A. Cornell s district energy systems include the following components:

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1 SECTION ENERGY MODELING GUIDELINES APPENDIX A Modeling the District Heating and Cooling Systems of Cornell University for LEED Projects PART 1: GENERAL 1.01 PURPOSE A. Cornell is continually improving its district heating and cooling system; specifically, Cornell s Climate Action Plan includes plans to improve supply and distribution efficiencies and add renewable energy sources. Therefore, this guidance will be periodically updated to reflect the latest information applicable. B. This document includes information for LEED Energy Modelers to properly incorporate Cornell s district heating and cooling system efficiencies into the energy analysis for the LEED New Construction (LEED-NC v2.2 or LEED-NC 2009), Energy & Atmosphere Credit 1 Optimize Energy Efficiency ( EA Credit 1 ) and associated prerequisite. This applies to all buildings utilizing Cornell s district chilled water and/or heating systems. Periodic updates to this guidance will continue to be made to reflect actual measured annual values. C. In addition, this guidance serves to document the basis for modeling input data applicable to LEED modeling of Cornell s District Heating and Cooling systems. By providing this documentation, energy modelers working on specific building projects can incorporate this information to obtain credits without having to independently understand the complex interrelationships of the Cornell chilled water, heat and power systems DES SYSTEM DESCRIPTIONS A. Cornell s district energy systems include the following components: 1. Lake Source Cooling. The majority of Cornell s chilled water cooling demand is provided by a deep-water cooling heat exchange system. Cold water (39F year-round) from the depths of Cayuga Lake is pumped through a series of heat exchangers that exchange heat and cool the (closed loop) chilled water system serving Cornell. Since the energy input to the system is exclusively for pumping energy, the system is many times more efficient than a typical cooling system using refrigeration. 2. Chilled Water Storage: A 4.4-million gallon chilled water storage tank improves Cornell s ability to meet peak cooling needs. DATE: 03/28/19 DATE: 03/28/19 APPENDIX A Page 1 of 5

2 3. Back-up Chillers: Cornell occasionally utilizes back-up chillers during peak summer days (typically for less than 1% of all cooling load). When this infrequent operation is included, the overall system COP is somewhat lower. 4. Gas Turbine Co-Generation. Cornell has two 15 MW gas turbines linked to dual-pressure heat recovery steam generators (HRSGs) which provides a portion of the campus power and heating demand. The HRSGs incorporate high-capacity supplemental duct heaters (gas burners) to boost the steam output of the system on demand. Because this gas is burned in an already-hot environment (with sufficient excess air a byproduct of gas turbine combustion), the combustion efficiency of duct burners is extremely high. 5. Steam Turbines. Cornell has two back-pressure steam turbines which take high pressure (400 psig) steam and generate power while reducing the steam pressure to the system delivery pressure (up to 85 psig). These units together can generate over 40,000 megawatt-hours of electricity per year. 6. Hydropower. Cornell has a hydropower plant on campus that generates power exclusively for Cornell. This plant includes two water turbines that can provide over 5,000 megawatt hours per year of renewable energy. 7. Multi-fuel boilers. In addition to the HRSGs, Cornell can produce steam using a series of natural gas fired boilers. This array of boilers allows an extremely flexible response to both fuel costs and system demand. B. As a result of these multiple variable-input systems and a sophisticated computerized monitoring, control, and operations system, Cornell can operate an overall combined heat and power district energy system that allows an optimized mix of generated steam and power to match campus demand. C. However, during periods of very low heating demand (mid-summer when heating demand is low and dining halls and similar hot-water uses are also reduced) the gas turbine output will be reduced such that no excess steam will be created; during these periods Cornell will purchase a portion of the electricity needed for campus from our local utility, New York State Electric and Gas (NYSEG) SOURCE OF PERFORMANCE DATA A. All performance data (energy in and energy out) is based on actual measured values. B. All electricity used for buildings on Cornell s main campus enters via a central, Cornell-owned, sub-station located at the Central Energy Plant. All natural gas used for CHP electrical production or additional boiler heating also enters Cornell at the Central Energy Plant via a dedicated, Cornell-owned, high-pressure gas pipeline. All input electricity and natural gas is metered at that location. DATE: 03/28/19 DATE: 03/28/19 APPENDIX A Page 2 of 5

3 C. Output energy (electricity, steam, and chilled water) is measured at each building. Therefore, central system and distribution inefficiencies and losses are already accounted for in our assessment of useful energy derived per unit of input energy DES CALCULATION PROCEDURES A. Cooling: The Modeling Consultant shall model a virtual chiller with a COP of 23.9 or 0.15 kw/ton to model the central plant efficiency of the Lake Source Cooling System. This COP can be incorporated directly into the modeling software without having to use an exceptional calculation method. This COP represents an average of chilled water performance over the last seven years. These figures are derived from comparing the total input energy (all system pumping and also all input energy for chillers, during the infrequent periods when they are needed to meet peak summer loads) to the metered usage in campus building, and as such includes all system losses. B. Heating and Power Systems: Modeling the Cornell CHP system in this case will require that an exceptional calculation method be employed. First, the building heat and electrical demands are calculated using a 100% efficient boiler to determine the building kwh/mmbtu ratio. Since the CHP plant is unable to generate 100% of the campus electrical demands, a minimum electricity purchase of 20% is calculated and subtracted from the overall electrical demand. The remaining electricity to be provided by the virtual CHP plant at the building is used to determine the generated kwh/mmbtu ratio. These building loads are compared to the matched loads of the CHP output, which on an annual basis, uses an average of 22.6 therms of natural gas (2.48 MMBtu) to deliver 144 kwh of electricity and 1 MMBtu of steam to a campus building connected to the central energy systems, INCLUSIVE of all system and distribution losses. This ratio will serve as the basis of determining whether the project uses a Scenario A or B calculation as described below 1. Scenario A: The building s allocation of CHP-generated electricity is less than or equal to its modeled electricity consumption. The additional electricity shall be assumed to be purchased from the grid at the market rate. This has been found to be the typical case for new buildings on campus, especially for hightech buildings. 2. Scenario B: The building s allocation of CHP-generated electricity exceeds its modeled electricity consumption. The steam shall be assumed to be generated using a virtual 73% efficient natural gas boiler (which includes an 85% efficient boiler plus a 86% distribution efficiency) that bypasses the backpressure steam turbines. Although this case may not be typical, it may represent a lower tech facility, such as a dormitory or athletic facility. DATE: 03/28/19 DATE: 03/28/19 APPENDIX A Page 3 of 5

4 C. The energy model template includes a Virtual CHP calculation that will automatically perform this calculation if the Option 1 utilities (building metered energy consumption in MMbtu and kwh) are properly filled out in the template. In addition, it will also calculate a virtual boiler efficiency that can be directly input into the modeling program to document the natural gas use. However, subtracting the free electricity generated by the Virtual Plant will still require the use of an exceptional calculation METHODOLOGY A. Even though LEED no longer requires the completion of both Option 1 and Option 2 models to show compliance with the associated Energy and Atmosphere Prerequisites and Credits, projects performing energy modeling of buildings connecting to the district energy systems (both heating and cooling) shall execute BOTH performance options to meet both Cornell and LEED requirements. The intent is to maximize the energy efficiency at the building level before taking into account the savings associated with the District Energy Systems. The Option 1 Model also serves to document compliance with the established EUI target for the project as well as Cornell s sustainability initiatives. B. Option 1 Model: Building Stand-Alone Scenario - Determine the efficiency of the building itself (not including supply-side system efficiencies) using delivered energy (Steam in MMbtu, Chilled Water in ton-hours, and Electricity in kwh) rates. 1. Baseline Model: Use the procedures outlined in ASHRAE 90.1 Appendix G for a Baseline Building. Building baseline HVAC system types shall be modified to be consistent with the purchased energy source. This means that a system required to be modeled with a Direct Expansion (electrical) source will be changed to use a chilled water source; and a system required to be modeled with a Fossil Fuel source will be changed to use a steam source converted to hot water at the building. 2. Proposed Model: Use the procedures outlined in ASHRAE 90.1 Appendix G for a Proposed Building. Model using delivered energy at Cornell s current billed steam, chilled water, and electric rates. 3. For this model, the following BILLED ENERGY RATES shall be utilized: a. Electricity: $/KW-hr b. Chilled Water: $/ton-hr c. Steam: $/MMBTU C. Option 2 Model: Aggregate Building / DES Scenario - Determine the efficiency of the building itself with the supply side systems included. DATE: 03/28/19 DATE: 03/28/19 APPENDIX A Page 4 of 5

5 1. Baseline Model: Use the procedures outlined in ASHRAE 90.1 Appendix G for a Baseline Building using Energy Code Compliant on-site, fossil-fuel (natural gas) heating and electric-powered cooling systems. 2. Proposed Model: Using the procedures outlined in Section 1.04 above, model the building using Virtual district energy systems. The energy source shall be the same as that modeled in the Baseline Model. 3. For this model, the following BILLED ENERGY RATES shall be utilized: a. Electricity: $/KW-hr b. Natural Gas: 7.00 $/MMBTU DATE: 03/28/19 DATE: 03/28/19 APPENDIX A Page 5 of 5