1、 VOLUME 14, NUMBER 6 HVAC specifically: themathematical procedures (as finding the maximum of a function)Merriam-Websteronline dictionary HVAC however, theweak definition still exists. The use of optimization with its rigorous meaning ensures that theresults are indeed optimum results. The larger th
2、e design space gets, the more important system-atic optimization becomes. Trial and error techniques, while helpful, will quickly become muchless productive as the number of alternative designs increase.An example of the limitation of the trial and error technique is heat exchanger optimization.Seve
3、ral heat exchanger designs can be used to serve the same load under the same geometricalconstraints. However, each design would have different hydraulic performance, volume, andcost. Thus, a simple optimization problem can be formulated to choose the best design. If thedesign space, for example, inc
4、ludes 2 off-the-shelf tube diameters, a range of acceptable tubelengthsrepresented by 20 discrete lengths, 5 tube rows, 10 vertical and horizontal tube spac-ings, 10 fin spacings, 5 fin patterns, and 10 tube circuitries, then the number of possible heatexchanger designs becomes 106designs. A trial-a
5、nd-error procedure will not be able to coverthe entire design space and would generally provide a design that was not optimum, as designerswill try to limit the design space and search between alternatives using their intuition and expe-rience. On the other hand, a systematic optimization technique
6、can search the entire designspace, yielding either a local or a global optimum design based on the algorithm being used.To find the global optimum for the above-mentioned heat exchanger problem, exhaustivesearch can be used as an alternative method to the trial-and-error procedure. In the exhaustive
7、search, all 106heat exchangers designs need to be evaluated and checked for constraint viola-tions. This method is generally acceptable for a small design space. But even in this simple opti-Reinhard Radermacher is a professor and Omar Abdelaziz is a graduate research assistant in the Department ofM
8、echanical Engineering at the University of Maryland, College Park. 818 HVAC accepted July 14, 2008A thermally driven air conditioner that uses liquid desiccants as the working fluid may be anattractive alternative to the compressor-based technology that is now used in most HVAC appli-cations. The op
9、eration of a liquid-desiccant air conditioner is first explained and several basicconcepts are reviewed. This review focuses on the development of liquid-desiccant condition-ers and regenerators that are better suited to comfort conditioning (as opposed to industrialdehumidification). This includes
10、work on conditioners and regenerators that use low flow ratesof desiccants and have internal heat exchange. These conditioners and regenerators will havelower pump and fan power than packed-bed units, and will be much less likely to introduce des-iccant droplets into the process air. Work to identif
11、y and develop regenerators that have COPsover 1.0 and research on alternative liquid desiccants is also reviewed.INTRODUCTIONIn the 20thcentury, the HVAC industry brought air conditioning out of the lab and into mil-lions of homes and commercial buildings. What was once a luxury is now a necessity i
12、n manycountries. However, this success now presents the industry with new challenges. If the air conditioner is to improve the quality of life for billions more people in a rapidlydeveloping world, we face many potential problems. The source of many of these problems isthe air conditioners heavy rel
13、iance on electricity. Tremendous amounts of fossil fuels are con-verted to carbon dioxide each year to produce the power needed by air conditioners. A rapidlygrowing demand for air conditioning could accelerate global climate change at a time when theworld is struggling to reduce it. Air and water p
14、ollution could also increase as more power plantsare built to meet the demand for electricity. Areas with limited water resources will find theseresources overtaxed by the need to cool the new power plants. The reliability of electric sys-tems could be compromised as air conditioning creates high pe
15、ak demands for power.Indoor air quality is another challenge to the HVAC industry, particularly in more humid cli-mates. Sick Building Syndrome is a problem that can be corrected through better ventilation.For many types of buildings, ASHRAEs standards have tripled the ventilation rates over thoseth
16、at were common following the energy crisis of the 1970s. However, in humid climates, theincreased ventilation can raise indoor humidity to levels that are both uncomfortable andunhealthy. The vapor-compression cycle is now the foundation of the HVAC industry and will remain sofor many years. The fol
17、lowing problems are being addressed through a number of approachesincluding: (1) more efficient designs for air conditioners, (2) more efficient buildings thatrequire less cooling, (3) the conversion of power generation from fossil fuels to sustainableresources, (4) the development of air conditione
18、rs that provide more dehumidification, or latentAndrew Lowenstein is president of AIL Research, Inc., Princeton, NJ.820 HVAC its electric demand is typically one-fourth that of avapor-compression air conditioner. The LDAC is exceptionally good at dehumidifying air; almost all of the cooling it provi
19、descan be latent cooling.The primary objectives of this article are to present a summary of current R liquid-desiccant technology must further reduce electricalloads if it is to become competitive in the HVAC market.Most industrial liquid-desiccant systems use packed-bed contact media, as described
20、above;some have also used conditioners and regenerators with internal heat exchange. For the condi-tioner, the contact surface between the desiccant and process air is a bank of water-cooled tubes.The desiccant is dripped or sprayed onto the tubes and the process air is drawn past them. For anindust
21、rial conditioner that uses a halide salt solution, the tubes would typically be a cop-per-nickel alloy to limit corrosion to acceptable levels. Although an internally cooled condi-tioner no longer relies on the thermal capacitance of the desiccant flow to limit the temperaturerise of the desiccant a
22、s absorption occurs, flooding rates are still comparable to those used in apacked-bed conditioner to ensure complete wetting of the tubes. Coil-type or tube-type condi-tioners are now rarely used in halide salt liquid-desiccant systems because of the very high costfor the corrosion resistant coils.P
23、AST R accepted July 31,2008Fundamental fluid dynamics equations and empirical data were used to develop a model capa-ble of estimating pressure drop for flow through a pleated filter. The model was developedthrough the systematic assessment of 20 different custom-manufactured filters utilizing vario
24、usconfigurations of the following design parameters: pleat height, pleat count, media thickness,permeability, and filter housing. A one-to-one correspondence was observed between themodels predictions and 600 pressure drop versus face velocity measurements. The model canbe used as a design tool to p
25、redict minimum initial pressure drop; maximum filtration area; andpreferred media properties with respect to permeability versus thickness, thus allowing the fil-ters useful life and operational energy cost to be improved. The article serves as the groundwork for a larger research effort to model pl
26、eated filters and banks of pleated filters as plat-forms for high-resistance materials such as adsorbent-entrapped media. INRODUCTIONOverview of the Research The demand for improved indoor air quality (IAQ) has created a need for gas phase filtrationunits capable of removing contaminants such as vol
27、atile organic compounds (VOCs), tobaccosmoke, carbon monoxide, and formaldehyde. Strategies to remove these harmful contaminantsinclude employing a packed-bed or an adsorbent-entrapped filtration media such as microfi-brous sorbent-supported media (MSSM). Through a wet-laid process, MSSMs sinter-loc
28、kedmatrix of micron-sized fibers can entrap sorbent particles with diameters as low as 30 microns,leading to better chemical removal efficiency and higher sorbent utilization than a traditionalpacked bed. The disadvantages of adsorbent-entrapped media are a high pressure drop createdby small, entrap
29、ped sorbent particles and a low saturation capacity due to the relatively thinthickness of the media (Harris et al. 2001). New tactics for building more efficient gas phase filters need to be researched in order tomaximize the usefulness of adsorbent-entrapped media. Pleated and V-bank filters are t
30、wodesigns that can improve both pressure drop performance and overall capacity for filtration unitsmade from these materials. By understanding the pressure drop limitations within these filtrationsystems, additional media and adsorbent material can be packaged into a unit to increase thecontaminant
31、removal capacity while maintaining an acceptable resistance. The following article, Part 1, discusses the creation and utilization of a model that can predictinitial flow resistance in a pleated filter with a depth of 89 mm (3.5 in.) or less. The second arti-cle, Part 2, will extend the model presen
32、ted below to include V-banks composed of multiplepleated filters. Ryan A. Sothen is a graduate research assistant in the Department of Chemical Engineering at Auburn University,Auburn, AL. Bruce J. Tatarchuk is a professor of chemical engineering at Auburn University and is the director for theCente
33、r of Microfibrous Materials Manufacturing Center, Auburn, AL.842 HVACChen et al. 1996). Rivers and Murphy concluded that the deviations in filtration media were theproduct of fiber compression due to the airs inertial force compressing the medias fiberstogether at higher operational velocities. The compression changes the internal void volume andPF KGVF2KMVM+=
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