A control-oriented semi-physical model for a direct expansion air conditioning system

Abstract

It is always a challenge to develop appropriate mathematical model for a direct expansion (DX) air conditioning (A/C) system, whose operational parameters are highly coupled and behave non-linearly. Different modeling approaches have their own merits. However, none of the currently available modeling approaches can solely satisfy the requirement, in terms of accuracy and sensitivity, for simultaneous control of air temperature and humidity using a DX A/C system, without any inadequacies. On the other hand, when developing a model for the purpose of controller development rather than investigating complete system characteristics, the focus would be on several key components, and the modeling for other components that are relatively less important may be simplified. Therefore, it is possible to utilize different modeling approaches for different physical processes to develop a novel control-oriented hybrid model, named as semi-physical model (SPM). In this paper, rationales for using different modeling approaches for different physical processes of a DX A/C system are firstly discussed, followed by the development and validation of the SPM. The development of a SPM-based controller for the simultaneous control of air temperature and humidity is also briefly introduced, and its control perform acts as additional evidence for validating the SPM.

Practical application: This paper presents a hybrid modeling method, which combines the complementary merits of various modeling approaches and avoid the inadequacies of them based on the analysis of the requirement of controller development. Such a new control-oriented hybrid modeling method can be applied to not only simultaneous temperature and humidity control using a variable-speed DX A/C system but also other control applications where control loops are coupled and system operational characteristics are complicated.

Keywords

Air conditioning direct expansion control oriented empirical modeling variable speed humidity control

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References

Toftum

Fanger

. Air humidity requirements for human comfort. ASHRAE Trans 1999; 105: 641–647.

Arens

Baughman

. Indoor humidity and human health: part II-buildings and their systems. ASHRAE Trans 1996; 102: 212–221.

Deng

Chan

. A new control algorithm for direct expansion air conditioning systems for improved indoor humidity control and energy efficiency. Energy Convers Manage 2008; 49: 578–586.

Kays

London

. Compact heat exchangers, 3rd ed. New York: McGraw Hill, 1984.

Gruhle

Isermann

. Modeling and control of a refrigerant evaporator. J Dyn Syst Meas Control 1985; 107: 235–240.

Wijeysundera

Mithraratne

. An experimental and numerical study of the dynamic behavior of a counter-flow evaporator. Int J Refrig 2001; 24: 554–565.

Wang

Cai

Soh

. A simplified modeling of cooling coils for control and optimization of HVAC systems. Energy Convers Manage 2004; 45: 2915–2930.

Martins-Costa

Parise

JAR

. Three zone simulation model for air-cooled condensers. Heat Recov Syst CHP 1993; 13: 97–113.

Ding

Cai

Jia

. A hybrid condenser model for real-time applications in performance monitoring, control and optimization. Energy Convers Manage 2009; 50: 1513–1521.

10.

Winandy

Saavedra

Lebrun

. Experimental analysis and simplified modeling of a hermetic scroll refrigeration compressor. Appl Therm Eng 2002; 22: 107–120.

11.

Wong

Ooi

. Adiabatic capillary tube expansion device: a comparison of the homogeneous flow and the separated flow models. Appl Therm Eng 1996; 16: 625–634.

12.

Zhang

Ding

. Approximate analytic solutions of adiabatic capillary tube. Int J Refrig 2004; 27: 17–24.

13.

Deng

. A DDC-based capacity controller of a direct expansion (DX) air conditioning (A/C) unit for simultaneous indoor air temperature and humidity control – part I: control algorithms and preliminary controllability tests. Int J Refrig 2007; 30: 113–123.

14.

Cecchini

Marchal

. A simulation model of refrigerating and air-conditioning equipment based on experimental data. ASHRAE Trans 1991; 97: 388–393.

15.

Chen

Deng

. Development of a dynamic model for a DX VAV air conditioning system. Energy Convers Manage 2006; 47: 2900–2924.

16.

Fisher

Rice

. The Oak Ridge heat pump models: I. A steady-state computer design model for air-to-air heat pumps. ORNL/CON-80/R1, Oak Ridge, TN: Energy Division, Oak Ridge National Lab, 1983.

17.

Mullen

Bridges

Porter

. Development and validation of a room air-conditioning simulation model. ASHRAE Trans 1998; 104: 389–397.

18.

Theerakulpisut

Priprem

. Modeling cooling coils. Int Commun Heat Mass Transfer 1998; 25: 127–137.

19.

Xia

Chan

Deng

. Dehumidification effects in the superheated region (SPR) of a direct expansion (DX) air cooling coil. Energy Convers Manage 2009; 50: 3063–3070.

20.

Ertunc

Hosoz

. Artificial neural network analysis of a refrigeration system with an evaporative condenser. Appl Therm Eng 2006; 26: 627–635.

21.

Navarro-Esbrı´

Berbegall

Verdu

. A low data requirement model of a variable-speed vapour compression refrigeration system based on neural networks. Int J Refrig 2007; 30: 1452–1459.

22.

Joeng

Yoon

. An empirical model for independent control of variable speed refrigeration system. Appl Therm Eng 2008; 28: 1918–1924.

23.

Xia

Deng

. Steady-state operating performance modeling and prediction for a direct expansion air conditioning system using artificial neural network. Build Serv Eng Res Technol 2012; 33: 281–292.

24.

Swider

. A comparison of empirically based steady state models for vapour-compression liquid chillers. Appl Therm Eng 2003; 23: 539–556.

25.

Xia

Chan

. Inherent correlation between the total output cooling capacity and equipment sensible heat ratio of a direct expansion air conditioning system under variable-speed operation. Appl Therm Eng 2010; 30: 1601–1607.

26.

Chen W. Modeling and control of a direct expansion (DX) variable-air-volume (VAV) air conditioning (A/C) system. PhD Thesis, The Hong Kong Polytechnic University, 2005.

27.

Leung

Chan

. Condensate retention on a louver-fin-and-tube air cooling coil. Int J Refrig 2007; 30: 409–417.

28.

Xia

Chan

. A modified McQuiston model for evaluating efficiency of wet fin considering effect of condensate film moving on fin surface. Energy Convers Manage 2008; 49: 2403–2408.

29.

McQuiston

. Fin efficiency with combined heat and mass transfer. ASHRAE Trans 1975; 81: 350–355.

30.

Schmidt TE. La production calorifique des surfaces munies d’ailettes. Bulletin De L’Institu international du Froid Annexe G-5, 1945.

31.

MÜller-Steinhagen

Heck

. A simple friction pressure drop correlation for two-phase flow in pipes. Chem Eng Process 1986; 20: 297–308.

32.

Deng

Han

. A novel hybrid steady-state model based controller for simultaneous indoor air temperature and humidity control. Energy Build 2014; 68: 593–602.