28 Figure 8 Illustration of ambient temperature district energy system with seasonal geoexchange and ground source heat pumps in each building Preparation We consider two scenarios: 1) centralized with high-temperature hot water and chilled water loops and 2) decentralized with a single ambient temperature water loop. The hot/chilled water solution would be centrally conditioned via industrial-sized water-based heat pumps. An ambient loop requires individual heat pumps in all campus buildings. Both scenarios use geoexchange as the heat source/sink and require the construction of a new hot water distribution system Prior to deployment, MIT should model heating and cooling demands of all current and planned buildings under different climate pathways from now through at least 2060 (building on the modeling framework described in this document). District heating and geoexchange systems are sized based on peak and annual heating and cooling demands. In order to ensure that campus energy demands are reliably met and that the system is cost-effective, it is important not to over- or under-size system components. Our modeling indicates that installing the maximum number of feasible bores on existing MIT land (500 bores) meets 60% of campus heating/cooling needs. As such, MIT should investigate acquiring nearby land to site additional bores and/or selecting supplemental heating/cooling sources (capacity and fuel type). MIT should also gather data on the time and expense to convert building HVAC equipment from receiving steam to hot water. We expect both our scenarios will require buildings to be vacated while new equipment is installed. In order to ensure that MIT can continue to meet its teaching and research missions, it will be important to develop a plan that shifts certain activities to different parts of campus while retrofits and pipe installation are underway. For buildings that currently use hot water as the circulating fluid, it may be possible to operate at a slightly lower temperature that matches the centralized distribution loop. MIT should begin “stress-testing” buildings to determine where this is feasible without sacrificing occupant comfort and equipment health, which would simplify conversion.
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