Optimisation of Direct Expansion (DX) Cooling Coils Aiming to Building Energy Efficiency

Liang Xia^1*, Tong Yang¹, Yue Chan², Llewellyn Tang¹, Yung-Tsang Chen³

¹Department of Architecture and Built Environment, University of Nottingham Ningbo China, Ningbo, China.
²School of Mathematical Sciences, University of Nottingham Ningbo China, Ningbo, China.
³Department of Civil Engineering, University of Nottingham Ningbo China, Ningbo, China.

DOI: 10.4236/jbcpr.2015.32006                

Abstract

Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number of a direct expansion (DX) cooling coil for minimizing the entropy generation in the DX cooling which functioned as evaporator in the A/C system was developed. The optimal tube row numbers were determined based on the entropy generation minimization (EGM) approach. Parametric studies were conducted to demonstrate the application of the analytical calculation method. Optimal tube row number for different air mass flow rates, inlet air temperatures and sensible cooling loads were investigated. It was found that the optimal tube row number of a DX cooling coil was in the range of 5 - 9 under normal operating conditions. The optimal tube row number was less when the mass flow rate and inlet air temperature were increased. The tube row number increased when the sensible cooling load was increased. The exergy loss when using a non-optimal and optimal tube row numbers was compared to show the advantage of using the optimal tube row number. The decrease of exery loss ranged from around 24% to 70%. Therefore the new analytical method developed in this paper offers a good practice guide for the design of DX cooling coils for energy conservation.

Keywords

Optimal Tube Row Number, Entropy Generation Minimization, Direct Expansion (DX) Cooling Coil, Building Energy Efficiency

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Bejan, A. (1996) Entropy Generation Minimization: The Method of Thermodynamic Optimization of Finite-Size Systems and Finite-Time Processes. CRC Press, Boca Raton.
[2]	Bejan, A. (1982) Entropy Generation through Heat and Fluid Flow. Wiley, New York.
[3]	Bejan, A. (2001) Thermodynamic Optimization of Geometry in Engineering Flow Systems. Exergy: An International Journal, 1, 269-277. http://dx.doi.org/10.1016/S1164-0235(01)00028-0
[4]	Vargas, J.V.C. and Bejan, A. (2001) Thermodynamic Optimization of Finned Crossflow Heat Exchangers for Aircraft Environmental Control Systems. International Journal of Heat and Fluid Flow, 22, 657-665. http://dx.doi.org/10.1016/S0142-727X(01)00129-1
[5]	Ogulata, R.T. and Doba, F. (1998) Experiments and Entropy Generation Minimization Analysis of a Cross-Flow Heat Exchanger. International Journal of Heat and Mass Transfer, 41, 373-381. http://dx.doi.org/10.1016/S0017-9310(97)00129-4
[6]	Lerou, P.P.P.M., Veenstra, T.T., Burger, J.F., Brake, H.J.M. and Rogalla, H. (2005) Optimization of Counterflow Heat Exchanger Geometry through Minimization of Entropy Generation. Cryogenics, 45, 659-669. http://dx.doi.org/10.1016/j.cryogenics.2005.08.002
[7]	Sahiti, N., Krasniqi, F., Fejzullahu, X.H., Bunjaku, J. and Muriqi, A. (2008) Entropy Generation Minimization of a Double-Pipe Pin Fin Heat Exchanger. Applied Thermal Engineering, 28, 2337-2344. http://dx.doi.org/10.1016/j.applthermaleng.2008.01.026
[8]	Naphon, P. (2006) Second Law Analysis on the Heat Transfer of the Horizontal Concentric Tube Heat Exchanger. International Journal of Heat and Mass Transfer, 33, 1029-1041. http://dx.doi.org/10.1016/j.icheatmasstransfer.2006.05.001
[9]	Reyes, E.T., Nunez, M.P. and Cervantes, J. (1998) Exergy Analysis and Optimization of a Solar Assisted Heat Pump. Energy, 23, 337-344. http://dx.doi.org/10.1016/S0360-5442(97)00079-0
[10]	Culham, J.R. and Muzychka, Y.S. (2001) Optimization of Plate Fin Heat Sinks Using Entropy Generation Minimization. IEEE Transactions on Components and Packaging Technology, 24, 159-165. http://dx.doi.org/10.1109/6144.926378
[11]	Saechan, P. and Wongwises, S. (2008) Optimal Configuration of Cross Flow Plate Finned Tube Condenser Based on the Second Law of Thermodynamics. International Journal of Thermal Sciences, 47, 1473-1481. http://dx.doi.org/10.1016/j.ijthermalsci.2007.12.009
[12]	Zumbair, S.M., Kadaba, P.V. and Evans, R.B. (1987) Second-Law-Based Thermoeconomic Optimization of Two- Phase Heat Exchangers. ASME Journal of Heat Transfer, 109, 185-195.
[13]	Incropera, F.P. and Dewitt, D.P. (1990) Fundamentals of Heat and Mass Transfer. 3rd Edition, Wiley, New York.
[14]	Pirompugd, W., Wang, C.C. and Wongwises, S. (2007) Finite Circular Fin Method for Heat and Mass Transfer Characteristics for Plain Fin-and-Tube Heat Exchangers under Fully and Partially Wet Conditions. International Journal of Heat and Mass Transfer, 50, 552-565. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2006.07.017
[15]	Shah, M.M. (1979) A General Correlation for Heat Transfer during Film Condensation inside Pipes. International Journal of Heat and Mass Transfer, 22, 547-556. http://dx.doi.org/10.1016/0017-9310(79)90058-9
[16]	Dittus, F.W. and Boelter, L.M.K. (1930) Heat Transfer in Automobile Radiators of the Tubular Type. Publications in Engineering, University of California, Berkeley, Vol. 2, 443.
[17]	Wang, C.C., Chi, K.Y. and Chang, C.J. (2000) Heat Transfer and Friction Characteristics Plain Fin and Tube Heat Exchangers. Part II: Correlation, International Journal of Heat and Mass Transfer, 43, 2693-2700. http://dx.doi.org/10.1016/S0017-9310(99)00333-6
[18]	Marathe, A.B. (2002) Selecting Cooling Coils without Proprietary Software. Air Conditioning and Refrigeration Journal.
[19]	Turaga, M., Lin, S. and Fazio, P.P. (1988) Performance of Direct Expansion Plate Finned Tube Coils for Air Cooling and Dehumidification. International Journal of Refrigeration, 11, 1-9. http://dx.doi.org/10.1016/0140-7007(88)90117-X