Performance evaluation of personalized ventilation personalized exhaust (PV PE) system in air conditioned healthcare settings 3

3.2 Experimental Facilities 3.2.1 Experimental Chamber 3.2.1.1 Indoor Environmental Chamber The closed space is to simulate a typical health-care consultation room with one Healthy Pe

Chapter 3 Research Methodology 3.1 Overview of Research Methodology

The research methodology involves a combination of experiments and CFD simulations in order to achieve the objectives stated in Section 3.1 This is summarized in Figure 3.21 Tracer gas measurements are taken to evaluate the effectiveness of the novel PV-PE system in enhancing the inhaled air quality and in reducing the transmission of infections Potential for energy savings is evaluated using CFD simulations to perform a few lower flow rates from 4 l/s

to 9 l/s of PE

The experimental facilities are described in Section 3.4 The design of

experiments and the indices used to evaluate the effectiveness of the PV-PE system are discussed in Section 3.5

3.2 Experimental Facilities

3.2.1 Experimental Chamber

3.2.1.1 Indoor Environmental Chamber

The closed space is to simulate a typical health-care consultation room with one Healthy Person (HP) and one Infected Person (IP) The experiments are conducted in an Indoor Environmental Chamber, 6.6 m (L) × 3.7 m (W) × 2.7

m (H), in the School of Design and Environment, NUS, as shown in Figure 3.1

Figure 3.1: Schematic layout of the Indoor Environmental Chamber

The Indoor Environmental Chamber is situated in a laboratory, measuring 9.6

m (L) × 7 m (W) × 2.7 m (H) in size and is fitted with two large fixed glass windows, 1.5 m (W) × 1.2 m (H), along one of the larger walls Three sides of the chamber were enclosed by an annular space, which minimized external environmental interferences The fourth side of the chamber adjoined a control room, which was controlled at the same temperature as the chamber

There are two air conditioning systems that serve the Indoor Environmental Chamber The primary system serving the chamber comprises a Fan Coil Unit (FCU) that supplies conditioned outdoor air (Fresh Air) through the PV air terminal device The secondary system consists of an Air Handling Unit (AHU), which delivers conditioned recirculated air as the ambient or

background MV/DV system The primary system contains a main duct that terminates into a plenum box, from which six branch ducts originate and enter the chamber through openings in the wall The conditioned outdoor air is then delivered to the occupant through PV air terminal devices The ambient

cooling to the chamber is served by re-circulated air stream, which is

conditioned in the AHU and distributed by ceiling-based re-circulated air duct

Two main ceiling supply diffusers controlled by a Variable Air Volume System (VAV) box controller are centrally and symmetrically located at the suspended ceiling of the chamber Another two floor-standing semi-circular displacement ventilation supply diffusers are also centrally and symmetrically located at the two ends of the chamber Two diagonally located ducted return grilles extract the return air from the chamber The background supply air diffusers and the return grilles are shown in Figure 3.2

Figure 3.2: Four-way supply diffuser (left), Floor-standing, low-velocity, semi-circular DV supply unit (middle) and return grille (right) in the

Indoor Environmental Chamber

The space temperature was controlled by adjusting the off-coil temperature and fan speed using the computer control system in the control room to

achieve the desired room conditions for each experiment The air-conditioning systems in Indoor Environmental Chamber are shown in Figure 3.3

Figure 3.3 Schematic layout of Indoor Environmental Chamber and its

air-conditioning system

3.2.1.2 Breathing Thermal Manikin

A Breathing Thermal Manikin (BTM) (P T Teknik Limited, Denmark), as shown in Figure 3.4, is employed throughout this doctoral research and is primarily used to simulate an Infected Person (IP) in a healthcare environment However, in the case of the experiments for Objective 1 involving the

investigation of the ability of the PV-PE system to pull the PV air towards the Healthy Person (HP), the BTM is used to represent the HP For all other experiments involving Objectives 2 and 3, the BTM is used for IP The BTM

is shaped as a 1.68 m tall female, placed in a sitting position The BTM has 26 body segments which can be heated to maintain the manikin surface at the same skin temperature of a human being in thermal comfort Since the

experiments simulate tropical conditions, the manikin is dressed in a clothing ensemble corresponding to a typical level of approximately 0.5 clo, which is a typical level of attire in air conditioning space in the tropics The joints of the

manikin are movable and adjustable so that the manikin can be placed into the right postures There is an artificial lung system inside the thermal manikin which enables the manikin to breathe so that it can simulate an Infected Person who exhales the contaminated air To simulate the normal breathing under light work, the pulmonary ventilation volume is set consisting of 2.5 s

inhalation, 2.5 s exhalation and 1s pause The pulmonary ventilation is 8.4 l/min, with a 10 times per minute breathing cycle 8.4 l/min corresponds to the breathing rate of an adult at a metabolic level during general light work

(Huang, 1977)The pulmonary ventilation is 8.4 l/min, or 0.84 l per breath The instantaneous ventilation is calculated at 0.84 l / 2.5 s = 0.336 l/s = 20.16 l/min

BTM breathing mode consisted of exhalation through the mouth and

inhalation through the nose The exhaled air is heated to 34 °C The breathing thermal manikin was controlled by a software that has four control modes, namely, measuring only surface temperature of the body segments, constant fixed surface temperature, constant heat flux from each body segment and heat loss from manikin’s body following the well-known comfort equation as shown in Equation 3.1 (Fanger 1972) During the experiments, the comfort mode was used

Teq = 36.4 – C(Qt) (Eq 3.1) Where:

ts - The skin surface temperature, [°C];

Qt - The rate of heat loss, [W/m2];

36.4 - the deep body temperature, [°C]; and

C - A constant depending on clothing, posture, chamber characteristics, etc [m2 · °C/W]

Figure 3.4 Breathing thermal manikin (left) and the control software

(right)

3.2.1.3 Thermal Manikin

The human body is not only a source of contaminants but also a heat source A study by Murakami (2004) concluded that the microenvironment around a human body directly affects the quality of air exhaled and inhaled by a person The thermal plume generates an upward flow around the human body that makes the air from below the head go up and reach the inhalation area In order to simulate this kind of thermal plumes generated by the difference of temperature between the skin and the room air around a Healthy Person (HP),

a thermal manikin is used The thermal manikin is shaped as a 1.78 m tall male, which can be placed in both standing and sitting position The thermal manikin is wrapped with heating element in its head, arms, legs and torso to provide heating to these surfaces so as to represent a more realistic human body as shown in Figure 3.5 The thermal manikin temperature is controlled

by three parts: head and torso, arms, and legs The temperature difference between the set point and the one the control box targeted is 0.1 degree The accuracy of the temperature control system is around ± 5%

Figure 3.5 Thermal manikin (left) and the control box (right)

3.2.1.4 Tracer-gas Analyser

Multi tracer gas techniques using sulphur hexafluoride (SF6) and Nitrous Oxide (N2O) will be used to evaluate the performance of the PV-PE system A Multipoint Sampler INNOVA and INNOVA 1412 Multi-gas Analyzer (Figure 3.6) are used to measure the concentrations of sulphur hexafluoride (SF6) and

N2O at sampling points Up to 12 tubes connect each channel on the

INNOVA multipoint sampler to the respective sampling point The 12

channels converge into one: a three-way valve then directs the gas sample to a gas monitor for analysis, or vents it to the waste-air outlet for purging the sampling lines While the gas monitor is measuring the sample, the next sample line is purged The gas monitor used together with the multipoint sampler is INNOVA 1412 It utilizes photo acoustic infrared detection method

to determine the presence and amount of tracer gas present in the air The monitoring system is easily operated through either the front panel or the PC software and is equipped with two standard interfaces: IEEE-488 and RS-232 (optional JV 0901 converter RS-232 to USB These enable the monitor to be integrated into automated process systems Innova AirTech instruments

application software type 7300 was used to control all of the sampling and monitoring functions remotely The data was also recorded in this software

Figure 3.6: INNOVA Multipoint Sampler and Multi-gas Monitor 3.2.1.5 Temperature, Relative Humidity, and Turbulence Intensity

Measurement Devices

The background air supply and return temperatures were recorded by HOBO meters (Figure 3.7)

Figure 3.7 HOBO meter

Dantec Dynamics comfort Sense system, as shown in Figure3.8, is used to measure the mean air velocity, temperature, turbulence intensity and Daft Rating (DR) in the chamber The Comfort Sense system consists of a main frame with input channels for up to 16 probes The omnidirectional probes measure both air velocity and temperature The software delivers statistical results based on user-defined measurement cycles

Figure3.8 Dantec Dynamics Comfort Sense System

As a summary, Table 3.1 shows the overview of the instruments required to measure the parameters in this study It also indicates the degree of accuracy

of each instrument of the data collected

Table 3.1 Instrumentations

Room air temperature, mean velocity

and draft rating

Dantec Dynamics comfort Sense system

Vel ± 0.02m/s Temp ±1% of readings

Concentration of N 2 O, SF 6 Photo acoustic spectrometer

multi-gas analyzer ± 2%

Local air mean velocity, turbulence

intensity and draft rating

Dantec Dynamics comfort Sense system

Vel ± 0.02m/s Temp ±1% of readings

3.3 Experimental Design

3.3.1 Ventilation Systems

The experiments are designed to simulate a consultation room in a healthcare setting (such as hospitals or clinics) in tropical climates It will involve three different parts of the air distribution system

The first part is the background air conditioning and air distribution system, which is either MV or DV in the Indoor Environmental Chamber The control system in the control room is capable of switching between ceiling supply MV

system and DV system The ceiling supply MV diffusers provide a typical mixing ventilation air flow pattern in the chamber based on the Coanda

principle The space temperature is controlled using a space thermostat in the main supply duct During the experiments, the ambient air temperature in the chamber is maintained at 23°C

The second part is the PV system that distributes 100% conditioned outdoor air through the PV Air Terminal Device (ATD) Only one PV ATD is used in this study: Round Movable Panel (RMP), which is shown in Figure 3.9 The outlet of the ATD is a 100 mm diameter perforated panel with 50% free area ratio A perforated flow equalizer with 50 mm diameter is installed inside the conical shaped cap of the ATD It supplies PV air at 23°C and two different flow rates (5 l/s and10 l/s) The PV air flow through each PV ATD is

individually controlled through the computer control system

Figure 3.9 Round Movable Panel (RMP) PV ATD

The third part is the Personalized Exhaust (PE) system Two types of PE integrated chair are fabricated One is called shoulder-PE, which has two local

exhaust devices with an adjustable opening integrated with the chair These chair PE devices are located behind and in the upper part of the chair The other one is called Top-PE, which has the inlet (suction) opening of the PE device raised and extended well above a seated person so that the suction is directly above a seated person’s head The PE device is able to move up and down in a range so as to be always at the optimal position according to the height of the person Each PE device is connected to a three speed external rotor motor by the soft duct so as to exhaust the air out of the Indoor

Environmental Chamber Flow rates through the PE devices, controlled by the motor and the damper at 10 l/s and 20 l/s, provides a fairly comprehensive assessment of the inhaled air quality in the microenvironment created by the combination of PV ATD and PE The shoulder-PE, top-PE and motor are shown in Figure 3.10

Figure 3.10 Top-PE (up-left), Shoulder-PE (Up- right) and the motor

(bottom)

The PE outlet is made of aluminium, with a round outlet having an inner

diameter of 95 mm The PE has a damper inside During the experiments, the top-PE will be located 0.12 m above the manikin’ head while the shoulder-PE

is located 0.06 m away from the manikin’s face as shown in Figure 3.11 The approximate location was chosen according to the CFD simulation to ensure the micro-environment it created or covered could exhaust the exhaled air Before the start of the experiments, a smoke generator was also used to choose the exact location for PE

Figure 3.11 Location of Top-PE (left) and location of Shoulder-PE (right)

3.3.2Evaluation of the novel PV-PE system in terms of enhanced delivery

of PV air to the Healthy Person

It has been demonstrated that PV has a better performance in terms of improving occupants’ Inhaled Air Quality (IAQ) in comparison with Total Volume (TV) system alone (Melikov, 2004; Li et al 2009) However, the PV air terminal devices are almost fixed or have little flexibility to move The Healthy Person (HP) is likely to move out of the PV air range when he/she is moving around the desk while remaining seated In order to maximize the advantages of a PV system in delivering personalized air to the breathing zone,

it is interesting to explore the use of the shoulder-PE in terms of assisting in pulling the PV air flow towards the seated person Thus, in the case of a seated person moving within certain limits in the workstation area, the shoulder-PE will serve to act as a directional control for the PV air plume The experimental design of this study is to examine the possible effective range of the PV-PE system in terms of pulling the PV air towards the occupants For this purpose, measurements of various parameters namely distance between

PV and PE devices, PV flow rate, PE flow rate and relative positions of PV and PE devices, are conducted in the chamber Furthermore, experiments will

be carried out in both MV and DV modes to examine the influence of different background ventilation systems on the local air flow pattern with PV-PE system, which is an important factor to be considered when designing PV-PE systems

During the experiments, the supply air temperature from MV or DV was set at

20 °C in order to achieve the room air temperature of 23 °C The air change rate (ACH) was 6 PV air was kept at 23°C The position of PV ATD was fixed, supplying PV air at a flow rate of 5 l/s or 10 l/s The Breathing Thermal Manikin is kept seated in the chair In order to simulate a typical working person at his/her desk, the chair was able to move around When the chair moves, the integrated PE device and the thermal manikin would also move together with the chair In this study, the chair is moved longitudinally to let the Breathing Thermal Manikin be positioned at 0.2, 0.3 and 0.4 m from the

PV ATD; as well as moving in an arc, leaving from the thermal manikin center line as 30°, 45° and 60° The positions of the Breathing Thermal

Manikin during this study are shown in Figure 3.12

Figure 3.12 Positions of the breathing thermal manikin

Considering the energy usage, draught discomfort, and the potential noise level, a lower PE flow rate is always preferred Previous CFD simulation show that the shoulder-PE device is able to increase the amount of PV air in the inhaled air of an occupant without causing high air velocity around facial area

at a flow rate up to 30 l/s (Yang & Sekhar, 2011) In this study, the PE flow rate changes from 0 l/s to 10 l/s to 20 l/s Details of the experimental

conditions are listed in Table 3.2

Table 3.2 Experimental conditions

12 DV 10 20

Tracer gas (SF6) measurements are performed to investigate the performance

of the PV-PE system in terms of the ability to pull the PV air towards the occupant The tracer gas is dosed in the air long before it entered the chamber

to achieve complete mixing of the tracer gas with the air supplied to the Indoor Environmental Chamber as shown in Figure 3.13

Figure 3.13 Tracer gas SF 6 cylinder and valve (left) and dosing point

(right)

SF6 was dosed until the concentration measured in the chamber increased to above 50 ppm in the return/exhaust air The first results of tracer gas concentration measurement used to analyze the performance of the system with regard to inhaled air quality was taken when the concentration in the return/exhaust air dropped to 50 ppm The personalized air is kept free of thetracer gas The concentration of SF6 is measured in the air inhaled by the thermal manikin, in the air supplied to the chamber, in the return grill at ceiling level, and in the air supplied by the PV system The chamber is well sealed to avoid any air/gas leakage The samples in each sequence are analysed one after another in a loop Each location is sampled at least 10 times

to make reliable statistical analyses The results of tracer gas concentration measurement are averaged and analysed to examine the performance of

thesystem with regard to inhaled air quality An index defined as Personal Exposure Effectiveness (PEE) was calculated to evaluate the PV-PE system The PEE index expresses the percentage of personalized air in inhaled air It is derived from the following equation (Melikov et al., 2002):

(Eq 3.2)

Where CI,0 is the concentration of tracer gas in inhaled air without PV (ppm),

CPV is the concentration of the tracer gas in personalized air (ppm),which is 0 since the PV is supplying conditioned outdoor air, CI is the concentration of the tracer gas in the inhaled air when PV is used (ppm) When PV is in use and

PE is not activated, the numerator of Equation 3.2 represents the reduction in the concentration of the tracer gas in the inhaled air due to the supply of

conditioned outdoor air by PV and thus the PEE shows the effectiveness of PV

in terms of supplying PV air to the occupants; and PEE expresses the

effectiveness of PV-PE as a whole system when both PV and PE are activated This index is equal to one if the inhaled air consists of 100% of the PV air and equal to zero if no PV air is inhaled When PE is used, its effects are indirectly assessed by the index since PE might cause the concentration of the tracer gas

in the inhaled air to reduce by pulling the PV air towards the zone of

m just besides the neck/ear region

a) Set up of the DANTEC instrument for room air velocity and Draft

Rating

b) Set up of the DANTEC instrumentfor local air velocity and Draft

Rating