| As the second largest energy-consuming components, usage of bus air conditioning would reduce its driving distance by 25% to 30%. Normally bus air conditioning is installed at the top of bus. In order to reduce driving resistance, height of bus air conditioning is required to be as small as possible. So how to optimize the design of Heat Pump Air Conditioning System(HPACS) for pure electrical bus within limited space, thus it could be lighter, more compact and efficient, this is the problem need to be solved.Performance enhancement of HPACS for 10 m pure electrical bus is researched through experiment and simulation. On the basis of height reduction of TFHEs,cooling(heating) capacity should optimize to 26 k W( 22 k W) of the new designed HPACS,while cooling(heating) should reach to 3.2(2.8). Firstly performance of the original HPACS applying φ7mm diameter Tube-Fin Heat Exchanger(TFHE) was tested and analyzed. On the basis of test results, φ5mm diameter tube was adopted to optimal design new TFHEs. Two phase refrigerant mal-distribution inside distributor and header was simulated using CFD, and performance of electrical bus HPACS under different air-supply schemes were simulated and compared. A steady-state simulation of bus air conditioning was developed and modified.Optimal distributor(header)、designed φ5mm diameter TFHEs and outside air supply scheme with fan mounted at top were applied gradually to the new HPACS. Simulation results showed performance of new HPACS got enhanced greatly but still couldn’t meet requirements of design goals. So a high efficiency R410 A scroll compressor was selected and applied, simulated results showed that cooling(heating) capacity reached to 26.477 k W(23.387 k W), while COP reached to 3.831(3.311). COP was calculated including power of compressor and fans. Main research conclusions are as follows:(1) Performance of electrical bus HPACS would be greatly affected by compressor speed and ambient temperature, optimal compressor speed of cooling and heating was 3300 rpm and 2400 rpm respectively. When ambient temperature decreased, cooling performance got better, while heating performance depended on frost severity of outdoor TFHE. Increasing of outside and inside air-supply would increase cooling performance a little bit, but had no help to heating performance improvement.(2) Fluent was used to optimize structure of distributor and header. Refrigerant mal-distribution of optimal distributor(header) reduced to 31.369%(29.003%) of the original distributor(header) respectively. And application of optimal distributor(header) would improve transferred heat of indoor(outdoor) TFHE by 2.347 %( 8.704%).(3) When air was sucked or blowed into the outdoor chamber, cooling performance of electrical bus HPACS was tested and compared. It was found that cooling capacity increased from 21.870 k W to 25.880 k W, COP increased from 2.630 to 3.110. This was mainly because that air blowing scheme could increase speed and turbulence of wind flowing through outdoor TFHE, so heat transfer of outdoor TFHE got enhanced, thus to improve cooling performance fatherly. And then different air-supply schemes were modeled and simulated, results showed that both scheme D3 and D4 would improve cooling performance greatly, while scheme D4 with fan mounted at top showed to be the best air supply scheme.(4) A steady-state simulation of bus air conditioning was developed and verified using Visual Basic. The verified program was then used to simulate new designed bus air conditioning system which have applied the designed φ5mm diameter TFHEs. Results showed that performance of new HPACS was worse than the original system, this was mainly because that height of new designed indoor TFHE reduced by 23.077%. Changing outdoor air-supply from air suction scheme to scheme with fan mounted at top, simulated results showed that cooling capacity and COP increased by 11.527% and 21.926%,while heating capacity and COP increased by 18.551% and 8.716% respectively.(5) On the basic of air supply scheme with fan mounted at top, applying selected high efficiency R410 a scroll compressor to the new electrical HPACS, simulated results showed that cooling(heating) capacity reached to 26.477 k W(23.387 k W) and increased by 11.968%(9.015%), while COP reached to 3.831(3.311) and increased by 12.170%(2.097%). Adding power of fans into system’s power, cooling(heating) COP was adjusted to 3.831(3.311). So optimation design goals of electrical bus HPACS were basically achieved. |
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