Document NEz27Zq2VRgp8DZ1JOmL9Q0bp

674' CHAPTER 38 . '1946'Guide 1. Stop---Start--Where the humidistat starts the dehumidifier on rising humidity and stops it on failing humidity. -- 2. By-pass--Where the humidistat modulates face and by-pass dampers located at' the wet air inlet of the dehumidifier. Thus the quantity of air passing through the dehumidifier is proportioned in accordance with the change in latent heat Toad. , .3. . Vapor Pressure Control (used with liquid absorbents)--Where the humidistat directly controls the temperature or concentration of the contacting solution, thereby matching the heat or moisture removal to the load requirement. ,Dehumidijication by Sorbent Materials 675 power required to drive air through the bed. It must also be borne in mind that the moisture 'removal efficiency of all solid adsorbents and absorbent solutions is related to the temperature of the medium as well as to its state of unsaturation. On the other hand, it will be noted that the lower limits of dehumidification, which can be obtained with absorbent solutions, are likely to be controlled by the equilibrium dew-point at the lowest temperature at which the solution will resist freezing or crystalli zation. For this reason, actual moisture removing capacity is determined from performance curves of the several materials under practical con- Fig. 7. Performance Data For Rotating Bed Direct Gas Fired Silica Gel Dehumidifier EQUIPMENT PERFORMANCE It is recognized that, whereas the curves relating temperature and vapor pressure of the several dehumidifying agents (Figs.' 1, 2 and 3) accurately define the equilibrium limits for these materials, these curves r cannot be used for predicting performance of available equipment. This occurs because (a) the materials themselves can only be utilized efficiently., within! certain ranges of moisture concentration, and (6)' the degree to which the vapor pressure of the air being treated approaches that at the surface of the material depends upon the completeness of the contact. It is obvious, for example, that the thickness of-a bed of solid adsorbent for a given, air flow will have a profound effect upon the degree' of moisture removal attained: However, it will have' an inverse effect upon the Fig. 8- Silica Gel Dehumidifier Performance Data Steam Activation Type ditions of temperature, concentration and contacting efficiency as shown in Figs. 7, 8, 9 and 10. While these curves by no means explore all the performance possibilities, they may be considered to be representative of sound design and application practice. -- Performance data for standard production designs of silica gel rotating bed dehumidifiers are shown in Fig. 7 for a direct gas fired type, and in Fig. 8 for steam activation types for steam pressures of 5 to 80 lb per square .inch. They are designed for normal comfort cooling and moderatehumidity industrial air conditioning applications. Performance data for a heavy duty type activated alumina dehumidifier are given in Fig. 9. . This. unit has extended surface coils, imbedded in the adsorber, which are supplied with high pressure steam for heating during activation and cool water for. direct bed cooling during adsorption. Capacities shown,in.