The importance of proper scheduling of energy equipment in combined heat and power plants for buildings: A case study

There is increasing interest in using Combined Heat and Power (CHP) systems to supply the energy needs in commercial/institutional buildings. However, due to the large diurnal and seasonal variability in building thermal and electric loads, such systems in buildings (BCHP) require more careful and sophisticated operation as compared to those in industrial CHP. Operating such systems consists of two separate issues: (i) equipment scheduling which involves determining which of the numerous equipment combinations to operate, i.e., is concerned with starting or stopping prime movers, boilers and chillers; and (ii) the second and lower level type of control, called supervisory control, which involves determining the optimal values of the control parameters (such as loading of primemovers, boilers and chillers) under a specific combination of equipment schedule. This paper is concerned with both these aspects, and presents case study results of a school under real-time electrical pricing (RTP) located in New York City, NY. A school has been selected for study because of its high diurnal and seasonal load variability. The approach first involved simulating the buildings using a detailed building energy simulation program to obtain hourly electrical and thermal loads which were then used to size the BCHP system components. Subsequently, a certain number of days in the year were identified, and simulation runs were performed for optimal scheduling control as well as for all the feasible (but non-optimal) equipment combinations. The energy and cost implications of operating the BCHP system in a non-optimal manner under various scheduling combinations are presented and discussed.