A simple method to determine the optimal gas turbine capacity and operating strategy in building cooling, heating and power system

• A new analytical method for designing BCHP is firstly put forward.
• Two values of the critical gas turbine efficiency are found for designing.
• For BCHP with TES, the optimal operating strategy is either FTL or FEL.
• For BCHP without TES, the result is part-time FTL and part-time FEL.

The gas turbine capacity and operating strategy selection of Building Cooling, Heating and Power (BCHP) systems play an important role in the system operating performance, leading to different primary energy consumption for the same building load. However, the optimal design problems of those two factors have not been solved very well. This paper presents a new simple method to determine the optimal gas turbine capacity and operating strategy. The gas turbine electricity efficiency, the Coefficient of Performance (COP) of absorption heat pumps, and the demand heat/power ratio are found to be the key factors. There exists two values of the critical gas turbine efficiency. More primary energy will be consumed when the selected gas turbine electricity efficiency is below the smaller critical value compared with the separated generation. When the selected gas turbine electricity efficiency is between the two critical values, the hourly optimal operating strategy and the gas turbine capacity can be determined by Following the Thermal Load (FTL). Otherwise, the optimal gas turbine capacity should be sized by Following the Electricity Load (FEL) with the consideration of the actual given conditions. Based on this method, some typical cases with or without TES are analyzed. The results agree well with the conclusions drawn in the current published papers. This method gives a new aspect to understand BCHP analytical design, and can be applied in the engineering area.