| Abstract: |
This is the first time that a self-operating, CO2 heat pipe system has been used with a direct surface heat condensing system to melt snow and ice on an asphalt street. This snow and ice melting system is completely controlled by on-site weather conditions. Evaporated warm CO2 rises to the top of the heat pipe because of geothermal heat sources. At the surface, the CO2 condenses through simultaneously occurring heat release and returns to the vaporization zone of the heat pipe as a cool liquid. This results in an automatic heat pipe cycle and heats the street surface without using any external energy. An intelligent de-icing and snow melting system based on the heat pipe principle is in use at a fire station in Bad Waldsee, Germany, as part of an EIFER/EnBW demonstration project. Specially designed register systems with varying diameter and distances are used to cover a 150m² area at the entrance to the fire station. A new theoretical model was developed for this project to take into account all coupled processes. With this model, it is now possible to conduct a complete heat balance of a coupled heat pipe solution. All relevant parameters (required pipe dimensions, filling rates, heat pipe designs of the surface and underground systems) as well as meteorological conditions were taken into consideration. A monitoring system consisting of fiber optic cable, PT100-sensors, a weather station and an infrared camera system was installed on site. Through the sophisticated monitoring system at Bad Waldsee, it is possible to check and validate theoretical calculations, the description of the snow-melting process, the model of pavement temperature distribution, as well as the heat and mass transfer on the pavement, the snow layer and ambient conditions. This heat pipe system installation has already proven that cooling loads can be transported into the underground and that the street can be heated through geothermal resources, even under very low surface temperatures. Measured and modeled values in this project are consistent and detailed theoretical calculations based on these findings will enable planning for new de-icing and snow melting systems. These may be made possible through using heat pipes and borehole heat exchangers and could be applied to airports and helicopter landing sites, parking areas, and garage entrances, for example. |