Study On Utilization Of Cold Energy Of Exhaust Air In Air Conditioning Systems

Exhaust air cold energy recovery is an important part of exhaust air energy recovery,which is an important mean of reducing energy consumption of the central air-conditioning, and which is one of the saving approaches meeting the needs of domestic market, so it arouses wide concern from scholars and research institutes. Making the most of exhaust air cold energy recovery units can effectively reclaim cold energy from exhaust air, and can cool or dehumidify fresh air simultaneously. Using the exhaust air cold energy recovery unit can reduce cool loads of fresh air drastically, and can reduce installed capacity of water chilling units, which not only undermine heat affecting to outdoor environment and saving energy from power equipments, but also decrease initial cost and improve economyof system. Stated thus, application of exhaust air cold energy recovery unit can achieve energy-saving, environmental protection and economy.?Based on typical sensible heat recovery type plate-fin sensible heat exchanger and total heat recovery type plate-fin total heat exchanger, two new type total heat recovery type exhaust air cold energy recovery units are suggested. Rounded analysis and study are carried on into the four exhaust air cold energy recovery units, for the sake of wide use of them, the following elements are studied.Firstly, sensible heat and latent heat of outdoor air in ChongQing area are quantitatively analysised, and the correlation of sensible heat exchange efficiency, latent heat exchange efficiency and total heat exchange efficiency is studied, offering reference for exact selection and evaluation of the recovery units. Two new type exhaust air cold energy recovery units are proposed: direct evaporative cooler plus plate-fin heat exchanger cold energy recovery unit and cooling tower plus pipe finned exchanger cold energy recovery unit. On account of he four exhaust air cold energy recovery units, operational principle and mechanism of heat and mass transfer are introduced detailedly. Meanwhile the utmost of the exhaust air cold energy recovery units are contrastively debated, and feasibility of the two new type units is studied.Secondly, based on the basic theories of heat and mass transfer, thermotechnical models for design calculation of the exhaust air cold energy recovery units are established, using efficiency -number of heat transfer unit (ε-NTU), dual efficiency and enthalpy potential method, thread and approaches of design calculation of the units are deduced, and steps and gist of the design calculation are clarified. By way of composing computer programs and simplifying design calculation, block diagrams are built. With regard to the two new exhaust air cold energy recovery units, interconnection between the core heat and mass transfer parts exist. Thus practical?ideas of the design calculation are brought forward. These analyses can offer references for the practical application of the units, and can offer warrant for the optimization in posterior chapters.Thirdly, considering profits of cold energy recovery, cost of attendance, initial cost and so on, using thermoeconomics method, optimizing model with the object functions of the maximization of annual economic return are founded. On the base of the anterior research fruit and product informations, optimal variables (design variables or decision variables) and constraint conditions are given. Using MATLAB 7.6.0, by means of particle swarm optimization (PSO), the optimal solutions of the four recovery units are calculated by the computer programs. Meanwhile all parameters of the unit ares listed, including geometry parameters, flow velocity, flow rate and so on. Finally contrastive studies of exchange efficiency and economy of them are made.Finally, according to results of the optimization, applied researches of the two exhaust air cold energy recovery units——plate-fin total heat exchanger and cooling tower plus pipe finned exchanger cold energy recovery unit——with perfect thermotechnical performance and economy are made. Combining practical engineering projects, conventional primary return air system and the primary return air system with the two exhaust air cold energy recovery units respectively are designed, including load calculation, air-quantity calculation of air supply and discharge air and selection of power equipments. Minimal economical enthalpy difference (Minimal startup enthalpy difference) is confirmed to quantitatively study strategies for rational and economical operation of the units. Besides, contrastive studies are made in energy saving property (quantity and rate of energy saving, and energy efficiency ratio) and economy (annual economic return and capital investment recovery period).In a word, allround studies and analyse are made in this thesis from macroscopic analysis to microcosmic reduction, from theoretical investigation to practical application, offering references to research, development and application of the exhaust air cold energy recovery units.