بهینه سازی برنامه ریزی خطی توزیع حرارتی در یک سیستم منطقه گرم شده توسط تنظیم سوپاپ و مقاوم سازی ایستگاه فرعی

The unbalanced distribution of heat in a district-heating system may be caused by the increase of hydraulic resistance of pipe network, decrease of heat transmittance of radiators inside buildings, and increase of heat transmittance of building envelope. This situation yields the overheating of some buildings and underheating of other buildings. A district-heating system is analyzed that consists of heat plant, primary pipe network, substation, secondary pipe network, and three buildings. A steady-state, bottom-up approach and the sequential linear programming is used to solve this optimization problem. Results show that significant improvement of thermal comfort may be reached by adjusting the valves of secondary pipe network and resizing of the substation heat exchanger.

The most common problem with district-heating systems (DHS) is the unbalanced distribution of heat to end-users [1]. This may be caused by: the increase of hydraulic resistance of pipe network, decrease of heat transmittance of radiators inside buildings, and increase of heat transmittance of building envelope. Unbalanced heat distribution yields in DHS and buildings the loss of thermal comfort and energy, the overheating of some buildings and underheating of other buildings. People in overheated buildings open windows to decrease the space temperature, and in underheated buildings they turn on additional heating devices (like fan-coil heaters) to increase space temperature [2]. To solve this problem and achieve thermal comfort in heated buildings and save energy, the hydraulic resistance of valves may be adjusted, and heat exchangers in substations resized [3]. A DHS is analyzed consisting of (Fig. 1) heat plant, primary pipe network, substation, secondary pipe network, and three buildings. A steady-state, bottom-up approach is used to design an energy module network corresponding to the DHS, and then derive a set of equations that describes the behavior of the system [4]. Furthermore, the sequential linear programming (SLP) method is used to solve the optimization problem [5]. Full-size image (23 K) Fig. 1. Schematic of the district-heating system. Figure options Three basic cases of the unbalanced distribution of secondary hot water are considered: the first case is due to changes in the hydraulic resistance of the pipe network from design value; the second case is due to changes in the heat transmittance of radiators in heated buildings from design value; the third case is due to changes of the heat transmittance of building envelope from the design value.

When during its use, the district-heating system changes its characteristics such as the hydraulic resistance of its pipe network, heat transmittances of its radiators and heat transmittances of its building envelopes, a thermal comfort in buildings is decreased. The thermal comfort can be retrieved either completely or partially by using valves and new heat exchanger in the substation. Valves are used to adjust flow rates of hot water and new heat exchanger is used to adjust a heat input to this hot water in the substation. The thermal comfort can be completely reestablished in all buildings for low and high hydraulic resistances of pipe network and for low heat transmittance of building envelope. When the hydraulic resistance in some pipe is lower than nominal, its valve is used to decrease the flow rate of hot water in this pipe. When the hydraulic resistance in some pipe is higher than nominal, the valve of other pipe is used to decrease the flow rate of hot water in this pipe. When the heat transmittance of building envelope is lower than nominal, the valve of the building-supply pipe is used to decrease the flow rate of hot water to this building, and new smaller heat exchanger is used in the substation to decrease heat input to this hot water. The thermal comfort can not be completely retrieved for variation in heat transmittance of radiators, and for high heat transmittance of building envelope.