The Hydronic Characteristics Of Pipe Networks And Regulation Of A Heating Network With Dual-heat Sources

Over the past decades,district heating has become ever more important and will presumably become even more so in the years to come.In recent years,multi-source network systems are continuously increasing,more and more centralized district heat supply systems are brought online because they are more cost efficient,better for the environment and more beneficial for the consumers.However,in multi heat source networks,the hydronic condition and regulation becomes more complex as additional heat sources are brought online because of the changes required in flow and pressure in the network.To understand the essence of hydraulic operating conditions and temperature regulation in a parallel operations of a DH system,research has been conducted based on tests of the YuJianPu boil room and heat & power plant in BaoJi city,as follows:(1) Based on tests of the heat & power plant and YuJianPu boiler room in BaoJi city, 11 typical sub-stations of the district heat supply network were chosen to carry out the hydraulic test and analysis.The 2 pressure diagrams and operating characteristics in the DH system were obtained from hydraulic analysis,which can typically express the pressure drop of the furthest substation from the sources.To understand the essence of hydraulic operating conditions in a DH system operating in parallel and to determine the optimal method of operation,the experimental sets of hydraulic operating condition in a parallel operation of a DH system was established.By altering the valve opening to simulate the changing of resistance in response to hydraulic balancing,among 17 tests,4 ways are verified to be effective in improving the pressure drop of the furthest substation from the sources,and have little influence on the other heat consumers.Based on the 17 hydraulic tests,it is concluded that it is better to replace the main pipes with larger diameter pipes for improving the pressure drop of the furthest substation from the sources.The preferable way is to change the main pipes of the distal end to larger diameter pipes in order to improve the pressure drop of the furthest substation from the sources.The solution to increase the pressure drop of the furthest substation from the sources is to replace the main supply pipes with larger diameter pipes.The research results are helpful in design and operational management of multi-source heating networks.(2) To make an assay of operational regulation with two heat sources,tests on the heat & power plant and YuJianPu boiler room in BaoJi city have been done.A method of stating the mathematical relationship is proposed which is defined by modifying the coefficient of the formula existed in a certain operating condition.Analysis shows:â‘ The power & heat plant operates on its own in the initial and the late phases of winter.Temperature adjustment of the network with two heat sources can be obtained by applying fitting to the modifying coefficient,only if the operating condition is the same or similar to the reference situation of the heating pipe system,by which hot water temperature can be adequately adjusted.â‘¡The YuJianPu boiler room is considered the primary heat resource when the power & heat plant is utilized as an auxiliary heating source in the extremely cold phase of winter.Temperature can be adjusted in the same way as above when the auxiliary heating source is not brought online.That is,temperature adjustment of the network with two heat sources can be obtained by applying fitting to the modifying coefficient,only if the operating condition is the same or similar to the reference situation of the heating pipe system in the extremely cold phase of winter,by which hot water temperature can be adequately adjusted.â‘¢The existing theoretical formula for heating system regulation is inadequate in practical application.A new formula is required for practical application,which modifies coefficients that accounts for complex factors of the practical operating condition.By using a new formula determined by data obtained from tests,the heating system will be more accurately regulated.(3) A method is determined by the analysis of operational strategy and operation regulation of the system with the two heat sources on-line providing the maximum design heat output(5.3million m~2) in BaoJing City.The heat & power plant is considered the primary heat source,and YuJianPu boiler room is utilized as an auxiliary heating source throughout the heating period,both of which operate in parallel.The results are listed in the following conditions:The power & heat plant operating on its own when the outside air temperature ranges between 4.2 and 5 degrees centigrade.The first boiler operating only with the primary heat source when the outside air temperature ranges between 1.2 and 4.2 degrees centigrade.The first and second boilers operating simultaneously when the outside air temperature ranges between -2 and 1.2 degrees centigrade.All three boilers operating when the outside air temperature ranges between -5 and -2 degrees centigrade.Heating curve adjustment is related to regulating the heating programme,the necessary adjustments should be based on the heat-conditioning programme.The system we discussed operates through indirect connections using heat exchangers to link the primary and secondary systems.The primary loop is regulated by quality-volume when the secondary system adjusted by qualitative(thermal) means,if the primary heat source operates paralleled with the auxiliary heat source.The entire heating regime is divided into three stages depending on outdoor air temperature whereby the flow in each stage is changed rather than remaining constant,and divided according to relative volume:(?)=0.60,(?)=0.80,(?)=1.00.At each stage of the flow remains unchanged,the application of quality adjustment,that is,only to change the heat medium temperature.Heating curve adjustment are given by calculating in this manner.