Simulation Study On Performance Of Multi-split Air Conditioning (Heat Pump) System

In recent years,energy consumed by air-conditioning in buildings in China have been rising.Different from the traditional air-conditioning system,multi-split VRF system requires less equipment and its layout is flexible,able to achieve the goal of ‘part of the time,part of the space’.It has been widely used in office buildings,hospital buildings and senior residential buildings.Multi-split VRF system under the design operation conditions can achieve set performance requirements.However,when the external conditions change,it is worth studying how its corresponding performance will change.As to this problem,this presented work has been conducted as followings: Firstly,the calculation method of thermal type in simulation is compared and analyzed.Then,the performance of the components(compressor,electronic expansion valve,condenser and evaporator)in the system is analyzed.In the end,the performance of whole system is analyzed.Main conclusions of this paper are as below:(a)in addition to consideration of accuracy,computing speed and stability of the refrigerant thermo-physical model,the reversibility of calculation must be included.Using the state equation,the calculation speed in the general case will be not compromised too much;(b)When the10-coefficient model is adopted in the compressor,the calculation speed and precision can be guaranteed;(c)In the two modeling methods of heat exchanger model,the parameters of the lumped parameter model are less than those of the distributed parameter model;(d)The performance of the air-cooled heat exchanger in the system is affected by a number of factors: the structure of the heat exchanger,the head wind speed outside the heat transfer tube,the wet air inlet parameters,the refrigerant inlet parameters and the refrigerant flow.These factors have different degrees of influence on heat transfer;(e)The overall system of the system is not only affected by the above factors,but also by the flow cross-sectional area of electronic expansion and the compressor speed.Simply adjusting the electronic expansion valve of an indoor unit will affect the performance of other indoor units,so the control algorithm must be combined to adjust the compressor speed to achieve good control effect.