Thermodynamic Study And Application On A Desiccant Coated Heat Exchanger Based Heat Pump System

Traditional vapor compression(VC)air conditioning systems handle latent load by cooling down the air below its dew point to condense out the moisture,which leads to low coefficient of performance(COP)and more energy is consumed to reheat the cool air.In addition,indoor condition is either too humid or too cold,since indoor temperature and humidity can hardly be satisfied with only condensation dehumidification.Desiccant cooling system utilizing sorption effect of solid and liquid desiccant can handle the latent load well,though limited by its poor sensible capability.Temperature and humidity independent control system(THIC)has been proposed,which combined the advantages of heat pump and desiccant cooling system.A typical THIC system consists of sensible subsystem and latent subsystem.However,besides large scale and high expense,low efficiency and high regeneration temperature caused by adsorption heat make THIC systems cannot be widely adopted up to now.Recently,internal cooling dehumidifier has been proposed,in which a second fluid(air,water or refrigerant)eliminates adsorption heat.As a result,dehumidification can be enhanced while regeneration temperature can be reduced.In this paper,a novel desiccant coated heat exchanger based heat pump system(DCHP)is proposed to overcome the obstacles of existing dehumidification systems.By combining the superiority of heat pump and desiccant dehumidification,the novel system can overcome the negative effect of adsorption heat by internal cooling dehumidification,and regenerate the desiccant with waste condensation heat.In this case,higher system COP and better indoor thermal comfort can be achieved simultaneously.Novel air conditioning heat pump system can be established,which has promising future.The work of this paper can be divided into 5 main parts as shown in the following:Firstly,the thermodynamic characteristics of several traditional dehumidification systems are analyzed.Based on this,a novel DCHP system incorporating internal cooling dehumidification and condensation heat recycling is proposed.The novel system can improve system performance and indoor thermal comfort,in winter especially,providing heating and humidification simultaneously.In this case,the novel system can be designed as a standalone desiccant heat pump for residential use.Furthermore,the novel system is analyzed using Carnot method and modified enthalpy difference method.The advantages of adsorption dehumidification are demonstrated in the view of thermodynamics and heat and mass transfer,compared with traditional condensation dehumidification.Secondly,as the core component for the novel system,performance enhancement of desiccant coated heat exchanger is discussed from the point of desiccant materials.Two heat exchangers coated with traditional desiccant and novel composite desiccant are fabricated.Then an experimental rig is set up and comparison study is conducted.Based on the test rig,effect of several key system parameters is studied in terms of water source temperature and process air condition.Furthermore,cycle switch mode is discussed to strengthen system performance.The sufficient analysis of desiccant coated heat exchanger can be helpful for further design and study on the novel DCHP.Thirdly,an experimental setup based on the proposed DCHP is established and tested in a constant temperature and humidity chamber.Then under typical cooling and heating operation condition,system performance in terms of COP and thermal comfort is tested and studied respectively.Furthermore,possible methods of system performance enhancement are discussed.It can be found from the experimental results that the maximum system COP can be 6.9 under summer condition,and 6.1 under winter condition.Meanwhile,experimental results during the whole test conditions show effective dehumidification and humidification capability as well.Fourthly,application of DCHP for public facility use is experimentally studied.Considering the extraordinary capability of dehumidification,DCHP can operate as DOAS to handle latent load(DESICA).While coorperating with variable refrigerant flow air conditioning system(VRF),a novel THIC system(JDVS)is proposed,in which DESICA handle the latent load and VRF handles the sensiable load.The experiment rig is set up in an office room with constant occupancy and a whole year field test is conducted.In addition,another conventional system(JHVS)consisting of heat recovery ventilator(HRV)and VRF is also set up in the same room as comparison.System performance of two systems in terms of COP and indoor thermal comfort is compared and analyzed.Finally,the energy calculation model of DESICA is embed into the dynamic building energy simulation software-EnergyPlus.With the existing calculation module of VRF,the novel JDVS is established and validated with experimental results.In the end,JDVS,JHVS and another VRF standlone system with dedicated fresh air(VRFSA)are established in EnergyPlus and comparison study through whole year is conducted under Shanghai weather condition.The simulation results show that novel JDVS system consumes 5% more energy than VRFSA,but 85% of its indoor condition locate in the thermal comfort zone,while that of VRFSA is only 32%.Meanwhile,as mostly widely adopted system,JHVS consumes 20% more energy than JDVS,and only 35% of its indoor condition locate in the thermal comfort zone.