不完全燃烧建筑给排水中英文对照外文翻译文献

2021年1月20日发(作者：kclo3)
建筑给排水中英文对照外文翻译文献



建筑给排水中英文对照外文翻译文献


(
文档含英文原文和中文翻译
)
















- 1 -
建筑给排水中英文对照外文翻译文献

外文：

Sealed building drainage and vent systems
—
an application of active air pressure transient control and suppression
Abstract
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
suppression in the form of air admittance valves and positive air pressure attenuators coupled with
the interconnection of the network's vertical stacks.

This
paper
presents
a
simulation
based
on
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 control devices in
maintaining system pressures at levels that do not deplete trap seals.

Further simulation exercises would be necessary to provide proof of concept, and it would be
advantageous to
parallel 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 terms of enhanced system security as well as increased
reliability and reduced installation and material costs.

Keywords:
Active control; Trap retention; Transient propagation

Nomenclature
C
+-
——
characteristic equations

c
——
wave speed, m/s

D
——
branch or stack diameter, m

f
——
friction factor, UK definition via Darcy
Δ
h=4fLu
2
/2Dg
g
——
acceleration due to gravity, m/s
2


K
——
loss coefficient

L
——
pipe length, m

p
——
air pressure, N/m
2


t
——
time, s

u
——
mean air velocity, m/s

x
——
distance, m
γ
——
ratio specific heats


- 2 -
建筑给排水中英文对照外文翻译文献

Δ
h
——
head loss, m

Δ
p
——
pressure difference, N/m
2


Δ
t
——
time step, s

Δ
x
——
internodal length, m

ρ
——
density, kg/m
3

Article Outline
Nomenclature

1. Introduction
—
air pressure transient control and suppression
2. Mathematical basis for the simulation of transient propagation in multi-stack building
drainage networks

3. Role of diversity in system operation

4. Simulation of the operation of a multi- stack sealed building drainage and vent system

5. Simulation sign conventions

6. Water discharge to the network

7. Surcharge at base of stack 1

8. Sewer imposed transients

9. Trap seal oscillation and retention

10. Conclusion
—
viability of a sealed building drainage and vent system
pressure transients generated within building drainage and vent systems as a natural
consequence
of
system
operation
may
be
responsible
for
trap
seal
depletion
and
cross
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 reliance is placed on cross connections and vertical stacks vented to

atmosphere [5] and [6]. This approach, while both proven and traditional, has inherent weaknesses,
including the remoteness of the vent terminations [7], leading to delays in the arrival of relieving
reflections, and the multiplicity of open roof level stack terminations inherent within complex
buildings. The complexity of the vent system required also has significant cost and space
implications [8].

The development of air admittance valves (AAVs) over the past two decades provides 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 as they respond directly to the local pressure conditions, opening as pressure

- 3 -
建筑给排水中英文对照外文翻译文献

falls to allow a relief air inflow and hence limit the pressure excursions experienced by the
appliance trap seal [9].

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 arrival of positive transients generated remotely within the sewer
system, possibly by some surcharge event downstream
—
including heavy rainfall in combined
sewer applications.

The development of variable 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 to be introduced into the design of building
drainage and vent systems, for both ‘standard’ buildings and those requiring particular attention t
o
be paid to the security implications of multiple roof level open stack terminations. The positive air
pressure attenuator (PAPA) consists of 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 transients generated. Together with the use of AAVs the introduction of the
PAPA device allows consideration of a fully sealed building drainage and vent system.

Fig. 1
illustrates both AA
V and PAPA devices, note that the waterless sheath trap acts as an
AA
V under negative line pressure.

Fig. 1. Active air pressure transient suppression devices to control both positive and negative surges.
Active
air
pressure
transient
suppression
and
control
therefore
allows
for
localized
intervention to protect trap seals from both positive and negative pressure excursions. This has

- 4 -
建筑给排水中英文对照外文翻译文献

distinct advantages over the traditional passive approach. The time delay inherent in awaiting 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.

atical
basis
for
the
simulation
of
transient
propagation
in
multi-stack
building
drainage networks.
The propagation of air pressure transients within building drainage and vent systems belongs
to 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 pressure 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
of
these
transients
at
the
system
boundaries,
including
open
terminations,
connections to the sewer, appliance trap seals and both AAV and PAPA active control devices,
may be simulated with proven accuracy. The simulation [11] provides local air pressure, velocity
and wave speed information throughout a network at time and distance intervals as short as 0.001 s
and 300 mm. In addition, the simulation 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. While the simulation has been extensively validated [10], its use
to independently confirm the mechanism of SARS virus spread within the Amoy Gardens outbreak
in 2003 has provided further confidence in its predictions [12].

Air pressure 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 generates positive transients. External events may also
propagate both positive and negative transients into the network.

The annular water flow in the ‘wet’ stack entrains an airflow due to the condition 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 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 airflow prior to falling across the water curtain at the stack base.

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 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
combined
discharge
flows
and
their
effect
on
air

- 5 -
建筑给排水中英文对照外文翻译文献

entrainment to be modelled.

The propagation of air pressure transients in building drainage and vent systems is defined by
the St Venant equations of continuity and momentum [9],


(2)
(1)

These quasi-linear hyperbolic partial differential equations are amenable to finite difference
solution once transformed via the Method of Characteristics into finite difference relationships,
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.

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
,
.

For the C
+
characteristic:

when

and the C
-
characteristic:

when

where the wave speed c is given by
(6)
(5)
(4)
(3)

- 6 -
建筑给排水中英文对照外文翻译文献

c=(
γp
/
ρ
)
0.5
.
(7)
These equations 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

(8)
Suitable equations link local pressure to airflow or to the interface oscillation of trap seals.
The case of the appliance trap 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 the U-bend trap seal water column may be
written at any time as

on the system side it can never exceed a datum level drawn at the branch connection.
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 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% depletion.

The boundary equation may also be determined by local conditions: the AAV opening and
subsequent loss coefficient depends on the local line pressure prediction.

Empirical 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 of 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.

3. Role of diversity in system operation
In complex building drainage networks the operation of the system appliances to discharge
water to the network, and hence provide the 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 venting paths will be established if the
individual stacks within a complex building network are themselves interconnected. It is proposed
that this diversity is utilized to provide venting and to allow serious consideration to be given to
sealed drainage systems.

In order to fully implement a sealed building drainage 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

- 7 -
(9)
It should be recognized that while the water column may rise on the appliance side, conversely
建筑给排水中英文对照外文翻译文献

not from the external atmosphere. This may be achieved by the use of air admittance valves or at a
predetermined location within the building, for example an accessible loft space.

Similarly, it would be necessary to attenuate positive air pressure transients by means of
PAPA 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 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 themselves alleviated by allowing trapped air to vent through the interconnected
stacks to the sewer network.

Diversity 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. Adverse pressure conditions will be distributed and the
network interconnection will continue to provide venting routes.

These concepts will be demonstrated by a multi-stack network.
4. Simulation of the operation of a multi- stack sealed building drainage and vent system
Fig. 3 illustrates a four-stack network. The four stacks are linked at high level by a manifold
leading to 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 generated 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 other stacks.
The network illustrated has an overall height of 12m. Pressure transients generated within the
network will propagate at the acoustic velocity in air
0.15s.

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 networks 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.
. This implies pipe periods, from
stack base to PAPA of approximately 0.08s and from stack base to stack base of approximately

- 8 -
建筑给排水中英文对照外文翻译文献


stack building drainage and vent system to demonstrate the viability of a sealed building system.
Ideally the four sewer 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 probability 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

network would in all probability be from buildings that included the more traditional open vent
system design so that a further level of diversity is added to offset any downstream sewer surcharge
events of long duration. Similar considerations led to the current design guidance for dwellings.

It is stressed that the network illustrated is representative of complex building drainage
networks. The simulation will allow a range of appliance discharge and sewer imposed transient
conditions to be investigated.

The following appliance discharges and imposed sewer transients are considered:

1. w.c. discharge to stacks 1
–
3 over a period 1
–
6s and a separate w.c. discharge to stack 4
between 2 and 7s.
2. A minimum water flow in each stack continues throughout the simulation, set at 0.1L/s, to
represent trailing water following earlier multiple appliance discharges.

- 9 -
建筑给排水中英文对照外文翻译文献

3. A 1s duration stack base surcharge event is assumed to occur in stack 1 at 2.5s.
4. Sequential sewer transients imposed at the base of each stack in turn for 1.5s from 12 to 18s.
The simulation will demonstrate the efficacy of both the concept of active surge control and
inter-stack 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.

The imposed water flows within the network are based on ‘real’ system values,
being
representative of current w.c. discharge characteristics in terms of peak flow, 2l/s, overall volume,
6l, and duration, 6s. The sewer transients at 30mm water gauge are representative but not excessive.
Table 1 defines the w.c. discharge and sewer pressure profiles assumed.

Table1. w.c. discharge and imposed sewer pressure characteristics








w.c. discharge characteristic
Time
Seconds
Start time
+2
+4
+6
Discharge flow
l/s
0.0
2.0
2.0
0.0
Imposed sewer transient at stack base
Time
Seconds
Start time
+0.5
+0.5
+0.5
Pressure
Water gauge (mm)
0.0
30.0
30.0
0.0
5. Simulation conventions
It should be noted that heights for the system stacks are measured positive upwards from the
stack base in 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 connection will be negative.

Airflow entering the network from the sewer connection or induced to flow up any stack will
be positive.

Water downflow in a vertical is however regarded as positive.

Observing these conventions will allow the following simulation to be better understood.

6. Water discharge to the network
Table 1 illustrates the w.c. discharges described above, simultaneous from 1s to stacks 1
–
3
and from 2s to stack 4. A base of stack surcharge is assumed in stack 1 from 2.5 to 3s. As a result it
will
be
seen
from
Fig.
4
that
entrained
air
downflows
are
established
in
pipes
1,
6
and
14
as

- 10 -
建筑给排水中英文对照外文翻译文献

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
pipe
19,
the
entrained
airflow
in
pipe
19
due
to
the
w.c.
discharges already being carried by pipes 1, 6 and 14, is reversed, i.e. up the stack, and contributes
to the entrained airflow demand in pipes 1, 6 and 14. The AAV on pipe 12 also contributes but
initially this is a small proportion of the required airflow and the AAV flutters in response to local
pressure conditions.

ned airflows during appliance discharge.
Following the w.c. discharge to stack 4 that 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 developed 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 and an increased
airflow from this source may be identified. The flutter stage is replaced by a fully open period from
3.5 to 5.5 s.

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 pressure 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 backpressure due to
the water curtain at the base of the stack.

- 11 -
建筑给排水中英文对照外文翻译文献


pressure profile in stacks 1 and 4 illustrating the pressure gradient driving the reversed airflow in
pipe 19.

The initial collapsed volume of the PAPA installed on pipe 13 was 0.4l, with a fully expanded
volume of 40l, however due to its small initial volume it may be regarded as collapsed during this
phase of the simulation.

7. Surcharge at base of stack 1
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 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.

pressure levels within the network during the w.c. discharge phase of the simulation. Note
surcharge at base stack 1, pipe 1 at 2.5s.


- 12 -
建筑给排水中英文对照外文翻译文献

It will also 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 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 stack base.

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 profiles 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 as
the pressure oscillations derived from the reflection of the transient at the stack termination at the
AAV/PAPA junction at the upper end of pipe 11.

Fig.7.(a) Sequential air pressure profiles in stack 1 during initial phase of stack base surcharge. (b)
Sequential air pressure profiles in stack 1 during final phase of stack base surcharge.

8. Sewer imposed transients
Table 2 illustrates the imposition of a series of sequential sewer transients at the base of each

- 13 -
建筑给排水中英文对照外文翻译文献

stack. Fig. 8 demonstrates a pattern that indicates the operation of both the PAPA installed on pipe
13 and the self-venting provided by stack interconnection.

nd airflows as a result of sewer imposed pressure transients.
As the positive pressure is imposed at the base of pipe 1 at 12 s, airflow is driven up stack 1
towards the PAPA connection. However, as the base of the other stacks have not a yet had positive
sewer pressure levels imposed, a secondary airflow path is established downwards to the sewer
connection in each of stacks 2
–
4, as shown by the negative airflows in Fig. 8.

As the imposed transient abates so the reversed flow reduces and the PAPA discharges air to
the network, again demonstrated by the simulation, Fig. 8. This pattern repeats as each of the stacks
is subjected to a sewer transient.

Fig. 9 illustrates typical air pressure profiles in stacks 1 and 2. The pressure gradient in stack 2
confirms the airflow direction up the stack towards the AAV/PAPA junction. It will be seen that
pressure continues to decrease down stack 1 until it recovers, pipes 1 and 3, due to the effect of the
continuing waterflow in those pipes.
The PAPA installation reacts to the sewer transients by absorbing airflow, Fig. 10. The PAPA
will expand until the accumulated air inflow reaches its assumed 40 l volume. At that point the
PAPA will pressurize and will assist the airflow out of the network via the stacks unaffected by the
imposed
positive
sewer
transient.
Note
that
as
the
sewer
transient
is
applied
sequentially
from
stacks 1
–
4 this pattern is repeated. The volume of the high level PAPA, together with any others
introduced into a more complex network, could be adapted to ensure that no system pressurization
occurred.

- 14 -
建筑给排水中英文对照外文翻译文献



pressure
profile
in
stack
1
and
2
during
the
sewer
imposed
transient
in
stack
2,
15s
into
the
simulation.


volume and AAV throughflow during simulation.
The effect of sequential transients at each of the stacks is identifiable as the PAPA volume
decreases between transients due to the entrained airflow maintained by the residual water flows in
each stack.

9. Trap seal oscillation and retention
The appliance traps connected to the network monitor and respond to the local branch air
pressures. The model provides a simulation of trap seal deflection, as well as final retention. Fig.
11(a,b) present the trap seal oscillations for one trap on each of the stacks 1 and 2, respectively. As
the air pressure falls in the network, the water column in the trap is displaced so that the appliance
side water level falls. However, the system side level is governed by the level of the branch entry
connection so that water is lost to the network. This effect is illustrated in both Fig. 11(a) and (b).

- 15 -
建筑给排水中英文对照外文翻译文献

Transient conditions in the network result in trap seal oscillation, however at the end of the event
the trap seal will have lost water that can only be replenished by the next appliance usage. If the
transient effects are severe than the trap may become totally depleted allowing a potential cross
contamination route from the network to habitable space. Fig. 11(a) and (b) illustrate the trap seal
retention at the end of the imposed network transients.

Fig.11.(a) Trap seal oscillation, trap 2. (b) Trap seal oscillation, trap 7.
Fig. 11(a), representing the trap on pipe 2, illustrates the expected induced siphonage of trap
seal water into the network as the stack pressure falls. The surcharge event in stack 1 interrupts this
process at 2s. The trap oscillations abate following the cessation of water downflow in stack 1. The
imposition of a sewer transient is apparent at 12s by the water surface level rising in the appliance
si
de of the trap. A more severe transient could have resulted in ‘bubbling through’ at this stage if
the trap system side water surface level fell to the lowest point of the U-bend.

The trap seal oscillations for traps on pipes 7, Fig. 11(b) and 15, are identical to each other
until the sequential imposition of sewer transients at 14 and 16s. Note that the


- 16 -