Evaluation of Air Exchange Efficiency in Rooms with ...ijens.org/Vol_19_I_06/190106-7575-IJMME-IJENS.pdf · 1Ala'a Abbas Mahdi, 2Qusay Rasheed Al-Amir University of Babylon, Faculty

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:06 49

190106-7575-IJMME-IJENS © December 2019 IJENS I J E N S

Evaluation of Air Exchange Efficiency in Rooms

with Personal Ventilation in Conjunction with

Displacement Ventilation Systems Asmaa Khudhair Yakoob, Ala'a Abbas Mahdi, Qusay Rasheed Al-Amir

Abstract— This paper aims to evaluating a new

ventilation concept: displacement ventilation (DV) aided with

personalized ventilation (PV) which is assessed for improving

indoor air quality. This approach could be improved

ventilation system design that could even provide individual

control of indoor microclimate. The airflow motion and

temperature distribution by adopting DV and PDV(personal-

displacement ventilation) systems investigated experimentally

and numerically with best flow rate from personal ventilation

and best situations of occupant distribution for DV and PDV.

This work includes a discussion of ventilation strategies, air

and temperature distribution including personal-displacement

ventilation (PDV) system in office room under Iraqi climate to

predict Indoor Air Quality (IQA) and thermal human comfort

by using computational fluid dynamics (CFD) modeling and

rigorous validation experiments. The experimental study was

performed to investigate how the use of the two different

arrangement would effect on thermal environment inside a

tested room of dimensions (3×1.75×3) m used as an office

room. The results of the experimental study were used to

validate the CFD simulations. The boundary conditions for

Computational Fluid Dynamics (CFD) study were obtained

from the same set-up measurement for one way direction-

rectangular displacement and personal ventilation system.

RNG, k-ε turbulence models are evaluated to show how the

shape and location of ventilation devices and occupant would

affect the air quality and thermal environment in the room.

The supply air device has been chosen according to the data

provided by manufactures depending on supply airflow rate in

order to avoid drafts. For DV supply temperature of 18◦C

(64.4◦F) and PV air supply temperature range of 18◦C to 22◦C

(64.4◦F to 71.6◦F), it was found that PV at flow rate 10 L/s

(21.19 cfm) in addition to the distribution of occupants could

improved the inhaled air quality in the breathing zone. And

that the arrangements at an office room for the air supply

diffuser DV and PV combined give accepted thermal human

comfortable depending on the magnitude of air distribution

performance index (ADPI) and effectiveness temperature(ɛt)

which are improved about 71% and about 1.8 respectively

Index Term— Displacement and personal ventilation,

CFD simulation, thermal comfort, Air Distribution

Performance Index, effectiveness temperature, Indoor air quality.

Asmaa Khudhair Yakoob

University of Babylon, Faculty of Engineering, Mechanical Engineering department,

Iraq,

[email protected] 1Ala'a Abbas Mahdi, 2Qusay Rasheed Al-Amir

University of Babylon, Faculty of Engineering, Mechanical Engineering department,

Iraq, [email protected], [email protected]

I. INTRODUCTION The purpose of a ventilation system is to provide

acceptable microclimate in the space being ventilated.

Microclimate refers to thermal environment as well as air

quality. These two factors must be considered in the design

of a ventilation system for a room or a building, as they are

fundamental to the comfort and wellbeing of the human

occupants or the performance of industrial processes within

these spaces,[1]. Numerous studies have associated the

quality of indoor air with people’s complaints and with their

performance. It has been shown that poor air quality causes Sick Building Syndrome (SBS) symptoms such as increased

prevalence of headache decreased ability to think, increased

dizziness, etc., [2]. Providing good air quality, on the other

hand, increases occupant’s productivity,[3]. Furthermore, it

has been documented that the quality of inhaled air of low

enthalpy (low temperature and humidity) is perceived to be

better than when the enthalpy is high,[4].

In today’s office environment, computers and other heat-

generating devices are widely used, and these internal heat

gains together with intense solar conditions can result in a

high heat load in enclosures. This posse challenges for

office ventilation,[5]. Although the specific agents

associated with these problems are not known, many studies

have demonstrated that these symptoms, most of illnesses

and complaints caused by poor indoor air quality and perceived physical discomfort,[6]. The designers and

operators of ventilation systems should be familiar with the

comfort requirements and the quality of air necessary to

achieve acceptable indoor conditions. These require

knowledge of the heat balance between the human body and

the internal conditions, the factors that influence thermal

comfort and discomfort as well as the indoor pollution

concentrations that can be tolerated by the occupants and the

nature of the physically activity,[1].

Indoor environmental conditions are important to the

health, comfort and productivity of occupants.

Accumulating evidence has shown that poor climate quality

is related to increase Sick Building Syndrome (SBS)

symptoms and decreased work performance,[7]. Ventilation

systems are therefore widely used to provide a good indoor environment with respect to thermal comfort and indoor air

quality. By delivering a sufficient amount of outdoor cool

fresh air into the room, excess heat and internally generated

contaminant concentration levels can be removed and

reduced. Natural ventilation appeared as an attractive

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strategy used in the past to provide an acceptable

microclimate in the space being ventilated, [1] but it is

limited to range of climates, microclimates, building types,

etc. Heat is exchanged between the human body and its

environment by four main modes: evaporation, radiation,

convection and, to an insignificant extent because of the small area of contact usually involved, conduction. Since

displacement ventilation was initially used in the welding

industry in 1978, it has been gaining popularity in

Scandinavia as a method of ventilation suitable to maintain

good indoor air quality(IAQ) in occupied zone and improve

energy-efficiency not only for large spaces with high

ceilings, such as assembly halls, but also for offices and

other commercial spaces use. In 1989 in Nordic countries, it

was estimated that displacement ventilation share represents

a 50% of industrial applications market and 25% in office

applications. A typical displacement ventilation system

provides cool air at a temperature several degrees below room air temperature and at a very low velocity of less than

0.5 m/s through large-area supply devices near the floor

level and extracts air at the ceiling level. The supply air

spreads over the floor and then moves up as it comes into

contact with hot surfaces, e.g. persons or electrical devices

exist in occupied space. A displacement system is not

suitable for heating as the outdoor supply air rises towards

the ceiling before it fills the occupied zone,[8]. The

displacement ventilation system could be used with under

floor systems and can provide higher thermal comfort

degree and better cooling efficiency comparing with the all air condition systems,[9]. The temperature different limit

between head and feet about (2-3°C) due to the comfort

requirements, therefore the inlet air cannot be too cold,[10].

Personal ventilation is a generic descriptor for desk- or workstation mounted air-conditioning registers that deliver

conditioned air directly to the breathing zone of office

workers. PV systems have the potential to improve occupant

comfort by increasing individual control over air

conditioning outlets as well as by improving indoor air

quality at the point of use. They may also have the potential

to reduce energy use by reducing the amount of conditioned

air delivered to a workspace [11]. Personalized ventilation

has been applied for many years in theatres and vehicle

cabins, in most cases in order to improve occupants’ thermal

comfort. Only few studies report on the performance of PV in office buildings [12]. The effectiveness of the

personalized ventilation depends greatly on the design of the

PV Air-Terminal Device [13]. Design of PV with high

ventilation effectiveness easily applicable in practice is not

an easy task. Apart of the ventilation effectiveness other

factors, such as background room air distribution, control

strategies, occupant activities, appearance of air supply

devices, etc., are also important [14]. Personalized

ventilation (PV) aims to supply clean air directly to the

breathing zone of room occupants and therefore it has

potential to achieve ventilation effectiveness substantially

higher (ventilation effectiveness §50 or more) than the

ventilation effectiveness of mixing and displacement

ventilation [15].

In rooms with DV the workstations are at a distance from

the supply devices in order to avoid draft discomfort at the

feet. The use of ducts for transporting clean air to the PV

systems installed at each desk is inconvenient and for many

cases unacceptable. A novel idea of “ductless” personalized

ventilation (DPV) has been explored [16]. The key feature is

the utilization of the displacement principle of air distribution, i.e., the creation of a layer of clean and cool air

above the floor. The air from this layer is sucked from,

transported, and supplied directly to the breathing zone of

each occupant by the DPV system.

K.C. Ng et.al.,[17], focused on the influence of changing

three design variables at the same time in displacement

ventilated offices, i.e. diffusers locations, temperature of

supplied air and position of exhaust grills on response

variables behaviour (air diffusion performance index).

Proving that the response surface methodology is an

efficacious method to carry out the detailed investigation of

air diffusion performance index when using different

combinations of three design variables. The accurate of

these models by comparing the ADPI values with values

obtained when CFD technique was used. Also, it was checked the used governing equations for their acceptability

with a confidence interval of 95%.

Kanaan et.al.,[18], assessed the air quality in spaces

conditioned by displacement ventilation (DV) aided with personalized ventilation (PV) on the basis of the average

CO2 concentration levels. The interaction between the

displacement ventilation flow, upward flow of the rising

occupant plume, exhalation flow, and personalized airflow

is modeled in order to predict the CO2 transport inside the

space and the inhalation zone of occupants to monitor the

air quality. The contribution of PV in lowering the CO2

concentration of the inhaled air is evaluated by computing

the personal exposure effectiveness in terms of the CO2

concentrations in PV air and inhaled air with and without

PV. The developed model was validated by comparing

model results of CO2 concentrations with results obtained from 3D simulations using commercial software and with

published experimental data for different PV distances from

the occupant, flow rates, and temperatures of PV jets. The

performance of PV in conjunction with DV regarding

inhaled air quality depends on the location with respect to

the human face and the PV airflow rate and temperature.

Different aspects of personal exposure at different

stratification heights in a displacement ventilated room were

examined by Nielsen,1996,[19]. For the experiments, a

thermal manikin was used to measure personal exposure.

The results showed that the flow in the boundary layer

around a person is able to entrain and transport air from



below the breathing zone to a great extent, thus improving

the quality of the inhaled air.

As mentioned in the literature, the air quality in an office

room conditioned by DV aided with PV ventilation systems

has not been explored. The present work aims to find out

how air quality affected in the breathing zone when the DV

system is aided by PV that introduces fresh air directly at

the breathing level. Also, studying the DV and PV

performance and determining the Air Distribution

Performance Index (ADPI), effective assessed.

II. EXPERIMENTAL METHOD

A. The Office Room Design

All experiments in this work were done in isothermal

tested room insulated by glass wool and a layer of thermal

nylon in a laboratory of Mechanical Engineering, College of

Engineering, University of Babylon as shown in Fig. (1).

A steady state working conditions were assumed in both

experimental and numerical analysis. Full-scale office room

was used to study temperature distribution, velocity

magnitude and flow rate by adopting two air supply diffuser

DV and PV under Iraqi climate with variation in location

and occupant situation. The test studied room dimensions

are:(3 x 1.75 x 3) m, which is included for case-I displacement ventilation only, two person office, two PC-

simulator, one grille located at north side and one door at

west side as shown in Fig. (2) and. The basic configuration

requirements for the test room have been indicated and they

are summarized in table I.

Fig. 1. Front view of experimental isothermal tested room insulated

by glass wool and a layer of thermal nylon

Fig. 2. Schematic diagram of office room with diffuser DV

The different objects which located at tested room and

adopted during experiment part were three types of heat

sources used in tested room and described by: two Human body properties represented by used human thermal

manikin, two computer with a heat of 45W and one

florescent lights were placed as heat sources and installed

in suspended ceiling as described in details in Fig.(2). Also,

commercial air-conditioner was used to deliver the cooled

air to indoor space of the room.

Table I

Room configuration for case-I

For case-II displacement and personal combined, one

person office, one grille located at north side and one door

at west side as shown in Fig. (3) and. The basic

configuration requirements for the test room have been

indicated and they are summarized in table II.



Fig. 3. Schematic diagram of office room with diffuser

DV and PV

The different objects which located at tested room and

adopted during experiment part were three types of heat sources used in tested room and described by: one Human

body properties represented by used human thermal

manikin, one computer with a heat of 45W and one

florescent lights were placed as heat sources and installed

in suspended ceiling as described in details in Fig.(3).

Also, PV system consists of a fan with different flow rates

controlled by an electric regulator where the air is pushed

from the bottom at 0.4 meters Through air terminal device

(ATD) to the top at the human seating level of 1.1 meters.

Table II

Room configuration for case-II

B. Supply System

There are some steps to find ventilation rate and supply air

temperature for displacement ventilation applications. The

procedures are based on the Iraqi cooling code, [21].

1- Ventilation air flow rate

The required air flow rate for cooling load, is:

𝑄 =0.295𝑞𝑜𝑒+0.132𝑞𝑙+0.185𝑞𝑒𝑥

𝜌𝑐𝑝∆𝑇ℎ𝑓 (1)

Q = U ∗ A ∗ ∆T (2)

(3)

2- Air supply temperature:

Equation (4) was used to predict temperature of supplied

air (Ts) during the experiments, [22].

The air change per hour (ACH) was determined by

equation (5) and its value 8.32, [23].

ACH = (Q/VRoom) ∗ 3600 (5)

The one direction air supply diffuser DV was shown in

Fig.(4). The air supply diffuser of personal ventilation was

shown in Fig.(5).

C. Measurement devices:

The measuring devices are divided into three main systems:

- Sample units: During all the tests there are three sample units ,each sample unit has six nods being

placed at various height levels of (0,0.4, 0.8, 1.1, 1.4 ,

1.8)m and used to record the parameters that are

located at first pole (x=2 m, y=0 m, z=0.875 m),second

pole(x=0.7 m, y=0 m, z=0.5 m) and third pole(x=0.7

m, y=0 m, z=1.25 m) for all cases as shown in Fig.(6).

- Air velocity: The hot wire thermo-anemometer sensors

model YK.2005AH.

- Temperature measurement tools: A large number of

thermocouples type K were used to record air

temperature. The thermocouples measure the

temperature with time average 600s.

w



Fig. 5. Air supply outlet for PV diffuser

Fig. 6. Photograph of pole with node level location and thermocouple

measurement

D. Experimental Procedures:

The experiment part has done in two stages according to

type of ventilation devices. the experiments were done in April 2019. The tested room was prepared by installed

suspended ceiling at distance (3 m) from floor. The

measurements of air parameters were taken after one hour of

cooling unit working. The experiment measurement

repeated for two cases at three times to be sure about

readings. Tables III and table V show the results of cases for

each pole.

1- Case-I (air supply system is DV only)

Table III

Temperature(oC)obtained by adopting DV System

2- Case-II (combined DV and PV system)

In this case personal system draw air at level 0.4m and

direct it to breathing zone at 1.1m by fan have flow rate

10l/s.

Table IV

Temperature (ºC) obtained by adopting DV and PV System

III. ANALYTICAL INVESTIGATION

A. General Governing Conservation Equations:

Problem of flowing fluid can be modeled by a

combining conservation equation for each of mass,

momentum, energy and transport species. In present

work simulation, air motion is assumed to be three

dimensional incompressible and at steady state.

-Conservation of mass:

Conservation of mass is given by the following

equation, [1].

(6)

Pole

No.

Thermocouple height from the foot level(m)

0

0.4

0.8

1.1

1.4

1.8

Air temperature (oC)

Pole1 20 21.6 22.1 22.4 23 23.6

Pole2 20.2 21.9 22.3 23.1 23.7 24

Pole3 20.4 22 22.5 23.4 23.9 24.3

Pole

No.

Thermocouple height from the foot level(m)

0

0.4

0.8

1.1

1.4

1.8

Air temperature (oC)

Pole1 20.1 22.3 23.3 23.5 24.3 24.6

Pole2 20.2 22.5 24.1 23.2 24.1 24.3

Pole3 20.4 22.7 23.9 22.8 23.8 24.1

Fig. 4. The supply air diffuser (DV) manufacturing



Conservation of momentum (Navier–Stokes Equations):

The resultant forces effecting a differential control volume

can be determined by applying momentum conservation law

in each coordinate direction to get three force components

in the x, y and z directions.

Conservation of thermal energy:

(7)

Where:

(Γ) is the diffusion coefficient (diffusivity), which is given

by:

(𝜎 =𝜇𝐶p ⁄k) is the Prandtl or Schmidt number for the

fluid.

The terms and are the turbulent

heat fluxes, St is a source term allowing for the rate of

thermal energy production.

-The concentration of species equation:

Equation of species concentration can be written as:

:𝜕

𝜕(𝜌𝑢𝑐) +

𝜕

𝜕𝑦(𝜌𝑣𝑐) +

𝜕

𝜕𝑧(𝜌𝑤𝑐) =

𝜕

𝜕𝑥(Г

𝜕𝑐

𝜕𝑥) +

𝜕

𝜕𝑦(Г

𝜕𝑐

𝜕𝑦) +

𝜕

𝜕𝑧(Г

𝜕𝑐

𝜕𝑧) +

𝜕

𝜕𝑥(−𝜌𝑢′𝑐′) +

𝜕

𝜕𝑦(−𝜌𝑣′𝑐′) +

𝜕

𝜕𝑧(−𝜌𝑤′𝑐′) + SC

(8)

In this equation, (c) is the time-mean concentration

and c' is the deviation from the mean. The terms

and are the turbulent diffusion

fluxes.

B. Computational Set and Numerical Scheme:

The present study includes an office room with DV only, two heat source above a solid tables and two person

for case-I, and DV combined with PV, one heat source

above a solid table and a single person for case-II, besides,

new case was studied numerically which was used DV only

with one person and one computer and named as case-III.

The effective draft temperature (EDT) was taken in (100)

points distributed along ten horizontal range at Y=0 and

Y=1.8 inside the occupied zone. Also, have been performed

to compare practical results with theoretical results through

pole (1) at distance (x=2 m, y=0 m, z=0.875 m).

Many steps in fluent part are used in (CFD) program. At

the begging simulation Problem setup and included Model. Also, the solution to flow field problems (temperature,

pressure, velocity, etc) is defined at nodes for each cell. The

number of elements for case-I, case II and case-III were

289496, 267492 and 199382, respectively as shown in Fig.

(7). Materials setup which included material properties

used in simulation such as density (ρ), specific Heat (Cp)

and thermal Conductivity (k)with values1.189, 1005 and

0.0258, respectively. The Boundary conditions which has a significant impact on CFD simulation success in giving a

reliable results for solved problem. Boundary conditions

that imposed in CFD simulation implemented in this work

consist of three types: velocity inlet and outflow as

tabulated in table V. wall boundary included Walls with

constant temperatures and also constant heat fluxes from

other internal source such as Person, Computer and Light

are 44.69, 176.47 and 2000 respectively.

(a)

(b)

(c)

Fig. 7. Meshed model for experimental domain (a)Case-I

(b)Case-II (c)Case-III

y

x

z

y

x

z

y

x

z



Table V Momentum boundary conditions

Part Type Momentum condition

Wall

motion Shear condition

Person Wall Stationary No Slipping

Computer Wall Stationary No Slipping side walls, floor, ceil,

Wall Stationary No Slipping

tables and lights Wall Stationary No Slipping Supply air diffuser

velocity inlet

magnitude, normal to boundary

Extract Grill Pressure outlet

-Gauge Pressure = (0 Pascal), [constant]. -Backflow direction specification Method: (Normal to Boundary).

When solving problem numerically it’s impossible to

get an exact solution, so accepted scaled error residuals

should be specified for different terms such as continuity,

velocity components and energy.

In this Distribution Performance Index (ADPI) was

evaluated to assessment diffusion performance of air for

different cases in a ventilated space. The effective draft

temperature (EDT) is calculated from equation below:

𝐸𝐷𝑇 = (𝑇𝑥 − Tav) − 8 ∗ (𝑉𝑥 − 0.15) (9)

The validation was carried out by comparing obtained

CFD results with data obtained from experiments in tested

room for case-I and case-II (displacement and personal

ventilation system). The comparison depends on the vertical

temperature which measured in tested room in six levels and

that of numerical studies. The overall average error calculations due to the following equation (10), [24].

The average percentage error were 10.5% and 13.5% for

case-I and case-II, respectively.

𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛(𝐸𝑎𝑣%) =1

𝑛∑

𝑋𝐶𝐹𝐷𝑖 −𝑋𝐸𝑋𝑃

𝑖

𝑋𝐸𝑋𝑃𝑖 ∗ 100𝑛

𝑖

(10)

IV. RESULTS AND DISCUSSION

A. Experimental and Numerical Results

The numerical and experimental results inside the

modeled room for case-I and case-II were studied.

Experimental results obtained at different diffuser and

locations for different occupant distribution. Besides

measured air temperature distribution, velocity distribution

from the three poles for the cases studied at locations first pole (x=2 m, y=0 m, z=0.875 m),second pole(x=0.7 m, y=0

m, z=0.5 m) and third pole(x=0.7 m, y=0 m, z=1.25 m) .

The numerical results in the present study for the tested

room was adopted using many computational runs at

various planes and for all the domain. Air Distribution

Performance Index (ADPI) and effectiveness temperature

were determined. Fig. (8) shows the relation of air

temperature versus the room height through poles 1,2 and 3.

Since the temperature changes directly proportional with the

room height. The reason of this temperature values increase

is due to increase of distance from air supply level.

(a)

(b)

Fig. 8. Measured temperature distributions for poles1,2 and 3, (a) case I,

(b) case-II.



Table-VI presents numerical results of Air Distribution

Performance Index (ADPI) and effectiveness temperature(ɛt)

for three cases. The maximum value of effectiveness and Air

Distribution Performance Index (ADPI) founded at case-II

that evaluated at five levels of room layers.

Table VI

Numerical values of ADPI and effectiveness temperature

Fig. (9) display numerically the contours of air temperature

distribution at five plans in the test room. Also, showed that the

temperature increases from 20 oC closely to the supply terminal

and reach about 30oC near the human body. It found in case-I

and case-III that the floor region near the supply diffuser zone

would show the lowest temperature values, due to the cooling

effect of the supply entering air. In addition, a gradual increase

in temperature obtained as elevation increase inside the room

except that case-III show little increase of temperature level

because of the heat source were less than case-I, for case-II

showed that PV draw the cold air at low level at 0.4 meter to seat level at 1.1 meter (breathing zone) so the temperature

degree at seat level is less than case-I and case- III. Also, an

increase in indoor temperature can be noted near the person,

computer, lighting for all cases.

(a)

(b)

(c)

Fig. 9. Compute temperature contours plans (1,2,3,4&5), (a) Case-I, (b) Case-II, (c) Case-III

In case-II (combined displacement and personal ventilation),

Fig(9-b) shows the computed temperature distribution is better

than case-I and case-III (displacement ventilation only) obtained

in Fig (9- a,c). For case-I and case-III where the person, computer and light located, the hot region around them effect on

all of room air temperature due to reduce ventilation efficiency,

for case-II suitable distribution and air circulation obtained near

the three heat source result from the movement of cold air from

personal ventilation which reduced heat emitted by the person

and computer.

From numerical results, the velocity field for the three cases

are shown in Fig. (10). High values of air velocity obtained at

the lower region due to location of air supply diffuser DV in

this zone. The heat transfer process at this location is more

efficient in reducing the temperature of the domain since the

supply air stream itself has low temperature, therefore it decreases the temperature in this zone.

(a)

(b)

Ventilation

devices

Case-I

DV

only

Case-II

DV combined

PV

Case-III

DV

only

ADPI% 0.6 0.71 0.65

Effectiveness 1.32 1.8 1.34

y

x

z

y

x

z

y

x

z

y

x

z

z

y

x



(c)

Fig. 10. Computed velocity contour at planes 1.2&5 at (a) Case-I (b) Case-II

(c) Case-III

Comparison between measured temperature profiles at pole-1 at

distance (1) m from air supply diffuser DV, with simulated

temperature profile using RNG, K-ε turbulence model. This

comparison shown in Fig.(11). The average deviation between

the experimental and numerical values, for case-I and case-II

were:10.5% and 13.5% respectively.

(a)

(b)

Fig. 11. Comparison between predicted and experimental results

using three direction-square diffuser

B. Comparison Between Cases

From the previous results for the three cases. Accepted results

can be obtained for three cases but case-II gives more suitable

thermal comfort in modeled room. Numerically and from RNG

K-ε turbulence model, amongst the three cases, for one

direction-rectangular diffuser for DV and PV at case-II and DV

only at case-III gives:

temperature contour for all plane inside occupied zone shown in

Fig. (12), the cold air spreads through the floor of the room

from the inlet close to the floor level where DV found, the

maximum velocity was found out at temperature 18oc which

spreading accumulated only at smallest zone at northern region,

besides PV drawing air from that zone to breathing zone, so that allows staying the occupied zone in thermal comfort.

Numerically, Fig. (13) presents streamlines flow patterns for the

case-II and case-III entered to room from diffuser at one

direction. The main face directed to the southern wall and

slightly raise towards the return grille. This process causes some

small eddies near opposite corner and then these streams moves

in similar path of the main stream towards return air grille. The

movement of air caused by buoyancy and inertia forces.

(a)

(b)

Fig. 12. Temperature contour at 1.1 m (breathing zone) plane-2 and plane5 (a)

Case-II (b) Case-III

y

x

z

y

x

z

y

x

z



(a)

(b)

Fig. 13. Computed streamlines flow pattern, (a) case-II (b) case-III

V. CONCLUDING REMARKS

From the results of the present study, the following

conclusions can be summarized as follow:

1. The performance of PV in conjunction with DV regarding

inhaled air quality depends on the location with respect to

the human face and the PV airflow rate and temperature.

2. At elevated room temperature, the supply of clean and cool

air to the breathing zone of occupants with DPV will

improve occupants’ thermal comfort, perceived air quality,

and quality of inhaled air in comparison with DV alone.

Under some conditions energy saving may be achieved with

this strategy.

3. RNG k-ε turbulence model gives a good agreement between

the experimental and numerical data in the validation cases

by predicting the airflow patterns and thermal behaviour of

displacement and personal ventilation devices in an office

room.

4. It was found that the PV air temperature may affect the

ventilation effectiveness of the system, where higher PV temperature results in better air quality in the breathing

zone.

5. The simulated data was found to be slightly underestimated

as compared to the measured data.

6. The situation of occupant distribution affects on result of Air

Distribution Performance Index (ADPI) and air

effectiveness.

7. From the results comparisons, the values of (ADPI) were

calculated to all cases. The maximum value was about 71%

and for (εt), the maximum value was about 1.8 and obtained

from case-II.

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Evaluation of Air Exchange Efficiency in Rooms with ...ijens.org/Vol_19_I_06/190106-7575-IJMME-IJENS.pdf · 1Ala'a Abbas Mahdi, 2Qusay Rasheed Al-Amir University of Babylon, Faculty