Performance evaluation of the coupling of a desktop personalized ventilation air terminal device and...

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Building and Environment 45 (2010) 1941–1950

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Building and Environment

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Performance evaluation of the coupling of a desktop personalized ventilation airterminal device and desk mounted fans

Kwok Wai Tham*, Jovan PantelicDepartment of Building, School and Design and Environment, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore

a r t i c l e i n f o

Article history:Received 12 November 2009Received in revised form20 January 2010Accepted 21 January 2010

Keywords:Desktop personalized ventilationDesk mounted fansComputational fluid dynamicsThermal manikinPersonal exposure effectivenessManikin-based equivalent temperature

* Corresponding author. Tel.: þ65 65163413; fax: þE-mail address: [email protected] (K.W. Tham).

0360-1323/$ – see front matter � 2010 Elsevier Ltd.doi:10.1016/j.buildenv.2010.01.019

a b s t r a c t

The performance of a coupled system of the Desktop Personalized Ventilation Air Terminal Device (DPVATD) and desk mounted fans (DMF) was examined in a field environmental chamber. Cooling effect wasevaluated using manikin-based equivalent temperature (Teq,), of each of the 26 body segments ofa breathing thermal manikin (BTM) and personal exposure effectiveness (PEE) was used as an indicatorfor effectiveness of ventilation. Computational fluid dynamics (CFD) was used to examine the velocityfield generated around BTM to provide better understanding of the relationship between air patternsgenerated and convective cooling effect on each of the body segments produced by DPV ATD coupledwith DMF. Four different positions of DPV ATD were examined: two positions each in front and on theside of the BTM. Measurements were conducted at ambient temperature of 26 �C and PV air temperatureof 23 �C at a flow rate of 10 L/s. The results indicate that coupling of DPV ATD and DMF distributes coolingmore uniformly across BTM surfaces and therefore has the potential to reduce risk of draft discomfort ascompared to usage of DPV ATD alone. Personalized exposure effectiveness was increased in 3 of thepositions examined when the coupled system was used.

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1. Introduction

A study conducted in the tropics [1] revealed that office workerspreferred a slightly cooler work environment within the range of20–24 �C. It was reported that the relationship derived from thesubjective votes on thermal comfort and thermal sensation indi-cated that tropically acclimatized subjects felt most comfortablewhen thermal sensation was around the mid-point between‘‘neutral’’ and ‘‘slightly cool’’ (thermal sensation¼�0.40) [2].Subjects in the temperate climate in the indoor air conditionedenvironment may prefer ‘‘neutral’’ sensation for comfort [3], whilein the tropics subjects show preference for thermal sensation‘‘between neutral and slightly cool’’. At an ambient temperature23 �C tropically acclimatized subjects prefer local air velocities(facial) ranging from 0.3 to 0.45 m/s and at the ambient tempera-tures of 26 �C tropically acclimatized subjects prefer local airvelocities (facial) ranging from 0.3 to 0.9 m/s [4].

Several studies have demonstrated that PV system couldaccommodate different cooling loads and subjects perceive thermalenvironment to be better with cooling effect of the body [5–9].Several types of PV ATD were investigated [7] and showed that the

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cooling effect of PV can lead to whole-body heat loss equivalent toroom air temperature decrease of 9.0 �C (manikin-based equivalenttemperature difference). The performance of the 5 PV ATDsinvestigated in [8], i.e., Horizontal Desk Grill, Vertical Desk Grill,Personal Environmental Module, Computer Monitor Panel andMoveable Panel indicated that the VDG provided greatest cooling ofthe manikins head (manikin-based equivalent temperaturedecreased by �6.0 �C when PV air flow was 10 L/s) among exam-ined ATD.

When higher ambient air temperatures are used in the airconditioned environment for example 26 �C, the cooling capacity ofthe PV which supplies cool air to a relatively small area of the bodymay not be enough to achieve thermal comfort to some userswithout causing local draught discomfort, although it significantlyimproves whole body thermal comfort [10].

CFD simulation of inhalation performed using seated compu-tational thermal manikin (CTM) concluded that buoyancy-drivenflow has the undesirable effect of drawing contaminants from thefloor region through the space between the legs of the manikin [11].In the inhalation region this air mixes with the outdoor air suppliedthrough Personalized Ventilation Air Terminal Device (PV ATD). Toprevent this undesirable mixing and also to reduce the thickness ofconvective boundary layer at the upper part of the body so as toenable more fresh air supplied by the DPV ATD to more effectivelypenetrate the boundary layer and be inhaled, Desk Mounted Fans

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Nomenclature

Ce concentration of SF6 in the exhausted air [ppm]Ci concentration of SF6 in the inhaled air [ppm]Cs concentration of SF6 in the supply air [ppm]Qt sensible heat loss [W/m2]ACMV air-conditioning and mechanical ventilationAHU air handing unitBTM breathing thermal manikinCFD Computational fluid dynamicsCTM computational thermal manikinDMF Desk Mounted Fans

FEC Field Environmental ChamberMV mixing ventilationOA outdoor airPEE or 3p personal exposure effectiveness [/]SF6 sulphur hexaflorideTeq manikin – based equivalent temperature [�C]DTeq manikin-based equivalent temperature difference [�C]C is the constant [Km2/W]DPV ATD Desktop Personalized Ventilation Air Terminal DevicePV Personalized VentilationYþ Wall Yplus a non-dimensional parameter

K.W. Tham, J. Pantelic / Building and Environment 45 (2010) 1941–19501942

(DMF) are introduced. DMF directs air streams towards theabdominal region of the body, effectively reducing the boundarylayer and weakening the updraft, resulting in a higher efficiency ofventilation from PV ATD.

The research objective in this study is to examine the influenceof the coupling between Desktop Personalized Ventilation AirTerminal Device (DPV ATD) and DMF on the concentration of PV airin the inhalation zone of the occupant and the potential ofenhanced cooling by decreasing the asymmetrical cooling gener-ated by DPV ATD alone.

2. Methods

2.1. Experimental equipment

This study was conducted in a Field Environmental Chamber(FEC) with the dimension of 11.12 m (L)� 7.53 m (W)� 2.6 m (H) atthe National University of Singapore (Fig. 1). The air-conditioningand mechanical ventilation (ACMV) system of the FEC is capableof switching between mixing ventilation (MV), displacementventilation and underfloor air-distribution. Personalized Ventila-tion (PV) is served from a dedicated outdoor air (OA) handling unitand can be used in combination with any of the total volume ACMVsystems. One of the workstations in FEC installed with DesktopPersonalized Ventilation Air Terminal Device (DPV ATD) and DMFwas used for this study (Fig. 1).

11120 mm

7525 m

m

DPV ATD

positions

Position

of BTM

CFD simulated

part of FEC

exhaust

supply

exhaust

Fig. 1. Field Environmental Chamber (FEC).

A Breathing Thermal Manikin (BTM) was used to simulate thePV user. The BTM is shaped as a 1.68 m tall female, in a seatedposition. BTM has 26 individually heated and controlled bodysegments, and is operated under the ‘‘comfort mode’’, which seeksto maintain the manikin surface temperature equal to the skintemperature of an average human being in thermal comfort. BTMwas dressed in a clothing ensemble corresponding to approxi-mately 0.7 clo, a typical level of office attire in the tropics. Investi-gation [12] was performed on the usage of BTM for measurementand prediction of indoor air quality. They made recommendationthat when amount of room and ventilation air in inhalation isobjective of the investigation breathing do not have to simulatedwith BTM therefore the lung system of the BTM was not activated inthis study.

An INNOVA 1312 photoacoustic spectrometer multi-gasanalyzer was used to measure concentrations of sulphur hexa-floride (SF6) used to determine the PEE under a constant injectionmethod.

Omni-directional low velocity anemometers were placed at thetarget positions in the BTM’s microclimate to record air velocity andair temperature with measurements taken at 1 s intervals. Oneomni-directional probe was placed in the FEC, near the BTM, tomonitor background temperature.

DPV ATD supplied 10 L/s of cool and clean outdoor air throughthe front surface containing 30 supply openings (5 vertical� 6horizontal). Each opening on the front surface of the DTV ATD iscircular with diameter of 8 mm. Openings covered top half of theDTV ATD front surface. Lower half of the DTV ATD (80 mm from thetable surface) was designed without any air openings to avoidinteraction of PV air stream and obstacles on the surface of thetable. Dimensions of the DMF are 80� 80 mm.

2.2. Experimental design

This study consisted of 4 different cases (Fig. 2). Case 1 (frontclose): Desktop PV ATD was positioned on the center line 330 mmfrom the desk edge: Case 2 (front far): Desktop PV ATD was

ATD positions

OCCUPANT

240

045033 Fans

OCCUPANTPV ATD

a b

Fig. 2. Measurement positions of PV ATD and DMF (a) top view; (b) side view.

Table 1Experimental conditions.

Air temperaturecombinations

PV flow rateper ATD [l/s]

DMF PV ATD types used

tambient [�C] tpv, [�C]

26 23 10 On Off Desktop 1-PV ATD

Table 2Measurement points along line of connection.

Cases Frontallyfrom theBTM[mm]

Left from theBTM centerline [mm]

Distance along theconnecting line(center of the supplyregion of ATD andBTM nose) [mm]

Measurementpositions alongthe connecting linestarting from theATD [mm]

Case 1 330 0 500 160, 320, 480Case 2 540 0 670 160, 320, 480, 640Case 3 330 240 600 140, 280, 420, 560Case 4 540 240 740 140, 280, 420, 560, 700

Fig. 3. Geometry applied in Gambit 2.4.

K.W. Tham, J. Pantelic / Building and Environment 45 (2010) 1941–1950 1943

positioned on the center line 540 mm from the desk edge: Case 3(side close): Desktop PV ATD was positioned 330 mm from thetable edge and 240 mm from the center line of the occupant: Case 4(side far): ATD at the side position 240 mm from the center line ofthe occupant 540 mm from the edge of the desk.

Air flow rate of the DPV ATD was calibrated using SF6 injectionat a known rate into the duct supplying outdoor air from thededicated air handling unit and concentration measurementdownstream the injection point using Innova 1312 [13].

Experimental conditions are listed in Table 1 and the matrix ofmeasurement positions for PV and DMF is shown in Fig. 2.Measurement of velocity was conducted using Omni-directionallow velocity anemometers. Velocity was measured along thestraight line connecting the center of the supply region of the DPVATD and the BTM nose and the measurement points are presentedin Table 2.

Constant injection of SF6 was done in the middle of the FEC(Fig. 1) at a height of 1.5 m. Steady state conditions were reached in60 min after the start of the injection. SF6 concentration wasmeasured at the steady state conditions at two exhaust locationsfor 30 min after steady state was achieved. A third measurementlocation was in the inhalation zone of the BTM. Results were then

0

0.5

1

1.5

2

2.5

3

3.5

0 100 200 300

Distance from DPV ATD towar

]s

/m

[y

ti

co

le

V

CFD front close Measured front clo

Fig. 4. Comparison of the measured and CFD p

averaged and used for calculation of the Personal Exposure Effec-tiveness (PEE). The measurement procedure was similar to thatused in [14].

PEE [14] and manikin-based equivalent temperature [15] wereused as assessment criteria in this study. PEE (3p) is defined as:

3p ¼Ce � Ci

Ce(1)

where Ce is concentration of SF6 in the exhausted air, Ciis theconcentration of SF6 in the inhaled air. Personalized Ventilationsupplied cool and clean outdoor air from the dedicated air handingunit (AHU); therefore SF6 concentration in DPV ATD supplied airwas 0. The assumption that the concentration in the exhaust air willrepresent conditions in the inhalation zone when only mixing MVis used. Simultaneous measurements of SF6 concentration insupply and exhaust air was performed and relative differenceðCe � CsÞ=Ce was < 10%. This measurement verified the assump-tion and justified the usage of exhaust concentration as a repre-sentation of conditions without DPV ATD.

The manikin-based equivalent temperature (Teq) was defined oneach of the 26 body segments of the BTM, as:

Teq ¼ 36:4� C$Qt (2)

400 500 600 700

ds inhalation zone of BTM [mm]

se CFD front far Measured front far

redicted velocities for Case 1 and Case 2.

Table 4BTM temperature [K] boundary conditions applied for CTM in CFD.

Case 1 Case 3 Case 1þDMF Case 3þDMF

L. Foot 306.4 306.4 306.5 306.8R. Foot 306.3 306.5 306.5 306.8L. Low leg 306.1 306.2 306.2 306.7R. Low leg 306.2 306.3 306.3 306.7L. Front Thigh 307.2 307.3 307 307.4R. Front Thigh 307.4 307.5 306.9 307.3L. Back thigh 308.1 308.1 307.7 308R. Back thigh 308.1 308.2 307.7 308Pelvis 308.4 308.4 308 308.4Back side 308.1 308.2 308 308.4Scull 308.2 308.4 308.2 308.6L. face 306.1 306.8 306.4 307.1R. Face 305 306.6 305.4 306.6Back of neck 306.7 307.7 306.9 307.9L. Hand 305 305.2 305.3 306.4R. Hand 305.2 305.9 305.4 306.7L. Forearm 305.3 305.4 305.5 306.4R. Forearm 305.6 306 305.7 306.6L. Upper arm out 307.1 307.2 307 307.6R. Upper arm out 307.2 307.4 307.2 307.5L. Upper arm in 307.6 307.7 307.1 307.8R. Upper arm in 307.3 307.5 307 307.4L. Chest 307.9 308 307.7 308.1R. Chest 307.8 308.1 307.7 308.1L. Back 308.2 308.2 308 308.5R. Back 308.1 308.3 308 308.5

Table 3Boundary conditions applied in simulation.

Turbulence model RNG k-3

DPV ATD Velocity inlet componentsCase 1: Vx¼ 0 m/s; Vy¼ 3.68 m/s; Vz¼�3.68 m/s;Case 2: Vx¼ 0 m/s; Vy¼ 2.6 m/s; Vz¼�5.04 m/s;Case 3: Vx¼�2.6 m/s; Vy¼ 3.25 m/s; Vz¼�3.24 m/s;Case 4: Vx¼�2 m/s; Vy¼ 2.54 m/s; Vz¼�4.1 m/s;and turbulence intensity Tu¼ 10%; T¼ 296 K

DMF Velocity inlet, V¼ 2 m/s Tu¼ 30%, T¼ 299 KRoom air inlet Velocity inlet, V¼ 0. 4 m/s Tu¼ 10%, T¼ 299 KRoom air outlet Pressure outletRoom wall Adiabatic wall, enhanced wall treatmentThermal Manikin

bodyDivided into 26 segments.Temperature measured at manikin surface foreach of the cases simulated and applied asboundary condition.

Radiation model None (only convection simulated)Thermal conductivity

of the skink¼ 0.209 [W/Km] [21]


where 36.4 is the deep body temperature (�C), Qt is the sensibleheat loss (W/m2), and C is the constant dependent on clothing,body posture, chamber characteristics and thermal resistance offsetof the skin surface temperature control system (Km2/W). The bodycooling effect of PV air supply is quantified by manikin-basedequivalent temperature difference (DTeq) from reference condi-tions (under the same settings but without PV).

Base case (only total volume mixing ventilation) as well as otherexperimental set points was maintained for 2 h in steady state andTeq of 26 body segments were recorded during this period.Temperature for each of the body segments was then averaged overthe 2 h time period. In order to calculate DTeq the averagetemperature in the base case for every body segment was deductedfrom the corresponding equivalent body segment temperature foreach of the cases examined.

2.3. Computational fluid dynamics (CFD)

2.3.1. Geometry of the computational thermal manikinDifferent levels of computational thermal manikin’s (CTM)

geometric complexity have been used previously. The geometry ofthe CTM in study [11] was an accurate representation of a nude

0

0.5

1

1.5

2

2.5

3

3.5

4

0 100 200 300 4

Distnce from DPV ATD toward

]s

/m

[

yt

ic

oe

V

CFD side close Measured side clo

Fig. 5. Comparison of the measured and CFD p

seated female occupant, whose arms are stretched out as the sittingposture beside the desk. Several other studies (eg. [16–19]) thathave also used accurate representation of CTM concluded thatwhen numerical research focused on global air flow patterns ina ventilated room a less detailed geometry was sufficient; howeveran accurate geometry of the human body was necessary whenstudying the local air flow pattern around the human body [20]. Toappropriately simulate DPV ATD and DMF flow details CTMgeometry was used in this study. The geometrical model wascreated using Gambit 2.4 (Fig. 3).

2.3.2. GridRoom geometry was divided into three sections: cuboid around

CTM enclosing the thighs and the region above the head, smallcuboid below the thighs of the CTM, and remaining room volume.Due to the complicated CTM geometry, unstructured tetrahedral

00 500 600 700 800

the inhalation zone of BTM [mm]

se CFD side far Measured side far

redicted velocities for Case 3 and Case 4.

Fig. 6. Convective cooling heat flux [W/m2]: (a) base case with mixing ventilation (b) front close (Case 1), (c) front close with DMF (Case 1).


mesh was used in the cuboid around the manikin (Fig. 4). Trial-and-error was necessary for proper characterization of the boundarylayers because Yþ can only be calculated after solving the flow field.Fifteen layers of uniform boundary layer cells were placed aroundthe manikin’s body with size of 0.002 m in order to achieve Yþ< 1across the body surface. Enhanced wall treatment was used for nearwall flow description. 2076875 unstructured cells were used forthe volume around the CTM and 565 792 hexahedral cells wereused for the rest of the computational volume. Grid independencyof the results was tested with the grid containing 134 8751unstructured cells in the volume around the CTM and 439 722hexahedral cells in the rest of the room volume. Calculated velocityand temperature results were in a good agreement which indicatedthat grid independency was achieved. Numerical results presentedin this study were calculated using the higher number of cells.

2.3.3. Turbulence modelStandard k-3 model was used in [11] in the CFD simulation of PV

system and the choice for this model was based on the assumptionthat this model is capable to simulate convective heat transfer ofbuoyancy-driven air flow as long as a reasonable value of Yþ isachieved. In the investigation of indoor air quality and thermalcomfort in a room supplied with mixing, displacement andpersonalized ventilation standard k-3 model was used to obtainnumerical results in manikin microenvironment. Standard k-3

model was used in the present study. CFD simulation was

Fig. 7. Air streamlines: (a) front close (Case 1), (b) front close with DMF (Case 1).

conducted using Fluent 6.3 and. Boundary conditions are describedin Tables 3 and 4.

2.3.4. DPV ATD boundary descriptionSupply openings on the front surface of DPV ATD created

a multiple jet structure which has much smaller core jet region ascompared to single jet supply. Due to this property the multiple jetsmix more intensively with surrounding air as compared to thesingle jet. Representing this boundary as a single jet supplied fromthe same area as total area of 30 openings will produce lowermixing with ambient air and higher momentum of the suppliedair. Several methods for diffuser description for CFD have beenused previously: direct description, simplified geometry, box,momentum and prescribed velocity. The random cell blockingmethod proposed by [22] satisfies momentum and mass flow rateconsistency by keeping the area ratio to be treated as openingsequal to the effective area ratio of the diffuser, but it was pointedout by the authors that this method performs the best for thediffusers with large supply area which is not the case for DPV ATD.In the present study in order to compensate for more rapidmomentum decay the DPV ATD flow field supply area wasincreased by 20% and a lower initial momentum was assigned atthe boundary in order to increase mixing with ambient air. Thismethod of PV diffuser description satisfies mass flow rate consis-tency. The numerically calculated velocities are compared withmeasured velocities in Figs. 4 and 5. For the points closer to the DPVATD, the difference between measured and calculated velocityvalues is larger, but at the further distance the CFD model is able topredict velocity with higher accuracy. The error between predictedand measured velocity reached 24% and 10% (Figs. 4 and 5)respectively. Correspondingly temperature predictions (not pre-sented) had errors of 15%, and less than 10% for the points closer tothe CTM face. Although applied method for PV ATD boundarydescription did not properly describe flow momentum at theboundary we believe that in the inhalation zone, which was thezone of the interest in his study this method achieved reasonableaccuracy. Since the random cell blocking method satisfy physicalconsistency of momentum and mass flow rate we believe that it isimportant for our future studies to focus on comparison betweendifferent methods ability to predict flow field in PV application.

3. Results and discussion

When the DPV ATD was at the front close position (Case 1) CFDresults indicate that convective cooling of the head was higher thanother segments of the body (Fig. 6 a–c). Manikin-based equivalent

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

front clse front clse +

DMF

front far front far +

DMF

side close side close

+ DMF

side far side far

+DMF

PE

E

PEE (experiment) PEE (CFD)

Fig. 8. Personalized Exposure Effectiveness – comparison of experimental and CFD values.

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Front Close Front Close+DMF

Fig. 9. Manikin based equivalent temperature difference for front close position (Case 1) of DPV ATD.

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Fig. 10. Manikin based equivalent temperature difference for front far position (Case 2).


Fig. 11. Streamlines: (a) DPV ATD front far (Case 2), (b) DMF for front far (Case 2) sideview.


temperature difference (DTeq) indicated this trend as well (Fig. 9). Inthe facial region the left and right face segments had DTeq of�1.6 �Cand �2.1 �C respectively.

CFD simulation performed in this study represented simplifiedexperimental conditions: exclusion of the thermal manikin clothesand chair. Clothes on the body surface provide thermal insulationand reduce convective heat transfer; therefore CFD results havelimit and they refer to the convective cooling of the skin surfaceexposed directly to the air stream.

When DPV ATD in the front close position was coupled withDMF, CFD simulation indicated higher convective cooling in theabdominal region. The CFD result of the DMF streamlines (Fig. 7b)showed that after hitting the surface of the manikin in theabdominal region, a fraction of the air flow moved upwardstowards the DPV ATD stream due to entrainment by the vortexmotion at the envelope of the DPV ATD jet, but was not able topenetrate the inhalation zone. A fraction of the air flow suppliedwith DMF went through the gap between manikins’ legs andaround the body. These air streams considerably weakened theconvective boundary layer of the body and prevented the buoyancyflow to raise pollutants from the floor level into the inhalation zone.

Experimental results revealed that when DPV ATD was coupledwith DMF, the PEE value increased from 0.4 to 0.471 shown in Fig. 8.The CFD simulation showed a similar increase in PEE, although toa lesser degree. The increase in PEE is most probably due to totalreduction of convective boundary layer next to the BTM body.

Experimental results for the coupling of DPV ATD in front closeposition DMF (Fig. 9) indicated enhanced cooling for left, right,

Fig. 12. Convective cooling heat flux [W/m2]: (a) convective heat flux front far po

front and back thigh and pelvis regions with DTeq ranging between�0.5 and �0.8 �C, but reduction of DTeq for the facial region to�1.3 �C for the left segment and �1.7 �C for the right. This lesserDTeq reduction in the facial region compared to the scenario withthe DMF has the potential to reduce draft discomfort. A similarhigher cooling of abdominal and thigh region was observed in CFDsimulation (Fig. 6a–c). Enhanced cooling was also observed for theleft and right upper arm and left and right part of the chest whereDTeq are respectively �0.9, �0.8, �0.6 and �0.5 �C. CFD results forthe upper arm region indicate higher convective heat flux whenDMF were used with DPV ATD. This is similar to the experimentalfindings for the DTeq. This was most likely due to DMF air streamswhich move around the neck, shoulders and upper arms regions.However a difference in trend was observed in the back regionwhen CFD convective heat flux is compared with measured DTeq.During the experiment thermal manikin was seated in the chairwith the back of the chair obstructing the air movement around theback of the BTM body. In the CFD simulation chair was not includedtherefore DMF created streamlines around the BTM back resultingwith higher convective heat flux.

Profile of the manikin-based equivalent temperature differencefor the front far position (Case 2) (Fig. 10) had the same shape as thefront close position (Fig. 9). DTeq for the left and right face were�1.6and�1.8 �C respectively which indicates DTeq increase of 0.2 �C and0.3 �C compared to the front close position. It is observed thatchanging the front position from close to far has the highestinfluence on cooling of the thermal manikin in the facial region.When DMF were coupled with DPV ATD in front far position DTeq

for the left and right thighs and pelvis had similar values as in thefront close position (Figs. 9 and 10). These results suggest thatcooling of these segments of the manikin body depend primarily onDMF induced air motion.

When DPV ATD is in front far position air stream mixes morewith surrounding air and spreads more before reaching the man-ikin’s face. DPV ATD stream has lower velocity compared to thefront close position and therefore less power to create vortexmotion and entrain the DMF stream from below. A fraction of DMFair flow is still entrained upwards, but larger fraction goes throughthe gap between the legs and around the manikin’s body (Figs. 11and 12 b). Air stream generated with DMF peels off convectiveboundary layer and prevents pollutants from the floor to bebrought into the inhalation zone. This can also be observed whenPEE values are compared for DPV ATD and coupled system. PEEshows improvement from 0.33 to 0.37 (experimental results)shown in Fig. 8.

Measurement results for side close position (Case 3) (Fig. 15)indicate that higher cooling was achieved in the facial region as

sition (Case 2), (b) convective heat transfer rate front far with DMF (Case 2).

Fig. 13. Convective heat cooling flux [W/m2]: (a) side close position (Case 3), (b) side position of PV ATD coupled with DMF (Case 3).

Fig. 14. (a) streamlines side close (Case 3) position, (b) streamlines side close DPV ATDwith DMF (Case 3).

-1.8

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Close Side

Fig. 15. Manikin based equivalent temperature difference


compared to the rest of the body. DTeq for the left and right facialpart are�1.4 and�1.6 �C respectively. CFD results showed that DPVATD in the side close position (Fig. 13 a) produced a higherconvective cooling of the chest, head and neck region than the restof the body.

When DMF was coupled with the DPV ATD in the side closeposition, experimental results (Fig. 15) show equivalent cooling forboth facial parts reaching DTeq¼�1.5 �C. Compared with theresults obtained without the DMF, lower DTeq (higher cooling) wasobserved for all the upper body parts except the skull, with thehighest difference for the arms and thighs. DTeq at the side closeposition as compared to the front close position suggest lessunequal cooling of the body and thus lesser risk of draft discomfortespecially in the case when DPV ATD is coupled with DMF. This canbe very important when higher room temperatures (26 �C orhigher) are considered and personalized ventilation is also used toachieve individual thermal comfort.

DMF streamlines (Fig. 14 b) show that in the side close positionDPV was able to draw the air from below the table surface, but stilla considerable fraction of air went around the body and through thegap between the legs. PEE value (Fig. 8) also indicates improvementwhen DPV ATD was coupled with DMF.

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for close side position (Case 3) of Desktop PV ATD.

Fig. 16. Convective heat cooling flux [W/m2]: (a) side far position (Case 4), (b) side far DPV ATD coupled with DMF (Case 4), (c) streamlines far side DPV ATD coupled with DMFposition (Case 4).

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Fig. 17. Manikin based equivalent temperature difference for side far position (Case 4) of Desktop PV ATD.


Convective heat flux (CFD prediction) indicated that when theDPV ATD was in the side far position (Case 4) cooling of the facialregion was lower when DMF was used as compared with the casewhen DMF was not used (Fig. 16 a and b). DMF still contributed tothe enhancing of the abdominal region cooling. Similar trend isobserved in the experimental results (Fig. 17). A fraction of DMFstreamlines moved through the gap between the legs, aftercolliding with the body, another fraction moved around the body,and the smallest fraction went upwards though the gap betweenthe table and CTM body. Streamlines of the DPV ATD indicate thatthe air flow spreads more than in other cases before reaching theface, due to the largest distance they have to traverse beforereaching the face. PEE value decreased when DMF were used(Fig. 8). This is most probably due to the large distance between theDPV ATD and BTM nose. Jets released from the DPV mixed withsurrounding air and its momentum decayed significantly beforereaching the BTM’s face. This indicates that initial momentum playsthe most important role in achieving high PEE value, and when theATD is far away from the user the ventilation effectiveness of thedevice rapidly decays. This further means that when ATD isdesigned with the ability to be positioned by and according to theuser’s preference, as was the case with DPV ATD, the area of thesupply surface should be carefully designed to achieve highereffectiveness for all the probable positions.

Experimental results showed that coupling of Desktop PV ATDin side far position with DMF (Fig. 17) produced enhanced coolingfor left and right thigh with DTeq¼�0.5 �C, left and right upper armwith DTeq �0.9 and �0.8 �C respectively, and chest withDTeq¼�0.5 �C. In the far position when DMF were used lessercooling of the facial region is observed as compared to cases whenonly PV was used which suggest possible reduction of draftdiscomfort.

4. Conclusion

The conclusions from the study are:

� Coupling of DPV ATD and DMF when compared to operation ofDPV ATD alone reduced DTeq for facial region and at the sametime increases DTeq for thighs and arms. In this way cooling ofthe body is more evenly distributed across the whole bodysurface. This has a potential of reducing the risk of draft causedby intensive cooling of small areas of the body for all the casesexamined. This property of this coupled system can be veryimportant when higher room temperatures (26 �C or higher)are considered and individual thermal comfort is targeted to beachieved with personalized ventilation.


� DMF were able to increase the PEE value for front close andfront far position as well as for side close position by signifi-cantly reducing the convective boundary layer, thus reducingthe convective updraft from bringing pollutants form the floorlevel into the inhalation zone.� Coupling of DMF decreased PEE value for side far position. DPV

ATD in side far position was vey far from the BTM’s face and jetdid not have sufficient initial momentum to reach BTM inha-lation zone. The coupling of the DMF increased mixing andlowered the ATD performance.

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