Study Of The Thermal Characteristics Of Pipe-embedded Radiant Floors Based On Frequency-domain Analysis And Its Optimal Control

Pipe-embedded radiant floor system,as a new kind of air conditioning technology,has attracted the interest of researchers due to its higher energy efficiency,better thermal comfort,lower investment,and higher possibility for utilizing low-grade energy resources etc.Different from the traditional air conditioning terminals,the pipe-embedded radiant floor is characterized by large thermal inertia and complex thermal interaction with the other parts of the room.Thus,it is important to quantify the actual thermal characteristics of this structure to guide the design of the pipe-embedded radiant floor system.Meanwhile,optimal control for the pipe-embedded radiant floor system is the premise to achieve its advantages in energy efficiency and thermal comfort etc.This dissertation mainly focuses on the dynamic thermal behavior,modelling and optimal control of pipe-embedded radiant floor,and the relevant contents and innovations are introduced as follows:(1)The frequency-domain finite-element(FDFE)model for the pipe-embedded radiant floor is firstly proposed to study its thermal characteristics.The frequency thermal characteristics of this structure under the disturbances from the circulating water and the indoor thermal environment etc.are analyzed using this model.Meanwhile,the time-domain thermal characteristics of the FDFE model are also obtained by means of discrete Fourier transform(DFT)and inverse discrete Fourier transform(IDFT).To validate the accuracy of the FDFE model,a time-domain finite element(FE)model is developed as the reference model.The results show that the FDFE model can predict the thermal characteristics of the pipe-embedded radiant floor as accurately as the time-domain FE model and yet takes much less calculation time.The FDFE model can predict the thermal responses of the pipe-embedded radiant floor directly and fast.(2)An algorithm for identifying the model parameters of the simplified heat transfer model for the pipe-embedded radiant floor in frequency domain is firstly proposed.A simplified RC-network model for the pipe-embedded radiant floor is developed.Then,the model parameters are identified based on the frequency thermal characteristics calculated by the FDFE model.Besides,a 2R1C model is developed to describe the heat transfer of the embedded pipe(i.e.,water loop),and the corresponding calculation formulas for the model parameters are obtained based on the e-NTU method.(3)An experiment test rig for the pipe-embedded radiant floor is built and a simplified RC-network model for the whole radiant floor room is developed.Measurements of the dynamic thermal responses of the pipe-embedded radiant floor or room are conducted under various experiment conditions,and the accuracy of the simplified RC-network model for the whole radiant floor room is validated against the experimental measurements.(4)An optimal control method,i.e.,offline predictive+robust feedback optimal control,for the radiant floor cooling system is firstly proposed.A control and simulation platform for radiant floor cooling system is built to investigate the control performance of the proposed control method and two existing methods,i.e.,PID control method and MPC control method.Comparisons are further made among these three control methods in terms of room temperature,power consumption of chiller,and operation of water valve.