Storing and transferring heat in soils is governed by the soil thermal properties and these properties are therefore needed in many engineering applications, including horizontal ground heat exchanger for ground-coupled heat pumps. This paper presents the evaluation results of the ground subsurface temperature and apparent thermal diffusivity of soils by using ground temperature data collected at the depths of 0.5 m, 1.0 m, 1.5 m, 3.0 m, and 5.0 m at four sites. The existing correlation assuming that the soil was homogeneous and of constant thermal diffusivity was applied to calculate the subsurface temperature and two analytical equations, amplitude and phase equation, were also used to evaluate the soil apparent thermal diffusivity. Comparison of the estimated and of the measured values of the subsurface temperature has shown that the empirical correlation predicts quite accurately the ground temperature at various depths. Based on the one-dimensional heat conduction equation, the apparent thermal diffusivity can be estimated by the two equations.

Performance of ground-source heat pumps (GSHPs) is mainly affected by ground heat exchangers which makes up more than 40% of construction cost. Exact construction and grout as backfill are important, because it is difficult to repair after being installed. As grout materials, bentonite grout material and cement material are used In this paper, thermal conductivity according to mix proportion of cement grout has been experimentally studied. Some variables were set to evaluate thermal conductivities according to change in cement content, unit water ratio, mass per volume of fresh mortar, and aggregate types. From the experimental analysis, high performance cement grout has been proposed.

Renewable energy is growing based on low-carbon green energy government policies. According to this policy, geothermal energy is highly efficient and environmental friendly energy which is being recently expanded. However, construction companies are generated disorderly but their ability has not been verified due to the poor geothermal facility which was reported in the media. In the this paper introduce on Busan region's largest geothermal facility, it was confirmed that thermal efficiency of the underground is close to heat exchanger performance. Therefore the study improving the efficiency of underground heat exchange found progressed. The results showed voids between borehole and ground heat exchanger should not be raised. And then geothermal facilities were installed very successfully through the principle grouting operation. As compared to the energy consumption on the basis of operating results energy usage was less than any other heat sources.

The objectives of this study are to analyze the performance of a heat pump system with the various heat source and to carry out economic assessment for the heat pump system. The COP of the river water and ground source heat pump system was 20% higher than that of the air source heat pump system because river water and geothermal provide stable operating temperature compared with air temperature throughout the year. In addition, the economic assessment of a heat pump system using air, river water, and geothermal as a heat source was carried out. The ratio of the life cycle operating cost to the life cycle cost increased with the increase of building capacity. The payback period was found to be less than 3.3 and 4.5 years, respectively when the capacity of the river water and ground source heat pump was larger than 10 RT.

In this study, control characteristics and energy performance with flow rate control methods were reviewed with the simulation. The heating system is classified such as fan coil unit and HVAC system currently used in buildings with valve control and pump inverter control. The simulation analysis program is made by TRNSYS ver. 15 with the actual data. As a result of this study, the central heating system with pump inverter control decreases electricity energy and reduces gas consumption. Inverter control method shows better performance in comparison with valve control one for energy saving.

In this study, heating performance and energy consumption characteristics with control strategies for central heating system were researched by the simulation. The simulation analysis is made by TRNSYS ver. 15 with the actual data. The parametric study on proportional factor, control time interval and outdoor air temperatures changes were done to compare control characteristics and energy performance, respectively. As a result, the simulation results with various parameter changes show good heating performance and energy saving.

Hybrid desiccant cooling system(HDCS) consists of desiccant rotor, regenerative evaporative cooler, heat pump and district heating hot water coil. In this study, TRNSYS and EES, dynamic and steady simulation programs were used for studying hybrid desiccant cooling system which is applied to an apartment house from June to August. The results show that power consumption of the hybrid desiccant cooling system is 70 kWh in June, 199 kWh in July and 241 kWh in August. Sensible and latent heats removed by the hybrid desiccant cooling system are 300 kWh, 301 kWh in June, 610 kWh, 858 kWh in July and 719 kWh, 1010 kWh in August. COP of the hybrid desiccant cooling system is 8.6 in June, 7.4 in July and 7.2 in August. COP of the hybrid desiccant cooling system decreases when latent heat load increases. Operation time of the system is 70 hours in June, 190 hours in July and 229 hours in August. Since the cooling load is largest in August, the operation time of August is longest for maintaining the indoor temperature at $26^{\circ}C$. Due to the characteristics of hybrid desiccant cooling system for efficiently handling both sensible and latent loads, this system can handle sensible and latent heat loads efficiently in summer.

Due to enhanced sealing and insulation of buildings, extensive use of glasses for building envelopes and increased use of heat generating office equipments, energy consumption of modem buildings for cooling is steadily increasing. With outdoor air cooling(ODAC) system, cooling load can be reduced by exchanging indoor air with the cold outdoor air during spring and fall seasons. If ODAC is operated based only on temperature, total cooling load may virtually increase if the outdoor humidity is high. To overcome this problem, ODAC should be controlled based on enthalpy. In this work energy saving characteristics of enthalpy controlled ODAC is studied using dynamic simulation. The result shows that cooling load can be reduced by 27% by adopting ODAC.

Feasibility study on energy saving system by utilizing exhausted heat from subway, which is one of the unused energy, was carried out. General heat source system using absorption chiller-heater was used for comparing to the energy saving system, and payback period method using initial cost and running cost of two systems, was used to perform economic estimation. Payback period was about ten years, and this period might be shortened if nation's economic support enact.

Recently, central and local governments of Korea have established and implemented various energy policies such as making energy map of city level and establishment of environment friendly city plan to materialize low carbon green city. To implement effectively these policies, however, conditions of energy consumption by each administrative district and each usage have to be verified exactly. This study is aimed to suggest a basic data for planing energy policy and energy demand prediction of city level by analyzing energy consumption unit and conditions of city gas by borough and usage in Busan.