Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland Paper ID 0141 ISBN: 978-83-7947-232-1 Prediction of exhaust gas stagnation in common corridor of apartments with gas water heater Takuro Nakamura 1,*, Takashi Kurabuchi 1 1 Tokyo University of Science, Tokyo, Japan * tenni.taku.tennis@gmail.com SUMMARY Gas water heaters are usually installed in common hallways of Japanese apartments. When the exhaust gas remains in the common hallway, there is a possibility that will leak into the living room through the air supply opening for ventilation. This can harm the health of the resident. In order to understand this problem, experiments were conducted using a full-scale common hallways model, and an analysis was performed using CFD(computational fluid dynamics). It is difficult to predict the diffusion of the exhaust gas injected at 15-. Therefore, we propose a visualization measurement of exhaust gas. The CFD result shows a good agreement with the retention state of the common hallways where the gas water heater is installed. The installable position of the gas water heater was explained by a case study. KEYWORDS Gas water heaters, CFD analysise, jet, ventilation 1 INTRODUCTION Gas water heaters are usually installed in the common hallways of Japanese apartment buildings. (Fig.1)When the exhaust gas stagnates in a corridor, it always leaks into the living room of an apartment through the air supply opening for ventilation. As a result, there is a possibility of the health of the resident being adversely affected. Therefore, it is important from the viewpoint of maintaining a healthy environment of the common hallways to determine the retention characteristics of the exhaust gas of a gas water heater. In order to understand the problem of exhaust gas stagenation, experiments were conducted using a fullscale hallway model and CFD analysis was performed. In addition, the insight gained from the findings of this research was utilized for formulating the installation standards for gas equipment in Japan. Fig. 1. Hallway of apartment buildings in Japan
2 METHODS 2.1 Experiment Assuming a case in which there is no opening for ventilation of common hallways in front of the gas water heater, an oblique exhaust type gas water heater equipped with a 15- deflection adapter was reproduced in the full-scale experiment model of a common hallways. For the measurements, an air supply opening for ventilation was set in the full-scale experiment model, duct suction was conducted to simulate the air flowing into the room, and the concentration of CO2 in the air was measured. The measured CO2 concentration value of 1,000 ppm was chosen as the reference value of Building Environmental Sanitation Control Standard. In Fig. 2, the measurement hallway with different setting positions of the air supply opening for ventilation are shown. For the hot water supply mode, the operation of the gas water heater reproduced the peak hour (19:-30-20:-30) of hot water usage time including simultaneous use in the kitchen from the hot water bathtub. (Fig. 3) When the corridor width was 1.2-2.0 m in the experiment model as shown in Fig.2, the gas appliance was moved by a distance of 1.00-1.25 m from the center of the corridor (hereinafter referred to as the shift distance of the gas water heater). In each case (Fig.2), a laser light sheet was irradiated on the cross section near the opening, and the exhaust jet flow was visualized when it passed through the-cross section. (Fig. 4) Move to the screen side by 1.0 m Move to the screen side by 1.25 m Move to the screen side by 1.0 m Move to the screen side by 1.25 m 15 deflection 15 deflection Fig.2 Measurement hallway and setting positions for the air supply opening for ventilation Gas Consumption [m 3 /h] 2.5 2 1.5 Filling bathtub with hot water (15L/m) Shower (10L/m) Shower (10L/m) Gas water heater HD camera 1 0.5 Kitchen (5L/m) Kitchen (5L/m) Kitchen (5L/m) 0 0 600 1,200 1,800 2,400 3,000 3,600 19:30 Time [s] Heating (5000kcal/h) 20:30 Fig.3 Gas water heater operation method Smoke generating device Sheet laser Inside corridor section view Front view Fig.4 Visualization method 2.2 CFD analysis To explore the shift distance of the gas water heater, a case study was conducted via CFD analysis and the positional relationship between the jet and screen was examined. The common hallway model with a width of 2.0 m in the experiments was chosen as the CFD analysis model. (Fig. 5) The CFD analysis conditions are presented in Table 1. For the boundary condition of the gas water heater, we used the actual value measured with a gas water heater without the deflection adapter and operating as a hot water output at 15 L/min. For the outside air condition, we used the actual measurement value obtained with experiment No.1 -with T1.00(refer Fig. 2). The CFD analysis area is shown in Fig.5. The common hallway and air outlet of the gas water heater were reproduced in a large space. We also
assumed an inflow of fresh outside air into the large space and modeled this real phenomenon. In this research, to reproduce the exhaust properties in more detail, as shown in Fig.6, the deflection adapter for the air outlet of the gas water heater was modeled and analyzed. The four cases studied are shown in Fig. 7,and Table 2. The shift distance of the gas water heater was varied from 1.00 m to 1.75 m at an interval of 0.25m. In each case, the CO2 concentration extraction point is indicated by a black circle in Fig. 7 at the center of the ceiling. Gas water heater Outlet air outlet of the gas water heater 10,000mm Inlet the deflection adapter of air outlet of the gas water heater Fig.5 CFD analysis model 1,00m 1,25m No.1 No.2 1,50m 1,75m No.5 No.6 Fig.7 Case study model Fig.6 Deflection adapter of the gas water heater Table1 CFD analysis conditions boundary condition item CFD code Turbulence model Analysis area air outlet of the gas water heater outlet Difference scheme Table2 Case study model Details Code C standard k-ε model 6 11 10(m) velocity,temperature, CO 2 density based on actual measurement Flow distribution outlet Secondary windward accuracy Width of common Measurement point(black dot) hallway(m) 2 common hallway center 3 RESULTS 3.1 Experimental results Fig. 8 shows the experimental results obtained from the measurement of CO2 concentration at different air supply opening positions. At the points T0.25 and T0.50 on the exhaust flow path, the CO2 concentration is higher than other air supply opening locations, however, in all the cases it does not exceed the reference value of 1,000 ppm. In the visualization experiments, when comparing the shift distance of the gas water heater, the ceiling CO2 concentration is higher when the gas water heater shift distance is 1.25 m (No.2 and 4) rather than 1.00 m (No.1 and 3). With respect to this factor, the visualization experimental results in Fig. 9 show that when the shift distance of the gas water heater is 1.00 m (No.1 and 3), the jet flow does not contact the screen, but passes through the opening. However, when it is 1.25 m (No.2 and 4), we observe that the jet is in contact with the screen.
Air supply opening CO 2 density(ppm) 1,200 1,000 800 600 400 200 0 U0.00 U0.25 T0.00 T0.25 T0.50 T0.75 T1.00 NO.1 736 696 881 761 NO.2 831 777 787 966 998 889 NO.3 709 796 603 938 850 837 NO.4 582 554 899 976 951 787 Air supply opening position/name Fig.8 Experimental results from the measurement of CO2 concentration at different air supply opening positions No.1 Opening cross-section in hallway No.2 Opening cross-section in hallway No.3 Opening cross-section in hallway No.4 Opening cross-section in hallway Fig.9 Results of the visualization experiments 3.2 CFD analysis results Comparison of CO2 concentration at the extraction point Fig. 10 shows the CO2 concentration at the extraction point. It was confirmed from the CFD analysis that consistency was almost obtained from experiment No. 1. When the shift distance of the gas water heater increases, the CO2 concentration increases. In particular, when the gas water heater shifting distance is 1.50 1.75 m, the CO2 concentration is 2,200 2,900 ppm, and when the former is 1.00 1.25 m, the latter rapidly increases. Position relationship between jet and screen
Fig. 11 shows the CO2 concentration distribution in the exhaust port high section (H = 2.2 m) for each shift distance of the gas water heater. Between 1.00 and 1.25 m, the jet passes through the opening and is released to the external space, but between 1.50 and 1.75 m, the jet flow contacts the screen and CO2 remains concentrated in the corridor. Air supply opening CO 2 density (ppm) 3500.0 3000.0 2500.0 2000.0 1500.0 1000.0 500.0 0.0 1014.0 870.1 969.9 2224.1 2897.1 1.00m 1.25m 1.50m 1.75m shift distace of the gas water heater Fig.10 CO2 concentration at the extraction point Gas water heater Outlet cross section CO 2 density Fig.11 CO2 concentration distribution in the exhaust port high section (H = 2.2 m) 4 DISCUSSION An oblique exhaust type gas water heater was installed in a common corridor having a general opening area to ascertain the state of exhaust gas retention. Even when the shift distance of
the gas water heater was 1.25 m, the CO2 concentration at the ventilation opening did not exceed the reference value. In addition, we investigated the shift distance of the gas water heater via CFD analysis, and found that when it is greater than 1.25 m, the jet may come into contact with the screen and remain in the corridor. For these reasons, it can be concluded that even if an oblique exhaust type gas water heater is provided with a wall on the front side, if the jet exhaust is released toward the opening, it is possible to install it with a shift distance of approximately 0.25 m. 5 CONCLUSIONS With regard to the criteria for installing an oblique exhaust type gas water heater, this study explained the installable position of the gas water heater and location of the air supply opening. 6 REFERENCES [1]Installation standards and practical guidelines for gas appliances: Japan Gas Equipment Inspection Association [2] JIS S 2071, Standard use conditions, standard acceleration mode and test conditions for domestic gas and oil water heater, 2008 [3] T.Nakamura et al : Installation standards of gas water heater in a hallway of an apartment buildings -CFD aimed analysts of Diffusion Characteristic of Exhaust Air from Gas Equipments- (SHASE Japan 2016)