1、 HVAC Institutional, US $199). Subscription rates elsewhere, including air- mail postage, are US $195 (ASHRAE member, US $134; Institutional, US $21 9). School and college libraries are eligible to receive a discount from the list price. The online-only subscription rate is US $54. IP addressaccess
2、isalso available. For details, contact ASHRAE Customer Service, 1791 Tullie Circle, Atlanta, GA 30329-2305 Telephone: 1- 800-527-4723 (United States and Canada only) or 404-636-8400 or Fax: 404-321-5478. Letters-Send letters to the editor to Dr. Reinhard Radermacher, HVAC nor may any part of this bo
3、ok be reproduced, stored in a retrieval system, or transmitted in any form or by any means-elec- ironic, photocopying, recording, or other-without permission in writ- ing from ASHRAE. Indexing and Abstracting Services-Abstracted and indexed by ASHRAE Abstract Center; Ei (Engineering Information, Inc
4、) Com- pendex and Engineering Index; IS1 (lnstitute for Scientific Informa- tion) Web Science and Research Alert; BSRIA (Building Services Research ACS (American Chemical Society) Chemical Abstracts Service and Scientific and Technical Information Network; CSA: Guide to Discovery CSA Materials Rese
5、arch Data- base with METADEX, CSA Engineering Research Database, and CSA High Technology Research Database with Aerospace; IIR (International lnstitute of Refrigeration) Bulletin of the IIR and Fri- doc; and Thomson Gale. Current contents are in IS1 Engineering, Computing But How?Srinivas Garimella,
6、 PhDMember ASHRAEThe meteoric and continuing rise in carbon-based energy utilization worldwide and the result-ing global climate change implications constitute the defining problem facing humankind today.These demand scenarios and the emissions from carbon-based energy utilization have been doc-umen
7、ted in depth, with implications ranging from changes in lifestyle to cataclysms. Instead offurther restatements of the problem, strategies are needed to address the opportunities for inno-vation presented by this scenario in energy conversion and utilization. The challenge in energyis not just one o
8、f more and more generation from fast-depleting nonrenewable sources or bur-geoning renewable sources. A more immediate and practical opportunity is the end-use aspect.Energy utilized in the thermal form directly accounts for at least 87% (coal 24%, oil 36%, natu-ral gas 21%, nuclear 6%) of the world
9、s current (2003) and projected (2030) primary energysupply (WEC 2006). Many renewables also traverse the thermal pathway, increasing the thermalfraction further. While this preponderance of thermal energy comes from relatively few sources,there are infinite routes for energy utilization and conversi
10、on, offering ample opportunities forinnovation, especially in the HVAC followed by intermediate temperature utilizationfor the generation or process steam or district space-heating or cooling loads in residential orcommercial communities; followed by low-temperature utilization for hot water supply,
11、 drying,desiccant regeneration, and a variety of other uses. Such efforts would lead to sustainable urbaninfrastructure with small energy footprints through communities planned around distributedgeneration and consolidated utilization. Such a matching would extract the last useful Joulefrom the ener
12、gy source. This near-lossless energy use approach offers opportunities to reduceSrinivas Garimella is a professor and director of the Sustainable Thermal Systems Laboratory, George W. WoodruffSchool of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA. 2008, American Society of He
13、ating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). For personal use only. Additionalreproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.324 HVAC b) surface areas, andthereby surface-to-volume r
14、atios, of devices must be increased to achieve the transfer rates inviable packages; and c) the available temperature differences must be utilized optimally.To address advances in energy utilization, research on thermal and thermochemical processesis required. On a broader scope, this may be viewed
15、as engineering carbon sources and sinkstoward carbon closure, where carbon is simply a carrier of energy in a fully recirculatory mode.To this end, renewed emphasis will be placed on low-grade waste heat recovery, energy harvest-ing, and amplification and boosting of the availability of such energy
16、sources. These include theplentiful opportunities in industrial (e.g., materials processing and fabrication), commercial(building energy systems, food processing, storage and transport, data centers) and residentialenergy recovery. Vehicular emissions reduction through thermal storage, energy recycl
17、ing, andefficiency improvement represent other avenues. With the lower temperature differences acrosswhich the lossless thermal energy cascade systems with aggregated end uses must function, pro-cesses with high heat transfer coefficients such as phase change at the microscales assume con-siderable
18、importance and may serve as enablers for the feasibility of high-flux thermal systems.Thermal process intensification techniques at the microscales, when implemented in larger sys-tems, will magnify the advantages of microscale heat transfer several-fold, improving systemspecific power and energy de
19、nsities and even system reliabilities.In the arena of energy-intensive devices and systems, thermal/thermochemical energy stor-age systems are sorely needed. Research should include reduction of losses during charge, dis-charge, and dormant storage through fundamental advances in material properties
20、 Largesurface-to-volume ratios offered at increasingly small scales should be exploited to increasebulk capacities of storage devices. Successful development of these devices will eventually seeapplication in the spatial and temporal concentration of renewable energy as well as in the har-vesting o
21、f low-grade heat for subsequent utilization to yield superior overall source utilizationefficiencies.The need for efficient utilization of thermal energy also engenders renewed interest in ther-mally activated cooling and heating systems using absorption, adsorption, and other thermody-namic cycles.
22、 The improved heat and mass transfer made possible by microchannel andmicroscale phase change enhances the economic viability of such systems. Microchannel-basedsystems also usually have the advantage of reducing fluid inventories, material utilization, andenvironmental impact. In addition, heating
23、and cooling systems using natural refrigerants andother novel working fluids and cycles as well as integrated water-heating and space-conditioningsystems, again facilitated by improved heat and mass transfer devices, will reduce the ecologicalfootprint of residential and commercial building energy s
24、ystems. Other means to reduce energyconsumption in space conditioning include wearable power and comfort cooling systems;micro-cooling environments; and combined cooling, heating, and power systems, especially inmulti-use commercial facilities such as hospitals, industrial parks, and campuses. Other
25、 sustain-able thermal systems with major energy impact on the worldwide urban infrastructure includegreen roofs facilitated by the understanding of transpiration cooling and improved energyVOLUME 14, NUMBER 3, MAY 2008 325harvesting in buildings for net zero energy use. Advances in microscale pumpin
26、g and compres-sion will also supply critical needs in developing countries such as portable medicine deliveryand storage.Many of the processes, devices, and systems outlined above require the development of inno-vative heat transfer fluids, colloids, surfactants and additives, natural refrigerants,
27、and otherenabling materials. Structured surfaces and coatings for catalysis, energy storage, process inten-sification, membranes for osmotic processes, desiccants for species and heat transport, andmetal hydrides for storage are other examples. On the other end of the spectrum, the ubiquitousbut gro
28、ssly underutilized thermal capacity offered by the ground as a cost-effective, reliable, andpredictable storage medium must be exploited. Similarly, for low temperature and low energyintensity applications, inexpensive, recyclable, and readily available materials such as paper,plastic, and others sh
29、ould be used as materials of construction for affordable heat recoverydevices to enable market penetration to the masses in the developing world.While the dependence of economic growth on energy consumption is often taken as an abso-lute truth, it is in fact possible to achieve the same level of sat
30、isfaction in the human enterprisewithout energy gluttony. One only needs to review the relationship between the Human Devel-opment Index (HDI) and energy intensity. As shown by Benka (2002), prosperity, humandevelopment, and all other monikers used to describe advancement show plateaus when plotteda
31、s a function of energy consumption, with countries such as Spain and Italy achieving the sameHDI as the United States with about one fourth the energy intensity of the U S. Regional, geo-graphical, climatic, and other factors account for some of the excess energy consumption in theUS; however, by no
32、 means can these factors account for it all. Scientific breakthroughs, tech-nological innovations, and implementation of existing but underutilized technology must allcontribute to the reduction of this energy intensity. In addition, common themes between dif-ferent sectors, e.g., transportation and
33、 building energy, should be exploited to maximize theimpact of advanced devices developed initially for one of these applications. Also, the dwin-dling availability of energy sources moves the market to a more tolerant stance on capital costs(implying the creation of additional markets for advanced
34、components) so that life-cycle costscan be minimized. The role of scientifically sound federal and local policies, incentives, andfostering of entrepreneurship in achieving this goal cannot be overemphasizedin fact, often,the bottleneck is not the lack of technology but instead the lack of availabil
35、ity of, or the misap-plication of, mechanisms to facilitate implementation. With the limited budget of energy andmaterials in the world, the directions outlined above will enable us to wisely control and har-ness their transformations, challenge the established limiting wisdom, and bring about chang
36、esthat affect lifestyles but not the quality of life.REFERENCESBenka, S.G. 2002. Special issue: The energy challenge. Physics Today 55(4):3839.EIA. 2006. Annual Energy Review 2005, p. 435. Washington, DC: Energy Information Agency.WEC. 2006. World Energy in 2006. London, UK: World Energy Council.VOL
37、UME 14, NUMBER 3 HVAC accepted December 20, 2007This paper is based on findings resulting from ASHRAE Research Project RP-1257.Two independent field intervention experiments involving a total of about 190 pupils were carriedout in winter and early spring of 2005 in five pairs of mechanically ventila
38、ted classrooms thatreceived 100% outdoor air. Each pair of classrooms was located in a different school. Electro-static air cleaners were installed in classrooms and either operated or disabled to modify particleconcentrations while the performance of schoolwork was measured. In one school, the used
39、supply-air filters in a ventilation system without recirculation were also replaced with new ones tomodify classroom air quality, while the filters in use in other schools were not changed. The con-ditions were established for one week at a time in a blind crossover design with repeated mea-sures on
40、 ten-to-twelve-year-old children. Pupils performed six exercises exemplifying differentaspects of schoolwork as part of normal lessons and indicated their environmental perceptionsand the intensity of any symptoms. A sensory panel of adults judged the air quality in the class-rooms soon after the pu
41、pils left. Operating the electrostatic air cleaners considerably reduced theconcentration of particles in the classrooms. The effect was greater the lower the outdoor air sup-ply rate. There were no consistent effects of this reduction on the performance of schoolwork, onthe childrens perception of
42、the classroom environment, on symptom intensity, or on air quality asperceived by the sensory panel. This suggests there are no short-term (acute) effects of particleremoval outside the pollen season. When new filters were installed, the effects were inconsistent,although this is believed to be due
43、to sequential and unbalanced presentation of filter conditionsand to the fact that the used filters retained very little dust.INTRODUCTIONMany studies have reported high concentrations of particles in classrooms (EFA 2001;Dijken et al. 2005; Simoni et al. 2006), but until recently none demonstrated
44、that removing par-ticles in classrooms improves the performance of schoolwork. The only study that directlytested this hypothesis was a recent field experiment in Sweden in which electrostatic air clean-ers were operated or disabled in two pair of classrooms (Mattsson and Hygge 2005). The studyfocus
45、ed on the possible benefits of air cleaners for children with allergies or hypersensitivityand was, therefore, performed during the pollen season. The air cleaners reduced the concentra-Pawel Wargocki is an associate professor, David P. Wyon is a visiting professor, and Kasper Lynge-Jensen is a doc-
46、toral student at the International Centre for Indoor Environment and Energy, Department of Mechanical Engineering,Technical University of Denmark, Lyngby, Denmark. Carl-Gustaf Bornehag is an associate professor associated withKarlstad University, Sweden; Swedish National Testing and Research Institu
47、te; and the International Centre of IndoorEnvironment and Energy, Technical University of Denmark. 2008, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). For personal use only. Additionalreproduction, distribution, or transmission in either print or d
48、igital form is not permitted without ASHRAEs prior written permission.328 HVAC however, multiple testing (i.e.chance) could be a possible reason for this isolated result.It has always been assumed that respirable particles in indoor air must have some negativeeffects on health and that this may have
49、 negative consequences for task performance. The originof this assumption is that in the absence of additional indoor sources, such as combustion, cook-ing, or smoking, indoor particles are, to a very large extent, the same particles found in outdoor(ambient) air (Fromme et al. 2005) where, according to reliable epidemiological evidence, theydo have negative effects on the health of older people with pre-existing medical problems, onasthmatics of all ages (NRC 2004; Dominici et al. 2006; Hartog et al. 200
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