Formation Mechanism Of Heat And Moisture Environment In Underground Hydropower Station And Its Energy-saving Control Strategy

In recent years, China’s hydropower station construction is gradually moving into ahigh-speed period. For some certain reasons, the underground form is mainly chosen.Because buried deeply underground, serious environmental issues, such as dampness,suffocation, fungus and condensation, can be easily found under inappropriate operationof ventilation system. To eliminate such issues, HVAC facilities with large capacity areusually adopted but still without satisfactory results. Current literatures mainly takeequipment heat load as the starting point and pay much more attention on heatenvironment rather than moisture environment. By ignoring the coupling relationshipbetween heat and moisture, it is impossible for current studies to reveal the formationmechanism of heat and moisture environment and take effective improvement actions.Environment in underground hydropower station is affected by multi-factors, fullunderstanding of the influence mechanism of different factors is the basis for solution ofenvironmental issues, establishment of controlling strategy and reduction of HVACenergy consumption.A systemic investigation is carried out in this paper. First, a prediction model aboutheat and moisture environment in underground hydropower station is established, theformation mechanism of this special environment is revealed after analysis of differentinfluential factors. Then the controlling strategy is proposed, which can effectively solveenvironmental issues and will be the basic foundation for the design and operation ofHVAC system. The work presented in this paper is financially supported by NationalNature Science Foundation of China titled by Formation mechanism of thermal andmoist environment in deeply buried underground hydropower station and it’senergy-saving control strategy (Project No.51178482).All the chambers in underground hydropower station can be divided into twocategories based on their shape and structural characteristics, that is large-space cavernand narrow tunnel. Two newly developed numerical models, which are suitable for thecalculation of heat and moisture transfer in different kind of chambers is proposed inthis paper. By applying “cell division” calculation method, the models are discretizedand the corresponding calculation code are written in MATLAB for numericalcomputation. Finally, the developed models are validated against the test results ofseveral experiments and field measurements. Underground tunnel, which can be considered as the pre-treatment section of theambient air before it entering power house, is the premise of environment analysis inunderground hydropower station. Through calculation, the paper reveals the heat andmoisture exchange features between tunnel and air stream as well as condensationphenomena. The impact of tunnel ventilation on power house environment and ACdesign parameters is also discussed. All the analysis about the heat and moistureexchange inside underground tunnel will provide an accurate reference for the rationalutilization of natural resources and scientific support for the design and operation of ACsystem.There is a coupling relationship between indoor air and surrounding envelope, thecurrent studies when dealing with underground structures always only focus onenvelope without consideration of this coupling characteristic, which is unreasonable.Therefore, by setting coupling relationship as the starting point, the paper launches afurther investigation on the heat and moisture transfer process of the envelope. Thenfinally the essence of this coupling property is revealed, by which the simplifiedformula using air parameters as independent variable is proposed, which can easilycalculate the dynamic heat and moisture exchange between envelope and indoor air.This simplified function can sharply reduce computation complexity and provideengineers a very practical way to determine heat and moisture transfer amount, evaluateAC capacity and adjust operation strategy. This paper also has an investigation onanother long-standing puzzle---construction water problem. Also starting from couplingrelationship, the influence degree of different factors is discussed and quantified. Then asimplified formula for the calculation of construction water transfer is proposed, whichcan provide a simple and reliable method for the estimation of construction waterinfluential period. Therefore, the reliable and practical damp-proofing method andstrategy can be easily got.Due to special geographical location and process characteristics, environment inunderground hydropower station is also affected by other special factors, includinggeneration facilities, water diversion system and airflow distribution. Therefore, thepaper carries out investigation on each different factors. For generation facilities, theheat releasing characteristics, such as intensity, time variation and spatial distribution,are discussed. Numerical modeling of important equipment, including generator,transformer as well as bus bar, is launched and then the heat releasing feature of eachequipment is got. For water division system, a two-dimension model with consideration of penstock is first established, by which the influential mechanism of water divisionsystem on environment is revealed. Also other heat and moisture issues caused by waterdivision system, such as condensation time and condensation place, are identified.While for the airflow distribution part, the influence of velocity and internal-circulationare discussed. Through the study of different influential factors, the revelation offormation mechanism of heat and moisture environment in underground hydropowerstation becomes more specific and comprehensive, which will provide scientific supportfor the entire HVAC system, including design, operation, optimization and energysaving control.Finally, taking an underground hydropower station as the example to analyze heatand moisture environment in different parts of the underground chambers, includingunderground tunnel, generator floor, bus bar floor, hydraulic turbine floor and volutefloor. Based on calculation results, the optimization method of HVAC system andcontrol strategy of heat and moisture environment is finally proposed.All-around investigation about the formation mechanism of undergroundenvironment and its control strategy are carried out in this paper. The results of thisresearch can greatly improve the application of coupled heat and moisture transfer inunderground constructions, and provide an important reference for further investigationon heat and moisture environment in underground hydropower station.