Diversity And Efficiency On Energy Mechanism Of Heat Pump System By Using Earth Energy

Renewable energy is the inevitable choice for the future sustainable energydevelopment, and earth energy utilization as well as its underground shallow as good heatreservoir to provide application space for heat pump technology, have aroused greatattention in the world. Earth energy utilization is promising in fields of building HVAC(Heating, Ventilation and Air Conditioning) engineering, and melting snow and deicing inroad traffic. However, imbalance problem between cooling load and heating load in theHVAC system has long plagued heat pump engineering application of using earth energy insevere cold region. People have been seeking a solution for best efficiency.The fundamental problem for diversity and efficiency on energy mechanism of heatpump system, and the calculation model and analysis method for heat pump system areproposed in this paper, which provide an approach for engineering design and operationprediction by digital method, and for the thermodynamic analysis of performance of systemyear by year and prospective study to guide the engineering practice.Demonstration project and computational analysis indicated that ground source heatpump(GSHP) adopted the obvious gap in combined cooling load and heating load or singleof heating load in severe cold region, which caused underground temperature annualdeclines, and increased energy consumption of heat pump system and reduced coefficientof performance because of imbalance between cooling load and heating load. Toeliminate or weaken the single energy consumption of earth reservoir, steps and adjustmentoperation mechanism must be taken, by various energy mechanisms such as combinedcooling load and heating load, active energy storage, intermittent operation and energysupplement of earth reservoir, to realize efficient operation and effective balance forunderground energy, and further help utilization of GSHP technology in northern area.Supported by the National Natural Science Foundation of China (No.41072198),simulation and experimental research on ground source heat pump system were conducted,which provides an effective approach for GSHP engineering design and operation condition prediction, understanding application of borehole GSHP system and energy characteristicof underground heat transfer and storage process, by the predictive operation condition andperformance analysis in years, to explore the energy diversity and optimization operationmechanism of heat pump system by using earth energy. The research work mainly includesthe application of underground heat exchanger G-function and model analysis, theintegration of heat pump system and modules establishment, simulation analysis ofthermodynamic process and experimental verification, combined mechanism andperformance analysis, the role of energy storage, etc. Innovative research in thecharacteristic of time step provides more effective guarantee for calculation precision forlong-period for years, minutes and hours for short period, fixed time domain for changeperiod. It systematically explored the establishment of modules, module scarf and couplingcall based on Matlab/Simulink calculation control platform, established the basic analysismethod of heat pump system, and provided an important mean for forecast analysis. Theoperation mechanisms for single or combined cooling load and heating load, combinedload and energy storage hybrid mode, and the dynamic control method for undergroundenergy storage were proposed. The underground heat transfer control technology providesnew control concept for underground storage and underground heat transfer energy flow,further helps the breakthrough of efficient utilization technology for underground energyand establishes a certain basis in severe cold region.In the analysis of heat transfer process of underground heat exchanger, the basicmathematical model was established by using the G-function and governing equations ofborehole temperature, for predictive analysis long-period for years and detailed analysis ofminutes and hours for short period, so the characteristic study of calculation step as one ofthe top issues in numerical simulation calculation method. This study shows that time stepis a key factor in computational process, especially it is particularly important forcomputation time in long time operation condition, and appropriate time step should bechosen according to the operation period of simulation environment to deal with thetemperature of underground heat exchanger at the corresponding pulse load. In addition, the borehole temperature response characteristic to load for different borehole number wasfurther analyzed.The study of underground heat exchanger heat transfer mode, the influence law of theborehole diameter, shank spacing, and grout conductivities on thermal resistance ofborehole are discussed systematically. The influence character of the fluid temperature atthe exit of ground heat exchange, the circulation flow velocity in ground heat exchange,underground original temperature and borehole spacing on the fluid temperature in groundheat exchange, the design depth of borehole and the heat pump power consumption wereanalyzed to lay the foundation for the study of long-term operation condition and powerconsumption.In heat pump thermodynamic integration system model, heat pump module,instantaneous solar radiation module, solar collector module, storage water tank moduleand building load module were established separately for further verification and analysisof the model. It systematically explored the establishment of modules, module scarf andcoupling call based on Matlab/Simulink calculation control platform, established the basicanalysis method of heat pump system, and provided an important approach for the couplinganalysis of diversity and efficiency on energy mechanism of heat pump system by usingearth energy.Combining a project experiment, the model calculation and experiment for long-termheating system in winter for years were studied, to analyze the influence character of thefluid temperature at the inlet and exit of ground heat exchange, the energy consumption andcoefficient of performance of heat pump and system, primary energy ratio and heat pumpthermodynamic perfectibility. In experiment period, the change of the fluid temperature inground heat exchange was consistent with model calculation, and the result anastomosedpreferably for the energy consumption and coefficient of performance, so the computationmodel and analytical method had been verified. The experiment further demonstrated thatground source system had no store and complement energy in the heat-based north, whichlead to energy consumption of system increases, the underground temperature drops year by year, the coefficient of performance of heat pump and system reduces for long-timeoperation.For severe cold region and hot summer and cold winter region, forecast and analysisof the combined cooling load and heating load or single of efficiency on mechanism of heatpump system, proved the change in underground temperature, increased energyconsumption and significantly reduced coefficient of performance of heat pump and systemfor single load operation for years. One of the solutions is to combine cooling load withheating load, to relieve the underground temperature deviate from initial temperature byunderground energy supplement of cooling or heating load, and increase coefficient ofperformance of heat pump. The results showed that the underground temperature changed,energy consumption enlarged and the coefficient of performance of heat pump and systemreduced year by year, in which no obvious improvement even combine cooling and heatingload if there are great difference, so imbalance between cooling load and heating load playsa leading role.To eliminate or weaken heat pump system deterioration because of the imbalancebetween cooling load and heating load, the effect of energy storage was studied based onMatlab/Simlink platform, and the simulation analysis of operation condition of system byregulating continuing energy storage ratio, intermittent energy storage mode, cooling loadand heating load and energy storage hybrid mode for long period were applied to study thefluid temperature of ground heat exchanger, and the coefficient of performance and energyconsumption of heat pump.The operation condition and efficiency of consecutive energy storage heat pumpsystem during unheating periods were calculated in20years by adjusting the ratio ofenergy storage load to building heating load, and it is benefit for the long-term operation ifthe ratio between energy storage load to heating load is0.8～1.0. From intermittent periodand peak load in the intermittent energy storage mode of heat pump system, dailyintermittent storage mode and low peak intermittent storage mode can realize the effectiveoperation of system devices. By comparing different transitional season storage modes for cooling/heating united supply and energy storage hybrid mode, the results indicate theenergy-saving effect can be strengthened by double modes of pre-transitional season andpost-transitional season with the extension of operating time, and it is good forcooling/heating united supply and storage and complement energy double mode. In thismode, the ratio of solar collector area to the length of underground heat exchanger has adistinct impact on system operation condition, device energy consumption and efficiency.The heat pump system by using earth energy is increasing very rapidly. Despite thecertain development of ground source heat pump and related underground storagetechnology, some work still should be strengthened, such as the dynamic heat transfermechanism and control of span time domain and periodicity in large scale boreholeunderground heat exchange system, which is one of the major measures to tackle theunbalance between heating and cooling load. In fact, in unbalance load area, the longerapplication of the large scale GSHP engineering has caused underground energy decay andsystem efficiency decline, and become bottleneck and obstacle to the sustainableapplication, so complex science and technical question in large-scale heat pump system byusing earth energy need to be researched, to provide the reference and analysis method forimproving the operation reliability in different regions and the evaluation analysis oflong-term operation efficiency on system, which can be used to guide engineeringapplications, to ensure the progress of science and technology and healthy development inearth energy utilization technology.