INFLUENCE OF VENTILATION RATES OF BATHROOMS ON ODOR REMOVAL

Shih-Cheng Hu*, Yun-Chun Tung, Tung-I Tsai, I-Lang Chang

Department of Energy and Refrigerating Air-Conditioning Engineering, National Taipei University of Technology, Taiwan, R.O.C.

*Corresponding author. Address: 1, Sec. 3, Chung-Hsiao E. Rd., Taipei, 106, Taiwan, R.O.C. Tel.: +886 2 27712171 ext. 3512; Fax: +886 2 27314949; E-mail address: [email protected]

Abstract

This paper presents an experimental modeling of odor dispersion from the toilet in a mock-up bathroom. A bathtub, a sink, and a toilet were arranged in the bathroom. A hypothetical odor (SF6 tracer gas) was emitted from a person sitting on the toilet in the bathroom. A new wall-exhaust, different from a traditional ceiling-exhaust, negative pressure ventilation system was employed in the bathroom. The impacts of ventilation rates of 6.5, 8.5, 17, and 24 h-1 on the concentration distribution of repugnant odors in the bathroom were evaluated. Local air quality index, QI, and pollutant removal efficiency, PRE, were introduced in the paper to evaluate the effectiveness of odor removal in the bathroom. Based on the results of our experiment, the quantitative assessment of the influence of odor removal in the bathroom was addressed in the paper.

Introduction

Bathrooms are one of the most lived-in areas and frequently used rooms in the house; consequently, the bathroom design is a high priority for many homeowners. Without proper ventilation, the bathroom will, without a doubt, begin to emit unwanted odors of all kinds. Conventional bathroom ventilation has a small exhaust fan, typically mounted in the ceiling, to pull the moist air and odors right out of the bathroom and send it up an exhaust pipe. Fresh air is coming from a door louver or an opened window in the bathroom. New bathroom ventilation uses mechanical ceiling-supply and wall-exhaust system to facilitate the removal of disgusting odors and moist air. The major difference between the conventional and new ventilation systems is how the moisture and smells created in the bathroom are effectively exhausted out of the bathroom. However, effective ventilation systems are ability to solve the embarrassing problem of toilet odors and moist air. The present study conducted hypothetical contaminant (SF6) release experiments in a mock-up bathroom so as to examine the bathroom ventilation rates (in terms of air changes rate per hour, ACH) and the odor concentration profile and to analyze quantitatively the influence of odor extraction with a local air quality index, QI, and pollutant removal efficiency, PRE.

Experimental Measurement

In this study, hypothetical odor (SF6) release experiments were performed in the mock-up isolation room, a test chamber with the internal dimensions of 2.36 m (length) x 2.22 m (width) x 2.36 m (height), as shown in Figure 1(a). A bathtub, a sink, and a toilet were arranged in the bathroom. Marked as P1-P12 in Figure 1(b), ten measuring points within the bathroom were selected to monitor the concentration levels of odors at these locations, and two extra measuring points were set up outside the room, one (P11) behind the exhaust air vent and another (P12) in front of the supply air vent; moreover, P was the location of a source of odors generated by a person sitting on the toilet in the bathroom and the generation rate of odors was assumed to 0.3 l/min. Points P1, P3, P5, P7, and P9 were the breathing height of the sitting person, while Points P2, P4, P6, and P8 were the breathing height of a standing person. The ratio of the height of points P1, P3, P5, P7, and P9 to that of the bathroom was 0.49, while the ratio of the height of points P2, P4, P6, and P8 to that of the bathroom was 0.66. P10 was located under the supply air vent and its relative height was 0.59.

P12

P8 P4 P6 P2 P10 P5 P9 P7 P3 P1

P11

P Z Y X (0.0.0)

(a) (b) Figure 1. (a) Isometric view of a bathroom, and (b) measurement locations of sampling points.

In the experiments, a pre-calibrated air capture hood (ALNOR, APM150) with accuracy of ± (3% of reading + 11.9 m3/h) and ± (4% of reading + 11.9 m3/h) was used to measure the flow rates of supply and exhaust air, respectively. The volume flow rate of air is read according to the digits indicated by the meter, which range from 85 to 3400 m 3/h. The room pressure differentials, on the other hand, was measured by a pre-calibrated differential pressure transmitter (DWYER, Model 668- 1) with ± 1% full scale accuracy and ranging from 0 to 62.5 Pa. A cylinder of SF6 tracer gas via Teflon tubes (inert to chemicals) was used to produce odors in the bathroom. The SF 6 injection rate was regulated by a pre-calibrated mass flow meter (AALBORG, GFM17), with ± 1.5% full scale accuracy and a range of 0 to 5 l/min. The concentration of SF6 in the bathroom was measured continuously by a pre-calibrated multi-gas monitor (INNOVA 1312), based on photoacoustic infrared detection and employing specific optical filters (Type UA-0988). Detection limit and repeatability of the gas monitor reads 0.006 ppm and 1% of measured value, respectively. Figure 2 shows a schematic of a sampling and measurement system. Sampling was performed with a multipoint sampler (INNOVA 1309) and 12 Teflon tubes. Measured data were then analyzed, graphed in real time, and stored in a database by application software (INNOVA 7300) installed on the personal computer.

Figure 2. Schematic of a tracer gas sampling and measurement system.

Results and Discussion

Concentration Profile of Odors The ventilation system in the bathroom employed downward ventilation with one supply air vent located in the center of the ceiling and one exhaust located at a lower level of one wall (Figure 1). The clean air was supplied from the ceiling supply and extracted from the wall exhaust. The odors generated from the person sitting on the toilet was diluted with abundant clean air and extracted from the bathroom. As revealed in Figure 3, the concentration of odors at the 10 measuring points (P1-P10) within the room was examined. In the four cases, point P1 reported the highest concentration of odors because this was the nearest location from the source of odors. These odors were close to a nose of the sitting person and let him feel the most distasteful; however, higher ventilation rates helped reduce the distasteful feeling. The odor concentration at P1 in the cases of 8.5, 17 and 24 ACH was 78.4%, 67.8%, and 62.5% of the one in the case of 6.5 ACH. It was observed that the cases of 17 and 24 ACH showed insignificant difference in the odor concentration at P1. Points P2, P4, P6, and P8 were positioned under the ceiling supply vent and at the relative height of 0.66; hence, their concentration was lower than the concentration of points P3, P5, P7, and P9, positioned at the relative height of 0.49. The concentration profile of odors in the cases of 8.5, 17 and 24 ACH was similar to the one in the case of 6.5 ACH; however, higher room ventilation rates resulted in lower concentration levels of odors.

90 6.5ACH 80 8.5ACH 17ACH 70 24ACH )

m 60 p p (

n 50 o i t a

r 40 t n e

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0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10P11 P12 Position Figure 3. Concentration profile at the sampling locations in the cases of 6.5, 8.5, 17, and 24 ACH.

Local Air Quality Index This study employed a local air quality index to describe the ventilation system’s efficiency in removing odors [1, 2]. The local air quality index expressed the ability of a ventilation system to extract odors in the place where local air concentration was measured. A higher score on the local air quality index referred to a lower concentration level, indicating better ventilation efficiency on removal of odors. The local air quality index, QI, is defined as follows:

Ce  Cs QI  , (1) C p  Cs where Ce and Cs are, respectively, concentrations of odors at exhaust and supply vents. Cp is the concentration of odors at any place P in the bathroom. As shown in Figure 4, it was observed that changes in the room ventilation rates affected QI at 10 points in the bathroom. Most monitored points in the case of 6.5 ACH had the smallest QI among those in the cases of 8.5, 17, and 24 ACH. It was noted that their QI levels were less than 1; hence, the ventilation rate of 6.5 ACH was not recommended to the bathroom ventilation system. The cases of 8.5, 17, and 24 ACH had better ventilation efficiency as their QI levels were more than 1. Changes in the ventilation rate from 6.5 to 8.5 ACH (1.31 times increase in ACH), or to 17 ACH (2.62 times increase), or to 24 ACH (3.69 times increase) led to an increase in QI by 8-15%, 10-18%, and 15-21% among points P1-P10, respectively. It was observed that error propagation resulted in larger error regions, and QI was inversely proportional to the concentration of odors. Furthermore, a higher ventilation rate resulted in less spreading of odors and improved the local air quality in the bathroom.

6.5ACH 1.5 8.5ACH 17ACH 24ACH I Q

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y t i l 1 a u q

l a c o L

0.5 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 Position Figure 4. QI at the sampling locations at ventilation rates of 6.5, 8.5, 17, and 24 ACH.

Pollutant Removal Efficiency Pollutant removal efficiency was used to express the ventilation efficiency of the whole room [2, 3]. A lower index indicated a greater difficulty in the removal of odors. The pollutant removal efficiency, PRE, is defined as follows:

Ce  Cs PRE  , (2) Cb  Cs where Ce and Cs are concentrations of odors at exhaust and supply vents, respectively, and Cb the average concentration of odors in the bathroom. As revealed in Figure 5, the ventilation system at lower ACH reported a lower PRE, suggesting a higher PRE in the bathroom. The PRE in the case of 6.5 ACH was less than 1 and not recommended to the bathroom, suggesting more than 8.5 ACH. Figure 5 further indicates that doubling the flow rate of supply air from 8.5 to 17 ACH led to a moderate 4% increase in PRE. If the PRE in Case 6.5 ACH was 1, the PRE in Cases 8.5, 17, and 24 ACH could be expressed, respectively, as 1.10, 1.14, and 1.18. The best and the worst choices among the four ventilation rates studied would be the cases of 24 ACH (PRE = 1.11±0.08) and 6.5 ACH (PRE = 0.94±0.09), respectively.

Conclusions Our study presents the results of the experimental study on the influence of ventilation rates of the mock-up bathroom on the odor removal. Two indexes, QI and PRE, are employed for quantitative analysis of the ventilation effect. The major goal of the ventilation system with the negative pressure differential in the bathroom is to prevent the disgusting odors from spreading into neighboring rooms or zones and to effectively remove the odors from the bathroom. Results indicate that the ventilation system of 24 ACH in the bathroom demonstrates the best ventilation efficiency to extract odors. Higher ventilation rates are found to be more capable of raising local air quality and the odor removal. The primary conclusions of this study can be summarized as follows: 1. It is observed that the concentration profile at each ventilation rate show similar trend among the monitored positions. The concentration of odors at the studied ventilation rates in the order from higher to lower levels are 6.5, 8.5, 17, and 24 ACH. 2. Both QI and PRE of more than 1 are recommended to the ventilation design of the bathroom; hence, the studied Case of 6.5 ACH is not recommended. 3. Doubling the flow rate of supply air from 8.5 to 17 ACH leads to a moderate 4% increase in PRE; hence, on the view of energy-saving, the ventilation rate of 8.5 ACH is appropriate.

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0.5 6.5 8.5 17 24 Air change rate per hour, ACH Figure 5. PRE at the sampling locations at ventilation rates of 6.5, 8.5, 17, and 24 ACH.

Acknowledgment The authors would like to thank the National Science Council of Taiwan ROC for financially supporting this research under Contract No. NSC 96-2622-E-027-052-CC3.

References [1] H. Qian, Y. Li, P. V. Nielsen, C. E. Hyldgaard, T. W. Wong and A. T. Y. Chwang, "Dispersion of exhaled droplet nuclei in a two-bed hospital ward with three different ventilation systems," Indoor Air, 16, 2006, pp. 111-128. [2] H. Brohus, Personal Exposure to Contaminant Sources in Ventilated Rooms, Ph.D. thesis, Department of Building and Structural Engineering, Aalborg University, Aalborg, Denmark, 1997. [3] W. J. Fisk, D. Faulkner, D. Sullivan and F. Bauman, "Air Change Effectiveness and Pollutant Removal Efficiency During Adverse Mixing Conditions," Indoor Air, 7, 1997, pp. 55-63.