Dry Drains: Myth, Reality or impediment to water conservation. - - PowerPoint PPT Presentation

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Dry Drains: Myth, Reality or impediment to water conservation.

Professor J.A. Swaffield Emeritus Profesor School of the Built Environment, Heriot Watt University, Edinburgh, Scotland.

j.a.swaffield@hw.ac.uk

Dry Drains presentation, CIBW62 Dusseldorf, 2009

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Dry Drains

The concept that ‘dry drains’ could be a consequence of water conservation was initiated in the US where ‘concerned groups’ argue that further reductions in w.c. flush volume will reduce the drain flow so solid transport – or ‘drainline carry’ - becomes impossible. In January 2009 IAPMO signed an MOU with - the Alliance for Water Efficiency (AWE), the Plumbing Heating and Cooling Contractors National Association (PHCC), the Plumbing Manufacturers Institute (PMI) and the International Code Council (ICC). The five associations agreed to call this coalition the Plumbing Efficiency Research Coalition (PERC).

Information provided by Pete DeMarco, IAPMO, e-mail to Goncalves, cc Swaffield

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PERC’s first joint project will be Drainline Transport PERC is developing a Request for Proposals to be sent to - * universities for the CFD work, * qualified test labs for the laboratory work, * plumbing contractors for the field study work , so that funding can be sought from the US government and

• ther entities to underwrite the research’.

PERC (Pete DeMarco, IAPMO) states that ‘of course, we also intend to conduct an international literature search. We have not conducted our searches yet, pending funding’. Dry Drains presentation, CIBW62 Dusseldorf, 2009

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Frankfurt ‘Dry Drains Forum’ March 2009 In March 2009 a Dry Drains Forum was hosted at the ISH exhibition by Jeff Patchell’s organisation and several speakers presented arguments for and against the concept. The US contribution harked back to the 1992 Energy Bill that introduced 6 litre w.c. flush volume without consultation and was concerned that any move towards 4 litres would be achieved in a similar fashion. The UK and Australian contributions emphasised the role of climate change and our ability to design for reduced flush volume – quite different approaches.

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It is necessary to rationally examine the concept of the ‘dry drain’. The following areas need to be considered –

• 1. What effect will climate change have on drain

throughflows?

• 2. What effect will demographic and social changes have
• n throughflow?
• 3. What can we learn from previous research?
• 4. What design or installation strategies might be used to
• ffset any perceived problem?

Dry Drains?

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Water conservation remains a major UK issue

‘..climate change is the biggest challenge facing the world today.. this landmark scientific evidence shows that we need to tackle the causes of climate change and deal with its consequences.’ Hilary Benn Environment Secretary June 18th 2009 on the release climate change

scenarios for the UK from 2050 to 2080.

2001 Issue already identified in the UK 2007

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UK mean annual rainfall, 1971 - 2000.

Source – Met. Office 2006.

At least a fourfold variation from North West to South East is apparent from this historic data across the UK

WET DRY

Possible changes by 2050 – West of Scotland winter rainfall to rise by 15 to 29% SE England summer rainfall to decrease by 19 to 41 %

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Demographics and user preferences have changed, and will change further, the water use pattern in the UK.

By 2030 ----- * England will have 27.8 million households - 6.3 million (29%) more than 2006, an INCREASE of 252,000 per year. * One person households are projected to increase by 163,000 per year, OR two-thirds of the overall increase in households. * 32% of households will be headed by those 65 or over, up 26% on 2006. * 18% of the total population will live alone, up from 13% in 2006. THESE CHANGES WILL AFFECT WATER DEMAND……. A single person uses – 2 times as much as a person in a group of 4 and 4 times as much as a person in a group of 8.

Domestic water usage and drain throughflow rises due to demographic shifts.

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Water usage and drain throughflow have risen over the past decades…

1976 115 litres per capita per day, Population 55m 2001 143 litres per capita per day, Population 60m 2009 UK Govt. figures suggest 150 litres per capita per day,

Note UK Govt. Building Regulations now propose a target of 125 litres per capita per day i.e. > 1976.

While water conservation will reduce individual usage, demograhics will increase the overall total. Water conservation remains essential, holding water usage at current levels will be the challenge.

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Toilet 31% Kitchen Sink 15% Outdoor use 4% Shower 5% Basin 9% Bath 15% Dishwasher 1% Washing m/c 20%

Data taken from 'Water efficiency in the home', Parliamentary Office

• f Science and Technology, Note

135, 2000.

Comparisons of UK appliance use data 2000-06 identifies water conservation targets…

% water use data, 2000 WRc water usage data 2006.

W.c.

31%

W.c.

34%

The w.c. REMAINS the major component of domestic and commercial building water usage. Major reductions have been made in the past 20 years.

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What can we learn from previous research?

• W.c. design is central,
• Identify and understand the parameters defining

solid transport and develop predictive models,

• Introduce careful drainage system design to minimise

probability of deposition,

• Understand and apply 30 + years of research freely

available through international published papers. Coping strategies…..

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5 10 15 20 25 30 35 40 45 1880 1900 1920 1940 1960 1980 2000 2020

Date Appliance flush volume, litres.

UK US Scotland US UK Sweden Rural UK Experimental UK Experimental EU UK US Microphor UK ODA Sweden Urban US Aus 6/3 Dual Flush UK 6/4 Dual Flush UK pneumatic Aus 4/2 Dual Flush

• Poly. (All appliances)

Reduction in w.c. flush volume from 1900 to 2007 - illustrating the potential for water saving based on appliance design rather than user opinion.

• 80
• 60
• 40
• 20

Australian proposals for the use of non circular section building drains may allow further reductions in flush volume without reduction in transport efficiency.

W.C design over past 100 years hhas demonstrated the potential for water conservation.

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ODA / Twyfords / Brunel 3 litre w.c. 1984 Low flush volume w.c. design is now the norm, eg Caroma and many other manufacturers. The understanding has been there for 25 years as shown by this 1983 Brunel University w.c. used in Botswana, Lesotho, China and Brazil but NOT the UK. Examples of this w.c. still exist at HWU

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Solid transport at reduced flush volumes

Reducing w.c. flush volume is a first line response to water conservation targets. Research has shown that this may be achieved WITHOUT exacerbating other drainage problems Extensive laboratory and site testing over 30 years allows the identification of the parameters defining solid transport and the development of predictive models that can be of direct value to the system and appliance designer.

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Transport distance dependency on selected variable groups referred to a datum condition.

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 2 3 4 5 6 7 8 9 10 C3 / C3(datum)

sg, datum value 0.2 F/FB, datum value 9 litre wc. Fwc/F, datum value 9 litre wc. wt/d^2, datum value 5% π (in turn sg, F/FB, Fwc/F, wt/d^2, wet/dry) / π ( datum value) Fwc/F wt/d^2 sg F/FB wet/dry

Based on extensive solid transport testing the distance to deposition DECREASES as - solid mass increases, flush volume behind solid decreases, specific gravity of solid increases, cross sectional area of solid increases,

• verall flush volume

decreases, drain slope decreases, and drain diameter increases.

Solid transport dependence on w.c. and solid parameters based on both laboratory and site testing.

NO UNKNOWNS LEFT HERE.

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0.4 0.8 1.2 15 20 25 30 35 40 45 50

Drain length and gradient combined as (L/G)^0.5 Solid velocity, m/s.

Vsolid, Run 581, Tissue, 200mm long, thick, flat. Vsolid, Run 641, Tissue, 425mm long, medium, flat Vsolid, Run 833, Tissue, 200mm long, thick, irregular. Vsolid, Run 846, Tissue, 200mm long, medium, irregular. Vsolid 1, Run 422 25mm long, 25mm dia stool, submerged. Vsolid 2, Run 422, 50mm long, 25mm dia. stool, submerged. Vsolid 3, Run 422, 150mm long, 37mm dia stool, submerged. Vsolid 4, Run 422, Tissue, 150mm long, v ery thick, flat.

Site testing of male and female restroom discharges, Greenwich Hospital, confirmed the identified mechanisms.

SITE TESTING CONFIRMED UNDERSTANDING 25 YEARS AGO

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W.c. flush parameters are CENTRAL to solid transport efficiency.

F - reduced flush volume Fwc - design w.c. flush volume

W.c. discharge, litre/second Time, seconds FB - Flush volume discharged behind solid Solid discharged from w.c.

W.c. Discharge Profile.

Probably the most important w.c. design parameter..

THE RELATIVE IMPORTSANCE OF W.C. DESIGN PARAMETERS ARE UNDERSTOOD

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Drain cross sectional shape is as important in building drainage as it has historically been in sewers.

THE ROLE OF DRAIN CROSS SECTION HAS BEEN UNDERSTOOD, AT LEAST SINCE THE PARIS SEWERS WERE BUILT IN THE 1800s

DEEP IS GOOD

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Comparative solid velocities along a 1/60 slope branch drain as a result of a 6 litre w.c. appliance discharge for each of the drain cross sectional area and w.c. types considered.

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2 4 6 8 10 12 14

Distance along branch drain, m. Solid velocity, m/s. 6 litre flush, 1/60 slope, EU 75 mm dia., best. EU Deepflow. EU 100 mm dia. BS 100 mm dia, worst.

Dependence of solid transport on drain cross sectional shape.

Transport distance increases as reduced cross section increases flow velocity.

Transport distance rises as cross section decreases.

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Non-circular cross section building drains – Caroma / HWU study 1997 - 2000

Comparative tissue transport performance, based on a 15 sheet tissue length discharged by a 3 litre flush and moved on by a second similar flush, for the 75 and 100 mm diameter branch drains and the Concept 6 cross section, all drains at 1/100 slope.

Tissue transport will become even more important.

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What design or installation strategies might be used to offset any perceived problem? Careful drainage system design can minimise the probability of deposition. In addition appliance design can play a major role in providing suitable discharge flows while flow booster solutions should also be recognised. System and appliance design interventions

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Minimum transport distance to the first joining flow junction is an essential parameter in determining drainline carry acceptance tests and has design implications. Accurate data is not available however experience suggests that the majority of w.c. connections to a flow confluence will be less than 5 metres. Drainline carry – solid transport.

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Probable w.c. distance to junction distribution.

Likely distribution of drain distance from discharging appliance to nearest joining flow junction.

10 20 30 40 50 60 70 80 90 100 5 10 15 20 25 30 35 40 45 50

Distance from appliance to junction, m. % appliances at less than this distance from the junction, m. W.c. Joining flow from upstream W.c. flow Combined flow Majority of situations probably in this range.

CENTRAL TO THE ARGUMENT BUT NO DATA EXISTS????

?

INFORMATION REQUIRED

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Junction design can enhance solid transport

Avoid top entry junctions and level invert 90o junctions as the formation of hydraulic jumps in the upstream drain decelerates any approaching solid.

Hydraulic jump formed as flow enters from the branch connection Approaching solid decelerates towards deposition

Top entry junction Level invert junction junction

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In addition flow boosters have been used in the UK and elsewhere from the mid 19th Century and are now being again considered. Two solutions have been used historically – TIPPING BUCKETS and SIPHON TANKS.

Appliance design and flow boosters

W.c. discharge, litre/second Time, seconds FB - Flush volume discharged behind solid Solid discharged from w.c.

W.c. design to maximise solid transport at low flush volume is possible by recognising the importance of the % flush discharged behind the solid.

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Tipping tanks as flow boosters. Ceramic Tipping Tank, wooden pivots, dating from 1860, found in a garden in Manchester and donated to HWU.

‘Bucket’ tips under action of water mass to deliver high energy wave.

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TIPPING TANKS HAVE BEEN USED SINCE AT LEAST 1860.

Used in Botswana in 1985 to support Brunel University / ODA 3 litre w.c. installations Initial high energy wave attenuates rapidly.

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Siphon tanks offer a more sustained wave.

Tipping tanks used in UK at least from 1860. 1989 Stockholm accepts Gustavsberg 3 litre w.c.s for installation in blocks of apartments provided that a 21 litre siphon boost tank is installed at the base of the stack to discharge to the sewer.

3 litre flush volume w.c’s, 1989 Stockholm 21 litre Gustavsberg siphon tank connected to sewer.

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REALTIME simulations REALTIME Simulations (1996) will be shown for both the tipping tank and siphon tank.

Tipping Tank Siphon Tank Discharge flow. Time. Leading edge of wave attenuates, efficacy decreases rapidly. Higher flow at rear of discharge reinforces leading edge prior to eventual attenuation.

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Modelling solid transport under reduced flow conditions.

The mechanisms and dependencies identified as well as the remedial design options mentioned are ALL confirmed by the HWU solid transport simulation, DRAINET, that models the relationship between the solid and water velocities to replicate the effect of w.c. discharge profile, drain slope, roughness and cross sectional shape and dimension, frequency of appliance discharge and the interaction of multiple appliance discharges to complex networks, including junction design and defective drain slopes and obstructions. Simulation is based on the 1980 collaborative work between NBS Washington D.C and Brunel University. What took 24 hours to run in 1980 will now be demonstrated in real time in this presentation.

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REALTIME simulations The output from the DRAINET simulation of solid transport may be presented in a visual format – as demonstrated by the following examples designed to reinforce the importance

• f the first junction and to demonstrate the

potential of flow boosters…. REALTIME 2 m and 8 m junction And Siphon and Tipping Tank discharge simulation. …

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Solid transport in attenuating flows – DRAINET simulation available through HWU.

Solid velocity depends on surrounding flow conditions. As the flush attenuates solid deposition occurs. This implies that for one w.c. in one pipe of fixed slope, diameter and roughness and where there is no other supporting flow, there is a MAXIMUM travel distance for any solid regardless of how many times the w.c. is flushed.. Vwater

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REALTIME simulations

REALTIME SIMULATIONS HERE….

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The current discussion may be informed by an understanding of 30 + years of research freely available through international published papers.

Since 1973 the Counseil International du Batiment Working Commission W62 has published extensively in this area. www.cibworld.nl/ In the USA NBS (now NIST) Washington DC and the Washington Suburban Sanitary Commission (Galowin) and the late Tom Konen’s group at Stevens Institute, Hoboken, New Jersey have published on solid transport and drainline carry – much within the CIBW62 papers referenced above. WRc has in recent years published and undertaken considerable laboratory testing on low flush w.c.s. http://www.wrcplc.co.uk/ Caroma have introduced non-circular drains in domestic sizes and published the research.

www.caroma.com.au/product-ranges

Heriot Watt University staff have published extensively in mainstream journals, including - Building Services Engineering Research and Technology www.sagepub.com/journalsProdDesc.nav?

currTree=Subjects&level1=V00&prodId=Journal201803

Building and Environment www.elsevier.com/locate/buildenv Building Research and Information www.tandf.co.uk/journals/titles/09613218.asp

Contribution of previous research funding to the Dry Drains discussion.

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Conclusions

Each of the objectives set out by PERC, inc. site testing, laboratory testing and simulation, has already been achieved by international research. Climate change and demographic evidence suggests that, while water conservation will continue to be a priority, water usage levels are much higher than 20 years ago and will continue to be so even if current government targets are achieved. Good design for both w.c.s and the drainage network has been proved to mitigate solid deposition and an appreciation of normal design suggests that supporting flows are relatively close to most w.c. installations. On the basis of this evidence Dry Drains are a MYTH.

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This presentation on the assessment of the ‘Dry Drains’ issue has been based on the work of the Drainage Research Group at Heriot Watt University and has drawn on earlier work at Brunel University and international industrial collaboration with NBS Washington and Caroma, Australia, as well as historic work with CBCSM and Twyfords. Thank you for listening Dry Drains presentation, CIBW62 Dusseldorf, 2009