Insulated PEX-pipe loops for deicing on existing bridge deck using geothermal energy: Laboratory tests, modeling, and performance analyses

Abstract

An external hydronic heating system utilizing geothermal energy is an innovative new method to de-ice in-service bridges that avoids detrimental environmental effects and damage to bridge deck structures stemming from chemical deicers and mechanical traction materials (e.g., sand). However, in these systems, the bottom surface of the bridge deck is usually fully covered by insulation materials and hence not accessible for visual bridge inspection. In this study, a new attached insulated, cross-linked polyethylene (PEX) pipe loop heating system is developed to heat existing bridges while maintaining a partly uncovered deck for visual inspection. The new loop consists of a PEX pipe, an aluminum plate, polyurethane foam insulation, and a high-density polyethylene jacket. Numerical simulations were first performed to determine the optimum shape and thickness of the insulation. Then the pre-made loop system was attached to the bottom surface of a concrete slab in a freezer box, where 62.3% of the slab bottom surface was covered by the system. A heated water bath was used to simulate the ground heat exchanger for heating the system. The heating tests were conducted at room temperatures of −2.78, −3.89, and −6.67 °C, with supplied water temperatures ranging from 24 to 45 °C. A 1-D steady-state thermal resistance model was then created to model the heat transfer processes and to estimate the slab surface temperatures. The results show that the deck surface heat flux fluctuated from 49.6 to 121.5 W/m2, depending on operating conditions and that an average of 16.3% of heat energy was transferred to the deck top surface. The results of misting tests indicate that the new system kept the bridge deck free from ice under mild winter conditions. These results demonstrate that the new insulated PEX pipe loop heating system is feasible for deicing existing bridges while minimizing the hindrance of bridge inspections.