Comfortable And High-efficient Heat Hump With Water-Sorbing Heat Exchanger By Temperature And Humidity Loosely-coupled Control

With the development of economy and the growth of disposable income of residents,HVAC systems have become a guarantee of better life.However,air conditioning will consume much electricity which are mostly produced from coal and oil.As a result,it dumps too much greenhouse gases(eg.C02)and solid particle pollutants(eg.PM2.5)into atmospheric environment,leading to climate change and serious haze.In this case,it is very urgent to achieve a considerable energy conservation for air conditioning industry.This is much important in the South China,where the summer is hot and humid and the winter is cold and wet.The key point is the lack of humidity control ability of the standard air conditioner.To solve these problems,a novel approach is proposed and investigated,which combines the benefits of desiccant dehumidification and vapor compression refrigeration.The key component is the so-called water-sorbing heat exchanger,produced by coating solid desiccants onto the surfaces of the coils of the traditional heat pump.In cooling/dehumidification mode,the desiccant film will treat the latent load and the refrigerant will take away the sensible load and the heat of adsorption.In this way,the desiccant will keep nearly isothermal that benefits the water uptake capacities of desiccant.So,it is expected that the outlet air of water-sorbing heat exchanger can directly meet the requirements of comfortable supply air with no need of reheating.Meanwhile,the desiccant can be regenerated by the heat of condensation of refrigerant when the evaporator/adsorber turns into a condenser/desorber.Looking at it from the other point of view,the water-adsorbed evaporating can dramatically enhance the airside heat transfer of the condenser,which is helpful to lower condensing temperature.Compared to traditional heat pump,a new control strategy,called temperature and humidity loosely-coupled control,can be used for this desiccant-enhanced DX heat pump.It means the required supply dry bulb temperature can be firstly satisfied by adj usting evaporating temperature and then the supply humidity ratio can be handled by changing the duration of adsorption on a water-sorbing heat exchanger.In other words,temperature and humidity loosely-coupled control can independently control the outlet temperature and humidity ratio on one heat exchanger at the same time.Besides,if the ice point of the desiccant film is lower the outdoor air temperature,the heat exchanger will be free of frost.Obviously,this is a big advance and will give a huge convenience to design a HVAC system.The main study of this paper can be concluded as following:First,we made a concept design of the novel approach and investigated its feasibility and energy saving potentials.Then,much efforts have been made to clarify the adsorption dynamics of the open system.At the beginning,a solid-side diffusion model was developed using chemical potential difference as driving force and a general solution of apparent diffusivity wat obtained.Next an improved linear driving force model has been developed and verigied.Following,a mathematic model was constructed to simulate the thermal response of water-sorbing heat exchanger when it turned from condenser into evaporator And these theoretical results eventually indicate that its airside heat and mass transfer had a weakly-coupled relationship,totally different from original heat exchanger.Next,to validate reliability of above models,an experiment was designed to test its ability of handling temperature and humidity of water-sorbing heat exchanger.At last,a test porotype of desiccant-enhanced DX heat pump was built and its cooling and heating capacities and energy efficiencies under different conditions had been measured.