Drainage Stack Research Articles

A data-processing approach for exploring water-use maneuver of high-rise building

Recognizing high-rise building water-use maneuver should be helpful for developing some practical strategies when indoor room space safety becomes a crucial feature in the building operation. This paper presents a data-processing approach for exploring the water-use maneuver of high-rise building. This approach combines the empirical mode decomposition and statistical analysis to process the mezzanine-floor air-pressure data measured in the drainage stack system of Li Ka-Shing building at PolyU of Hong Kong on 28th of April of 2008. Because the mezzanine-floor air-pressure signals in the building drainage system are recorded within about 10 hours with a recording rate of one signal per second, data re-sampling is obviously needed. Otherwise, the direct application of empirical mode decomposition should be unavailable because the mezzanine-floor air-pressure data are too massive. Statistical analysis is further encompassed after the empirical mode decomposition to seek the influences of re-sampling time interval and the empirical mode decomposition index so that the building water-use maneuver can be understood in detail. Practical application: From the viewpoint of Building Services Engineering, any occupied space should be safeguarded, because the depletions of the trap seals 1 and the bathroom floor drain traps 2 can result in cross-contamination via the drainage system. This suggests that it is crucial to investigate building water-use maneuver when indoor room space safety becomes urgent. To explore the water-use maneuver, an indirect way is by analyzing the mezzanine-floor air-pressure in the drainage stack system in terms of an appropriate approach. Since the mezzanine-floor air-pressure in the drainage stack system of an 18-floor building, i.e. Li Ka-Shing building at PolyU of Hong Kong has been recorded, 3 it can be used to propose the water-use maneuver approach which is helpful for developing some practical strategies for indoor room space safety when the safety should be carefully and urgently faced.

Environmental conditions and the prevalence of norovirus in hospital building drainage system wastewater and airflows

A potential cross-transmission route, first identified in the spread of the SARs virus in South East Asia, in which infection was spread by virus-laden aerosolised droplets entering habitable space via defective water traps is investigated. The main aim of this work was to detect norovirus in wastewater from the collection drain in a hospital Building Drainage System and attempt to trace it in the BDS vent airflow. The methodology employed polymerase chain reaction tests on waste water samples and indicated strong positives for the norovirus GII strain from the collection drain, corresponding to an outbreak in the building, confirming that the BDS is contaminated in such circumstances and poses a threat. Pathogens were not detected in the BDS vertical stack airflows; however, the methodology employed to collect samples from the airflow was considered ineffective requiring further research. An average temperature of 24.3℃ was recorded, together with an average humidity of 96.6%. This research also confirmed that inside the building drainage stack, air flow movement occurs in both the ‘up’ and ‘down’ direction. Thus, aerosolised pathogens could travel from the contaminated horizontal collection drains upwards and enter wards via defective traps or little used showers, sinks, baths and sluices. Practical application: The detection of norovirus from raw, unprocessed samples taken from the collection drain of a hospital complex highlights the need for caution in dealing with these large contaminated systems. The obvious area affected by these findings is in the awareness by building managers and facilities managers that this contamination exists and that all appropriate measures are taken to minimise infection spread due to normal o&m operations. While it was not possible to detect the virus in the airflow itself, it is considered significant that the identification of the direction and magnitude of these airflows confirms that building drainage stacks could act as conduits for the transmission of aerosolised pathogen-laden water droplets. This research suggests that there is a need for a secure and verifiable seal between the building drainage/sewer network and habitable space within a building to minimize the likelihood of any potential cross-contamination and consequent risk to human health.

Predicting air pressure in drainage stack of high-rise building

It is necessary to understand the features of air pressure in a drainage stack of a high-rise building for properly designing and operating a drainage system. This paper presents a mathematical model for predicting the stack performance. A step function is used to describe the effect of the air entrainment caused by the water discharged from branch pipes. An additional source term is introduced to reflect the gas-liquid interphase interaction (GLII) and stack base effect. The drainage stack is divided into upper and base parts. The air pressure in the upper part is predicted by a total variation diminishing (TVD) scheme, while in the base part, it is predicted by a characteristic line method (CLM). The predicted results are compared with the data measured in a real-scale high- rise test building. It is found that the additional source term in the present model is effective. It intensively influences the air pressure distribution in the stack. The air pressure is also sensitive to the velocity-adjusting parameter (VAP), the branch pipe air entrainment, and the conditions on the stack bottom.

Mathematical Modeling of Air Pressure in a Drainage Stack of a High-Rise Building Test Platform

AbstractThe air pressure in a drainage stack of a high-rise building test platform (HBTP) is mathematically modeled by unsteady one-dimensional (1+1) partial differential equations, in which an additional term is introduced to reflect the gas-liquid interphase interaction, the stack top-base effect. This model is crucial for understanding the characteristics of air pressure variation, which is significant for the recognition of the HBTP’s operational performance. A time-splitting based characteristic line method is used to solve the 1+1 type governing equations, with the model parameters being calibrated by the measured data obtained on the HBTP. It is concluded that the generally used Saint-Venant equations should be extended appropriately so that the stack air pressure can be satisfactorily predicted.

A-49 集合住宅の共用排水立て管更新に関する実態調査とその課題

A-49 集合住宅の共用排水立て管更新に関する実態調査とその課題

Air Pressure Fluctuations of Drainage Stacks at a High-rise Office Building

This study examines air pressure variations along a discharging stack with unsteady discharging flow rates, including the fluctuation frequency, the maximum and average pressures with their respective standard deviations at a drainage stack of an in-use office building. With a modified constant, the maximum air pressure at the drainage stack could be described by the probability density function of the measured data using earlier proposed mathematical expressions for steady discharging flow rates. The average prediction and the maximum under-prediction of the absolute peak pressure were determined with the margin of errors taken within certain confidence levels. The results would be useful for understanding the air pressure in drainage stacks and help increase the potential of installing a real-time monitoring system in a high-rise drainage stack.

Experimental application of particle imaging to fluid velocity analysis in building drainage systems

Previous research into the hydraulic and pneumatic conditions in the pipework associated with building drainage waste and ventilation (DWV) systems has been interpreted as suggesting that the flow regime within the vertical stack consists of an annular water flow entraining a central air core with an associated pressure drop. However, previous evidence had suggested that a significant proportion of the water was found in the air core by Pink [A study of the effect of stack length on airflow in drainage stacks. BRE Current Paper, 1973; 38/73] and Wyly and Eaton [1961. Capacity of stacks in sanitary drainage systems for buildings. U.S. Department of Commerce, National Bureau of Standards, Monograph 3]. A new model has recently been proposed by Campbell and MacLeod [Investigation of the causative factors of airflow entrainment in building drainage-waste-ventilation (DWV) systems. Building Services Engineering Research Technology 1999; 20(3): 99—104] which suggests that the airflow entrainment is due to the distribution of work between the water annulus and the droplets falling in the central air core. This article describes the investigation of the velocity profile of mixed-phase fluid flow in building DWV systems utilising the particle tracking velocimetry (PTV) flow measurement technique previously established by Campbell [The application of particle tracking velocimetry as a velocity measurement technique. Building Services Engineering Research Technology 2006; 27(4): 327—40]. PTV is a non-intrusive optical flow measurement technique that supplies an instantaneous sample of velocity throughout a two-dimensional plane in the flow field. The results of the PTV investigation support the assumption that water droplets exist in the air core and have a velocity greater than that of the water annulus. Practical application: This article describes the application of particle tracking velocimetry (PTV) to the interaction between air and water in typical building drainage waste and ventilation (DWV) systems. Results indicate an unexpected distribution of mass across the stack discharge which, together with the nature of the air/water interface, governs air movement. The technique of PTV is particularly suited to this area, and represents the first steps towards eventual refinement of mathematical models designed to simulate building DWV system behaviour.

Empirical study on drainage stack terminal water velocity

A building drainage network is an essential provision of each developed city all over the world. The terminal velocity at discharging drainage stack is a crucial issue as it provides the permitted flow rate of a building drainage system. The National Plumbing Code (NPC) of the US has specified the permitted flow rate for drainage systems. Mathematical expressions for terminal velocity were reported in research studies since the 1920s but discrepancies among calculations remained. This study proposes an empirical approach in determining the terminal velocity in a drainage stack using the air pressure distribution mechanism. New experimental observations of the stack terminal velocity using a digital high-speed video camera were presented as a validation database. The proposed model was validated in terms of the measured terminal velocities and the locations of the maximum air pressure in a discharging stack at a steady water flow rate (1.0, 2.0, 3.0 and 4.0 L/s). This article offers an empirical approach and validation for terminal velocity instead of using the existing deductive approach. Practical applications: This article proposes an empirical approach with experimental validation for terminal velocity at a drainage stack. New evidence presented would lead to a review of the terminal velocity in drainage stacks in future drainage network designs. Due to the importance of terminal velocity, it is anticipated that this result would be used to lead the new technical development of building drainage system.

Fluctuation Behaviors of Air Pressure in a High-Rise Building Drainage System

Air pressure fluctuation behaviors in a high-rise building drainage system (HBDS) are presented by probability density functions and statistical analysis of measured data in the drainage stack in a real-life eighteen-floor building, the Li Ka-Shing (LKS), at PolyU of Hong Kong. Three observation points, at the mezzanine (M), 6th, and 12th floors, are arranged to record the air pressure in the primary building stack. The measured data are stored in a personal computer with a sampling period of 1 s. Statistical analysis revealed that there is an evident floor dependence of the air pressure in the real-life HBDS. The flatness factor of the pressure fluctuation increases with floor number, whereas the skewness factor has a reversed variation tendency; it decreases from a positive value in the M floor to negative values at higher floors. Probability density functions show the pressure fluctuation behaviors are far from normal distributions.

A-25 通気弁による排水立て管システムの排水能力改善手法に関する研究 : その4.二箇所・排水横枝通気弁システムの場合の詳細検討

A-25 通気弁による排水立て管システムの排水能力改善手法に関する研究 : その4.二箇所・排水横枝通気弁システムの場合の詳細検討

Characteristics of air pressure fluctuations in high-rise drainage stacks

Maximum air pressure in a drainage stack can deplete the appliance water trap seals that prevent the ingress of foul gases and odors into a habitable space. This study investigates the air pressure fluctuation frequency, as well as the maximum and average air pressures with their respective standard deviations, in a 38 m high drainage stack of a full-scale experimental tower under steady flow conditions of flow rates 1 Ls −1 to 4 Ls −1 discharging at a height between 15 m to 33 m above the stack base. Mathematical expressions are proposed to correlate the maximum air pressure with the probability density function of the data measured. The average prediction and the maximum under-prediction of the absolute peak pressure were determined with the margin of error taken within certain confidence levels. It was demonstrated that water seal failure would likely be occurred at some heights below the discharge locations. The outcome enhances the understanding of the characteristics of air pressure fluctuation within a drainage stack of a high-rise building.

Drainage demands of domestic washrooms in Hong Kong

Drainage demand estimation for an effective and healthy drainage stack design is examined in this study. Empirical expressions that incorporate building occupant load, simultaneous usage patterns and discharge flow attenuation along a horizontal pipe into the probable drainage load determination for a stack serving a number of domestic washrooms as installed in typical high-rise buildings in Hong Kong are proposed. Patterns of probable drainage demand and probable discharge flow in the stack are determined via Bayesian analysis and Monte Carlo simulations, respectively. The study outcome enables more effective sizing of a drainage stack for some residential buildings in a dense urban environment. Practical application: Providing a mathematical model for drainage load calculations, this study is a useful tool to aid drainage stack sizing for some high-rise residential buildings.

Air pressure variations at drainage stacks of high‐rise residential buildings

PurposeThe purpose of this paper is to examine the air pressure variations in an in‐use drainage stack of high‐rise residential buildings with the probable influence of occupant loads.Design/methodology/approachThe air pressure variations in a drainage stack of a typical in‐use high‐rise residential building in Hong Kong were correlated to the number of water closet (WC) flushes of the building. In particular, measured diurnal WC flushing patterns of the residential buildings were used to correlate the diurnal pressure variations measured at 16 m above the stack base in a 115 m high, 150 mm diameter fully vented drainage stack of a typical high‐rise residential building of Hong Kong.FindingsThe occurrence of the maximum air pressure in the stack could be correlated with the expected hourly WC flushes of the high‐rise residential buildings with mathematical demonstrations.Research limitations/implicationsThere may be high speed transients in the stack (>1 hertz) which was not measured.Originality/valueThe result would be a useful source of reference for the development of control strategies against probable appliance seal loss in high‐rise residential buildings.

A-45 通気弁による排水立て管システムの排水能力改善手法に関する研究 : その1排水横枝通気システムの検討

A-45 通気弁による排水立て管システムの排水能力改善手法に関する研究 : その1排水横枝通気システムの検討

A-42 超節水型大便器による排水立て管システムへの影響評価に関する研究

A-42 超節水型大便器による排水立て管システムへの影響評価に関する研究

An evaluation tool of infection risk analysis for drainage systems in high-rise residential buildings

This study proposes a simple risk analysis tool and evaluation level for the probable infection due to a contaminated drainage stack in residential high-rise buildings in some Asian cities which have equivalent drainage systems. The methodology would follow the conception of FMEA (Failure Mode Effects Analysis). In particular, key risk factors including connections between appliance and stack, the plumbing system, ventilation, equipment life and maintenance were surveyed and used to evaluate the overall risk associated in high-rise residential buildings with Monte Carlo simulations. With the proposed tool, regional risks of infection due to the building drainage systems were estimated, with respect to the city building age and height profiles. The results showed that a city with a high-rise environment would associate a higher spreading risk due to the drainage system. Practical applications: Following the outbreak of SARS (Severe Acute Respiratory Syndrome) in early 2003, the operational performance of drainage systems in high-rise residential buildings has become a major concern. The assessment system would be practical and sensible for evaluating the infection risk in building drainage systems for both existing buildings and new construction. The assessment tool may provide the government, designers and the occupants a source of reference to judge drainage system performance in either new construction or the existing building, so that improvements would be conducted.

An empirical approach to determine peak air pressure within the 2‐pipe vertical drainage stack

Following the massive outbreak of SARS (Severe Acute Respiratory Syndrome) in early 2003, the drainage systems in high‐rise residential buildings have become a major concern. Inappropriate drainage system design may cause pressure fluctuations and depletion of the water trap seal. In Taiwan, most vertical drainage stack pipes serving medium‐height apartment blocks are designed as 2 or more vertical pipe systems. A prediction method to determine the air pressure distribution within the single‐stack vertical drainage system with a single discharge has already been established. This paper expands this prediction method to allow the air pressure distribution of the 2‐pipe vertical drainage and vent system, which is widely used in Taiwan, to be predicted. Comparisons between the measured data and calculated values reveal that the prediction method can reproduce the negative and positive peak air pressure values within the 2‐pipe vertical drainage stack given single point discharge and steady flow conditions. A prediction model based on empirical parameters offers a reference for drainage system designers designing and maintaining water trap functions in buildings. This prediction method can be easily applied to drainage system design.

尿流量測定装置を有する大便器システムの性能評価に関する研究開発

Water-closet system equipped with uroflowmetry analyzer to measure out urine flow rate and volume was developed, to improve the medical treatment environment. This is an experimental study to evaluate the performance of the watercloset system, setting up in drainage stack and horizontal fixture branch piping system. As a result of examinations, allowable measurement accuracy with uroflowmetry and the reliability of system are confirmed quantitatively, under the pipe pressure fluctuations which is given by actual drainage load. The Watercloset system can be available for 2-pipe vertical drainage stacks equipped with loop-vent pipes, under the condition of permissible pipe pressure within ±100Pa.

STUDY OF THE PERFORMANCE EVALUATION OF AIR ADMITTANCE VALVES BY MEANS OF THE DRAINAGE CAPACITY PREDICTION METHOD FOR DRAINAGE STACK SYSTEMS

This study discusses the evaluation of influences on the drainage capacity of a drainage stack system with an air admittance valve by means of the drainage capacity prediction method, which was previously proposed by the author, while looking into the effectiveness of the method. The study also aims to propose a method to reduce labour and cost incurred by drainage capacity experiments. To be more specific, through this study, the following two points have been clarified: (1) Vent characteristics of five commonly available air admittance valves were identified using a simple experimental apparatus and the relationship between the airflow rate and the air flow resistance coefficient was acquired; (2) The results acquired from (1) were applied to the previously proposed drainage capacity prediction method and subsequently, it was found that the discrepancy between the estimated value and the actual value remained within ±10%, demonstrating that the method is effective in practical application.

Air pressure transient generation as a result of falling solids in building drainage stacks: definition, mechanisms and modelling

The consequences of air pressure transients in building drainage and vent systems (DVS) can be serious, as they compromise the integrity of the appliance trap seal - the last line of defence between the potentially hazardous foul air in the drainage and sewer network, and the habitable space within buildings. Pressure transients are caused by rapid changes in flow conditions in fluid systems. Much previous research has defined the nature and effect of air pressure transient generation and propagation on the air pressure regime within DVS. This paper confirms that falling solids have an effect on the pressure regime in a vertical stack; that transients are generated and that pressures are modified in a way hitherto undefined.