Research On Pattern Optimization Of Distributed Thermal Storage In District Heating System

In district heating systems,users’ s heat demand flucturates in one 24-hour period.But in order to guarantee the operation efficiency of the heat source,the fundamental heat source’s heat output remains constant in a period.It causes when heat demand is low,some of the heat source’s heat output is wasted and when heat demand is high,peak heat source needs to produce heat to meet the demand.The appearance of heat storage technique can solve the above problem better.Distributed heat storage system adjusting one heat exchange station’s heat demand is a burgeoning technique.It has higher flexibility which can do planning and design aiming at different types of heat demand.The paper mainly analyze and optimize distributed heat storage system’s economic character.The paper modles the distributed heat storage system in district heating system and analyzes the different connection types between distributed heat storage tank and heat networks and advantages compared with centralized heat storage system.Models a residential building and a public building model and simulates the heat load using De ST.Calculates the residential building and public building’s distributed heat storage tank’s maximum capacity bringing in characteristic day of the heating period.Life cycle cost’s total present value is set as the economical evaluation index.Through calculation,the residential heat exchange station’s distributed heat exchange station’s life cycle cost is reduced by 43.7% and the public heat exchange station’s distributed heat storage system’s life cycle cost is reduced by 62.0%.Four factors having influence on distributed heat storage system’s economic character are analyzes.The four factors are distributed heat storage system’s service life,discount rate,natural gas’ s unit price and the basic heat source capacity coefficient.Their influence trends are: the longer the service life is,the smaller the discount rate is,the higher the natural gas’ s price is,the saving percent of the distributed heat storage system’s life cycle cost is larger.As the basic heat source capacity coefficient increases,the saving percent of the life cycle cost increases rapidly and then tends to be steady,and there is an optimal value.The paper performs sensitivity analysis on the four factors,and the result is: within the range of-30% to 0%,the basic heat source capacity coefficient’s sensitivity is the highest;within the range of 0% to 30%,natural gas’ s price’s sensitivity is the highest.The paper sets three heat load circumstances for n heat exchange stations in the heating networks.They are uniform heat load,incremental heat load and degressive heat load respectively,the three load circumstances’ total heat load is equal.Derives the formulas of circulating water pump’s electric power under three circumstances and obtains some laws.Under uniform and incremental heat load circumstances,the farther the distributed heat storage tank is set from the heat source,the circulating pump’s eclectric power is smaller when the heat storage tank releases heat.Under degressive heat load circumstances,the circulating pumps’ electric power flucturates when heat storage tank is set near different heat exchange stations.When the heat storage tank is set near the terminal heat exchange station,the fewer the heat exchange stations there are in the heating networks,the circulating pump’s electric power is smaller when the heat storage tank releases heat.When distributed heat storage tank is set in the middle and front of the heating networks,circulating pump’s electric power is the smallest under degressive heat load circumstance.When distributed heat storage tank is set in the back of the heating networks,circulating pump’s electric power is the smallest under incremental heat load circumstance.In the last,taking water pump’s power consumption into consideration,the paper calculates and verifies an engineering project’s life cycle cost and comes to conclutions: the larger the heat exchange station’s heat load is,the farther the heat exchange station is from the heat source,the better the economic character is when setting distributed heat storage tank at this station.And heat exchange station’s heat load’s influence on the distributed heat storage system’s life cycle cost is larger than the influence of the distance between heat exchange station and heat source.