31 Key Assumptions We make the following assumptions: - The ground beneath MIT’s campus is suitable for borefield drilling (~300m deep) - The electricity used to operate geoexchange heat pumps is provided using low-carbon sources - The costs of drilling bores and installing distribution infrastructure are consistent with ASHRAE’s current estimate Model The results from a comprehensive, campus-scaled building energy model are used to extract the hourly loads, monthly load, and annual load for the MIT campus. For Scenario #1, assuming a high temperature district heating loop, no synchronous heating and cooling loads across different buildings are considered. The peak hourly, monthly load, and total annual load are used. Any imbalance between the heating and cooling loads will be addressed through supplemental heating and cooling sources (i.e. cooling towers, natural gas boilers, etc.). Using the equations and workflows described in the 2019 ASHRAE Handbook, an estimate can be given for the number and length of the boreholes. For Scenario #2, assuming an ambient district loop, synchronous heating and cooling loads across different buildings are considered. The revised peak hourly, monthly load, and total annual load are used. Any imbalance between the heating and cooling loads will be addressed through supplemental heating and cooling sources. The ASHRAE method is used to size the borefield. First buildings in West Campus will be used to calculate the borefield size and depth, following the ASHRAE method, with a phased approach for the rest of the campus. These phases could even produce independent ambient loops that are connected over time. We obtained cost information from two sources: Oh and Beckers (2023) analyze five district energy systems in the US (including both centralized and distributed configurations) and find similar capital cost estimates for each. Mattson and Neupane (2017) collect cost data for 13 district energy projects and produce a regression for levelized heating cost as a function of annual heating consumption.
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