1、2008 ASHRAE 355ABSTRACT There have been a number of concerns regarding thebalcony spill plume equation provided in North Americanstandards and codes. These include: lack of verification by full-scale experiments and application of the equation for highatria even though it was developed for low-heigh
2、t atria. As aresult of these concerns, the American Society of Heating,Refrigerating and Air-Conditioning Engineers (ASHRAE)initiated a project to evaluate the balcony spill plume equationused in North American codes and standards (RP-1247). Theresearch project included CFD modeling studies to inves
3、tigatesmoke entrainment in the balcony area and smoke entrainmentin high atria. The primary research conducted, as part of RP-1247, was a series of full-scale experiments conducted to inves-tigate smoke flow in balcony spill plumes and the resultingmechanical exhaust requirements for an atrium. The
4、full-scaleexperiments included measurements inside the fire compart-ment and in the opening between the fire compartment and thebalcony area. It also included measurements in a simulatedatrium space. In Part 2 of this paper, the results of the measure-ments in the simulated atrium area are discussed
5、. Also, thedata was analyzed to estimate the mass flow rate at the end ofthe balcony and the air entrainment in the atrium space. Theexperimental entrainment rates are compared with algebraicequations, which are used to estimate the mass flow in anatrium.INTRODUCTIONThere have been a number of conce
6、rns regarding thebalcony spill plume equation provided in NFPA 92B (2005)and IBC (2003). These include:1. Lack of verification by full-scale experiments.2. Application of the equation for high atria even though itwas developed for low-height atria.As a result of these concerns, the American Society
7、ofHeating, Refrigerating and Air-Conditioning Engineers(ASHRAE) initiated a project to evaluate the balcony spillplume equation used in North American codes and standards(RP-1247). Three research activities were undertaken: Full-scale experiments.CFD modeling to investigate smoke entrainment belowth
8、e balcony and at the balcony edge as the plume spillsinto an atrium.CFD modeling of smoke entrainment into a balconyspill plume for high atria.The CFD modeling studies were undertaken to addresstwo concerns with the experimental program: 1. The distance between the balcony and the ceiling in theexpe
9、rimental facility was limited (5-7 m). This distanceexceeds the distance required in the initial request forproposals. However, in comparison to scenarios in manyNorth American atria, this distance was a concern. 2. The second concern was the inability to fully investigatethe effect of the parameter
10、s that affect air entrainment inthe balcony area using full-scale experiments. To address these issues, an effort was made to verify aCFD model using NISTs Fire Dynamic Simulator (FDS) soft-ware (McGrattan et al 2002a; 2002b) for determining smokeentrainment into a spill plume. Detailed results of t
11、he model-Balcony Spill Plumes: Full-Scale Experiments, Part 2G.D. Lougheed, PhD C.J. McCartneyMember ASHRAEG.D. Lougheed is a senior research officer and C.J. McCartney is a technical officer in the Fire Research Program, National Research Council,Ottawa, Canada.NY-08-041 (RP-1247)2008, American Soc
12、iety of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 114, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written per
13、mission.356 ASHRAE Transactionsing studies are provided in masters degree theses by Ko (2006)and McCartney (2007) and summarized in Ko et al. (2008) andMcCartney et al. (2008). The primary research conducted, as part of RP-1247, wasa series of full-scale experiments, which investigated smokeflow in
14、balcony spill plumes and the resulting mechanicalexhaust requirements for an atrium. An extended set of full-scale experiments was conducted for a fire located in acompartment. Parameters that were varied included the widthof the compartment opening and the fire size. Tests wereconducted with and wi
15、thout a downstand in the compartmentopening and with and without draft curtains used to channelthe flow below the balcony.The full-scale experiments included measurements insidethe fire compartment and in the opening between the firecompartment and the balcony area. It also included measure-ments in
16、 a simulated atrium space. In Part 1 of this paper, theresults of the measurements in the fire compartment area arediscussed (Lougheed, McCartney and Gibbs 2008). In this paper, the results of measurements in the simulatedatrium space are discussed. The data was analyzed to estimatethe mass flow rat
17、e at the end of the balcony and the air entrain-ment in the atrium space. The experimental entrainment ratesare compared with algebraic equations that are used to esti-mate the mass flow in an atrium.EXPERIMENTAL STUDIESThere have been several experimental studies of balconyspill plumes. Most of the
18、se were conducted at the BuildingResearch Establishment (BRE) in the UK using 1/10thscalemodels (Morgan and Marshall 1975; Morgan and Marshall1979; Hansell et al. 1993; Marshall and Harrison 1996).Experiments were also conducted by at the University ofCanterbury, New Zealand using salt-water modelin
19、g (Yii1998) and a 1/10thscale model similar to that used at BRE(Harrison 2004). Reviews of the experimental studies areprovided by Harrison (2004) and Lougheed et al. (2007). Abrief summary of the experimental studies is provided inLougheed et al. (2008).BALCONY SPILL PLUME CALCULATION METHODSSevera
20、l methods for estimating air entrainment in balconyspill plumes have been developed. These include the BRE spillplume method (Morgan and Marshall 1975 and 1979), thecorrelations developed by Law (1996 and 1995) and the meth-ods developed by Thomas (1987), Poreh et al. (1998) andThomas et al. (1998).
21、 A brief summary of each method isprovided in this Section.The first method that was developed to estimate airentrainment in balcony spill plumes was the BRE spill plumemethod. The initial physical model studies conducted byMorgan and Marshal (1975; 1979) were used to develop andconfirm the method.
22、This approach provides methods for esti-mating the smoke flow approaching the end of the balcony, theair entrainment as the plume rotates around the spill edge andthe smoke production in the ascending plume. The method forestimating the air entrainment in the rising plume was basedon the approach us
23、ed for infinite line plumes developed by Leeand Emmons (1961). Since the balcony spill plume has a finitelength, an additional term was developed for use in estimatingair entrainment into the ends of the plume. Subsequent exper-imental and theoretical studies (Morgan 1986; Morgan andHansell 1987; Ha
24、nsell, Morgan and Marshall 1993; Marshalland Harrison 1996) were used to further develop the method.Morgan et al. (1999) provide full details for this method.The BRE spill plume method involves a complex series ofcalculations. Law (1986) developed a simple correlation foruse by designers. The correl
25、ation was based on the physicalmodel studies conducted by Morgan and Marshall (1975;1979). The underlying assumptions in the approach by Lawwere that a balcony spill plume was analogous to the smokeflow from a window and that the theory developed by Yokoi(1960) for flows from rectangular heat source
26、s could be usedas the basis for a simplified equation. Yokoi (1960) defined three zones for the smoke flow froma rectangular heat source: 1) near zone where the flow is rect-angular; 2) intermediate zone where the smoke flow will besimilar to that from a line source and 3) the remote zone wherethe s
27、moke flow will be similar to that from a point source. Theheight for each zone was dependent on the initial dimensionsof the rectangular source and its aspect ratio. Law (1986) usedthe equations developed by Yokoi for the intermediate zoneand thus assumed that the balcony spill plume was analogousto
28、 a line plume with a virtual origin below the balcony. The basic assumption in the methods for estimating themass entrainment into a spill plume including those developedby Law is that it is analogous to a line plume. Based on thisassumption, all the simplified equations for air entrainmentinto the
29、rising plume are linear with the height of the plumeabove the balcony edge:(1)where= mass flow rate at height zb(kg/s);zb= height above the balcony (m);A = linear coefficient for air entrainment in line plume (kg/s m); B = coefficient defining initial conditions for line plume atbalcony edge (kg/s).
30、The coefficients A and B are dependent on parameters such asfire size, opening width, balcony height and mass flow at theend of the balcony. Using the equations developed by Yokoi (1960) for theintermediate zone, Law (1986) developed relationships for thecoefficients A and B in terms of fire size, w
31、idth of the openingand the height of the balcony. The resulting equation was:(2)mbAzbB+=mbmbApQcW2()13zbBp+=ASHRAE Transactions 357where= mass flow rate at height zb(kg/s);= convective heat output (kW); W = length of the spill (m);zb= height of plume above the balcony edge (m);Ap= linear coefficient
32、 for spill plume (kg/s m5/3kW1/3); Bp= virtual origin term (kg/s).Law (1986) used the results from the initial physicalmodel experiments conducted at BRE (Morgan and Marshall1975; Morgan and Marshall 1979) to determine a value for thelinear coefficient, Ap, and an estimate for the virtual origin, Bp
33、,based on the height of the balcony. Law (1995) slightly modi-fied the estimate for both the linear coefficient and the virtualorigin to derive the following relationship for the mass flowrate in balcony spill plume rate using the experimental dataprovided by Hansell, Morgan and Marshall (1993):(3)w
34、here= mass flow rate at height zb(kg/s);= convective heat output (kW); W = length of the spill (m);zb= height of plume above the balcony edge (m);H = height of the balcony above the base of the fire (m).Equation 3 is in the form used in CIBSE (1995), whichwas derived from Law (1995). The principle d
35、ifference is thatthe total heat release rate was used in the algebraic relationshipin Law (1995) as well as the earlier paper (Law 1986). Theversion provided in Equation 3 was developed assuming aradiative fraction of 0.35.The equation in NFPA 92B (2005) was derived from therelationship given in Law
36、 (1995). However, the NFPA 92Bequation is given in terms of the total heat release rate. Ifconverted to the same form as Equation 3 assuming a radiativefraction of 0.35, the linear coefficient Ap= 0.41. Law (1995) also provides a method for estimating thewidth of the spill plume for the scenario wit
37、h no draft curtainslocated below the balcony to channel the flow. In thisapproach, the depth of the balcony, b, is added to the width ofthe opening to obtain the spill plume width. This approach isalso used in NFPA 92B (2005).Several other algebraic relations for the mass flow rate inbalcony spill p
38、lumes were developed. Morgan et al. (1999)noted four different methods for calculating smoke productionrates developed at BRE: BRE spill plume method, Method byThomas (1987), Method by Poreh et al. (1998) and Method byThomas et al. (1998). All of these relationships have the samegeneral form as Equa
39、tion 2 but differ in the value for the linearcoefficient Apand the parameters used to define the virtualorigin. At the same time as Law (1986) developed the initialcorrelation for the balcony spill plume, Thomas (1987)provided an alternative correlation for the physical model data(Morgan and Marshal
40、l 1975; Morgan and Marshal 1979). Thisapproach was based on the relationship developed by Lee andEmmons (1961) for an infinite line source. A term wasincluded in the equation for determining air entrainment intothe ends of the plume. There are two major concerns regardingthe Thomas (1987) method: 1)
41、 the equation includes thedensity of the smoke and 2) the location of the virtual sourceis dependent on the compartment and fire parameters. Morganet al. (1999) provide a method for estimating the virtual originfor this approach. Poreh et al. (1998) used dimensional analysis to deter-mine the mass f
42、low rate for a line plume and the convectiveheat output of the fire. This approach includes a method fordetermining the location of the virtual origin. This methodestimates the air entrainment into the sides of the spill plume.However, it does not allow for entrainment into the ends of theplume.Thom
43、as et al. (1998) used rigorous dimensional analysisto develop a relationship for the mass flow rate in a balconyspill plume. This approach does not require the specificationof a virtual origin for the plume. However, it does require anestimate for the convective heat release rate and the mass flowra
44、te at the balcony edge. It does not include entrainment intothe end of the plume but a separate equation was developed.The full Method by Thomas (1987) consists of a linearportion for air entrainment in the form of Equation 2. Assum-ing the virtual origin is determined using the same approach asused
45、 by Poreh et al. (1998), the coefficients for the linearportion of Thomas (1987) equation reduce to a form similar tothat given by Poreh et al. (1998). The main difference in thetwo methods is the term for end entrainment, which alsoincludes terms involving the height above the balcony and thevirtua
46、l origin.Harrison (2004) also developed equations for the airentrainment into a balcony spill plume. The equations have asimilar form to those developed by Poreh et al. (1998) andThomas et al. (1998). However, the linear coefficient, 0.2, ishigher than that used in the earlier correlations (0.16).Ho
47、wever, the linear coefficient developed in Harrison (2004)was determined by a fit to a set of physical model experimentsand thus includes air entrainment into the end of the plume.The earlier correlations were developed assuming an infiniteline plume with an additional term used in some cases to est
48、i-mate end entrainment. The correlations developed by Harrison (2004) werebased on physical model experiments with a downstand at theend of the balcony. The downstand depth was 0, 0.1 and 0.2 mfor the 1/10thscale model. The linear portion of the equationis comparable to correlations used for line pl
49、umes (CIBSE1995):(4)mbQcmb0.36 QcW2()13zb0.25H+()=mbQcml0.21QcLl23z=358 ASHRAE Transactionswhere= mass flow rate for line plume at height z (kg/s);= convective heat release rate (kW);Ll= length of longest side of rectangular source (m);z = height above the base of the fire (m).In summary, the simplified methods for balcony spillplumes all assume a linear equation for the air entrainmentwith height above the balcony (Equation 2). However, twodifferent approaches were used to determine the linear coeffi-cient, Ap, and the virtual origin term, Bp. 1. Law (1985 and 1995) used
