Research On Inverse Model And Energy Efficiency Of Installed Ground Source Heat Pump Systems

Be using renewable geothermal energy in shallow ground layer, a ground source heat pump (GSHP) technology is known as one of air conditioning techniques which have the greatest developmental. The GSHP has great potentials in energy reduction and in reducing CO2 emissions to conventional HVAC systems. In China, energy shortage and environmental issues pose a serious challenge accompanied by rapid economic growth. GSHP has been spotlighted as both energy efficiency and environmental benefits. Generally, the initial investment for a GCHP system is higher than that of a conventional system. GCHP energy savings will offset the higher installing cost in future. However, there are many aspects affecting the actual amount of energy saved, such as climate, building load, ground heat exchanger, heat pump, control, etc. Recently, a lot of research on the energy performance of GCHP has been carried out. However, most of these previous research projects evaluated the performance of GCHP system based on a laboratory scale or a small capacity system. There is little data documenting the long-term performance of a large-sized GCHP. Evalution and research on real world installed GCHP will provide a more accurate understanding of the current technology's performance.The paper presented that the energy performance evaluation of two types of GSHPs based on actual operational data. The two types of GSHPs were ground-coupled heat pump system (GCHPs) and groundwater heat pump system (GWHPs) which were, respectively, installed in two apartment buildings of Wuhan, China. In one year, we monitored various operating parameters, including the outdoor temperature, the flow rate, electrical consumption, and the water temperature. The coefficient of performance (COP) values of system and chiller were determined based on a series of measurements. During residential GCHP system operation, the heat injection rate into soil is larger than the heat extraction rate out of soil. The COP of chillers of the GCHPs decreased significantly during the heating season due to the lowering of ground soil temperature. The system power consumption exhibited a strong linear relationship with outdoor temperature in both seasons and this suggests that normalizing power consumption against degree-days is a highly practical index in energy analysis in resident buildings, especially in winter.Some research topics were studied on the two actual cases. An exergy analysis of a ground water heat pump system on the actual operation was conduced. The energy efficiency and exergy loss and efficiency in each of the components of the system are detemined for the average measured parameters obtained from the monitored results of the hottest month and the coldest month. Inefficient facts are found out and increased energy efficiencies of two proposed improvement measures were estimated. Lower approach temperature is effective energy saving. In addition to the energy analysis, a full exergy analysis helps to identify the components where inefficiencies occur. An economic analysis model for GWHP was established to calculate energy consumption and operating cost based on a baseline condition. Plate heat exchanger flow rate and groundwater flow rate were optimization parameters according to different water price of the groundwater:GWHP survey data shows the impact of water price on groundwater flow rate in design. The long-term energy performances of the GWHPs and the GCHPs were investigated and compared with conventional HVAC systems and other GSHPs on literature data. A performances model was established base on the two cases to constrast the predicted performance with the actual performance.Based on superposition theorem of geothermal heat exchangers (GHE), a inverse model for GHE, G-functions interpolation approach was proposed. Linear interpolation method was adopted to fit G-functions. The method presented here uses the Nelder and Mead simplex algorithm as part of a parameter estimation algorithm to estimate G-function. For verification of G-functions interpolation approach, a numerical experimentation had been conducted where synthetic load on GHE was established. The simulation results with error and no error, were inversely modeled by G-functions interpolation approach and DST calibrated approach. The actual dataset of a small sized and a large sized GSHPs were also used in inverse modeling to verify the results from the G-functions interpolation approach. The small sized GSHPs was from literature. The large sized vertical GSHPs was the monitored case in the paper. A detailed DST model of a GHE has been calibrated to monitored data. The second year predicted temperatures calculated by the two models were compared with the measured. The results show the two approaches are reliable and have good performance of error tolerance. The error of GHE water temperature calculated by G-functions interpolation approach was less than DST calibrated approaches. The data error inversely modeled was mainly from recorded day data. As a extension study of the G-functions interpolation model, degree-day G-functions approach was proposed. The model was based on degree-day prediction load and can be applied on the residential buildings. The standard deviation of GHE water temperature by degree-day G-functions approach was larger than DST calibrated approaches. The result shows the appropriateness of degree-day G-functions interpolation approach for the quantitative modeling of GHE.This paper shows that the research on actual performance according measured data and presents two inverse models:G-functions interpolation model, degree-day G-functions model approach, which provides new methods for GHE inverse modeling...