The Evaluation System Of Running Carrying Capacity Of Existing Hot-water Heat Supply Network

Carrying capacity is an expression of ultimate load when an object is in normaloperation, which measures the contact of structures between the internal and external.As a part of heat transport in centralized heat supply systems, thermal network divertsthe heat form one place to another. Heat source and heat consumers are connected bythermal network. The running condition of thermal network has an effect on the rationalutilization of energy, optimal allocation of resources and environmental protection etc.The concept of carrying capacity is gradually quoted in the study of thermal network.The ultimate effect of the heating system is embodied by the running level ofsystem, and the actual running parameters and the heating effect can reflect the level ofability, which allows us to make a quantified assessment of the economic efficiency,stability, reliability of the thermal network. Thus, we propose the concept and establishevaluation index system of running carrying capacity. According to the physicaldefinition of carrying capacity, on the basis of heat consumption model and relevantprinciples, we consider the differences between the design and standard of the pipenetwork to evaluate the running carrying capacity of existing hot-water heat supplynetwork from two aspects: utility and safety and reliability. The running condition ofthermal network is reflected by the utility, and restricted by the safety and reliability inthe evaluation system. It takes two indicators into account: the gross heat input andthermal efficiency in the utility. The former is composed of circulating flow and heatingtemperature; the latter considers the loss of thermal network due to heat dissipation,water leakage, heat exchange, hydraulic misadjustment and quadratic loss.The paper quantifies the index by the form of ratio, and introduces the concept ofcarrying degree and improvement degree. It determines the standard values of index inaccordance with the design values and standards. The weight of heat loss layer isdetermined by the loss rate, while the others are made by AHP in calculative process. Itcombines carrying degree with corresponding weight to make a determination ofcalculation method of running carrying capacity, which is divided into three levels:low load, saturation and overload according to the numerical results. It has selected thethermal network of the city of Wuchang as an object instance of assessment, andcalculates the value of running carrying capacity because of different connections,which verifies science and rationality of the index system to a certain extent.The running condition of thermal network quantifies the running level and makes adetermination of the actual loading situation and room for improvement, which makes adifference to the rational utilization of resources, the upgrading of the system functionsas well as the reconstruction and expansion of thermal network.The paper comes from “study on evaluation technology of carrying capacity of heating system”, which is one of the “12th Five-Year” National Science and TechnologySupport Program of China “the key technology and engineering demonstration ofheating system in cold districts”(2011BAJ05B04) and “the key technology research anddemonstration of efficient use and planning of urban district heating energy”(2012BAJ04B01).