建筑給水排水畢業(yè)設(shè)計(jì)專業(yè)外文翻譯--密封的建筑排水系統(tǒng)和通氣系統(tǒng)

1、<p><b>　　翻譯</b></p><p>　　Sealed building drainage and vent systems</p><p>　　—an application of active air pressure transient control and suppression</p><p><b>

2、;　　Abstract</b></p><p>　　The introduction of sealed building drainage and vent systems is considered a viable proposition for complex buildings due to the use of active pressure transient control and s

3、uppression in the form of air admittance valves and positive air pressure attenuators coupled with the interconnection of the network's vertical stacks. </p><p>　　This paper presents a simulation based o

4、n a four-stack network that illustrates flow mechanisms within the pipework following both appliance discharge generated, and sewer imposed, transients. This simulation identifies the role of the active air pressure cont

5、rol devices in maintaining system pressures at levels that do not deplete trap seals. </p><p>　　Further simulation exercises would be necessary to provide proof of concept, and it would be advantageous to pa

6、rallel these with laboratory, and possibly site, trials for validation purposes. Despite this caution the initial results are highly encouraging and are sufficient to confirm the potential to provide definite benefits in

7、 terms of enhanced system security as well as increased reliability and reduced installation and material costs. </p><p>　　Keywords: Active control; Trap retention; Transient propagation </p><p>

8、;　　Nomenclature</p><p><b>　　C+- </b></p><p>　　characteristic equations </p><p><b>　　c </b></p><p>　　wave speed, m/s </p><p><b&g

9、t;　　D </b></p><p>　　branch or stack diameter, m </p><p><b>　　f </b></p><p>　　friction factor, UK definition via Darcy Δh=4fLu2/2Dg </p><p><b>　　

10、g </b></p><p>　　acceleration due to gravity, m/s2 </p><p><b>　　K </b></p><p>　　loss coefficient </p><p><b>　　L </b></p><p>　　

11、pipe length, m </p><p><b>　　p </b></p><p>　　air pressure, N/m2 </p><p><b>　　t </b></p><p><b>　　time, s </b></p><p><

12、b>　　u </b></p><p>　　mean air velocity, m/s </p><p><b>　　x </b></p><p>　　distance, m</p><p><b>　　γ </b></p><p>　　ratio spec

13、ific heats </p><p><b>　　Δh </b></p><p>　　head loss, m </p><p><b>　　Δp </b></p><p>　　pressure difference, N/m2 </p><p><b>　　Δt

14、 </b></p><p>　　time step, s </p><p><b>　　Δx </b></p><p>　　internodal length, m </p><p><b>　　ρ </b></p><p>　　density, kg/m3<

15、;/p><p><b>　　Suffix</b></p><p><b>　　A </b></p><p>　　appliance side of trap </p><p><b>　　B </b></p><p><b>　　branch &l

16、t;/b></p><p><b>　　local </b></p><p>　　conditions at node </p><p><b>　　T </b></p><p><b>　　trap </b></p><p><b>　

17、　atm </b></p><p>　　atmospheric pressure </p><p><b>　　F </b></p><p><b>　　friction </b></p><p><b>　　R </b></p><p>&

18、lt;b>　　room </b></p><p><b>　　S </b></p><p>　　system side of trap </p><p><b>　　w </b></p><p><b>　　water</b></p><p

19、>　　Article Outline</p><p>　　Nomenclature </p><p>　　1. Introduction—air pressure transient control and suppression </p><p>　　2. Mathematical basis for the simulation of transient

20、propagation in multi-stack building drainage networks </p><p>　　3. Role of diversity in system operation </p><p>　　4. Simulation of the operation of a multi-stack sealed building drainage and ve

21、nt system </p><p>　　5. Simulation sign conventions </p><p>　　6. Water discharge to the network </p><p>　　7. Surcharge at base of stack 1 </p><p>　　8. Sewer imposed tran

22、sients </p><p>　　9. Trap seal oscillation and retention </p><p>　　10. Conclusion—viability of a sealed building drainage and vent system </p><p>　　1. Introduction—air pressure trans

23、ient control and suppression</p><p>　　Air pressure transients generated within building drainage and vent systems as a natural consequence of system operation may be responsible for trap seal depletion and c

24、ross contamination of habitable space [1]. Traditional modes of trap seal protection, based on the Victorian engineer's obsession with odour exclusion [2], [3] and [4], depend predominantly on passive solutions where

25、 reliance is placed on cross connections and vertical stacks vented to atmosphere [5] and [6]. This approach, while</p><p>　　The development of air admittance valves (AAVs) over the past two decades provides

26、 the designer with a means of alleviating negative transients generated as random appliance discharges contribute to the time dependent water-flow conditions within the system. AAVs represent an active control solution a

27、s they respond directly to the local pressure conditions, opening as pressure falls to allow a relief air inflow and hence limit the pressure excursions experienced by the appliance trap seal [9]. </p><p>　　

28、However, AAVs do not address the problems of positive air pressure transient propagation within building drainage and vent systems as a result of intermittent closure of the free airpath through the network or the arriva

29、l of positive transients generated remotely within the sewer system, possibly by some surcharge event downstream—including heavy rainfall in combined sewer applications. </p><p>　　The development of variable

30、 volume containment attenuators [10] that are designed to absorb airflow driven by positive air pressure transients completes the necessary device provision to allow active air pressure transient control and suppression

31、to be introduced into the design of building drainage and vent systems, for both ‘standard’ buildings and those requiring particular attention to be paid to the security implications of multiple roof level open stack ter

32、minations. The positive air press</p><p>　　Fig. 1 illustrates both AAV and PAPA devices, note that the waterless sheath trap acts as an AAV under negative line pressure. </p><p><b>　　(39K)

33、 </b></p><p>　　Fig. 1. Active air pressure transient suppression devices to control both positive and negative surges. </p><p>　　Active air pressure transient suppression and con

34、trol therefore allows for localized intervention to protect trap seals from both positive and negative pressure excursions. This has distinct advantages over the traditional passive approach. The time delay inherent in a

35、waiting the return of a relieving reflection from a vent open to atmosphere is removed and the effect of the transient on all the other system traps passed during its propagation is avoided. </p><p>　　2. Mat

36、hematical basis for the simulation of transient propagation in multi-stack building drainage networks</p><p>　　The propagation of air pressure transients within building drainage and vent systems belongs to

37、a well understood family of unsteady flow conditions defined by the St Venant equations of continuity and momentum, and solvable via a finite difference scheme utilizing the method of characteristics technique. Air press

38、ure transient generation and propagation within the system as a result of air entrainment by the falling annular water in the system vertical stacks and the reflection and transmission</p><p>　　Air pressure

39、transient propagation depends upon the rate of change of the system conditions. Increasing annular downflow generates an enhanced entrained airflow and lowers the system pressure. Retarding the entrained airflow generate

40、s positive transients. External events may also propagate both positive and negative transients into the network. </p><p>　　The annular water flow in the ‘wet’ stack entrains an airflow due to the condition

41、of ‘no slip’ established between the annular water and air core surfaces and generates the expected pressure variation down a vertical stack. Pressure falls from atmospheric above the stack entry due to friction and the

42、effects of drawing air through the water curtains formed at discharging branch junctions. In the lower wet stack the pressure recovers to above atmospheric due to the traction forces exerted on the</p><p>　　

43、The application of the method of characteristics to the modelling of unsteady flows was first recognized in the 1960s [13]. The relationships defined by Jack [14] allows the simulation to model the traction force exerted

44、 on the entrained air. Extensive experimental data allowed the definition of a ‘pseudo-friction factor’ applicable in the wet stack and operable across the water annular flow/entrained air core interface to allow combine

45、d discharge flows and their effect on air entrainment to be </p><p>　　The propagation of air pressure transients in building drainage and vent systems is defined by the St Venant equations of continuity and

46、momentum [9],</p><p>　　These quasi-linear hyperbolic partial differential equations are amenable to finite difference solution once transformed via the Method of Characteristics into finite difference relati

47、onships, Eqs. (3)–(6), that link conditions at a node one time step in the future to current conditions at adjacent upstream and downstream nodes, Fig. 2. </p><p><b>　　(18K) </b></p><p

48、>　　Fig. 2. St Venant equations of continuity and momentum allow airflow velocity and wave speed to be predicted on an x-t grid as shown. Note , . </p><p>　　For the C+ characteristic:</p>

49、<p><b>　　when</b></p><p>　　and the C- characteristic:</p><p><b>　　when</b></p><p>　　where the wave speed c is given by</p><p>　　These equat

50、ions involve the air mean flow velocity, u, and the local wave speed, c, due to the interdependence of air pressure and density. Local pressure is calculated as</p><p>　　Suitable equations link local pressur

51、e to airflow or to the interface oscillation of trap seals, Table 1. </p><p><b>　　Table 1. </b></p><p>　　Boundary conditions </p><p>　　The case of the appliance tra

52、p seal is of particular importance. The trap seal water column oscillates under the action of the applied pressure differential between the transients in the network and the room air pressure. The equation of motion for

53、the U-bend trap seal water column may be written at any time as</p><p>　　It should be recognized that while the water column may rise on the appliance side, conversely on the system side it can never exceed

54、a datum level drawn at the branch connection.</p><p>　　In practical terms trap seals are set at 75 or 50 mm in the UK and other international standards dependent upon appliance type. Trap seal retention

55、 is therefore defined as a depth less than the initial value. Many standards, recognizing the transient nature of trap seal depletion and the opportunity that exists for re-charge on appliance discharge allow 25% depleti

56、on. </p><p>　　The boundary equation may also be determined by local conditions: the AAV opening and subsequent loss coefficient depends on the local line pressure prediction. </p><p>　　Empirical

57、 data identifies the AAV opening pressure, its loss coefficient during opening and at the fully open condition. Appliance trap seal oscillation is treated as a boundary condition dependent on local pressure. Deflection o

58、f the trap seal to allow an airpath to, or from, the appliance or displacement leading to oscillation alone may both be modelled. Reductions in trap seal water mass during the transient interaction must also be included.

59、 </p><p>　　3. Role of diversity in system operation</p><p>　　In complex building drainage networks the operation of the system appliances to discharge water to the network, and hence provide the

60、 conditions necessary for air entrainment and pressure transient propagation, is entirely random. No two systems will be identical in terms of their usage at any time. This diversity of operation implies that inter-stack

61、 venting paths will be established if the individual stacks within a complex building network are themselves interconnected. It is proposed that th</p><p>　　In order to fully implement a sealed building drai

62、nage and vent system it would be necessary for the negative transients to be alleviated by drawing air into the network from a secure space and not from the external atmosphere. This may be achieved by the use of air adm

63、ittance valves or at a predetermined location within the building, for example an accessible loft space. </p><p>　　Similarly, it would be necessary to attenuate positive air pressure transients by means of P

64、APA devices. Initially it might be considered that this would be problematic as positive pressure could build within the PAPA installations and therefore negate their ability to absorb transient airflows. This may again

65、be avoided by linking the vertical stacks in a complex building and utilizing the diversity of use inherent in building drainage systems as this will ensure that PAPA pressures are themsel</p><p>　　Diversity

66、 also protects the proposed sealed system from sewer driven overpressure and positive transients. A complex building will be interconnected to the main sewer network via a number of connecting smaller bore drains. Advers

67、e pressure conditions will be distributed and the network interconnection will continue to provide venting routes. </p><p>　　These concepts will be demonstrated by a multi-stack network.</p><p>

68、　　4. Simulation of the operation of a multi-stack sealed building drainage and vent system</p><p>　　Fig. 3 illustrates a four-stack network. The four stacks are linked at high level by a manifold leading to

69、a PAPA and AAV installation. Water downflows in any stack generate negative transients that deflate the PAPA and open the AAV to provide an airflow into the network and out to the sewer system. Positive pressure generate

70、d by either stack surcharge or sewer transients 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 the </p><p>　　Fig. 3. Four s

71、tack building drainage and vent system to demonstrate the viability of a sealed building system. </p><p>　　The network illustrated has an overall height of 12 m. Pressure transients generated within the

72、 network will propagate at the acoustic velocity in air . This implies pipe periods, from stack base to PAPA of approximately 0.08 s and from stack base to stack base of approximately 0.15 s. </p><p&

73、gt;　　In order to simplify the output from the simulation no local trap seal protection is included—for example the traps could be fitted with either or both an AAV and PAPA as examples of active control. Traditional netw

74、orks would of course include passive venting where separate vent stacks would be provided to atmosphere, however a sealed building would dispense with this venting arrangement. </p><p>　　Ideally the four sew

75、er connections shown should be to separate collection drains so that diversity in the sewer network also acts to aid system self venting. In a complex building this requirement would not be arduous and would in all proba

76、bility be the norm. It is envisaged that the stack connections to the sewer network would be distributed and would be to a below ground drainage network that increased in diameter downstream. Other connections to the net

77、work would in all probability be from bu</p><p>　　It is stressed that the network illustrated is representative of complex building drainage networks. The simulation will allow a range of appliance discharge

78、 and sewer imposed transient conditions to be investigated. </p><p>　　The following appliance discharges and imposed sewer transients are considered: </p><p>　　1. w.c. discharge to stacks 1–3 ov

79、er a period 1–6 s and a separate w.c. discharge to stack 4 between 2 and 7 s.</p><p>　　2. A minimum water flow in each stack continues throughout the simulation, set at 0.1 l/s, to represent t

80、railing water following earlier multiple appliance discharges.</p><p>　　3. A 1 s duration stack base surcharge event is assumed to occur in stack 1 at 2.5 s.</p><p>　　4. Sequential sew

81、er transients imposed at the base of each stack in turn for 1.5 s from 12 to 18 s.</p><p>　　The simulation will demonstrate the efficacy of both the concept of active surge control and inter-stack

82、venting in enabling the system to be sealed, i.e. to have no high level roof penetrations and no vent stacks open to atmosphere outside the building envelope. </p><p>　　The imposed water flows within the net

83、work are based on ‘real’ system values, being representative of current w.c. discharge characteristics in terms of peak flow, 2 l/s, overall volume, 6 l, and duration, 6 s. The sewer transients at 30 

84、mm water gauge are representative but not excessive. Table 2 defines the w.c. discharge and sewer pressure profiles assumed. </p><p><b>　　Table 2. </b></p><p>　　w.c. discharge a

85、nd imposed sewer pressure characteristics </p><p>　　5. Simulation conventions</p><p>　　It should be noted that heights for the system stacks are measured positive upwards from the stack base in

86、each case. This implies that entrained airflow towards the stack base is negative. Airflow entering the network from any AAVs installed will therefore be indicated as negative. Airflow exiting the network to the sewer co

87、nnection will be negative. </p><p>　　Airflow entering the network from the sewer connection or induced to flow up any stack will be positive. </p><p>　　Water downflow in a vertical is however re

88、garded as positive. </p><p>　　Observing these conventions will allow the following simulation to be better understood. </p><p>　　6. Water discharge to the network</p><p>　　Table 2 i

89、llustrates the w.c. discharges described above, simultaneous from 1 s to stacks 1–3 and from 2 s to stack 4. A base of stack surcharge is assumed in stack 1 from 2.5 to 3 s. As a result it will be seen fro

90、m Fig. 4 that entrained air downflows are established in pipes 1, 6 and 14 as expected. However, the entrained airflow in pipe 19 is into the network from the sewer. Initially, as there is only a trickle water flow in pi

91、pe 19, the entrained airflow in pipe 19 due to the w.c. discharges</p><p>　　Fig. 4. Entrained airflows during appliance discharge. </p><p>　　Following the w.c. discharge to stack 4 tha

92、t establishes a water downflow in pipe 19 from 2 s onwards, the reversed airflow initially established diminishes due to the traction applied by the falling water film in that pipe. However, the suction pressures de

93、veloped in the other three stacks still results in a continuing but reduced reversed airflow in pipe 19. As the water downflow in pipe 19 reaches its maximum value from 3 s onwards, the AAV on pipe 12 opens fully an

94、d an increased airflow from</p><p>　　Fig. 5 illustrates the air pressure profile from the stack base in both stacks 1 and 4 at 2.5 s into the simulation. The air pressure in stack 4 demonstrates a press

95、ure gradient compatible with the reversed airflow mentioned above. The air pressure profile in stack 1 is typical for a stack carrying an annular water downflow and demonstrates the establishment of a positive backpressu

96、re due to the water curtain at the base of the stack. (40K) </p><p>　　Fig. 5. Air pressure profile in stacks 1 and 4 illustrating the pressure gradient driving the reversed airflow in pipe 19. <

97、;/p><p>　　The initial collapsed volume of the PAPA installed on pipe 13 was 0.4 l, with a fully expanded volume of 40 l, however due to its small initial volume it may be regarded as collapsed during

98、this phase of the simulation. </p><p>　　7. Surcharge at base of stack 1</p><p>　　Fig. 6 indicates a surcharge at the base of stack 1, pipe 1 from 2.5 to 3 s. The entrained airflow in pipe 1

99、 reduces to zero at the stack base and a pressure transient is generated within that stack, Fig. 6. The impact of this transient will also be seen later in a discussion of the trap seal responses for the network. (44K)

100、</p><p>　　Fig. 6. Air pressure levels within the network during the w.c. discharge phase of the simulation. Note surcharge at base stack 1, pipe 1 at 2.5 s. </p><p>　　It will also

101、 be seen, Fig. 6, that the predicted pressure at the base of pipes 1, 6 and 14, in the absence of surcharge, conform to that normally expected, namely a small positive back pressure as the entrained air is forced through

102、 the water curtain at the base of the stack and into the sewer. In the case of stack 4, pipe 19, the reversed airflow drawn into the stack demonstrates a pressure drop as it traverses the water curtain present at that st

103、ack base. </p><p>　　The simulation allows the air pressure profiles up stack 1 to be modelled during, and following, the surcharge illustrated in Fig. 6. Fig. 7(a) and (b) illustrate the air pressure profile

104、s in the stack from 2.0 to 3.0 s, the increasing and decreasing phases of the transient propagation being presented sequentially. The traces illustrate the propagation of the positive transient up the stack as well