influence of the floor-based obstructions on contaminant removal efficiency and effectiveness

Building and Environment 37 (2002) 55–66www.elsevier.com/locate/buildenv

In uence of the oor-based obstructions on contaminant removale$ciency and e&ectiveness

K. Hagstr)oma ;∗, A.M. Zhivovb, K. Sir/ena, L.L. ChristiansonbaDepartment of Mechanical Engineering, Helsinki University of Technology, P.O. Box 4100, 02150 Hut, Finland

bBio environmental Engineering Research Laboratory, Department of Agricultural Engineering, University of Illinois, Urbana, USA

Received 12 July 2000; received in revised form 15 August 2000; accepted 14 September 2000

Abstract

Dimensioning of dilution ventilation is often made using the perfect mixing approximation, assuming uniform contaminant concentrationthroughout the room space. However, the contaminant removal e$ciency and e&ectiveness of air conditioning system should be accountedfor during design. The e&ectiveness is in this context used as a measure of the contaminant distribution uniformity within the occupiedzone. In uence of an occupied zone obstruction level, air distribution method, air change rate, cooling load and contaminant sourcenon-uniformity on the contaminant removal e$ciency and occupied zone contaminant concentration uniformity were studied in scalemodel. The room air distribution method results in contaminant concentration non-uniformity inside the occupied zone. A method wasdeveloped to take this into account during the design of air distribution system. Contaminant supply non-uniformity was found to have greatin uence on the concentration non-uniformity with two tested air distribution methods. c© 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Air distribution; Industrial ventilation; Contaminants; Modeling; Air quality; E$ciency

1. Introduction

The outdoor air ow rate and heating and cooling capacityneeded for room air conditioning depends upon the ratiosof temperature and contaminant concentration between ex-haust and occupied zone. Contaminant concentration strati->cation in ventilated spaces is characterized by contaminantremoval e$ciency, which is a relation of the exhaust air con-centration to the average concentration inside the occupiedzone. A dilution air ow rate should be reduced or increased,if the contaminant removal e$ciency with designed air dis-tribution system is higher or lower than 1.0.Another seldom considered factor in uencing the supply

air ow rate is the contaminant removal e&ectiveness. Thee&ectiveness in this context is the level of contaminant dis-tribution uniformity within the occupied zone, which is de->ned using relative occupied zone concentration standarddeviation. This factor shows how the maximum contami-nant concentration di&ers from the average concentration.Neglecting this factor leads into a situation, where half of

∗ Corresponding author. Tel.: +358-9-825-4000; fax: +358-9-8254-0030.

E-mail address: [email protected] (K. Hagstr)om).

the room space is more contaminated than the actual targetlevel.Studies of air distribution in rooms with the ceiling

mounted air di&users and high side wall grilles were con-ducted by Grimitlyn in the physical model and in >eld incommercial and industrial buildings [1,2]. He suggestedthat the average velocities and temperatures in the occupiedzone can be described by assessing the air jet maximumvelocity, Vx, and temperature di&erence, Itx, at the point,where the jet enters the occupied zone. For velocities, thedeviations created in the occupied zone are incorporatedinto the jet analysis using spatial velocity standard devia-tion, �v, that is calculated based on the average velocitiesin each measurement location,

V aveoz = Vx + 2�v: (1)

Thus, the resulting range of velocities in the occupiedzone is based on the maximum velocity in the jet enter-ing the occupied zone determined from the air jet theory.Using twice experimental deviation will provide a con>-dence that 95% of the averaged occupied zone velocitieswill be within the predicted range. The similar equation wasused for temperature distribution in the occupied zone, too.Zhivov suggested that similar approach could be used also to

0360-1323/02/$ - see front matter c© 2001 Elsevier Science Ltd. All rights reserved.PII: S 0360 -1323(00)00088 -3

56 K. Hagstr1om et al. / Building and Environment 37 (2002) 55–66

Nomenclature

C concentrationCc contaminant removal e$ciencym contaminant generation rateq volume air owSc concentration variation coe$cient, relative

standard deviationSF safety factorV air velocity� standard deviation

Subscripts0 supply air (concentration)

Ave averagec concentrationexh exhaust airoz occupied zones supplyTL threshold limitv velocityx jet throw

Superscriptsmax maximumave average

determine if contaminant concentrations in the ventilatedroom are within an acceptable range [3].The objectives of the research were to predict contami-

nant concentration distribution in occupied zone and con-taminant removal e$ciency as a function of an occupiedzone obstruction level, air distribution method, air changerate, cooling load and contaminant source non-uniformity.Final objective was to develop a concentration variation co-e$cient to be used for design of air distribution systems.

2. Equipment

2.1. Room ventilation simulator

The experiments were conducted in the room venti-lation simulator (RVS) at the University of Illinois atUrbana-Champaign [4]. The RVS consists of an adjustableinner test room and an outer room for controlling the ambi-ent environmental conditions of the inner test room. Duringthe experiments, the inner test room (RSRR) was set at(7:2 m × 3:6 m × 2:4 m) to model a full-scale ventilatedroom (FSRR), and the structures were set at 3:10 scale. Theindependent HVAC system provides constantly conditionedsupply air for the inner test room.

2.2. Obstructions and heat sources

Sheet metal boxes, 0:57 m×0:57 m×0:36 m, were usedas obstructions in the experiments. The boxes, 72 in all, werepositioned in the room in di&erent ways in order to createthe desired room layout, obstruction area and height ratios,see Figs. 1 and 2.The cooling load inside the obstructions was created with

light bulbs. The accuracy of the power supply was ±2%,depending on the network voltage. The actual power con-sumption and obstruction surface temperature was moni-tored during each experiment.

2.3. Measurement and control systems and equipment

Supply and exhaust air ow rates were controlled with fre-quency transformers. The volume ow rates of individualsupply openings were adjusted using a factory-made mea-surement and adjustment unit (accuracy ±5%) connected tothe ductwork. The exhaust air ow was adjusted by keepingthe pressure di&erence between the inner and outer room atzero. A temperature controller kept the supply temperatureat the set point during the test. A data acquisition systemmonitored the air temperatures in supply, exhaust, and outerroom. The measurement accuracy was ±0:1 K.

2.4. Tracer gas supply

Tracer gas SF6 was used to model contaminant sourcesinside the room. Pure tracer gas was mixed with outdoor airand pumped inside the room. The tracer gas concentration inthe supply was less than 0.2%. Supply air was taken outdoorsto ensure absolute purity from tracer gas. Realization wasalso controlled during the measurements. Exhaust air fromthe test roomwas exhausted directly outdoors to the oppositeend of the simulator building to prevent short-circuiting ofthe tracer gas into supply air.

2.5. Tracer gas measurement system

Air was pumped constantly (total rate 5.5 ml=min)through measurement hoses from the measurement pointsinside the room and exhaust duct. Air samples were takenfrom each hose and injected into the gas chromatographcolumn. It was used to separate SF6 from the air, and anelectron capture detector was used to measure the con-centration. The whole measurement system was calibratedusing premixed 500 and 1000 ppb solutions of SF6 and ni-trogen. The measurement accuracy of a single measurementwas ±4% of the reading.

K. Hagstr1om et al. / Building and Environment 37 (2002) 55–66 57

Fig. 1. Experimental room layout (RSER), and air temperature and velocity measurement points. Obstruction area ratio 30%. Dimensions in meters.

Fig. 2. Location of supply air outlets during experiments, (a) 2 1=h, (b) 4 1=h, (c) 6 1=h. Obstruction area ratio 15%. Dimensions in meters.

2.6. Method for scaling

Experiments were made using approximate mod-elling method in reduced scale 3:10 in order to simulateair-conditioning in a large industrial hall. The modellingprinciples that were respected are explained below. How-ever, during this analysis the main emphasis was put onthe relative in uence of the di&erent parameters on thestudied non-dimensioned measures — not on the absoluteconcentrations.

2.6.1. Air :ow similarity.For approximate modelling of turbulent ow, it is suf-

>cient to ensure that the dimensionless Archimedes and

Prandtl numbers are identical in the full-scale reference andin the scale model. Moreover, the dimensionless Reynoldsnumber in the supply outlet has to exceed a threshold limitvalue in both the full-scale reference and in the scale model.To maintain the similarity of a turbulence spectrum in venti-lation models, the Reynolds number to be exceeded is 10,000[5,6]. On the temperature scales used, the Reynolds numbersfor the inlets were: nozzles 4× 104 and grilles 1:6× 104.

2.6.1.1. Similarity of thermal boundary conditions Nat-ural convection: When natural convection is modelled un-der ventilation conditions, turbulent convection ow occurs[7], if

(Gr Pr)�(Gr Pr)l; (2)


where the limit value depends on the surface direction andthe shape of the source. The limit values for di&erent surfacetypes are [8]

• large horizontal surfaces: (Gr Pr)l¿ 1× 106,• square single surfaces: (Gr Pr)l¿ 2× 107;• vertical surfaces: (Gr Pr)l¿ 2:3× 108:

These criteria were respected during the simulations.Partitions: If the environment of the test room is held at

the same temperature as the average temperature in the testroom, and if the walls and the ceiling are insulated, the heat ow through partitions is very small compared with the heat ow due to ventilation, and can thus be neglected [9]. Thisis a necessary condition if the environment of the test roomis neglected during simulations.

3. Experimental procedure

During the physical experiments, totalling 150 separatecases, data were collected to develop the concentration vari-ation coe$cient as a function of used air distribution meth-ods and obstruction levels. The experiments were conductedunder steady-state conditions. Several researchers has beenapplied the steady-state method for contaminant removal ef->ciency measurements, such as [12–15]. Number of paperson contaminant distribution uniformity is very limited. Intheir paper Shaw et al. presented the development of the uni-formity with time [11]. Based on that information the occu-pied zone uniformity still develops with time. Thus in orderto avoid these transient errors it was chosen to do uniformitymeasurements in steady state conditions. To avoid randomerrors during measurements, each measurement point withinoccupied zone was measured three times and the exhaustair concentration ten times during each setup. Two di&erentkinds of approaches were used:

• While changing parameters (cooling loads, obstructions,air change rate) the tracer gas was supplied into the testroom uniformly on top of the heat sources.

• The in uence of contaminant sources non-uniformityto the occupied zone concentration distribution in and

Table 1Temperature di&erence between supply and exhaust air and air supply rates with di&erent cooling loads in reduced scale experimental room (RSER) andin the full scale reference room (FSRR)

Supply air ow rate Cooling load (W=m2)

FSRR RSER

FSRR RSER 0 50 100 150 0 116 231 347ACH m3=s ACH m3=s Texhaust − Tsupply (

◦C)

2 1.28 4.7 0.081 0 9.4 0 15.54 2.56 9.4 0.162 0 4.7 9.4 0 7.8 15.56 3.84 14.1 0.243 0 3.2 6.3 9.4 0 5.2 10.4 15.5

contaminant removal e$ciency were studied separately,while keeping other parameters unchanged.

3.1. Air change rate & cooling load

Range of internal cooling loads was selected to cover alarge variety of industrial premises with permanent workingplaces.Air change rates were varied so that each heat load could

be studied using two di&erent air change rates and tempera-ture di&erences. Temperature di&erence between supply andexhaust air with selected cooling loads and air change ratesare represented in Table 1 for both experimental room andfull-scale reference. Later in the text, full-scale values areused when air change rate or cooling load is discussed.

3.2. Air supply methods

Three di&erent air supply methods were studied in theexperiments:

1. Horizontal, “concentrated air supply”, in which theoccupied zone was ventilated by reverse ow. The air wassupplied from nozzles horizontally by the west wall to theupper room level at a height of 2.1 m. The outlet diameterof the nozzles was 78 mm.2. Horizontal grilles air supply, which the occupied zone

was ventilated directly by the jet. The air was supplied bygrilles horizontally from the south wall at a height of 1.2 mfrom the oor. The outlet size of the grille was 102 mm ×114 mm. The vertical vanes of the grille were adjusted atthe 90◦ angles for greater expansion of the jet in a horizontaldirection.3. Vertical air supply by jets projected downwards. The

air was supplied from grilles vertically from a height of2.1 m. The grilles and air velocities were the same as inmethod 2.The scheme of the air supply methods is shown in Fig. 3.

The jet momentum through a single inlet was kept constant.Thus, the number of air supply depended on the air changerate: at an air change rate (1=h) of 2, two nozzles or threegrilles were used; at 4 1=h, four nozzles or six grilles, and


Fig. 3. Studied air supply methods.

at 6 1=h, six nozzles or nine grilles were used, respectively.The air supply devices were located symmetrically in eachmeasurement. The location of the air supply outlets is shownin Fig. 2.

3.3. Obstruction area and height

Only in few cases can the issue of a typical process layoutbe solved, as all layouts refer to certain processes. Resultswith more general applicability were thus obtained using aparametric approach. The parameters applied here were theratios of obstruction area to oor area (Aobs=Arm) and of ob-struction height to room height, (hobs=hrm). The positionsof obstructions and the width of the aisles between themwere selected on the basis of layout information on existingfactories. The minimum width of an aisle, e.g. in mechan-ical work-shops can be considered 3–4 m, if forklifts areused. The position of obstructions in the experimental-room(RSER) is shown in Figs. 1 and 2.The following obstruction levels, which cover a large

range of factory, were used in this study:

• Height ratio (hobs=hrm): 0; 15; 30, and 45% of room height.• Floor area ratio (Aobs=Arm): 0; 15, and 30% of room area.

3.4. Contaminant source

Tracer gas SF6 was injected with a constant injection rateon top of the obstructions. There were total of 12 tracer gassupply points inside the experimental room to provide uni-form distribution of tracer gas into the room. Thus, the con-taminant type was gaseous, warm and only slightly heavierthan air, and no speci>c source type was modeled.Tracer gas concentrations were measured in 15 locations

in the occupied zone at 0.55 m height (corresponding 1.8 min full-scale room), thus representing the breathing heightconcentrations of the workers. Prior actual experiments itwas tested by spot checks that no strati>cation of the tracergas concentration was found between oor level and themeasurement height. The measurement points were in themiddle of the aisles to represent general occupied zone con-centrations, see Fig. 1. No actual maximum points, whichcan be expected very close to contaminant supply points,were searched. The philosophy behind this is that maxi-mum concentrations are to be handled by local ventilation,

whereas general ventilation, which is studied here, mainlyin uences the general air concentrations. The exhaust airconcentration was measured from the exhaust duct. Eachpoint was measured three times during each setup. Analysingtime of each measuring point was approximately 1 min, andthe total duration of the measurement period was 1 h.

3.5. Contaminant source non-uniformity

The validity of the results gathered from tests with uni-form contaminant sources were tested in non uniform con-ditions by supplying contaminant load only on west half ofthe room, see Fig. 1. Thus, for “concentrated” air supply thecontaminant sources were in the area closest to the supplyjets. The room was divided symmetrically for two other airdistribution methods. During non-uniformity tests other pa-rameters were kept constant. (air changes rate 4 1=h, coolingload 50 W=m2 uniformly divided; obstruction ratios: heightand area 30%).

3.6. Measurements and de@ned measures

The e&ect of di&erent parameters was studied with theaid of the following global variables calculated from themeasurements:Relative occupied zone concentration standard devia-

tion:

Sc = �c=Coz; (3)

where �c is the standard deviation of the contaminant con-centration distribution and Coz is the average concentrationin the occupied zone. Sc describes the uniformity of the con-centration distribution throughout the measured area.Contaminant removal eAciency:

Cc = (Cexh − C0)=(Coz − C0); (4)

where Cexh is exhaust air concentration and C0 is concen-tration in supply air. Cc is a measure of the concentrationstrati>cation inside the room and describes how e&ectivelythe contaminants are removed out of the room.

4. Results

4.1. Method

The in uence of di&erent parameters on the variablesstudied was quanti>ed using a factor consisting of the slopeof the linear regression line multiplied with the correlationcoe$cient >tted into data. It was thus possible to analyse theimportance of di&erent parameters in each case. The gen-eral trends of the relationships found are presented in Table2 using +, o or − signs to show positive, zero or negativeregression. (++) or (−−) indicate that the regression wasclear and strong. The measurement results are presented in


Table 2In uence of the studied parameters on the standard deviation of thecontaminant distribution in the occupied zone and on the contaminantremoval e$ciencya

Obstruction Obstruction Air change Coolingheight area rate load

(a) Concentrated air supplySc o o o oCc o o o o

(b) Horizontal direct jet air supplySc o ++ o −−Cc o o − +

(c) Vertical air supplySc o −− o oCc o o o +a(−−): x¡− 0:25, clear negative correlation; (−): −0:25¡x¡− 0:1,weak or unclear negative correlation; (o): −0:1¡x¡ 0:1, no correla-tion; (+): 0:1¡x¡ 0:25, weak or unclear positive correlation; (++):x¡ 0:25, clear positive correlation, where x= slope× correlation (of thelines >tted to the measurement data).

Figs. 4–11 as a function of each variable. The symbols usedto characterise the values of other variables in >gures areC for air change rate, L for cooling load, A for obstructionarea ratio and H for obstruction height ratio. The horizontallines in Figs. 4, 6, 8 and 10 show the range where the mea-sured uniformity is within the standard deviation of all themeasurements with each air supply method.

Fig. 4. Relative contaminant concentration standard deviation as a function of the relative obstruction height.

4.2. Obstruction height

The obstruction height level was found to have no clearin uence either on the occupied zone uniformity or on thecontaminant removal e$ciency with any of the studiedair-supply methods. A small increase could be seen fromFig. 4 on the non-uniformity with vertical supply. However,this variation remains within the shown standard deviation.In Figs. 4 and 5, the results from the contaminant unifor-mity and the contaminant removal e$ciency measurementsare presented as a function of obstruction height.

4.3. Obstruction area

With vertical air supply the increase in obstruction areaimproved occupied zone uniformity but with horizontal di-rect air supply the uniformity was impaired. In concentratedair supply case, the obstruction area level did not have in u-ence on the uniformity. Measurement results are presentedin Fig. 6.The level of obstructed room area was found to have no

e&ect on contaminant removal e$ciency with any air supplymethod, see in results Fig. 7.

4.4. Air change rate

The contaminant concentration deviation inside the occu-pied zone was not a&ected by the change of air change rate


Fig. 5. Contaminant removal e$ciency as a function of the relative obstruction height.

Fig. 6. Relative contaminant concentration standard deviation as a function of the relative obstruction area.

with any of the air supply methods. With vertical supplysome cases showed a slightly improving trend while the oth-ers did the opposite. These variations remained for the mostwithin the standard deviation. Results of the measurementsare shown in Fig. 8.Increase of an air change rate decreased contami-

nant removal e$ciency a little in horizontal air supply

case. No clear in uence for the vertical air supply wasfound, although it seemed that the e$ciency improved innon-isothermal situations when the air change rate wasincreased. The air change rate did not have in uence onthe contaminant removal e$ciency in concentrated airsupply. The results of the measurements are shown inFig. 9.


Fig. 7. Contaminant removal e$ciency as a function of the relative obstruction area.

Fig. 8. Relative contaminant concentration standard deviation as a function of the air change rate.

4.5. Cooling load

Cooling loads did not have any in uence either on the con-taminant concentration variation or the contaminant removale$ciency in concentrated air supply. Cooling load wasfound to have the greatest in uence on the horizontal air sup-

ply. Increase in cooling load improved clearly contaminantremoval e$ciency and uniformity inside the occupied zone.In vertical air supply case the contaminant removal e$-ciency was improved, too, but only small change within stan-dard deviation in the uniformity was found due to coolingload. The measurement results are shown in Figs. 10 and 11.


Fig. 9. Contaminant removal e$ciency as a function of the air change rate.

Fig. 10. Relative contaminant concentration standard deviation as a function of the cooling load.

4.6. Summary of the measurements in uniform sourceconditions

The results of the experiments show clearly that there ex-ists non-uniformity of the contaminant concentrations insidethe occupied zone. This should not be neglected when de-

signing room air distribution. Although some clear correla-tion between used parameters and measures were found, therange of change was small.The average standard deviation of the occupied zone con-

centration non-uniformity for all the concentrated air distri-bution cases was 0.12 with the standard deviation of 0.02.


Fig. 11. Contaminant removal e$ciency as a function of the cooling load.

The average of the measured contaminant removal e$cien-cies was 1.0 with the standard deviation of 0.05. The corre-sponding values for vertical air supply were 0.10±0.03 and1.26±0.07.In horizontal grilles air supply, the average standard de-

viation of the occupied zone concentration non-uniformityfor all the cases was 0.08±0.02. Cooling load increased thecontaminant removal e$ciency. The average contaminantremoval e$ciency for all isothermal cases was 0.92 ±0.03and for the non-isothermal cases 1.14±0.09.

4.7. Contaminant source non-uniformity

Contaminant supply non-uniformity was found to have re-markable in uence on the occupied zone concentration uni-formity when the horizontal grilles air supply and the ver-tical air supply methods were used. In horizontal grilles airsupply cases, the occupied zone concentration standard de-viation was four folded from the case with uniform sources,when the contaminant sources were on the west-half of theroom only. Respectively, for vertical air supply method,the value almost tripled. The concentrated air supply wasless a sensitive method towards the contaminant supplyingnon-uniformity. The results are presented in Fig. 12.Non uniform supply of contaminants improved the con-

taminant removal e$ciency of the concentrated air supplybut impaired it with the other two methods (see Fig. 13).The probable explanation for this is that locating sourcesbelow supply jets improves the transportation of contami-nants from the occupied zone in the concentrated air supply.With the two other air supply methods, improper mixing in

horizontal direction caused more “uncontaminated” air to beexhausted.

5. Discussion

There exists contaminant concentration non-uniformity inthe occupied zone. Thus, the dilution air ow should beincreased from the value calculated based on total mixing tokeep the maximum concentration inside the occupied zonebelow the target level. This can be taken into account byusing safety factor, which can be developed for di&erentmethods of air supply.

5.1. Contaminant removal eBectiveness and safety factor,a theoretical application of the experimental data

Design of dilution ventilation is based on the target levelfor the contaminant concentration, CTL, inside the occupiedzone. The extreme target level is threshold limit value ofspeci>c contaminant, but usually much more stringent targetlevel is chosen.When the total mixing approximation is applied (Cexh =

CTL), the su$cient air ow rate to dilute contaminant emis-sion by general ventilation system can be calculated usingequation:

qs = m=Cexh ; (5)

wherem is a contaminant generation rate and Cexh is exhaustair concentration.When strati>cation of contaminants exists, the contami-

nant removal e$ciency, Cc, should be included in the calcu-


Fig. 12. In uence of the contaminant source non-uniformity on the occupied zone contaminant concentration uniformity.

Fig. 13. In uence of the contaminant source non-uniformity on the contaminant removal e$ciency.

lations [10]. If contaminant removal e$ciency can reliablybe expected to be di&erent from 1, the dilution air ow canbe calculated as

qs = m=(CozCc): (6)

Usually, even when the contaminant removal e$ciencyis considered, the occupied zone is assumed to be equallymixed. However, the contaminant concentration in the occu-pied zone is not uniform, but local concentrations can di&erremarkably from the average, depending on the e&ectivenessof the room air distribution. Thus, a safety factor is neededto con>rm that concentrations throughout the occupied zoneare under the chosen target level concentration. The safetyfactor, SF, is an inverse value of the contaminant removale&ectiveness

CTL = SF× Coz: (7)

Assuming normal distribution for the concentrations andusing a 95% con>dence interval for the maximum concen-tration one gets

CTL = Coz + 2�c; (8)

where �c is an occupied zone concentration standarddeviation. Using the relative occupied zone concentrationstandard deviation, which was de>ned earlier in Eq. (2),the relation between maximum and average conditions inan occupied zone can be expressed as

CTL = Coz + 2ScCoz = (1 + 2Sc)Coz: (9)

Thus, we get a de>nition for the safety factor using con-centration variation coe$cient

SF = 1 + 2Sc: (10)

Finally, the needed amount of supply air ow, which guar-antees desired conditions throughout the occupied zone withthe 95% con>dence interval, can be calculated from

qs = m=((Coz=SF)Cc) = (SFm)=(CozCc) (11)

or

qs = m(1 + 2Sc)=(CozCc): (12)

Applying the results of the experiments to the theory, thefollowing safety factors, SF, can be used for the studied airdistribution methods:

Concentrated air supply: 1.24.Horizontal grilles air supply: 1.16.Vertical air supply: 1.20.

However, for horizontal grilles and vertical air supplymethods, the use of these safety factors is limited to caseswith uniform contaminant sources only. For those methodsthe source non-uniformity was found to have major in uenceon the concentration uniformity conditions. More research isneeded to develop safety factors for non-uniform situations.


6. Conclusions

The room air distribution method results in contaminantconcentration non-uniformity inside the occupied zone. Amethod was developed to take this into account during thedesign of air distribution system.In uence of air distribution method, air change rate, level

of room obstruction and cooling load, on occupied zone con-centration uniformity and contaminant removal e$ciencywere studied. Their in uence was found small.Non-uniform distribution of the contaminant sources in-

side the room was found to have the biggest in uence onthe studied measures. However, the in uence is unique foreach air supply method, and their ability to eliminate thein uence of the non-uniformity varies greatly.

Acknowledgements

This project was funded by the Technology DevelopmentCentre in Finland (TEKES), ABB Fl)akt Oy, Halton Oy,JP-Building Engineering Oy and Valmet Papermachines Oy.

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influence of the floor-based obstructions on contaminant removal efficiency and effectiveness

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