Development And Simulation Of A Heat And Mass Coupled Snow Melting Model For Hydronic Heated Pavement

In winter, traffic accidents occur frequently during snowfall, sleet andfreezing rain. Therefore, preventing ice formation and snow accumulation onroad surface is of high priority to improve the safety of driving. In recent years,due to certain inherent advantages, such as, high energy efficiency, strong systemcontrollability, convenient installation and wide energy source, hydronic heatingis the most promising candidate to be practically applied for the applications ofpavement snow melting. But the neglection of melted water on the thermalparperties of pavement material is the main reason for low prediction precisionof snow melting model. On the other hand, the lack of test data also restricts thedevelopment of snow melitng model.In this paper, a large-scale hydronic snow melting test system has been built.And a 2-dimensional snow melting model coupling the thermal and hydrologicalprocess is developed. A research implementation of this model has been used insnow melitng characteristic study and snow melting performance study.Operation strategy for hydronic snow melting system is suggested, and requiredheat fluxes for hydronic snow melting system in China is proposed. The mainresearch contents and achievements are summarized in the following:Firstly, a large-scale hydronic snow melting test system has been developed.In this test system, both solar energy and ground thermal energy are adopted asenergy source. Heat pump with inverter, pavement structure with differentembeded pipe depth and pipe spacing make up the multiple operating conditions.The system reliability and stability is validated by the data collected fromsolar-ground source coupled snow-melting test systems for pavement. Besides,the factors which have an impact on temperature distribution characteristic arealso investigated. It indicates that this system could be used in a widetemperature range.Secondly, a two dimensional snow melting model coupling the heat andmass transfer process is developed, which accounts for the effect of melted waterpenetration into pavement. A Fortran code is written and numerical implementedin HVACSIM+ simulation environment. The collection of operating data, and corresponding weather data, from the snow melting test system (Achievement 1)is used in the model validation. The prediction difference between the heat andmass coupled snow melting model and heat only snow melting model iscompared. The role of melted moisture transport to pavment is discussed.Thirdly, based on the heat and mass coupled snow melting model, snowmelting characteristic for hydronic heated system for pavement is analyzed. It isindicated that idling period, snow melting period and after-snow period are thethree periods during the snow melting process. The snow melting characteristicduring snow melting process are represented by waiting time, averagesolid-liquid phase change heat flux during snow melting process, and averageliquid-steam phase change heat flux within the first 5 hours in after-snow process,respectively. The factors which have an impact on snow-melting characteristicare also investigated. Based on the results above, operation strategy for hydronicsnow melting system is suggested. The proposed method will give a lot ofsuggestion in the operation of hydronic heated system for pavementAt last, based on the heat and mass coupled snow melting model, thepercentage of snow-free hours during snowfall is adopted to represent the snowmelting performance of hydronic snow melting system. The effect of idling time,heat fluxes, pipe spacing, embeded pipe depth, pipe material, thermal property ofmaterial, meteorological condition and control strategy on the snow meltingperformance have been discussed. The effect of the snow melting aim andcalculation depth of the model on the snow melting performance evaluation isalso studied. According to the research on snow hazard regionalization in China,different locations have been chosen to represent a range of climates andsnowfall characteristics. According to the weather data corresponding to snowevent from 1981 to 2010 in representative cities, the limit snowfall conditions ata 95% confidence level is proposed. Based on the limit snowfall conditions at a95% confidence level , required heat fluxes for hydronic snow melting system inChina is suggested. The proposed heat fluxes will give a lot of suggestion in thedesignation of hydronic heated system for pavement in China.A series of creative researches, such as the development of hydronic snowmelting test system, the development of a heat and mass coupled snow meltingmodel for hydronic heated pavement, the operation strategy and required heat for hydronic snow melting system, were carried out in this paper. Theseresearches will promote the development and application of hydronic heatedpavement in China.