The influence of the cooling load profiles on the cogeneration conceptual design considering different timescales for building applications

Recent methods for supporting the conceptual design of cogeneration systems in existing building applications have been supported by fair amounts of data for characterizing their demand profiles. This fact is contrasted with the engineering practice, where the lack of data is common, and a regular measurement of energy-use parameters is not usual. In fact, whenever available, data may be reported using a large timescale (e.g., days, weeks, etc.). Given these circumstances, this paper adopted six different timescales for comparing the selection and sizing of the supply technologies in two building applications. The first corresponds to a hospital whose cooling load profile was estimated adapting the cooling degree-days method, while the second is an office building whose demand profiles have been obtained through a simulation model. A technology selection problem was formulated as a mixed-integer linear programming (MILP) model minimizing the annual costs of the system. This model was supported by an additional linear programming (LP) model used for maximizing the thermal output of cogeneration modules. Given that the hospital electricity consumption had a strong correlation with the ambient temperature, even for timescales as small as 1 h, the elaboration of detailed profiles was possible. The MILP model indicated, for both cases, the inclusion of hot-gases-driven absorption chillers. For the Office building, with a larger size, an additional module and a hot-water-driven absorption chiller were included. Regarding the timescale used, two clear trends were identified: undersized structures obtained adopting one-day or longer timescales, and proper-sized structures obtained from smaller timescales.