지열원 히트펌프를 이용한 도로 융설 시스템의 성능 평가 및 예측에 관한 연구

Abstract

In accordance to the Kyoto Protocol, developed industrialized nations must cut back on their greenhouse gas emissions. Also, new renewable energy is in the spotlight as it is realized to run out of fossil fuels. Most part of the carbon dioxide are released in the energy field. Besides, it is cooling and heating systems that consume most of the household energy. The heating and cooling system for building must satisfy both heating load and cooling load but generally the heating load is about 60 percent of the cooling one. In order to ensure convenience and safety of drivers and pedestrians, about 40 percent of the load remaining after energy consumption in the winter time was grafted into the road snow melting system in this thesis.

The performance of the system was evaluated with the goal of development of a hybrid system for both the heating and cooling and the road snow melting by using geothermal energy. The evaluation data was analyzed by the CFD program and then the results in different conditions were predicted by changing the conditions of the analysis.

The result of the performance evaluation of the hybrid system showed that the coefficient of performance (COP) in the real operation was higher than that written in the specification. The COP in the specification was 2.65, but the real operation showed the COP of 4~6.

In the process of combining and supplying the energy needed for heating and cooling into the buffer tank, a problem of heating and cooling occurred due to the large size of the road snow melting load. Method of directly supplying the energy to the room for heating and cooling, not to the buffer tank, was introduced to solve that problem.

The data from the real operation was examined to confirm the CFD analysis. It has shown that there was a very small difference of 0.4℃ (degree Celsius) between the real operation data and the CFD analysis. Also, pavement materials of a road such as concrete and brick were numerically studied because all roads were not paved with Ascon, even though the road where the actual system was installed was made of Ascon. In addition, the results obtained from changes in the intervals and depths of the pipes laid for snow melting and the working fluid temperatures were compared. The result of the comparison shows that the influencing variables on the road surface temperature are the pipe interval, the working fluid temperature, and the pipe burying depth in decreasing order.

Furthermore, it was judged that the road snow melting could occur with ground heat only and without operating a heat pump (GSHP) in order to reduce the operation cost. This means the road snow melting can be achieved in the concrete pavement. On the basis of the feasibility, when applying ground heat before operating a heat pump(GSHP), the time to reach the target temperature decreased by 30 minutes but the operation expense increased by 15%. Moreover, as the interval of underground pipes is adjusted 150mm to 200mm, the initial cost of materials can be saved by 2,158,000 won, but the operation cost has grown by 211%.