A generalized coefficient of performance for conditioning moist air Ehab M. Mina * , Ty A. Newell, Anthony M. Jacobi Department of Mechanical and Industrial Engineering, University of Illinois, 1206 W. Green St., Urbana, IL 61801, USA Received 2 April 2004; received in revised form 19 July 2004; accepted 23 September 2004 Available online 17 March 2005 Abstract The psychrometric chart is a useful tool for calculating the energy change between any two states and visually identifying the contribution of ‘sensible’ and ‘latent’ effects. However, the amount of work needed to move from one state to another is not read directly from the chart. In this paper, temperature and vapor pressure changes are cast into terms of minimum work relative to a dead state, and work contours are plotted on the psychrometric chart. These contours show the minimum work needed to move the state of the air further from the ambient conditions or the maximum work produced by letting a state approach the ambient conditions. A dividing line between heat pump and refrigeration operation is set on the basis total energy of the conditioned space relative to the ambient. Finally, an example is used to illustrate the implementation of the analysis. q 2005 Elsevier Ltd and IIR. All rights reserved. Keywords: Air conditioning; Humid air; Process; Calculation; Performance; COP Coefficient de performance global dans le conditionnement d’air humide Mots cle ´s : Conditionnement d’air ; Air humide ; Proce ´de ´ ; Calcul ; Performance ; COP 1. Introduction In air-conditioning systems, the general goal is to effect a change of state of air from one condition to another—one that is more desirable. The work of Carrier [1] provides the foundation for a simplified understanding of energy changes that accompany changes of state for moist air. Of course, understanding work and heat transfer interactions is essential to understanding the energy changes in air- conditioning processes. For the simple cases of sensible heating or cooling of air, the ‘coefficient of performance’ (COP) may be useful for characterizing these interactions. In particular, if the limiting case of reversible system performance is considered, the Carnot efficiency provides the ideal COPs for heat pump and air conditioning systems operating between constant-temperature thermal reservoirs and causing sensible changes in the state of air (Stoecker [2]). Although the psychrometric chart allows easy visualization of the combined sensible and latent heat processes, the minimum effort (work) required to achieve the desired change of state is not represented. In order to determine the minimum effort required to change the state of air, second-law considerations must be used. International Journal of Refrigeration 28 (2005) 784–790 www.elsevier.com/locate/ijrefrig 0140-7007/$35.00 q 2005 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2004.09.015 * Corresponding author. Tel.: C1 217 244 8830. E-mail address: ehabmina@uiuc.edu (E.M. Mina).