Drainage Stack Research Articles

A pilot study on the antimicrobial efficacy of a novel UV-LED system against drainage stack bioaerosol emissions during flushing episodes

Inactivation of airborne microorganisms by ultraviolet (UV) light has been considered one of the most effective procedures among disinfection methods. Ultraviolet light-emitting diodes (UV-LEDs) have a unique place as an emerging technology in air disinfection processes because of their rapid effectiveness and lack of material deterioration. In this study, the efficacy of high-power 285 nm UV-LEDs was explored for Escherichia coli (E. coli) (ATCC15597) inactivation in drainage stack airflow under continuous- and pulsed-UV irradiation conditions. Most relevant photoelectric properties influencing the device operation and performance, including duty cycles and input voltage, were thoroughly investigated. Antimicrobial efficiency varied from 29.0% to 88.0%. The antimicrobial efficiency of pulsed UV irradiation at different duty cycles but the same UV dose was similar. Antimicrobial efficiency was positively correlated with input voltage but negatively correlated with airflow velocity. Moreover, antimicrobial efficiency increased almost linearly with input power per airflow volume (P/Qa). The estimated Z-values of E. coli ranged from 0.0027 to 0.0341 cm2/µJ, and about 29–370 μJ/cm2 of UV dose can be used to obtain one-log inactivation of E. coli, depending on the experimental conditions. The results of this investigation indicate that UVB units can inactivate gastrointestinal drainage stack bioaerosols effectively. This study provides critical information and guidelines for disinfecting drainage stacks with UV, which may aid pathogen infection control in public environments during outbreaks.

The influence of different offset modes on the drainage characteristics of a double stack drainage system in a high-rise building

To meet the functional requirements of high-rise buildings, drainage stacks usually employ an offset pipe in the structural transfer floor. At the offset point, the flow direction changes and the air pressure fluctuates, which significantly influences the drainage system capacity and water seal effectiveness. Different offset modes have different degrees of influence on drainage characteristics. To better understand the influence of different offset modes on drainage characteristics, five different test conditions in double stack building drainage systems were established and investigated. DS1 was a standard double-stack drainage system with anti-reflux H-tube joints for every two floor levels. The remaining four systems were developed from DS1 by adopting various offset pipes (or pipe joints) on the fourth floor. DS2 adopted an S-shape offset pipe joint at the offset point. DS3 adopted double S-shape offset pipe joints. DS4 adopted a 1.0-m-long horizontal offset pipe. DS5 adopted a 1.5-m-long horizontal offset pipe. The pressure fluctuations and water seal losses were chosen as the experimental parameters to determine the maximum discharge capacity according to the Standard for Capacity Test of Vertical Pipe of the Domestic Residential Drainage System CJJ/T 245. The experimental results demonstrated that the installation of offset pipes (or pipe joints) contributed to the abrupt positive pressure and severe water seal losses at the position where flow direction shifted. As the length of the offset pipe increased, the positive pressure was more severe, and maximum discharge capacity was minor. The relationships among the maximum discharge rate, pressure fluctuation limits, and water seal losses are discussed. Lastly, a nondimensional analysis was adopted to understand the relationship between water seal losses and pressure limit values under different discharge rates for current test facilities. Practical application: Pipe offset has the potential to influence a drainage system discharge capacity. As the length of the horizontal offset pipe increases, the discharge capacity will decrease. In the actual design, the length of the offset pipe section should be reduced and this study demonstrates that the application of S-shape offset pipe joints is an efficient solution.

Design Methodologies for Sizing of Drainage Stacks and Vent Lines in High-Rise Buildings

Diameters for drainage stacks and vent lines within high-rise building drainage systems are determined by consulting building standard agencies’ design codes. While these are critical design decisions, codes are based upon dated research (1940s to 1970s), which has numerous inherent limitations, and the methodologies employed within the codes are unclear. Thus, a new methodology is presented which is based upon an analogy with other forms of multiphase flow transport systems. This methodology assumes, as a pre-condition, that flows of air and the flow of water within the stack are reasonably steady over time. Component diameters must then be chosen which ensure an acceptably large air supply or air–water flow ratio, and an acceptably small pressure excursion within the stack. Two ways to implement this methodology are presented: an ‘explicit approach’, in which component diameters are directly calculated using empirical correlations, and an ‘implicit approach’, in which component diameters are determined by iteration, using a hydraulic model. The methodology pre-conditions of the approach are then discussed. The physical geometry of the stack and branches tends to promote steady water flow but to render air flow very susceptible to temporary interruptions. A need to maintain the air pathway within high-rise drainage systems using components to supplement the air feed drawn in through the roof vent as required is highlighted.

Analysis of COVID-19 clusters involving vertical transmission in residential buildings in Hong Kong.

The Appendix is available in the online version of this article at 10.1007/s12273-022-0929-5.

Overcoming the influence of a 2 metre long pipe offset on water flow capacity of drainage with secondary ventilation in a high-rise building

A potential consequence of installing a 2 m long pipe offset on a ventilated drainage system in a high-rise buildings is that the water seal could be damaged when the flowrate exceeds the maximum discharge capacity of a drainage system, thereby threatening the indoor health safety. Some high-rise buildings are designed for commercial and residential use to achieve economic and social benefits, so the whole building use and layout changes in the vertical direction. The drainage stack may be designed with an offset between floors to avoid structural obstacles inside the building. The flow direction change could destroy the water seal of sanitary appliances and threaten the health of residents. To better understand the influence of the form of a pipe offset on the drainage capacity, a full-scale experiment was conducted to study the secondary ventilated system with an antireflux H-tube pipe, which was equipped with two guide plates inside to improve the air-water flow pattern and prevent backflow, installed between floor. This study also considered a kind of offset where the offset distance was 2.0 m rather than the S-shaped offset joint, which is more common in commercial and residential complexes. The influence on the discharge capacity of installing an extra antireflux H-tube pipe was compared with normal 90-degree elbow and only one antireflux H-tube pipe above the offset point. The pressure fluctuation and water seal losses under constant discharge rates were adopted as experimental parameters to determine the maximum discharge capacity according to Standard for Capacity Test of Vertical Pipe of the Domestic Residential Drainage System. Results show that the installation of an extra antireflux H-tube pipe can release the air accumulation caused by pipe offset, and the combined installation of a large curvature elbow and an extra antireflux H-tube pipe can effectively improve the discharge capacity.Practical Application: 2 metre long offsets are not unusual in ventilated drainage systems in high-rise buildings, however, designers and builders do not pay sufficient attention to the adverse consequences of the pipe offset. An extra antireflux H-tube pipe can be installed above the offset joint to optimise the drainage system to perform as it would without the offset. In a system with 2 m long pipe offset, installing a large curvature elbow together with an extra antireflux H-tube pipe together provides a better effect.

Explosive outbreak of SARS-CoV-2 Omicron variant is associated with vertical transmission in high-rise residential buildings in Hong Kong

The phenomenon of vertical transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in high-rise residential buildings (HRRBs) is unique in our densely populated cosmopolitan city. The compulsory testing of a whole building under the scheme of restriction-testing declaration (RTD) during the fourth wave (non-Omicron variant) and fifth wave (mostly Omicron variant) of COVID-19 outbreak in Hong Kong allowed us to study the prevalence of this phenomenon, which may represent a form of airborne transmission. From 23 January 2021 to 24 March 2022, 25,450 (5.8%) of 436,397 residents from 223 (63.0%) of 354 HRRBs under RTD were test-positive for SARS-CoV-2. Using the clustering of cases among vertically aligned flats with shared drainage stack and lightwell as a surrogate marker of vertical transmission, the number of vertically aligned flats with positive COVID-19 cases was significantly higher in the fifth wave compared with the fourth wave (14.2%, 6471/45,531 vs 0.24%, 3/1272; p < 0.001; or 2212 vs 1 per-million-flats; p < 0.001). Excluding 22,801 residents from 38 HRRBs who were tested negative outside the 12-week periods selected in fourth and fifth waves, the positive rate among residents was significantly higher among residents during the fifth wave than the fourth wave (6.5%, 25,434/389,700 vs 0.07%, 16/23,896; p < 0.001). Within the flats with COVID-19 cases, the proportion of vertically aligned flats was also significantly higher in the fifth wave than in the fourth wave (95.6%, 6471/6766 vs 30.0%, 3/10, p < 0.001). The proportion of HRRBs with COVID-19 cases was significantly higher during the corresponding 12-week period chosen for comparison (78.2%, 219/280 vs 11.1%, 4/36; p < 0.001). Whole-genome phylogenetic analysis of 332 viral genomes showed that Omicron BA.2 was the predominant strain, supporting the high transmissibility of BA.2 by airborne excreta-aerosol route in HRRBs of Hong Kong.

CFD Numerical Simulation in Building Drainage Stacks as an Infection Pathway of COVID-19.

Being aware of global pandemics, this research focused on the potential infection routes in building drainage systems. Case studies have found that dysfunctional building drainage systems not only failed to block contaminants but also potentially became a route for the spreading of viruses. Several fluid simulations in pipelines were conducted in this research using COMSOL Multiphysics. In particular, virus transmission from one patient’s room to other uninfected residential units through pipelines was visualized. A 12-story building, which is commonly seen in the local area, was designed as a simulation model to visualize the transmission and analyze its hazards. Furthermore, five environmental factors were filtered out for discussion: distance, time span, pressure, initial concentration, and environment temperature. By manipulating these factors, the relationship between the factors and the behavior of the contaminant could be explored. In addition, a simulation with a different pipeline arrangement was included to observe the virus diffusion behavior under different scenarios. The visualized simulation concluded that the contaminant would spread through the drainage system and arrive at the neighboring four floors within an hour under the circumstances of a 12-story building with broken seals and constant pressure and contaminant supply on the seventh floor. Meanwhile, the whole building would be exposed to infection risks by the continuous virus spreading through a drainage system. Distance, time span, and pressure were considered critical factors that affected indoor contamination in the system. On the other hand, initial concentration and environmental temperature did not have significant roles. Visualizing the behavior of viruses provides a glimpse of what happens behind walls, paving the way for recognizing the importance of maintaining functional drainage systems for individuals’ health.

Mathematical model and experiment analysis of pressure fluctuation inside dual-stack drainage system in residential buildings.

The final velocity was put forward to study the water flow characteristics inside the building drainage system; however, it is more suitable for low-rise and multi-storey buildings, not for high-rise buildings. This study revealed the drainage transient characteristics of a double stack drainage system in high-rise residential buildings. Based on the final velocity, the air-water interaction mechanism and two-phase flow conditions in high-rise residential drainage stacks were discussed. An influence model of drainage system flow rate on pressure fluctuation under the change of state parameters such as ventilation rate, pipe wall roughness and building height was established. The pressure limit and flow rate data were obtained through full-scale experiments. The pressure limit and flow rate model were simplified to Pn = A ċ Q2 + B ċ Q1:81 + C. After the data were verified, the fitting coefficients A, B and C were linear to the floor height.

Spread of SARS-CoV-2 aerosols via two connected drainage stacks in a high-rise housing outbreak of COVID-19

Vertical transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) along a vertical column of flats has been documented in several outbreaks of coronavirus disease 2019 (COVID-19) in Guangdong and Hong Kong. We describe an outbreak in Luk Chuen House, involving two vertical columns of flats associated with an unusually connected two-stack drainage system, in which nine individuals from seven households were infected. The index case resided in Flat 812 (8th floor, Unit 12), two flats (813, 817) on its opposite side reported one case each (i.e., a horizontal sub-cluster). All other flats with infected residents were vertically associated, forming a vertical sub-cluster. We injected tracer gas (SF6) into drainage stacks via toilet or balcony of Flat 812, monitored gas concentrations in roof vent, toilet, façade, and living room in four of the seven flats with infected residents and four flats with no infected residents. The measured gas concentration distributions agreed with the observed distribution of affected flats. Aerosols leaking into drainage stacks may generate the vertical sub-cluster, whereas airflow across the corridor probably caused the horizontal sub-cluster. Sequencing and phylogenetic analyses also revealed a common point-source. The findings provided additional evidence of probable roles of drainage systems in SARS-CoV-2 transmission.

Aerosol transmission of SARS-CoV-2 due to the chimney effect in two high-rise housing drainage stacks

Stack aerosols are generated within vertical building drainage stacks during the discharge of wastewater containing feces and exhaled mucus from toilets and washbasins. Fifteen stack aerosol-related outbreaks of coronavirus disease 2019 (COVID-19) in high-rise buildings have been observed in Hong Kong and Guangzhou. Currently, we investigated two such outbreaks of COVID-19 in Hong Kong, identified the probable role of chimney effect-induced airflow in a building drainage system in the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We injected tracer gas (SF6) into the drainage stacks via the water closet of the index case and monitored tracer gas concentrations in the bathrooms and along the facades of infected and non-infected flats and in roof vents. The air temperature, humidity, and pressure in vertical stacks were also monitored. The measured tracer gas distribution agreed with the observed distribution of the infected cases. Phylogenetic analysis of the SARS-CoV-2 genome sequences demonstrated clonal spread from a point source in cases along the same vertical column. The stack air pressure and temperature distributions suggested that stack aerosols can spread to indoors through pipe leaks which provide direct evidence for the long-range aerosol transmission of SARS-CoV-2 through drainage pipes via the chimney effect.

Time-Variant Positive Air Pressure in Drainage Stacks as a Pathogen Transmission Pathway of COVID-19

Time-variant positive air pressure in a drainage stack poses a risk of pathogenic virus transmission into a habitable space, however, the excessive risk and its significance have not yet been sufficiently addressed for drainage system designs. This study proposes a novel measure for the probable pathogenic virus transmission risk of a high-rise drainage stack with the occurrence of positive air pressure. The proposed approach is based on time-variant positive air pressures measured in a 38 m high drainage stack of a full-scale experimental tower under steady flow conditions of flow rate 1–4 Ls−1 discharging at a height between 15 m to 33 m above the stack base. The maximum pressure and probabilistic positive air pressures in the discharging stack ventilation section with no water (Zone A of the discharging drainage stack) were determined. It was demonstrated that the positive air pressures were lower in frequency as compared with those in other stack zones and could propagate along the upper 1/3 portion of the ventilation pipe (H’ ≥ 0.63) towards the ventilation opening at the rooftop. As the probabilistic positive pressures at a stack height were found to be related to the water discharging height and flow rate, a risk model of positive air pressure is proposed. Taking the 119th, 124th, 140th and 11,547th COVID-19 cases of an epidemiological investigation in Hong Kong as a baseline of concern, excessive risk of system overuse was evaluated. The results showed that for a 20–80% increase in the frequency of discharge flow rate, the number of floors identified at risk increased from 1 to 9 and 1 to 6 in the 34- and 25-storey residential buildings, respectively. The outcome can apply to facilities planning for self-quarantine arrangements in high-rise buildings where pathogenic virus transmission associated with drainage system overuse is a concern.

ALC中層集合住宅専用排水立て管システムの提案と性能評価 （その2）排水横主管の拡径に伴う適用階数の検討

ALC中層集合住宅専用排水立て管システムの提案と性能評価 （その2）排水横主管の拡径に伴う適用階数の検討

ALC中層集合住宅専用排水立て管システムの提案と性能評価 （その1）通気方式の違いによる排水性能への影響

ALC中層集合住宅専用排水立て管システムの提案と性能評価 （その1）通気方式の違いによる排水性能への影響

SARS-CoV-2: The Growing Case for Potential Transmission in a Building via Wastewater Plumbing Systems.

SARS-CoV-2: The Growing Case for Potential Transmission in a Building via Wastewater Plumbing Systems.

Study on Measurement Indexes of Radiated Noise from Drainage Stacks and Fittings

Study on Measurement Indexes of Radiated Noise from Drainage Stacks and Fittings

Live stack replacement in high-rise residential buildings

There are approximately 4,500 tall buildings under local authority control in the UK. Many were built in the postwar period, which means that refurbishment programmes are required at regular intervals to keep the buildings operational and comfortable for local authority residents. While many refurbishment programmes are focused on the aesthetic properties of a building, there is a growing need to address the drainage systems in high-rise buildings, which can often be overlooked until a problem occurs and is reported. Local authorities can arrive at a situation where essential drainage system maintenance work needs to take place, but can only be completed by moving residents out of buildings temporarily, or to another site altogether. This is a costly undertaking, which often brings a range of unknown factors that can increase the time needed to complete work and the cost of rehousing residents. Manufacturers are beginning to work with networks of approved installers to offer an alternative, more efficient approach and have developed a drainage stack replacement method that takes place section by section within a building, without putting a full drainage system out of commission. The process that has been developed also makes provision to improve the fire protection systems within a building, with a range of passive fire protection products for use with plastic-based drainage systems. This paper outlines the problems found in many high-rise residential buildings under local authority control and sets out a solution, which has been incorporated into a growing number of refurbishment and maintenance programmes, that allows for project cost control, minimises disruption to residents, and provides for effective building fire protection improvements as a matter of course.

Influence of the vent pipe diameter on the discharge capacity of a circuit vent building drainage system

Experiments on different vent pipe diameters (nominal diameters of 100, 75 and 50 mm; DN100, DN75 and DN50, respectively) in a full-scale circuit vent building drainage system were conducted in a 60 -m high structure, and the wastewater discharge capacities as a function of vent pipe diameter were measured. Critical pipe pressures, water seal losses of sanitary fixtures and air flow rates were measured. The ultimate pressure values in pipes on lower floors were larger than those in pipes on higher floors using DN100 and DN75, which was opposite to the results with DN50. A positive correlation between the ultimate pressure values and floor heights, as well as between ultimate pressure values and water seal losses, was found for DN100 and DN75. The maximum discharge flow of the three systems using DN100, DN75 and DN50 vent pipes was 17.0 L/s, 14.0 L/s and 7.5 L/s, respectively. Nevertheless, in China, the maximum wastewater discharge capacity in a circuit vent system adopting a DN100 vent pipe connected to a DN100 drainage stack in tall residential buildings is 11.5 L/s according to the Code for Design of Building Water Supply and Drainage. Thus, the vent pipe diameter DN75 can fully meet the design requirements of drainage systems for high rise buildings in China. The engineering cost associated with material expenses for building drainage systems can be minimised by optimising the size of vent pipe based on required capacity rather than using a single size universally. Practical application: The engineering cost associated with material expenses for building drainage systems can be minimised by optimising the size of vent pipe based on required capacity rather than using a single size universally.

Experimental study on air pressure variation in a horizontal pipe of single-stack drainage system.

The water trap seal under the sanitary appliances is the primary defense against the ingress of foul gases and odors. However, research on air pressure variation in a horizontal pipe of a single-stack drainage system is very limited. Thus a physical model study was conducted to investigate the air pressure variation in a horizontal pipe. Four parameters were studied that affect the pressure variation; that is, water flow rate, inlet height, ventilation condition and outlet condition. When the top of the vertical drainage stack and the outlet were fully open to the atmosphere, the flow in the horizontal pipe changed from free surface flow to slug flow at certain times. The mean values and magnitudes of pressure fluctuation at measuring points on the horizontal pipe increased with Qw but decreased along the horizontal pipe. The inlet height had relatively small influence on the pressure variation. Three ventilation conditions; that is, top fully open, half open and sealed, were tested, and a choking flow was formed in the vertical drainage stack and the pressure in the horizontal pipe decreased under the top sealed condition. Three outlet conditions; that is, outlet fully open, half submerged and fully submerged, were tested. The pressure in the horizontal pipe increased significantly under the outlet fully-submerged condition, which should be avoided in the actual operation by careful designing.

業務用ビルの水廻りスペースのフリープラン化に対応する小型圧送排水システムに関する研究 その4 既存排水立て管に圧送排水システムが与える排水能力影響に関して

業務用ビルの水廻りスペースのフリープラン化に対応する小型圧送排水システムに関する研究 その4 既存排水立て管に圧送排水システムが与える排水能力影響に関して

Pressure transient suppression in drainage systems of tall buildings

ABSTRACT The suppression of pressure transients in building drainage systems is essential for reducing cross-contamination by the spread of pathogens. The topic is now much better understood due to work following the invention of the first drainage-specific positive-pressure transient-attenuation device in the year 2000. The present research addresses the attenuation of much larger problematic air-pressure transients found in tall buildings. The development of a new technique is described for the attenuation of positive air pressure transients of approximately 2000 mm water gauge (wg) (20 kPa) for which there is currently no means to alleviate. The performance of the new technique was validated by numerical simulation and full-scale test-rig experiments. The full-scale test rig represented a 44-storey building with a 150 mm main drainage stack. The pressure wave generator applied a 2000 mm wg pressure transient from a large accumulator compressor delivering 270 litres of air at 10 bar pressure. This resulted in a capacity of 2700 litres of air at atmospheric pressure delivered into the system within 0.2 s. Results show that a prototype device using the new technique is capable of reducing the applied pressure transient by 88%, rendering it harmless and returning the system to normal operation in a matter of seconds.