BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns building drainage and ventilation systems wherein air may be admitted into a ventilation system while avoiding the discharge of air therefrom caused by positive air pressure transients in the system. More particularly, it is concerned with a system whereby a positive air pressure attenuation device and an air admittance valve may be employed in combination, and also a system including a plurality of ventilation conduits which are connected to one or more common vent pipes.
2. Description of the Prior Art
It is common for buildings to include plumbing systems which include ventilation stacks as a part of the drainage system. The drainage systems lead to a sewer system, such as a municipal sewage system, a combined sanitary sewer and stormwater sewer system, or a septic tank, and as a consequence foul odors must be prevented from entering the building from the sanitary sewer system. This is accomplished in large measure by the use of generally U-shaped water traps within the drainage system, whereby water held in the trap blocks the escape of foul air into the building. It is important to maintain a sufficient quantity of water in the trap to avoid direct passage of the air in the drainage system into the environment of the building. It is thus desirable to control pressure fluctuations within the drainage system and its ventilation system, including both overpressurization and underpressurization.
Traditional modes of trap seal protection rely predominantly on passive solutions where reliance is placed on cross-connections and vertical stacks vented to the atmosphere. This approach, while both proven and traditional, has inherent weaknesses, including the remoteness of the vent terminations and the multiplicity of open roof level stack terminations inherent in complex buildings such as buildings having multiple tenants. The complexity of the vent system required also has significant cost and space implications. Moreover, air transient gradients generated within the building drainage and ventilation system as a natural consequence of system operation may be responsible for trap seal depletion and contamination of habitable space within the building.
The development of air admittance valves (AAVs), such as is shown by U.S. Pat. No. 6,532,988 and companion International Application Publication No. WO 00/46454, the disclosure of which is incorporated herein by reference, provides the designer of drainage and ventilation systems with a means of alleviating negative transients generated as random appliance discharges contribute to the time dependent water-flow conditions within the system. AAVs are one active control solution to the problem presented by the need to allow air to enter into the drainage system freely but inhibit the release of foul air from the drainage system into the atmosphere. However, these AAVs also prevent positive air transients which arise within the drainage system from escaping to the atmosphere, which in consequence leads to a reduced performance of the drainage system. The positive air pressure transient propagation within the building drainage and ventilation system as a result of intermittent closure of the free airpath through the system or the arrival of positive transients generated remotely within the sewer system, such as possibly by some surcharge event downstream including surcharges caused by heavy rainfall in combined sewer applications, is not addressed by AAVs.
It is also known to have address positive air transients by the employment of a positive air pressure attenuation device (PAPA). PAPAs, such as disclosed in published International Application No. WO 03/021049, the disclosure of which is incorporated herein by reference, may include a variable volume bag that expands under the influence of a positive transient and therefore allows system airflows to attenuate gradually, therefore reducing the level of positive air transients generated in the system.
SUMMARY OF THE INVENTION
The present invention is directed to a complete building drainage and ventilation system which combine the advantages of each of the foregoing devices to provide greater protection against the introduction of diseases such as SARS or terrorist attack by the introduction of biological or chemical agents. Moreover, the present invention includes a system whereby in a complex or multi-tenant building, multiple drainage and ventilation systems may be interconnected at the upper level of the system into a common discharge stack, thereby offering a completely closed-off drainage system providing a maximum of protection against the introduction of infectious biological disease or chemical or biological attack, save for that limited amount of air which may enter through the AAV during a limited period of system underpressure.
The drainage and ventilation system hereof preferably includes a building having a plurality of stacks each having drainage pipes which are interconnected to one or more common ventilation pipes, and including the use of both a PAPA and an AAV which are in fluidic communication with the stacks and function as a part of the system. The PAPA and AAV may be positioned at various locations of the system, such as, for example, local devices positioned in fluidic communication with the pipes of the system at sensitive areas of the system, positioning PAPAs at a lower area of the stack by use of a diversion pipe, positioning one or multiple AAVs at or adjacent water traps in the pipes, or by providing a PAPA and an AAV in fluidic connection at the upper end of the system so as to be in fluidic communication with a plurality of stacks. This latter approach, as may be seen in the following description, provides a simple and elegant solution which utilizes the fluidic communication between the stacks when connected to common ventilation pipes in combination with the PAPA and AAV to address pressure fluctuations throughout the system. The building may be a building of the type wherein the intrusion of outside agents, odors and the like are controlled and or limited in their ability to reach at least certain rooms within the building. As used in the description hereof, the stacks include, in addition to the drainage pipes, water sources such as drains, sinks, toilets, water closets and the like which permit water to enter the drainage pipes, and each such water source is fluidically connected to the associated drainage pipe via water traps or equivalent devices which permit the flow of water through the drainage system but inhibit the escape of odors and agents from the drainage system to the water sources. The combined usage of the PAPA and AAV in such a system provides a closed-off drainage system offering a maximum of protection against the intrusion of infections, biological contaminants, and chemical agents into a secured building by limiting the introduction of air into the system through the AAV. The combined use of the PAPA and AAV protects the water traps or equivalent devices against either underpressure conditions by the use of the AAV, and also overpressurization by the use of the PAPA, which could otherwise occur in the system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a sealed building drainage and ventilation system in accordance with the present invention, showing a building arrangement having four stacks each with a respective water source which is connected to respective drain and ventilation pipes, and having a common ventilation pipe provided with a PAPA and an AAV in a T or parallel arrangement;
FIG. 2 is a schematic view of a sealed building drainage and ventilation system similar to that shown in FIG. 1, but having the PAPA and AAV connected in series with the AAV positioned remotely relative to the PAPA;
FIG. 3 is an exploded view of an AAV useful in accordance with the present invention;
FIG. 4 is a vertical sectional view of a PAPA useful in accordance with the present invention;
FIG. 5 is a graph illustrating water closet discharges showing flow rate over time in a test system according to FIG. 1;
FIG. 6 is a graph illustrating entrained airflow rates over time in annular water flows through a test system according to FIG. 1;
FIG. 7 is a graph illustrating stack height versus stack air pressure in a test system according to FIG. 1;
FIG. 8 is a graph illustrating the relationship of air pressure within drainage pipes time over time during water closet discharges in a test system according to FIG. 1;
FIG. 9 is a graph showing air pressure profiles comparing stack height to stack air pressure from the base of a stack to the common pipe leading to the AAV and PAPA during an initial phase of a water closet discharge as shown in FIG. 8;
FIG. 10 is a graph similar to the graph of FIG. 9 showing air pressure profiles comparing stack height to stack air pressure from the base of a stack to the common pipe leading to the AAV and PAPA during a later phase of a water closet discharge as shown in FIG. 8;
FIG. 11 is a graph showing air pressure over time during sequentially applied sewer air pressure transients imposed at the base of each stack in a test system according to FIG. 1;
FIG. 12 is a graph showing entrained airflows in the respective stacks during the sequentially applied sewer air pressure transients shown in FIG. 11;
FIG. 13 is a graph illustrating the stack air pressure at various heights of two of the stacks of the test system according to FIG. 1 at 15 seconds into the application of the sewer air pressure transients of FIG. 11;
FIG. 14 is a graph showing PAPA volume and AAV airflow over time during the applied sewer air pressure transients imposed at the base of each stack as shown in FIG. 11;
FIG. 15 is a graph showing trap seal water levels in pipe 2 of stack 1 during a surcharge event and subsequent sewer transient in a test system according to FIG. 1;
FIG. 16 is a graph showing trap seal water levels in pipe 7 of stack 2 during a surcharge event and subsequent sewer transient in a test system according to FIG. 1;
FIG. 17 is a graph showing trap seal water levels in pipe 15 of stack 3 during a surcharge event and subsequent sewer transient in a test system according to FIG. 1;
FIG. 18 is a graph showing trap seal water levels in pipe 20 of stack 4 during a surcharge event and subsequent sewer transient in a test system according to FIG. 1; and
FIG. 19 is a graph showing trap seal water retention in pipes 2, 7, 15 and 20 following a surcharge to the network and subsequent sewer imposed transient in a test system according to FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In connection with the above-referenced invention, a building 30 is schematically shown in FIG. 1 which includes a sealed off drainage and ventilation network or system 32 as typically used in for handling and discharging water in a plumbing system. The system 32 is vented to the surrounding atmosphere and liquid or liquid/solid discharges from the system 32 are illustrated as being delivered to a sewer 34, which as used herein includes not only a municipal sewage system but septic tank systems and the like as is well known to those skilled in the art. The building 30 as illustrated includes a simplified plumbing arrangement serving four individual compartments 36, 38, 40 and 42, but is to be appreciated that the showing of four compartments is merely illustrative of buildings having multiple compartments however denominated such as offices, rooms or apartments. While in the illustration of FIGS. 1 and 2, the individual compartments 38 and 40 are shown as being at a higher level than the compartments 36 and 42, the system hereof is not limited to multiple level compartments and with respect to the example described hereinafter, this is for convenience of illustration only. In the example described hereinafter, all of the compartments and their respective components (dry stack pipes, feed pipes, discharge sources, traps, dead end pipes, wet stack pipes, and the like) are actually located at substantially the same relative elevation, i.e. that all traps are at substantially the same elevation, all dead end pipes are at substantially the same elevation, and so on.
To assist in further understanding of the present invention, FIG. 1 illustrates a simplified system 32 having four stacks A, B, C and D. The four stacks are linked or fluidically interconnected at an upper level within or outside the structure by a suitable junction, here shown as a common pipe or manifold 11. As used herein, the stacks each have wet stack portions which include discharge pipes and feed pipes, and dry stack portions which do not typically come into contact with liquid. These portions may be part of a continuous pipe, but more typically and for ease of understanding in the example, the description of the system 32 hereof refers to pipes which are fluidically interconnected as part of a stack. Thus, the wet stack portion of the four stacks A, B, C and D have respective wet stack discharge pipes 1, 6, 14 and 19 which deliver discharges from the system to the sewer 34, and feed pipes 2, 7, 15 and 20 which deliver water to the wet stack discharge pipes 1, 6, 14 and 19 respectively from respective discharge sources 46, 48, 50 and 52. The feed pipes 2, 7, 15 and 20 each include respective U-shaped traps 54, 56, 58 and 60. The discharge sources 46, 48, 50 and 52 are also referred to herein as “appliances” and are illustrated as water closets, also known as toilets or commodes, but it may be appreciated that these sources may include a variety of plumbing hardware or fitting items, such as by way of example but not limitation, floor drains, sinks, shower stalls, bidets, water fountains or the like. Each stack A, B, C and D further includes wet stack upper pipes 3, 8, 16 and 21 which are located just above the junctions where the feed pipes connect to the stacks, dead end pipes 4, 9, 17 and 22, and upper pipes 5, 10, 18 and 23. The wet stack upper pipes and the dead end pipes are considered herein as part of the wet stack portion of the stacks, and the upper pipes 5, 10, 18 and 23 are considered dry stack pipes, meaning that typically only air and not liquid is typically held therein and communicated therethrough. The upper or dry stack pipes may be directly or indirectly fluidically coupled for connecting each of the respective stacks A, B, C, and D at an upper level, i.e. above the respective dead end pipes. While such connection means may be a direct connection of one dry stack pipe to another, more typically an interconnecting member is used to fluidically connect the stacks at an upper level. Such an interconnecting member or means may be a pipe, hose or fitting, and is here illustrated as a common pipe or manifold 11 which fluidically connects the stacks and extends upwardly for connection to other connectors for ventilation. In the illustration of the system shown in FIGS. 1 and 2, the common pipe 11 in turn is connected at its uppermost end to a T fitting 62 which connects to PAPA pipe 13 and AAV pipe 12. A PAPA 68 is then connected to the terminal end of the PAPA pipe 13 and an AAV 70 is then connected to the AAV pipe 12. Because both the AAV and PAPA are designed to be positioned either within the ambient atmosphere or within a closed environment, the T fitting 62 and the pipes 12 and 13 may be located above the roof 72 of the building 30. Thus, in the system 32 of FIG. 1, the T fitting 62 provides that the PAPA 68 and the AAV 70 are connected in parallel. While the positioning of the PAPA 68 and the AAV 70 at the upper end of the system 32 is a preferred arrangement of these components, it is to be understood that the invention hereof contemplates other placement options for the PAPA 68 and AAV 70 within the system 32. For example, one or a plurality of the AAVs 70 may be located at alternate locations such as adjacent and fluidically connected to the traps 54, 58, 60 and 62, or one or more PAPAs could be installed proximate the stacks A, B, C and D by the use of a diversion pipe fluidically connected to the stack, including positioning the diversion pipe for connection to the wet stack portion. Positioning the PAPA 68 and the AAV 70 at these alternate locations within the building 30 would still fulfill the goal of providing air to the system 32 from controlled sources.
FIG. 2 shows an alternate configuration of the system 32A which is similar to the system 32 in most respects, and in which similar reference characters are used to identify similar components. In the system 32A, however, the T fitting 62 is removed and the PAPA 68 is connected either directly to the common pipe 11 or by a further pipe or the like. A connector pipe 74 is then provided between the PAPA 68 and the AAV 70 which, as in system 32, is able to receive air from the ambient atmosphere or, as illustrated, from an accessible loft space to provide an enclosed, sealed building source of air to the AAV 70.
One AAV 70 useful in accordance with the present invention is shown in U.S. Pat. No. 6,532,988, the disclosure of which is incorporated herein by reference and shown in an exploded view in FIG. 3. Such an AAV broadly includes a valve body 76 having a lower part comprising a normally vertical tubular member 78 adapted to be connected to a pipe including a common pipe or manifold as described above which is part of a sanitary discharge and ventilation system. The upper end of the tubular member 78 has a conical shaped restriction 80 which is closed at its extremity. The conical upper portion 80 of the tubular member 78 is provided with two diametrically opposed passages 82 each of which has a moulded-in grid 84 to prevent the entry of strange objects, such as animals or insects. The conical upper portion 80 of the tubular member 78 is surrounded by an oblong bowl-shaped housing 88, extending upwards from the tubular element 78 and having an upper edge 90 which is situated about a horizontal plane crossing the upper extremity of the conical portion 80 of the tubular member 78.
The space between the bowl-shaped housing 88 and the conical portion 80 of the tubular member is subdivided by a partition 92 into mutually opposed orthogonally arranged pairs of first and second chambers. The first pair of chambers are delimited by the partition 92 and closed sections 94 of the conical portion 80 and are in communication with the surrounding atmosphere via openings 96 in the bowl-shaped housing 88. The second pair of chambers are delimited by the partition 92 and the bowl-shaped housing 88 and are in communication with the lower tubular member 78 via the passages 82 in the conical portion 80 of the tubular member 78. The upper edge of the partition 92 is located about the horizontal plane and is configured so as to form a valve seat 98. A valve member 100 is carried on the upper edge of the partition 92 and is normally seated on the valve seat 98 to isolate the first pair of chambers from the second pair of chambers when the internal pressure in the system 32 (or 32A) is at least equal to the atmospheric pressure.
The valve member 100 is lifted or elevated above the valve seat 98 in response to a lowering of the internal pressure below the atmospheric pressure to thereby place the first pair of chambers in communication with the second pair of chambers, thus admitting atmospheric air into the system 32, 32A connected to the lower tubular member 78. The valve member 100 and the corresponding valve seat 98 preferably have a butterfly-shaped form which is positioned in a longitudinal direction inside the oblong bowl-shaped housing 88. The openings 96 in the bowl-shaped housing 88 are also provided with a grid 102 to avoid interference between the valve member 100 with any foreign object. The closed extremity of the conical portion of the tubular member 78 is provided with a closed cavity 104 extending downwards and being arranged as a fixed female guiding means for the valve member 100 which is, for that purpose, provided with a projection 106 (movable male guiding member) having similar dimensions as the cavity 104. The main or inner part of the valve member 100 is of hard plastic or the like, while the peripheral border part 108 is made of a soft plastic material to seal with the valve seat 98. The valve body 76 is closed with an upper lid 110 which encloses the upper edge in a tight manner by slightly conical normally downwardly extending side walls 112.
An example of a PAPA 68 useful in accordance with the present invention is shown in International Application PCT/IB02/03577 published as International Publication Number WO 03/021049 published 13 Mar. 2003, incorporated by reference and in a corresponding national stage U.S. patent application Ser. No. 10/588,420 filed Aug. 16, 2004 and published on Dec. 30, 2004 as Patent Publication No. 20040261870, the disclosure of which is incorporated by reference herein. Such a PAPA 68 comprises an external casing 114, a housing 116, a flexible reservoir 118 and an end cap 120. The assembled PAPA 68 is shown in FIG. 4. The flexible reservoir 118 covers the central portion of the housing and is secured to a housing receiving end 122 and the housing remote end 124 by means of an “0” ring 126. The flexible reservoir 118 is sealed against the housing receiving end 122 and the housing remote end 124 by the “0” ring 126 compressing a layer of sealant (not shown). This allows the flexible reservoir 118 to operate without any leakage.
The housing receiving end 122 and the housing remote end 124 are linked together by means of separator plates 128 leaving between them open spaces in contact with the flexible reservoir 118.
The external casing 114 fits partly over the housing 116 and over the flexible reservoir 118. The external casing 114 has a plurality of means of ventilation 130, such as openings, shown for example in FIG. 4 in a base surface 132. These means of ventilation 130 allow the flexible reservoir 118 to be in permanent contact with the atmospheric air at atmospheric pressure whilst preventing the flexible reservoir 118 from being damaged by any external event. A graduated connector 134 may be provided for attaching the PAPA 68 to, e.g., pipe 13, T-fitting 62, or common pipe 11 of a drainage and ventilation system 32 or 32A. The graduated connector 134 allows the connection of at least two different sized pipes together in a secure manner, and may be made of an elastomeric material. The housing 116 includes a remote section 136 which leads to the housing remote end 124, a receiving section 137 which extends remotely from the housing receiving end 122, and the separator plates 128 which allow airflow to continue through the PAPA when the flexible reservoir 118 is fully collapsed. The separator plates 128 do not extend fully around the circumference of the housing 116, but rather provide gaps 140 between the separator plates 128 allow air from the drainage and ventilation system 32 or 32A to enter the flexible reservoir 118 and inflate the latter in the case of positive pressure within the system 32 or 32A, thus absorbing the energy of any transient pressure wave. Two or more PAPAs 68 may be connected in series, with the connections between the PAPAs 68, or between a PAPA 68 and an AAV 70, or to connecting pipes or other connectors, being a push fit connection.
In complex building drainage systems, the operation of the system is designed to accommodate the discharge of water into the system by various appliances such as the discharge sources 46, 48, 50 and 52. Multiple discharge sources are typically provided in a discharge network or system, and their operation is almost always entirely random. As a consequence, these discharge sources provide conditions which result in air entrainment and pressure transient propagation, which are entirely random. No two systems will be identical in terms of their usage at any time. This diversity of operation implies that inter-stack venting paths will be established if the individual stacks within a complex building network are themselves interconnected. The present invention takes into account this diversity and utilizes it to provide system venting and a sealed drainage and ventilation system 32 or 32A. While it is contemplated that the best mode of operation of such a sealed drainage and ventilation system will employ the interconnection within the system at a relatively upper location with respect to the building, which is that sector of the system which would normally be considered the “dry stack” region above water discharge sources, it may be possible to provide the interconnection between the stacks of the system at a lower level including the alternate positioning of the PAPA 68 and AAV 70 as described above.
To provide a most preferable sealed building drainage and ventilation system 32 or 32A as illustrated herein, negative air transients in the system would be alleviated by drawing air into the network from a secure space providing either purified or segregated air, rather than from the external atmosphere. This may be provided by the use of AAVs 70 positioned to deliver air to the system at locations adjacent the discharge sources 46, 48, 50 and 52, or from a purifying mechanism, or at a predetermined location within the building, such as an accessible loft space 142 as an alternative to being located in the ambient atmosphere above roof 72. Similarly, to provide such a preferable sealed building drainage and ventilation system 32 or 32A, it is necessary to attenuate positive air pressure transients by means of PAPA devices 68 mounted within the building envelope. While it might be considered that this would be problematic, positive air pressure could build within the PAPAs and therefore negate their ability to absorb the positive air pressure arising from transient airflows within the system. This problem is largely addressed in the present invention by linking generally upright stacks in a complex building and thereby utilizing the diversity of use inherent in building drainage systems. Such diversity helps to ensure that pressure transients delivered to PAPA devices 68 are themselves alleviated by allowing trapped air to vent through the interconnected stacks and downward into the sewer 34. The present invention also utilizes the complexity of the system 32 or 32A to protect the system 32 or 32A from sewer driven overpressure and positive transients. Typically, a complex building's drainage and ventilation system 32 or 32A will be interconnected to the main sewer 34 and its inherent piping systems at least initially via a number of connecting smaller bore drains. The larger bore size of the sewer 34 advantageously ensures that adverse pressure conditions will thereby be distributed among the stack piping and the network interconnection will continue to provide venting routes.
EXAMPLE
The following example of the operation of the system 32 utilizes the AIRNET simulation developed through research at Heriot Watt University. The AIRNET simulation of system operation provides local air pressure, velocity and wave speed information throughout a network at time and distance intervals as short as 0.001 seconds and 300 mm. In addition, the AIRNET simulation utilized in the example hereof replicates local appliance trap seal oscillations and the operation of active control devices, thereby yielding data on network airflows and identifying system failures and consequences. The example is illustrated with reference to system 32 as shown in FIG. 1 which illustrates a four stack network. The four stacks A, B, C and D are fludically connected at a high level by common pipe 11 leading to the PAPA 68 and AAV 70. Water downflows in any stack generate negative transients which typically deflate the PAPA 68 and open the AAV 70 to provide an airflow into the system 32. Positive pressure generated by either stack surcharge (which, as used herein, includes introduction of liquid into a stack) or sewer transients (which, as used herein, involves increases or decreases in pressure arising from an event in the sewer such as fluid flow, a drop in liquid volume in the sewer, or an increase in liquid volume in the sewer) are attenuated by the PAPA and by the diversity of use that allows one stack-to-sewer route to act as a relief route for fluid in other stacks.
In the example of the system 32 illustrated in FIG. 1, the overall height of the system 32 from bases 150, 152, 154 and 156 of the respective stacks A, B, C and D to the PAPA 68 and AAV 70 is 12 meters. Each of the bases is preferably connected to the respective stack independent of the connection between the other bases and the sewer. Pressure transients generated within the network will propagate at the acoustic velocity of air, i.e., 330 m/s. In the context of the system 32 as illustrated herein, this implies pipe periods, which is the round trip travel time of a pressure transient from stack base to a PAPA 68 of approximately 0.08 seconds and from stack base to stack base of approximately 0.15 seconds.
In the example of the system 32, which is a simplified illustration of a complex building drainage and ventilation system used in the example hereof, no local trap seal protection is included, that is, while the traps 54, 56, 58 and 60 in the present example do not have active transient controls such as AAVs or PAPAs, such could be provided at the traps. Traditional networks as known in the art could include passive venting where separate vent stacks would be provided to the atmosphere. Also, as shown in FIG. 1, the bases 150, 152, 154 and 156 of the respective stacks A, B, C and D are ideally connected separately to the sewer 34 either directly or to separate connection drains so that diversity in the system 32 or 32A acts to aid in system self-venting. In a complex building this arrangement would not be arduous and would in all probability be the norm.
In the present example, the pipes 1, 3, 6, 8, 14, 16, 19 and 21 are all considered wet stack pipes. Each of the pipes 1 through 10 and 11 through 23 are 0.1 m in diameter, with pipes 1-4, 6-9, 14-17, and 19-22 being 2 meters in length. Pipes 5, 10, 18 and 23 are 6 meters in length in the present example. Again, as described above, while the illustration of the system in FIGS. 1 and 2 show the compartments and their respective system components at different elevations, this is for purposes of illustration only and in the example all similar system components for each respective stack A, B, C and D are at substantially the same respective elevation. Further, in the example hereof:
- discharges from discharge sources 46, 48 and 50 are water closet (abbreviated in the figures as “w.c.”) or toilet discharges to stacks A, B and C and are over a period starting at 1 second and extending to about 6 seconds, and a separate discharge from discharge source 52 to stack D occurs at a period between 2 and 7 seconds;
- a minimum water flow in each stack A, B, C and D continues throughout the example, set at 0.1 liters per second, to represent trailing water flowing through multiple appliance discharges;
- a stack base surcharge event is assumed to occur in stack A at about 2.5 seconds; and
- sequential sewer transients are imposed at the base of each stack A, B, C and D in turn for a duration of 1.5 seconds during the period beginning at 12 seconds and extending to 18 seconds.
It is believed that in this example in the system 32, the water flows within the network simulate actual system values, being representative of current water closet discharge characteristics in terms of peak flow being about 2 liters per second, overall volume about 6 liters, and duration of discharge being about 6 seconds. The sewer transients in the present example are at 30 mm water gauge pressure, which are representative but not excessive. Heights for the system stacks A, B, C and D are measured in a positive manner upward from each stack base. Thus, entrained airflow towards the stack base is shown as a negative value, and airflow upward is shown as a positive value. Airflow entering the system 32 or 32A is therefore indicated with a negative value, and airflow exiting the system to the sewer 34 is indicated as a positive value, and airflow induced to flow up a stack will also have a positive value. Water downflow is indicated with a negative value.
Water Discharge to the System
- Referring now to FIG. 5, the discharge sources 46, 48, 50 and 52 are illustrated as described above. FIG. 6 then illustrates the measured air downflows which are established in pipes 1, 6 and 14 as expected. However, the entrained airflow in pipe 19 is into the system 32 from the sewer 34. Initially, as there is only the minimum flow, essentially a trickle, in pipe 19, the initial entrained airflow in pipe 19 due to the discharge sources 46, 48, 50 already being carried by pipes 1, 6 and 14, is reversed, that is, up the stack D. This initial entrained airflow in pipe 19 contributes to the entrained airflow demand in pipes 1, 6 and 14. The AAV 70 connected to pipe 12 further contributes to the entrained airflow demand, but initially this is a small proportion of the required airflow and as seen in FIG. 6. Further, the valve member 100 of the AAV 70 may flutter in response to local pressure conditions. Following the discharge source 52 discharge to stack D that establishes a water downflow in pipe 19 from the time period at 2 seconds onward, the reversed airflow initially established diminishes due to the traction applied by the falling water film within the pipe 19. However, the suction pressures developed in stacks A, B and C still reults in a continuing but reduced reversed airflow in pipe 19. As the water downflow in pipe 19 reaches its maximum value from 3 seconds onward, the AAV 70 connected to pipe 12 opens fully and an increased airflow from this source may be identified as shown in FIG. 6. The flutter activity of the valve member 100 is replaced by a fully open period from 3.5 to 5.5 seconds.
FIG. 7 illustrates the air pressure profile starting from the stack bases 150 and 156 of stacks A and D, respectively upwardly to pipe 11, at about 2.5 seconds into the example hereof. The air pressure in stack D demonstrates a pressure gradient compatible with the reversed airflow mentioned above. The air pressure profile in stack A is typical for a stack carrying an annular water downflow and demonstrates the establishment of a positive backpressure due to the water curtain at the base of the stack A. Following completion of the discharges of water from discharge sources, the airflows will naturally attenuate over a period of time based on the frictional resistance in the system 32. As a minimum or trickle flow is assumed to continue in each stack, the rate of attenuation of the entrained airflows is low. The initial collapsed volume of the PAPA 68 installed on pipe 13 was 0.4 liters, with a fully expanded volume of 40 liters. However, due to its relatively small initial volume it may be regarded as collapsed during the phase of the example illustrated in FIG. 7.
Surcharge at the Base of Stack A
FIG. 8 shows a surcharge at the base 150 of stack A for pipe 1 at 2.5 to 3 seconds. The entrained airflow in pipe 1 reduces to zero at the stack base 150 and a pressure transient is generated within stack A as illustrated in FIG. 5. The impact of this transient will also be seen later in a discussion of the trap seal responses for the system 32. It will also be seen from FIG. 8 that the predicted pressure at the bases 150, 152, and 154 of stacks A, B and C at pipes 1, 6 and 14 conform to that normally expected. That is to say, a small positive back pressure as the entrained air is forced through the water curtain at the base of each stack and into the sewer is shown. In the case of stack D, FIG. 6 also shows the pressure at base 156 of stack D at pipe 19, with the reversed airflow drawn into the stack demonstrating a pressure drop as it traverses the water curtain present at that stack base 156.
Utilizing the AIRNET simulation practice allows the air pressure profiles up stack A to be modeled during and following the surcharge illustrated in FIG. 8. FIGS. 9 and 10 illustrate the air pressure profiles in stack A during the period of 2.5 to 3.0 seconds of the example, the increasing and decreasing phases of the transient propagation being presented sequentially. The traces illustrate the propagation of the positive transient up the stack A as well as the pressure oscillations derived from the reflection of the transient at the stack termination where the upper end of pipe 11 joins to the T fitting 62.
Sewer Imposed Transients
FIG. 11 illustrates the imposition of a series of sequential sewer transients at the bases 150, 152, 154 and 156 of the pipes 1, 6, 14 and 19 for each stack A, B, C and D, respectively. FIG. 12 demonstrates a pattern that indicates the operation of both the PAPA 68 installed on pipe 13 and the self-venting within the system 32 provided by stack interconnection.
As the positive pressure is imposed at the base 150 of pipe 1 at 12 seconds, airflow is driven up stack A towards the PAPA 68 connection to pipe 13. However, as the bases 152, 154 and 156 of the other stacks B, C and D have not yet had positive sewer pressure levels imposed, a secondary airflow path is established downwards to the connections to sewer 34 at the bases 152, 154 and 156 in each of stacks B, C and D, as shown by the negative airflows in FIG. 12.
As the imposed transient abates, so the reversed flow reduces and the PAPA 68 discharges air to the system 32, again demonstrated by FIG. 12. This pattern repeats as each of the stacks is subjected to a sewer transient. Diversity implies that simultaneous sewer transient imposition would not be a likely condition and one that would be prudently avoided by ensuring connection to several sewer outlets (here shown at bases 150, 152, 154 and 156). In a complex building arrangement, the provision of a plurality or multiplicity of such connections to the sewer 34 should not present an issue.
FIG. 13 illustrates a typical air pressure profile in stacks A and B during the sewer transient propagation in stack B at 15 seconds into the example. The pressure gradient in stack B confirms that airflow direction up the stack towards the T fitting 62 where pipes 12 and 13 lead respectively to the AAV 70 and PAPA 68. It will be seen that pressure continues to decrease down stack A until the pressure recovers in lower portions of the stack A at pipes 1 and 3. This is due to the effect of the continuing waterflow in pipes 1 and 3.
The use of the PAPA 68 in the present example reacts to the sewer transients by absorbing airflow. The flexible reservoir 118 is expandable and enables the PAPA 68 tp accumulate air inflow until it reaches its assumed 40 liter volume. At that point, the PAPA 68 will pressurize and will assist the airflow out of the network via the stacks which are unaffected by the imposed positive sewer transient. As shown in FIG. 13, as the sewer transient is applied sequentially from stack A to stack D, this pattern is repeated. The effective volume of the PAPA 68, positioned at a relatively high level with respect to the system 32 and the building 30, together with any other PAPAs 68 utilized in a more complex network than the system 32 shown in FIGS. 1 and 2, could be adapted to provide that virtually no system pressurization occurred.
FIG. 14 illustrates the airflow absorbed by the PAPA 68 during the sewer transient of the example hereof. The effect of sequential transients in each of the stacks A, B, C and D is identifiable as the PAPA 68 effective volume decreases between transients due to the entrained airflow maintained by residual water flows in each stack.
Trap Seal Oscillation and Retention
The appliance traps 54, 56, 58 and 60 connected to the system 32 monitor and respond to the local branch air pressures. Utilizing the AIRNET simulation, FIGS. 15, 16, 17 and 18 show the trap seal oscillations for each respective trap for the four stacks A, B, C and D. It is to be understood that the term “trap seal” refers to the accumulated water retained in each U-shaped trap to provide a barrier to resist the introduction of gas or vapors from the stacks into the environment of a compartment or the building as a whole. The term “appliance side” in reference to the traps 54, 56, 58, and 60 refers to the side of the trap more proximate the respective discharge source, while the term “system side” in reference to the traps refers to the side of the trap more proximate the junction of the respective feed pipe (2, 7, 15 and 20) to its corresponding wet stack discharge pipe (1, 6, 14 and 19).
FIG. 15, representing the trap seal at trap 54 of pipe 2, illustrates the expected induced siphonage of trap seal water into the system 32 as the stack pressure falls. The surcharge event in stack A interrupts this process at the 2 second point of the example. The trap oscillations abate following the cessation of water downflow in stack A. The imposition of a sewer transient is apparent at the 12 second point of the example by the water surface level rising in the appliance or discharge source side of the trap 54. A more severe transient could have resulting in “bubbling through” the trap seal at this stage if the trap system side water surface level fell below −50 mm.
FIGS. 16 and 17 show the trap seal oscillations for the traps 56 and 58 of pipes 7 and 15. FIGS. 16 and 17 are substantially identical to each other until the sequential imposition of sewer transients at the 14 and 16 second periods. As shown in FIGS. 16 and 17, the surcharge event imposed for pipe 1 of stack A does not affect the traps 56 and 58 as they are sufficiently remote from base 150 of stack A. As may be seen in FIG. 18, the trap 60 on pipe 20 displays a later initial reduction in pressure due to the delay in applied water downflow. The imposed sewer transient in pipe 19 is seen as it affects trap 60 at around 18 seconds into the example.
As a result of the pressure transients arriving at each trap during the example event hereof there will be a loss of trap seal water. This overall effect results in each trap 54, 56, 58 and 60 displaying an individual water seal retention that depends entirely on the usage within the system 32. FIG. 19 presents this data for the example hereof for each of the traps 54, 56, 58 and 60. It may be noted that the traps 56 and 58 for pipes 7 and 15 effectively were exposed to the same levels of transient pressure despite the time difference in the arrival of sewer transients.
The example of operation of the system 32 set forth above is believed to be applicable also to system 32A. While the specific results may vary, the overall effect of maintaining trap seal integrity should be similar. This is because the arrangement of system 32A where the AAV 70 is positioned in-line with the PAPA 68 with the PAPA 68 more proximate the discharge sources and bases of the respective stacks, the AAV 70 will still limit discharges of gas or vapors from the system 32A into the environment, with the PAPA 68 positioned to accumulate gas and thus absorb pressure transients up the stack in communication with the AAV 70.
It is believed that the foregoing example demonstrates that the systems 32 and 32A will effectively function to provide a sealed building drainage and ventilation system and that such is a viable option for complex buildings. As may be seen, the trap seal integrity may be maintained during system operation experiencing both discharges from the discharge sources and sewer imposed transients. Maintenance of trap seal integrity is a primary component of limiting or avoiding system contamination from entering the building 30. The introduction of ambient air from the environment into the system 32 or 32A from AAV helps to maintain trap seal integrity during discharges of water into the system 32 or 32A, and system security may be further enhanced when the air so introduced is provided from a controlled space or purification source. In addition, the placement of the PAPA 68 in parallel with the AAV 70, or alternatively in series with the AAV 70 remotely placed as shown in FIG. 2, allows the system 32 or 32A to maintain trap seal integrity during pressure transients coming into the system from a sewer 34. A sealed building drainage and ventilation system 32 or 32A would provide the following advantages over existing systems:
- system security would be immeasurably enhanced as all high-level open system terminations would be redundant;
- system complexity would be reduced while system predictability would increase;
- space and material savings would be provided during the construction phase of any building installation, as the system of the present invention utilizes both system diversity and the use of AAV and PAPA devices to maintain trap seal integrity.
These benefits would thus preferably be provided by a system which incorporates both active transient control and suppression into the design of the building's drainage and ventilation system, where air admittance valves are used to suppress negative transients and variable volume containment devices such as PAPAs are used to control positive transients, with both most preferably positioned uppermost within the system within an enclosed loft or other secure space. Such a system would dramatically reduce the risk of building contamination due to the introduction of chemical or biological agents as experienced, for example, in the SARS spread mechanism within the Amoy Gardens complex in Hong Kong in 2003. The diversity inherent in the operation of building drainage and ventilation systems and the sewers connected to the system have a role in providing interconnected relief paths as part of the system of the present invention which provides an elegant and simplified solution to such threats.
Although preferred forms of the invention have been described above, it is to be recognized that such disclosure is by way of illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. For example, the invention hereof contemplates that the stacks need not be substantially vertically oriented but may also be inclined or otherwise positioned such that the base is positioned below the discharge sources and the connection of the stacks at the upper level of each is above the feed pipes. Further, several AAVs and PAPAs may be used, so that there are several PAPAs and AAVs in parallel, or several connected PAPAs and AAVs as shown in FIG. 2 arranged in parallel. It may also be appreciated that the stacks may be any combination or configuration of pipes, connectors, and other fittings, and each may include a plurality of discharge sources.
The inventor hereby states his intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.
Patent Application
20060201088
