Exergy and Investment Thresholds for Campus Heat Recovery Under Academic Calendars

Campus heat recovery depends on the coincidence of computing output, thermal demand and required delivery temperature. This study develops an hourly energy–exergy model with bounded storage, boiler backup and an explicit investment threshold expressed as recovered-source utilisation. A synthetic annual campus profile is evaluated at 45, 55 and 70 °C, with three storage capacities and 100 computing-load realisations. Without storage, raising delivery temperature from 45 to 70 °C increases the supplied heat share from 83.1% to 87.2%, yet reduces recovered-source utilisation from 60.6% to 52.5% because compressor electricity contributes more heat. Corresponding net present values are £333,374 and −£347,066 under stated assumptions. At 55 °C, adding 2.4 MWh storage raises supplied heat from 1,696.2 to 1,817.5 MWh but changes investment value from £57,349 to −£13,933. An equal-demand calendar counterfactual changes the direction of the schedule effect as storage increases. The results distinguish thermal feasibility, operating savings and capital recovery, providing conditional screening thresholds rather than validated campus forecasts.