Investigation of thermal performance of ground coupled space cooling system with underground energy storages

This thesis presents the numerical investigation of thermal performance of ground coupled space cooling system with an underground thermal energy storages (UTES) using analytical and computational methods. The cooling system consists of an underground spherical thermal energy storage tank, a chiller unit and a house to be cooled during summer season. An analytical model for the cooling system in order to obtain annual thermal performance of the system is developed. The analytical model consists of a solution of transient temperature field problem around the storage tank, an anlytical model for the chiller unit and heat gain calculations for the house. The UTES is an essential part of the cooling system under investigation. The transient temperature field problem consists of a partial differential equation, an initial and boundary conditions and an energy balance for the storage. The problem formulation is put into dimensionless form using a transform and dimensionless variables. The dimensionless formulation of the problem is transformed by an application of Complex Finite Fourier Transform (CFFT) technique, which yields another form of the problem formulation. Analytical solution of the problem is obtained to find the annually periodic temperature distribution in te storage tank and in earth surrounding tank. A formulation is obtained as algebraic equations to find the energy consumption of the compresor in the chiller unit and heat gain of the house. An analytical model for the cooling system is improved combining the solution of the transient tempreture field problem, work consumption of the chillerunit and equations for the heat gain of the house. A computational procedure is prepared, which is based on an iterative solution method. An interactive computer simulation program based on the present analysis was prepared in Fortran 90 for computing annual variation of water temperature in the spherical storage tank, temperature in earth surrounding the tank, compressor's work, space heat gain, and annually periodic performance of the ground coupled space cooling system. Also, effects of temperature of the deep earth, water in the storage, storage volume, system size on the COP are investigated. Key Words: Space cooling system, ground coupled system, energy storage