Thermal plume simulation of VRF air conditioners for cooling system in high-rise buildings: a case study in China

  • Yin Zhang Sichuan University
  • Xiao Zhang HUAWEI Technologies Limited Company
  • Shurui Guo Sichuan University
  • Enshen Long Sichuan University
Keywords: air conditioning, outdoor air, temperature variation, thermal plume, simulation

Abstract

Variable refrigerant flow (VRF) air conditioning system is widely used in commercial and residential buildings for space cooling and heating, due to its great energy saving potential, low greenhouse gas emissions, high flexibility and reliability. However, the thermal performance of VRF system highly depends on its working conditions and environment. In real applications, some VRF systems used in high-rise buildings cannot work efficiently or even stop working because of the relatively high ambient air temperature, caused by the thermal plume effect of exhaust heat from outdoor units. In this paper, the thermal plume air flow of the layer-based VRF systems is investigated through computational fluids dynamics (CFD) simulation. Moreover, an illustrative example of practical VRF system in a 30-storey office building in China is conducted and analyzed to optimize the layout of the outdoor units. Preliminary results show that the exhaust heat of outdoor units can cause ascending thermal plume flow, leading to higher inlet temperatures for VRF air conditioners on upper floors, even exceeding the warning upper threshold value. It also indicates that enlarging the distance between outdoor units on different floors is an effective way to impair the thermal plume effect for VRF outdoor units and improve the thermal performance of the whole system. For the studied case, a modified layout of VRF outdoor units is presented with floor interval and the average inlet temperatures can be decreased substantially by 22%. This work can offer guidance the optimization layout design of practical VRF air conditioning systems used in high-rise buildings.

References

Aloraier, A., Al-Fadhalah, K., Paradowska, A.M. & Alfaraj, E. 2014. Effect of welding polarity on bead geometry, microstructure, microhardness, and residual stresses of 1020 steel. Journal of Engineering Research 2 (4): 137-160.

Aynur, T.N., Hwang, Y. & Radermacher, R. 2008. Experimental evaluation of the ventilation effect on the performance of a VRV system in cooling mode—Part I: experimental evaluation. HVAC&R Research 14: 615–630.

Choyu, W., Ei-ichiro, O., Masafumi, H., Katsuaki, N. & Hiroshi, N. 2009. Evaluation of annual performance of multi-type air-conditioners for buildings. Journal of Thermal Science and Technology 4: 483-493.

Gan, G.H. & Riffat, S.B. 2004. CFD modelling of air flow and thermal performance of an atrium integrated with photovoltaics. Building and Environment 39 (7): 735-748.

Hasan, A. 2009. Kurnitski J. and Jokiranta K., A combined low temperature water heating system consisting of radiators and floor heating. Energy and Buildings 41: 470-479.

International Energy Agency. 2006. Key World Energy Statistics.

Li, Y.M., Wu, J.Y. & Shiochi, S. 2009. Modeling and energy simulation of the variable refrigerant flow air conditioning system with water-cooled condenser undercooling conditions. Energy and Buildings 41: 949–957.

Li, Y.M., Wu, J.Y. & Shiochi, S. 2010. Experimental validation of the simulation module of the water-cooled variable refrigerant flow system under cooling operation. Applied Energy 87: 1513–1521.

Lin, X., Lee, H., Hwang, Y. & Radermacher, R. 2015. A review of recent development invariable refrigerant flow systems. Science & Technology of Built Environment 21: 917-933.

Liu, J.Y., Hu, Y.P., Chen, H.X., Wang, J.Y., Li, G.N. & Hu, W.J. 2004. A refrigerant charge fault detection method for variable refrigerant flow (VRF) air-conditioning systems. Applied Thermal Engineering 107: 284-293.

Luis, P.E., Jose, O. & Christine, P. 2008. A review on buildings energy consumption information. Energy and Buildings 40 (3): 394-398.

Johansson, P. & Davidson, L. 1995. Modified collocated SIMPLEC algorithm applied to buoyancy-affected turbulent-flow using a multigrid solution procedure. Numerical Heat Transfer Part B-Fundamentals 28 (1): 39-57.

Karmare, S.V. & Tikekar, A.N. 2010. Analysis of fluid flow and heat transfer in a rib grit roughened surface solar air heater using CFD. Solar Energy 84 (3): 409-417.

Ozbek, A. 2016. Energy and exergy analysis of a ceiling-type air conditioning system operating with different refrigerants. Journal of Engineering Research 4 (3): 144-162.

Shu, C.W. 2003. High-order finite difference and finite volume WENO schemes and discontinuous galerkin methods for CFD. International Journal of Computational Fluid Dynamics 17 (2): 107-118.

Shwehdi, M.H., Rajamohamed, S., Smadi, A.A., Bouzguenda, M., Alnaim, A.A. & Fortea, S. 2015. Energy savings approaches of buildings in hot-arid region, Saudi Arabia: case study. Journal of Engineering Research 3 (1): 127-136.

Tu, Q., Dong, K., Zou, D. & Lin Y. 2011. Experimental study on multi-split air conditioner with digital scroll compressor. Applied Thermal Engineering 31: 2449–2457.

Yamada, T. 1982. A numerical-model study of turbulent air-flow in and above a forest canopy. Journal of the Meteorological Society of Japan 60 (1): 439-454.

Yasushi, N., Masaru, I., Shinji, N. & Tomoyuki, H. 2009. Effects of wall clearance of a vertical channel on natural air cooling capability. Journal of Thermal Science and Technology 4 (3): 372-381.

Yun, G.Y., Lee, J.H. & Kim H.J. 2016. Development and application of the load responsive control of the evaporating temperature in a VRF system for cooling energy savings. Energy and Buildings 116: 638-645.

Zhai, Z.Q., Xue, Y. & Chen, Q.Y. 2014. Inverse design methods for indoor ventilation systems using CFD-based multi-objective genetic algorithm. Building Simulation 7 (6): 661-669.

Zhang, Y., Kacira, M. & An, L.L. 2016. A CFD study on improving air flow uniformity in indoor plant factory system. Biosystems Engineering 147: 193-205.

Zhang, Y., Wang X., Zhang, Y.P. & Zhuo, S.W. 2016. A simplified model to study the location impact of latent thermal energy storage in building cooling heating and power system. Energy 114: 885-894.

Zhang, Y., Zhang, Y.P., Wang X. & Chen, Q. 2013. Ideal thermal conductivity of a passive building wall: determination method and understanding. Applied Energy 113: 967-974.

Zhao, B., Li, X.T. & Yan, Q.S. 2003. A simplified system for indoor airflow simulation. Building and Environment 38 (4): 543-554.

Zsebik, A. & Sitkujr, G. 2001. Heat exchanger connection in substations - a tool of decreasing return temperature in district heat networks. Energy Engineering 98 (5): 20-31.

Published
2019-08-07
Section
Civil Engineering