Study Of The Thermal And Humid Environment In Hydroelectric Station Underground Plants

Recent two decades, many existing, under-construction or proposed hydroelectric power stations are limited by surrounding terrain conditions and influenced by many other factors. Underground plant has become the best type to choose. Indoor heat and moisture environment is decisive factor to influence the physical healthy of equipment maintenance staffs and the safe of equipment operation, for the reason of deep underground and covered by rocks. The heat and moisture transfer process in porous material, heat and moisture absorbing and desorbing process on wall surface and thermal and humid environment in the underground plants are first researched systemically in this paper.The heat and moisture transfer process and principle of porous material are extremely complex. Moisture transfer is under the influence of several moisture transfer mechanism. No single theory can generalize the moisture transfer process of porous material under all conditions, and heat and moisture transfer models are developed by researchers of different countries which mainly focus on specific application conditions. The coupled heat and moisture transfer model is advanced in this paper with driven potential of relative humidity relative to saturate moisture in pores and temperature based on the result of former research. The model describes the diffusion process of vapor and water, and it fully depicts actual moisture transfer process of in porous envelop. Especially calculating of heat and moisture transferring on lining and interlining walls, humidity parameter is continuous at the boundary and connection of multilayer walls. And humidity parameters can reflect obviously the dampness extent of porous material.The heat and moisture absorbing and desorbing process of porous envelop will inter-influence and interact with indoor temperature and humidity parameters, and the heat and moisture absorbing and desorbing process of porous envelop must be considered for accurate heat and humidity load calculating or else deviations will happen. The mathematical model of heat and moisture absorbing and desorbing process of porous envelop is presented in this paper, and the model takes latent heat into consideration. Additionally, the method to determine the thickness of boundary at the remote of porous envelop is suggested considering the character of underground plant. The discrete heat and moisture transfer equation and control conditions are obtained with finite volume method. The temperature and moisture distribution and transient heat and moisture absorbing and desorbing of porous envelop are calculated with numerical method. The program for porous envelop heat and moisture transfer are developed by use of FORTRAN. The heat and moisture transfer model is verified using the examples given out in the reference [41] and testing data of funk hole located in A zone Chongqing university.The heat and moisture absorbing and desorbing of envelop surface in underground hydropower station plants are influenced by indoor heat and humidity parameters and air flow velocity, besides, they are also influenced by physical properties, temperature and humidity of rocks. For the convenience for designers, monthly heat and moisture absorbing and desorbing index and month average heat and moisture absorbing and desorbing fitted formula for limestone no lining wall are lined out in the paper under the temperature scope of 16 to 28℃and humidity scope of 60% to 80% of rocks, the usual fluctuation scope of indoor temperature and humidity by HVAC controlling conditions. According locale investigation of Yunnan Dachao mountain hydropower station and Chongqing Jiangkou hydropower station, understand the real heat and moisture condition of underground plants, find out the disadvantage of HVAC designing, obtain the basic material of improving HVAC system, make the following HVAC design of underground plants more reasonable. Furthermore, the reliability of heat and moisture absorbing and desorbing index is verified by use of testing data, and the correctness of heat and moisture transfer model is verified indirectly in this paper.In this paper, the indoor air thermal and humid balance equation is founded considering the heat and moisture absorbing and desorbing effect of porous envelop, while the thermal and humid simulating program is worked out by incorporating the coupled heat and moisture transfer model of porous material with the heat and moisture absorbing and desorbing model. Moreover, it is simulated and analyzed the thermal and humid environment of generator floor in Longtan hydroelectric station the 2nd largest hydroelectric station that under constructed. It is also presented a new HVAC system design idea for underground plants of hydropower station, namely, adapting the HVAC system designing objective from primary controlling thermal environment to controlling humid environment. Finally, according to this new designing method, adopting the designing index mentioned above, re-design the Longtan hydropower station HVAC system, and the simulation result reflects that the indoor heat and moisture environment fulfils the operating equipments security requirement, the new designing method can be used in real projects.