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Rainwater System Design – the Role of Header Tanks and Pressure Vessels in
Energy Efficiency
Grace TjandraatmadjaDecentralised Systems
Science Forum, 19-20 June 2012
Urban Water Security Research Alliance
Objective• To identify the factors impacting energy footprint of rainwater supply in
urban areas reduce energy requirements
Background
1. Gardner et al (2006),Beal et al (2008), 2. Retamal et al (2009), 3. Cunio and Sproul (2009), 4. SEWL (2009), 5. SEWL (2010), 6. Hood et al (2010), 7.Talebpour et al (2011), 8.Umapathi et al (2012), Centralized (Brisb) (Kenway et al 2008), Desalination (Apostolidis 2010), IPR (Knights et al 2006).
Methodology
End use requirements
System configuration
Pump characteristics
Energy requirements
Infrastructure characteristics (Pipe length,
diameter, configuration)
Ancillaries:pressure vessels,
header tanks, filters
Pump design
Pump + switch selection
Water use patterns(frequency and pattern of use)
End use characteristics
(type, flow, volume)
Experimental set-up
“Controlled and reproducible environment”
2.5 stars 3 stars 4 stars
15.7L/wash 3/6L/flush 115 L/wash (T)45 L/wash (F)
5
System componentsPump A B C D
Manufacturer X X Y X
Type of pump External External External Submersible
Output Power 200 watts 550 watts 750 watts 600 watts
Maximum Head 31m 33 m 45 m 32m
Type of switch Pressure Mains automaticPressure
Pressure Pressure
Stand by pipe pressure
250 kPa 650 kPa 380 kPa 650 kPa
Pressure vessel 8, 18, 40, 80 L
Header tank 300L
Infrastructure Diameter 19 mm + 25 mm
Monitor Pump operation: P(kPa), Q(L/m), Energy use (KWh), i (A) and Volume.
Results – Rainwater end usesWater service requirements for household end uses are dictated by design
constraints (manufacturer, WELS)
Design specificationsAppliance/Fittings Minimum Pressure
(kPa)Maximum Pressure
(kPa)Since 2006
(WELS)Washing machine* 40-100 800-1000Dishwasher 30-150 800-1000Toilet cistern* 150
25 (low pressure)400 9/4.5L, 6/3L, 4.5/3L
(2-4 stars)Tap n.a. n.a. 2 -7 L/min
(6 - 4 stars)
Minimum pressure (Appliances)
Maximum flow (Fittings)
Energy footprint versus flow requirements
Pump Performance
Energy distribution depends on pump design and operation.
Over-run
Header tank
257L
QPump operation for header tank supply
Tank volume > minimum water requirement (L/pe.d)
Header tank
Header tanks: largest reduction in energy footprint.Pressure supplied was insufficient for service.
The Role of Pressure Vessels
Air reservoir
Water reservoir
• Purpose : to reduce the need for pump start-ups for provision of small volumes of water (e.g. leaks).
• Range of sizes: 5 -450L ($100 -$1600)
12
Pressure monitoring
0
500
Time
Pres
sure
(kPa
)
Pressure vessel fill up
Opening tap for 15 seconds
0
500
1000
1500
2000
2500
3000
-505
101520253035
Pow
er (W
)
Flow
(L/m
in)
Time
Typical pressure vessel fill up Pressure vessel fill
Pressure Vessel Operation
Pressure Vessels
• PV holds approx. 1/3 of its nominal volume. • PV effectiveness depends on match of volume of end use, PV size and
pump settings.
The Role of Pressure Vessels
• Pump C (0.75kW): energy reduction for low volume applications• e.g. Toilet cistern - 33% reduction in specific energy
Conclusions
End use requirements
System configuration
Pump characteristics
Energy requirements
Infrastructure characteristics (Pipe length,
diameter, configuration)
Ancillaries:pressure vessels,
header tanks
Pump design
Pump + switch selection
Water use patterns(frequency and pattern of use)
End use characteristics
(type, flow, volume)
Conclusions• Energy footprint in urban dwellings is determined by:
• End uses• Pump selection (size and design)• System configuration
• End uses: restricted by design (manufacture/standards) individual end uses (Q<15L/min)
• Pumps: Energy use depends on design/manufacturer– Best energy efficiency at flows (Q>15L/min)
• Mismatch between end uses and pump operation for energy efficiency
Ancillaries:• Header tanks
Have potential to produce the largest energy savingsBut current housing and appliance design limits service
• Pressure vesselsReduce energy compared to pumps aloneEfficiency determined by vessel size and pump pressure settings
Conclusions
Recommendations
How to reduce the energy footprint for rainwater supply:
• Consider dwelling end uses• Understand pump energy requirements (energy vs flow)• Match pump size and end uses • Use of ancillary devices such as pressure vessels (properly
sized and suited for pump).
Acknowledgements
• Co-authors - Chris Pollard, Ashok Sharma, Ted Gardner
CSIRO Land and WaterGrace Tjandraatmadja
Phone: +61 3 9252 6564Email: [email protected]: http://www.csiro.au/people/grace.tjandraatmadja.html
Contact Us Phone: 1300 363 400 or +61 3 9252 6000
Email: [email protected] Web: www.csiro.au
Tank
Level gaugeDataloggerPressure and
flow meters
Questions?
Urban Water Security Research Alliance
THANK YOU
www.urbanwateralliance.org.au
