Research On Energy Efficiency Standards For Heat Pump Water Heater And CO₂Transcritical Water-water Heat Pump

On the background of energy saving and emission reduction, the research onenergy-efficiency standards for heat pump water heater and CO₂transcriticalwater-water heat pump cycle were carried out in this dissertation.Thermodynamic perfectibility was theoretically analyzed in this dissertation.Thermodynamic perfectibility is the Second Law Efficiency of Thermodynamics andit reflects the departure degree between the practical efficiency of refrigeration andheat pump products and the ideal efficiency. The significance of thermodynamicperfectibility is that it can evaluate not only the energy-efficiency of the same type ofthe refrigeration and heat pump products in variable condition but also theenergy-efficiency of the different types of the refrigeration and heat pumpproducts.The status of energy efficiency of heat hump water heaters in Chinesemarket was surveyed，and the statistical results showed that the lowest COPhof thecommon air-source heat pump water heater and water-source heat pump water heaterare2.93and3.55,respectively. On the basis of the statistical data and the theoreticalanalysis of thermodynamic perfectibility, the suggested values of energy efficiencygrades standard on heat pump water heater were put forward. For example, thesuggested COPhvalues of the common air-source heat pump water heater from3grade to1grade respectively are3.7,4.0and4.3.The annual coefficient ofperformance （ACOP） was brought forward as the evaluation index of economicoperation for air-source heat pump water heater，and the caculation method wasintruoduced.Based on the old test table, a CO₂water-water heat pump system using a betterdouble pipe gas cooler and flooded evaporator was established. The visualizationexperiment on the gas cooler was done on this system. By visual observation on theflow state of the postmedian experimental section B and rear experimental section Cof the gas cooler, the flow states of experimental sections B and C experiencedsuccessively five states: transparent,dark white,bright white,darkwhite,transparent,while the working high pressure increases gradually and the coolingwater inlet temperature keeps constant. In the cooling water temperature15℃～24℃,the reduced pressure of the experimental section B in the dark white,bright white,dark white states is0.94～1.02, and these states are under two phase region near criticalarea or critical area.The experimental results and the visual observation on theexperimental sections B showed that the heat transfer rate between experimentalsections B and C reached the maximum under the optimum high pressure.A newly developed CO₂flooded evaporator was introduced in this dissertation.The tube bundle of the flooded evaporator adopted smooth tubes or enhanced tubes.The comparison test on the flooded evaporator using smooth tubes or enhanced tubeswas carried out in this dissertation. The experimental results showed that the localboiling heat transfer coefficient of the smooth tube arrays increased with the increaseof the vertical height of tube arrays at the same heat flux. Whereas the local boilingheat transfer coefficient of the enhanced tube arrays increased with the decrease of thevertical height of tube arrays. In according to the experimental data, the local boilingheat transfer correlation equation of the enhanced tube arrays was deduced, and thepredicted data agreeed with the experimental data within about±15%.The boiling heat transfer of the flooded evaporator using smooth tube bundle wasobserved by the high speed photography. The visualization results showed that thetotal progress of growth, departure, rise and break of CO₂bubble lasts about172ms;the rise speed of bubble is0.3m/s～0.45m/s and the bubble departure diameter is0.4mm～0.8mm.