Comparative Study Of The Design And The Actual Operation Of The Secondary Heating Network

Central heating system has been develioped very fast in our country, designers are inaccordance with design specifications when they are designing.In the actual heatingpipe network, most of the heating pipe network do not run with the designparameters,but they are running very well, there is no problem. Overall, the designparameters are generally "small flow and big temperature difference" and the actualoperation is "large flow and small temperature difference."There is a big differencebetween the actual operating parameters and design parameters,it is worthy to researchthat which condition runs better between the two working conditions.In this paper,use the numerical simulation method to study the "large flow and smalltemperature difference" of the secondary heating network. Investigates the operatingconditions of a secondary heating network of a district in the city of Jinzhong, get theactual operating parameters of this secondary network such as the supply and returnwater temperature, flow, pressure, heat load and so on,in this research make this districtas an example to analyze the economic of the secondary heating network.The operatingconditions of the heating system are divided into three types in this study: the first is theactual condition;the second is the design condition; the third is the design condition runswith the actual load operation. Because there is a big gap between the design load andthe actual load.If we just compare the actual working condition and the design condition.The prerequisite for comparing is different,so we increase the third condition. In thispaper, we will do the following researchs:Firstly, analysis various parts of the secondary heating network which generate costsand the heat loss of the pipe,found the mathematical models of the economy and heatloss of the heating system.Secondly, put the heat-related data into the two mathematical models under actual operating condition and designed condition,for the economy andheat loss in both cases were analyzed and compared.Third,the sensitivity factors for theeconomy for the heating system are analyzed,take into differernt data, analysis andcompare their effects for the economic of the heating network system.Fourth, calculatethe differences of the heating system economy and the heat loss of the secondaryheating network when occupancy changes.Fifth, simulate residential indoor temperatureunder the actual condition and the design condition with airpak software, then calculatethe heat losses through the exterior wall of the actual condition and the designcondition.Sixth, optimize the secondary network according to the results.Through this study, we can get the following conclusions.Firstly, the economy of theheating network system under the two design conditions is better than the actualoperating conditions.The total running costs of the first design condition is about30%less than the actual working condition,the total running costs of the socond designcondition is about20%less than the actual working condition.Second,the heat loss ofthe pipe in the two design conditions are more than the actual operating conditions, theheat loss of the first design condition is about30%more than the actual operatingcondition,the second design condition is about40%more than the actual operatingcondition. Third, the indoor temperature of the actual conditions is20℃-22℃, while theindoor temperature of the design condition is18℃, the heating room has a betterthermal comfort in actual condition.And the heat loss from the radiator distributes to thethe surrounding air through the exterior wall in the actual condition is less than thedesign condition.Fourth,after we optimize the secondary network,we get the the mosteconomical supply and return water temperatures at different outdoor temperatures,provide a reference for the actual operation of the secondary network.These results suggest that:the advantages of the secondary heating network using theoperation mode "big flow and small temperature difference" in practice is able to reducethe heat loss of the heating pipe network. And in this condition, the heating room has abetter thermal comfort. The drawbacks are that it increases the total cost of the heatingsystem operation, resulting the waste of energy.