Study on the Operating Characteristics of Water Loop Variable Refrigerant Flow Heat Pump Air Conditioning System
|School||Harbin Institute of Technology|
|Course||Heating,Gas Supply, Ventilation and Air Conditioning Engineering|
|Keywords||Water loop variable refrigerant flow heat pump air conditioning system loading center of VRF large building air source heat pump computersimulation|
Variable refrigerant flow air conditioning system (VRF) is recognized as largeamount of advantages. However, because of its own limitations, it is difficult to meetthe demands for high or large buildings in cold area. Water loop heat pump (WLHP) isan air conditioning system with heat recovery function. But it makes big noise andwastes energy quality. The defects of VRF and WLHP are analyzed here. To solve theproblems, water loop variable refrigerant flow heat pump air conditioning system(WLVRF) is proposed for the first time, which integrated advantages of both VRF andWLHP. The new system combines benefits of the two old systems and overcomes theirshortcomings. To optimize the energy structure, a few kinds of renewable energy isintroduced to WLVRF. Thus, application schemes of WLVRF with different renewableenergy are raised. Among these schemes, WLVRF with air source heat pump is the mostavailable. Therefore, air source WLVRF is studied in detail. To promote the new system,its operating property, energy efficiency, applicability, economy and methods of designand control are investigated.To study the operating property of WLVRF, mathematical modals of its mainequipments are established. Based on experimental data in reference，the accuracy ofthe modals are verified. The modal of air conditioning load for a building is also set upto couple with WLVRF system. The heating conditions of air source heat pump (ASHP)and water source variable refrigerant flow air conditioning system (WSVRF) inWLVRF are simulated based on the mathematical modals. When ASHP works in aWLVRF system, its outlet water temperature is much lower than when it works in atraditional ASHP system. So ASHP works more safely and efficiently in WLVRF. Themain parameters of ASHP in the low-temperature condition are calculated, andparametric curves are drawn. This provides a basic to the calculation of energyefficiency for the whole WLVRF system. The fact is proved that WLVRF offers a betterworking condition to ASHP than traditional ASHP system. The result lays a foundationfor the calculation of energy efficiency on WLVRF.The working conditions of WSVRF unit in WLVRF are simulated and comparedwith the working conditions of air source variable refrigerant flow air conditioningsystem (ASVRF) in winter. Seen from the result, VRF units in WLVRF are lesssensitive than ASVRF to outdoor climate. To elaborate the benefit on the deflation ofVRF units in WLVRF system, the concept of VRF loading center is proposed. Thevariation of heating capacity loading center and energy efficiency loading center withdifferent load distribution and loading rate is researched. A simple calculation method ofloading center with acceptable accuracy is given. The concept and calculation method of loading center can provide assistance in the design and economic analysis of VRFsystem. Loading center explains the scale of VRF well, and shows the profit of smallerscale for VRF unit in WLVRF system.Based on the research for the operating property of ASHP and WSVRF unit, theinfluencing factors to instantaneous energy efficiency of WLVRF in winter areinvestigated by coupling WLVRF system with the building. The influencing factors areincluding cooling load ratio, outdoor temperature and loop water temperature. It isanalyzed that how these factors influence the instantaneous energy efficiency ofWLVRF system. For a certain building, the cooling load ratio and outdoor temperaturecan never be controlled. Thus, the only way to improve the energy efficiency is to adjustwater temperature. That’s why the optimal water temperature is studied. With watertemperature maintaining the optimal value, the energy efficiency and primary energyratio for WLVRF of buildings with different inner area ratios in representative cities arecalculated. The results are given in a table. It can be regard as a standard to expect ifWLVRF is energy saving or not.To improve the characteristics and promote the use of WLVRF system, optimaldesign schemes and control methods are researched. Simulation results show that themeans to decide capacity of ASHP basing on the optimal economic balance point canreduce the initial investment; moreover, two position control method on watertemperature can slash energy consumption of the system. It stabilizes the workingcondition obviously but saves almost no energy by increasing the number of ASHP unitsand expanding diameter of water loop. So the first two methods should be selected tocreate a low energy consumption WLVRF system.Finally, the economy of WLVRF system is analyzed by establishing acomputational modal of the costs for WLVRF system. The optimal economic balancepoints of ASHP for WLVRF in cities are calculated. It can be used as a basis forengineering design. The economic comparison of WLVRF system with other commonair conditioning systems is carried out in different climate zone. The economiccomparison gives designers and users a visual impression on the economy of WLVRFsystem. It is helpful to promote the application of WLVRF system quickly and rationally.The ultimate goal is to make the WLVRF system with great advantages to contribute toHVAC career as early as possible.