you will use to follow the DES guidelines.  Any columns that represent normal building usage (lighting, fans, receptacle) should get multiplied times the virtual rate for Gas or Electricity (found on the EAC1 report). The Chilled Water and Hot Water use is multiplied times the rates given in the DES Guidance and you will have a spreadsheet that documents total energy cost for your building.

In some cases, the Baseline building may not be a chilled water system so EnergyPro will configure a baseline with DX equipment.  In this case, you can force EnergyPro to use a chilled water system by changing one of the Zones to a Floor Number of 5 and it will structure the baseline as chilled water.

Option 2 – With this option you are allowed to model the actual efficiencies of the central plant in EnergyPro only you will scale the actual equipment according to the load served.  Be sure you understand the documentation requirements given in the DES Guidance document from USGBC since this approach requires supporting data on the efficiencies you are using.

*If you have only pumps as part of the CUP, discard the pump number from the calculation since it is part of the purchased commodity.  However, if you have local pumps at the building, model those and include them in the building energy usage numbers.

 

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Category: 9b. LEED

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