GROUND-SOURCE BRIDGE DECK DEICING AND THE INFLUENCE OF GROUNDWATER FLOW ON SEASONAL THERMAL STORAGE

Ground-source energy is a renewable resource used for heating and cooling of buildings. In this system, ground is utilized as a thermal mass and the stored thermal energy is harvested with borehole loops connected to a ground-source heat pump (GSHP). Recent developments in ground-source heat exchange systems involve the retrofitting of deep foundations with circulation pipes, such that structural foundation elements can be converted to heat exchangers. One of the promising aspects of energy foundations is to use them to extract thermal energy from the ground for heating and deicing of bridge decks in the winter. Warm fluid extracted from the circulation tubes within the energy foundations is circulated through a tubing system in the bridge deck slab to heat the bridge deck against snow accumulation and icing in the winter. This operation is considerably different than the use of heat exchangers for heating and cooling of buildings where thermal energy is injected into the ground in the summer and extracted in the winter. Heating and cooling of buildings enable the seasonal thermal loads to remain reasonably balanced in well-designed systems as opposed to bridge deck deicing involving only heat extraction in the winter. Consequently, bridge deck deicing has the potential to progressively cool the ground unless precautionary measures are taken. Furthermore, restriction the foundation’s size limits the ground thermal mass that can be utilized for geothermal energy. As a result, our studies show that we need to rely on thermal recharge of the ground using the heat collected from the bridge deck slab in the summer. In this case, the circulation system is operated in reverse and the thermal energy collected from the heated slab is injected into the ground through the circulation tubes to offset the temperature drops in the ground from the preceding deicing operations in the winter. This study focuses on the role of groundwater flow on the efficiency of energy foundations and other shallow geothermal systems used for bridge deck deicing. Thermal recharge is most effective in the absence of any ground water flow and convective effects. This study considers various groundwater flow scenarios and seeks to quantify the short and long-term effects of groundwater flow on a bridge deck deicing system’s operational efficiency.