Methodology and a Continuous Time Mathematical Model for Selecting the Optimum Capacity of a Heat Accumulator Integrated with a CHP Plant

This paper contains the results of a study in which a novel approach using continuous time notation was applied in the search for the optimum capacity of a heat accumulation tank to be combined with an existing CHP (combined heat and power) plant. The necessary condition associated with the economic profitability of the application of heat accumulation tanks in CHP plants is based on the condition that the profit from the exploitation of the modernized CHP plant does not decrease in relation to this profit before the process was initiated. Hence, the applied methodology provides a dependence that has universal application as it can be used to establish the optimal capacity of a heat accumulation tank suitable for any CHP plant design, i.e., for any thermal capacity of such a plant. The results also demonstrated that the specific enthalpies of the extracted steam before the base load heater and the maximum increase of the flow rate of the extracted steam feeding the base load heater in winter form the only necessary inputs for such calculations. The construction of the heat accumulation tank is only profitable for the case when the difference in the purchase prices at the times corresponding to peak load and base load electricity demand is sufficiently high.