I am modelling a project receiving chilled water from the district cooling plant with an ice storage and wondering how to account for energy use shifting in the building model if I use Option 2 Full Accounting DES.
The guideline, Treatment of District or Campus Thermal Energy page 22, says “For thermal energy storage, the percentage of peak or mid-peak thermal energy shifted to off-peak periods in the building model shall be identical to the value metered or modeled in the district energy plant”
Does this mean I need to have the following in my building model?
1) an air-cooled chiller so I can input the average efficiency of the district cooling plant
2) an ice storage that has the same percentage of peak or mid-peak thermal energy shifted to off-peak periods as the district cooling plant.
Appreciated any suggestion!
Tyler Thumma
7GroupLEEDuser Expert
60 thumbs up
May 4, 2018 - 10:34 am
Assuming you are modeling the virtual plant using method 1 (DES average efficiency accounted for in energy model) described in Appendix C of the DES guidance,
1) Yes, the cooling plant is generally modeled using an air-cooled chiller with the average efficiency of the district cooling plant. Make sure you are properly accounting for the district heat rejection and pumping energy in the average efficiency.
2) Yes, you would also monitor virtual ice storage that shifts energy in the same percentage as the district ice storage system. As explained on page 22 of the DES guidance, make sure you apply the same granularity to the energy shifting as the efficiency calculations.
This might be a case where method 2 (DES average efficiency accounted for in post-processing) could be easier to apply than trying to model the chiller plant with ice storage directly using method 1. In this case you would model the cooling energy as purchased, export the results to a spreadsheet, and manually apply the average efficiency and thermal energy shifting at the same granularity that these were calculated for the district cooling plant.