Research Of Active Insulation Technology Based On Low Grade Energy

Faced with the problem of China's building energy consumption and energy crisis,it is important to use low-grade energy effectively and reduce the energy consumption of building envelopes.The active insulation technology has been proposed,which means directly uses low-grade energy(including solar energy,groundwater,industrial waste heat,etc.)to achieve efficient utilization of energy,reduce heat loss of building envelopes and so on.By combining the active insulation technology with engineering applications,such as flat plate solar collector,Trombe wall system and embedded-pipe wall has been studied.The main research works and achievements are as follows.1.The concept of active insulation technology has been expounded.The feasibility of applying active insulation technology to building envelope structure and solar thermal utilization device was studied.The source of low-grade energy was analyzed.2.The computational fluid dynamics(CFD)method was used to study the heat transfer and flow characteristics in a two-dimensional enclosure with semitransparent medium.The indoor device of steady-state heat transfer for rectangular cavity was built.The simulation data can agree very well with practical ones.The conditions of heat collecting and dissipation and heat modes were both studied.The effects of transmittance and thermal conductivity of TIM were analyzed.When the external boundary conditions are periodic,the response analysis of temperature was presented.The feasibility of active insulation technology integrated with solar thermal utilization devices is demonstrated.3.According to the active insulation technology,a new type of solar flat plate collector has been proposed,which added a TIM sheet inside the air gap to improve its efficiency.A three-dimension model was build and a numerical anslysis was used to evaluate the thermal performance of the new designed collector.The effects of ambient temperature,solar radiation intensity,external wind speed,inlet flow rate,collector inclination angle and transmittance of TIM on the performance of the new flat plate collector were studied.The parameters of the collector were optimized to obtain the best operating conditions.4.The plexiglass sheet has been used as TIM materials.The performance of the new designed collector in cold weather conditions was investigated.The effects of plexiglass sheet's thickness and mounting position on the performance of FPC were analyzed under steady state conditions.The nature convection inside the air gap was studied.Based on the Yushu area in Qinghai,the operation performance of the new collector under three typical meteorological conditions were studied.The results show that the daily efficiency is higher than that of the traditional collector,and the cpllector's efficiency can be higher 5.6%.5.A new type of Trombe wall is proposed,which introduced the active insulation technology.The outer layer of the composite Trombe wall is a water wall.The composite Trombe wall could effectively solves the problem of excessive heat dissipation at night.The results show that it can reduce heat loss by 30%.6.The active insulation technology has been integrated with pipe embedded wall.The low-grade heat is used to achieve the goal of water(below room temperature)heating and water(above room temperature)cooling.The steady-state and transient analysis methods were used to study the effects of inlet temperature,flow rate and position of the embedded tube on the temperature change in the room.The results of the transient analysis show that the summer can reduce the loss of cooling by 13%,and the heat loss can be reduced by 33% in winter.