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

Chapter 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 l/s to 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) × 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 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 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 Parameter Instrument Accuracy Room air temperature, mean velocity and draft rating Dantec Dynamics comfort Sense system Return air temperature HOBO meter ± 5% Concentration of N2O, SF6 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 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 Cases Figure (Plan) Figure (Elevation) PE flow rate for IP (l/s) PV flow rate for HP (l/s) PE flow rate for HP (l/s) A (Base case) AIpHp5 AIpHp!!"# 20 AIpHp!!"#$ 20 AIpHp10 10 AIpHp!" !"# 10 20 AIpHp!" !"#$ 10 20 AIp!!" Hp 10 AIp!!!" Hp 10 AIp!!" Hp5 10 AIp!!!" Hp5 10 AIp!!" Hp!!!!" 10 20 AIp!!!" Hp!!!" 10 20 AIp!!" Hp10 10 10 AIp!!!" Hp10 10 10 AIp!!" Hp!" !!!" 10 10 20 AIp!!!" Hp!" !!" 10 10 20 AIp!!" Hp 20 AIp!!!" Hp 20 AIp!!" Hp! 20 AIp!!!" Hp! 20 AIp!!" Hp!!!!" 20 20 AIp!!!" Hp!!!" 20 20 AIp!!" Hp!" 20 10 AIp!!!" Hp!" 20 10 AIp!!" Hp!" !!!" 20 10 20 AIp!!!" Hp!" !!" 20 10 20 Two types of tracer gas are used during the experiments. SF6 is dosed in the supply air of the background air distribution system i.e. ceiling supply MV or the DV system, and will represent a contaminant release into the room air. In order to have the tracer gas well mixed with the supply air, the tracer gas is dosed in the air before it entered the chamber. The PV air is conditioned 100% outdoor air without any tracer gas. The exhaled air from the Breathing Thermal Manikin (Infected Person) is also marked using the second tracer gas N2O, which is used by Qian et al. (2006). The air exhaled from the mouth of the Breathing Thermal Manikin is heated to 34°C (Hoppe, 1981). The heated air is exhaled through the mouth and room ambient air inhaled through the nose, so that a shortcut of exhaled air containing a tracer gas to the inhaled air can be avoided. The dosing set-up consisted of a gas cylinder, 2-step reduction valve, and a mass flow controller as shown in Figure 3.16.The mass flow controller has a regulated range of to 50 ml/min. During the experiments, 50 ml/min is set for both SF6 and N2O. Figure 3.16 Tracer gas dosing set-up: N2O cylinder (Top-left), N2O valve (Top-right), SF6 cylinder and valve (bottom-left), mass flow controller (bottom-right) Several tracer gas sampling points shown in Figure 3.17 are distributed and include the following: 1. Inhaled air - At the upper lip at a distance of mm from the face of the HEALTHY MANIKIN or Healthy Person, as reported by Melikov and Kaczmarczyk, (2007), air sampled at the upper lip at a distance [...]... 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. .. DANTEC instrument as shown in Figure 3. 14a The local air mean velocity, turbulence intensity and Draft Rating of the inhaled air are recorded in the inhaled air region at heights of 1 .35 m as shown in Figure 3. 14b The local air mean velocity, turbulence intensity and Draft Rating of the face region is also recorded at a height of 1.4 m just besides the neck/ear region a) Set up of the DANTEC instrument... instrument for room air velocity and Draft Rating b) Set up of the DANTEC instrumentfor local air velocity and Draft Rating Figure 3. 14 Set up of the DANTEC instrument 3. 3 .3 Evaluation of the novel PV-PE system in terms of preventing the transmission of exhaled contaminated air during normal consultation process The normal consultation procedure between a Healthy Person (HP) and an Infected Person (IP)... personalized air in inhaled air It is derived from the following equation (Melikov et al., 2002): εp = C I ,O − C I C I ,O − C PV (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. .. 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 inhalation The room air temperature, mean velocity and Draft Rating are recorded at heights of 0.5 m, 1.25 m and 1.7 m using... juncture of F5 in Figure 3. 18 Figure 3. 19 Set up of the DANTEC instrument 3. 3.4 Evaluation of the novel PV-PE system in terms of preventing the transmission of exhaled contaminated air during simple medical check-up procedure Besides the normal consultation procedure with a distance of 0.6 m between the two manikins, three different arrangements with a closer distance simulating the careful examination... risk of the transmission of infectious diseases In order to exhaust the exhaled contaminated air before it mixes with the room air, experiments are designed to explore the two types of PE in terms of preventing the airborne transmission disease during normal consultation procedure In this case, the Breathing Thermal Manikin and the Thermal Manikin are sitting face to face at the center of the Indoor... supplied to the Indoor Environmental Chamber as shown in Figure 3. 13 Figure 3. 13 Tracer gas SF6 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... for Infected Manikin in all scenarios is fixed As shown in Figure 3. 19, the room air temperature, mean velocity and Draft rating will be recorded at heights of 0.1 m, 0 .3 m, 0.7 m, 1 .3 m, 1.65 m, 1.95 m using the DANTEC instrument located at H2 and H6 in Figure 3. 18 Local air mean velocity, draft rating and temperature will also be recorded at heights of 1.2 m, 0. 03 m away from the Infected Manikin’s... 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 . 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. 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. using the DANTEC instrument as shown in Figure 3. 14a. The local air mean velocity, turbulence intensity and Draft Rating of the inhaled air are recorded in the inhaled air region at heights of