Program Development Of Vertical U-tube GSHP Air Conditioning System Designing

Ground source heat pump (GSHP) systems are increasingly popular in both residential and commercial applications. Because of its lower Energy conservation and lower operating costs. Heat pumps have been identified as an efficient and economical alternative to the conventional heating and cooling systems. The ground is an attractive heat source and heat sink, since its temperature retains near constant throughout the year except for the upper 4 to 6 meter. It is a thermally more stable heat exchange medium than air, essentially unlimited and always available. Therefore, it has been utilized as the heat source or heat sink in HVAC systems for air conditioning, space heating, and water heating for both residential and commercial buildings. The high initial cost of the ground coupled heat pump system and the large land requirement are the major drawbacks, and have moderated the acceptance of these systems.Ground source heat pump systems are consists of three heat exchanging loop—under ground loop,refrigerator loop in the heat pump unit and water to water (or water to air ) heat exchanging loop of user' side. So the ground heat exchanger model,heat pump unit model and load calculating model are developed in this paper. The relationships between three loops are analyzed. A ground source heat pump design program has been developed by Visual Basic language. The ground heat exchanger is the most important in the whole system, several models have been developed for the analysis and sizing of the ground-loop heat exchangers. The models are mainly based on the Kelvin's line source theory, cylindrical source theory, or numerical methods. The aim of this study is to establish a relationship between the thermal resistance of a borehole and its geometry, grouting conductivity, volume flow rate of the hear carrier fluid, etc. A method of G- function and conduction shape factors are employed to calculate the borehole resistance in the design program of the ground heat exchanger. For heat pump model, the capability of the condenser and the evaporator are studied. In the actual projects of HVAC, the packaged heat pumps have been more and more attractive, so the combine performance between condenser and compressor has been analyzed. Based on the test data, the relationships between the refrigerating capacity,heating capacity,COP of the GSHP and the exiting fluid temperature of the borehole are analyzed. The heat exchanging capacity of the ground source heat exchanger is decided by the building's loads. So the instantaneous loads calculating model are developed to calculate the hour to hour loads of the building, and a conic relationship between the building loads and borehole heat exchanger(BHE)' capacity is worked out. To prove the design program is applicable in all situations, the capacity of the vertical U-tube borehole heat exchangers are tested. This paper introduced a test method of the capacity of the vertical GSHP system. The affect factors of the heat transfer are analyzed. Comparing with the test data, the design program is proved that the calculating model of the Ground source heat pump could forecast the capacity of the vertical U-tube BHE accurately. Based on this, the paper prospects the GSHP appliance as a economical air conditioning form. And a basic study have been offered to hope the paper could as a reference for design, construction, management, and its development.