rainwater harvesting: as a runoff reduction practice · total 780,192 0 building sq footage (ft2)...

Rainwater Harvesting: As a Runoff Reduction Practice

Date: September 2011Presented by: Greg Kowalsky

UrbanGreen Rain Water Harvesting

Agenda

– RWH – why now?

– System Components

– Calculating Benefits

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Divided Water Management

Drinking

WasteStorm

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VA Water Management: Drinking, Waste, Storm

Wastewater

Evap: 840kBlowdown: 160kCondensate: 750K

2M gal

Commercial Development• 43,000 ft2 roof• 43,000 ft2 parking• 43,000 ft2 landscape• 172,000 ft2 office• 45” per year

1M gal

Potable100k gal

Toilets

Cooling1M gal

1M gal

Irrigation

Municipal Water

3.1 M gal

Stormwater

45” Annual rainfallRooftop: 1M galSurface: 1M gal

2M gal

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Commercial Office Building

Stormwater Selection Staircase

RWH is a runoff reduction practice included in many

LID regulations

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RWH and LEED

Sustainable Sites• 6.1 Stormwater Quantity

– Pre‐development peak and quantity – 1 Point• 6.2 Stormwater Quality

– Reduce annual TSS by 80% – 1 PointWater Efficiency• 1.0 Water Efficient Landscaping

– Reduce by 50% ‐ 2 Points– No Potable Use – 4 Points

• 2.0 Innovative Wastewater Technologies– Reduce potable water used for sewage – 2 points– OR– 50% onsite treatment – 2 points

• 3.0 Water Use Reduction– 30% reduction from Baseline – 2 points– 35% reduction from baseline – 3 points– 40% reduction from baseline – 4 points

LEED 12• SS 6.1 (Quality) 1• SS 6.2 (Quantity) 1• WE 1 (Irrigation) 4• WE2 (Wastewater) 2• WE 3 (Indoor water) 4

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Typical System Components

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System Components

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Pre‐treatmentPre‐treatment

Storage Storage

CatchmentCatchment

MechanicalsMechanicals

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System Components: Catchment

Catchment• Rooftop – cleaner, needs treatment• Surface – more pollutants

Pretreatment • Reduce maintenance• Protect downstream equipment• Reduce potential for odor• Screening: 500 um to 2000 um • Filtration/Separation: 20um to 200um

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Storage Storage

CatchmentCatchment


Code Note: may limit catchment to rooftop

PretreatmentPretreatment

Code Note: First flush and pretreatment may be required

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System Components: Storage

• Above ground, Below ground • Metal, plastic, concrete, fiberglass • 1k gal to 1M gal• Calming inlets, floating outlets

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Storage Storage

CatchmentCatchment


Code Note: Calming inlet and floating outlet may be required

UrbanGreen SRPE Cistern – Decatur, GA

UrbanGreen SRPE Cistern – Seattle, WA

Integrated Mechanical Systems

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Storage Storage

CatchmentCatchment


Code Note: disinfection may be required – even for irrigation

Code Note: air gap may be required, separate reuse lines required

Mechanical System – Install Location

IndoorSkid Mounted

Outdoor Enclosure

UndergroundVault

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Calculating Benefits

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Daily Continuous Model

Modeling•Continuous daily model•Local rainfall history• Seasonal and daily demand •Seasonal and daily supply•Outputs:

– Runoff reduction– Water savings – Financial savings

Daily/Seasonal Demand

HVAC Demand

Toilet

Irrigation

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Basic Design Information

Info for Feasibility• Project location• Site areas (roof, hardscape, landscape)• Type of development (commercial,

institutional, residential…)

Info for final Design• Application• Instant demand and pressure• Cistern Preference• Mechanical location – inside/outside• Power/Voltage

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VA Runoff Reduction Model – Supply Inputs

Landscape Hardscape TotalTraditional Green Roof

Area 43,000 0 43,000 43,000 129,000Runoff C 0.95 0.50 0.05 0.90Area 0 0 0 0 0Runoff C 0.95 0.50 0.05 0.90

Area 0 0 0 0 0Runoff C 0.95 0.50 0.05 0.90 2

40,850 0 2,150 38,700 81,700

% of Peak gal/month

172,000 Jan 0% 0 0gal/hr/ft2 0.0007 Feb 0% 0 0gal/hr 246 March 0% 0 0gal/day 5,897 April 25% 44,229 0

Peak gal/month 176,914 May 50% 88,457 0Assumptions: June 75% 132,686 0

July 100% 176,914 0Aug 100% 176,914 0Sep 66% 116,763 0Oct 25% 44,229 0Nov 0% 0 0Dec 0% 0 0Total 780,192 0

Building Sq Footage (ft2)

Condensation Rate

Secondary Sources of Re‐Use Water

Rooftop

Basin 1

Basin 2

Basin 3

AC Condensation Gray Water Capture

(gal/month)

Effective Runoff Area

RooftopArea

LandscapeArea

HardscapeArea

AC Condensation Gray Water

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Units People/Unit Occupancy GPD/Person Cooling Makeup0 0 100% 8

Weekday Weekend Weekday Weekend3,058 153 1.28 3,914 196

Jan 0.0 0 0Weekday Weekend Weekday Weekend Feb 0.0 0 0

0 0 1.28 0 0 Mar 0.0 0 0 Apr 0.3 6,701 3,939

Weekday Weekend Weekday Weekend May 1.0 26,803 5,718 0 0 1.28 1 0 0 Jun 2.0 53,607 7,878

3,914 196 July 2.0 53,607 7,623 Daily Average Aug 2.0 53,607 7,623 Annual Total Sep 1.0 26,803 5,908

Oct 0.3 6,701 0Loads/Day Gallons/Load Cold Fraction Daily Total Nov 0.0 0 0

Residential 0 40 70% 0 Dec 0.0 0 0Non‐Res 0 0 50% 0 951,518 1,181,640Daily Total 0

Annual Total 0 Area (ft2) Occupancy172,000

0 764Residential 0 0 0Non‐Res 0 0Daily Total 0Annual Total 0

Total Building Space

RetailSchool

Gallons of blow down makeup required per

day

Annual Demand

Inches per weekInput Units

IrrigationArea (ft2)43,000

2,8441,038,177

Total

Toilet

Laundry

OtherVolume( gal per

Daily Demand

Wash Water

Daily Average

Residential

Office/Com

Demand (gal)0

Flushes per day Volume(gal per flush)

Daily Demand

Flushes per day Volume(gal per flush)

Daily Demand

Visitor Flushes (per Visitor)

Office/Com

Retail

VA Runoff Reduction Model – Demand Inputs

ToiletFlushing

Laundry

WashWater

Irrigation CoolingMakeup

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Include? Area/Volume Include? Annual Volumeyes 40,850 no 0

7 no 0 no 00.00 40,850 no 02.00 no 0 yes 1,065,433

no 0 no 00 1,065,433

WA DC Dulles

Cistern Size (gallons) 50,000

Rooftop ( effective ft2)Surface (effective ft2)

Total (ft2)Irrigation

LaundryWash water

Location

First Flush Bypass (in)Design Storm (in)

ToiletStormwater

ScondaryAC Condensate (ga l lons)Gray Water (ga l lons )

Total (ga l )

ApplicationSource

Cooling MakeupTotal

DemandSupply

Years Modeled

VA Runoff Reduction Model – Scenario 1

User Variables• Dulles Rain Data 1990‐1996 (avg 45in, max 58in)

• Supply Sources: Rooftop ~1.1M gal/yr• Demand Sources Irrigation ~ 1M gal/yr• Cistern Size 50,000 gal• First Flush Bypass No• Design Storm 2”• Water Rates $0.003 water, $0.009 sewer

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Runoff Reduction52%570,000 gal/year

Water Savings53%560,000 gal/year

Financial Savings$6,800/yr

Include? Area/Volume Include? Annual Volumeyes 40,850 no 0

7 no 0 no 00.00 40,850 no 02.00 no 0 yes 1,065,433

no 0 no 00 1,065,433

Total Targeted Targeted Peak Targeted Total Water Rate $0.0030Average 44.7 43.3 1,102,410 36,594 1,102,410 1,139,004 1,065,433 569,011 Sewer Rate $0.009Max 58.1 56.1 1,429,502 64,931 1,429,502 1,478,391 1,065,433 731,307Total 313.1 303.1 7,716,867 256,159 7,716,867 7,973,027 7,458,028 3,983,074

Diameter Length4 5326 236

Average 569,011 52% 561,868 53% 569,011 50% $6,828 8 133Max 731,307 56% 731,307 69% 731,307 55% $8,776 10 85Total 3,983,074 52% 3,933,074 53% 3,983,074 50% $47,797 12 59

WA DC Dulles


Water Savings



LaundryWash water

Demand Captured

Runoff Retained (Targeted Rainfall)

Water Savings Total Retained(Targetd, Peak, Secondary)

Savings

Stormwater Total: SW + SecondaryRainfall

Cistern Dimensions

Location


ToiletStormwater

ScondaryAC Condensate (ga l lons)Gray Water (ga l lons )

Total (ga l )

ApplicationSource

Cooling MakeupTotal

DemandSupply

Years Modeled

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Scenario 1 – Rooftop Runoff and Irrigation Only

Overflow: Cistern is full in winter, when there is no irrigation demand.

Option: increase cistern (runoff reduction increases from 52% to 60% for 100k gal)

Suggestion: find more demand in winter

Overflow

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Include? Area/Volume Include? Annual Volumeyes 40,850 yes 1,038,177

7 no 0 no 00.00 40,850 no 02.00 no 0 yes 1,065,433

no 0 no 00 2,103,609

Total Targeted Targeted Peak Targeted Total Water Rate $0.0030Average 44.7 43.3 1,102,410 36,594 1,102,410 1,139,004 2,103,581 999,859 Sewer Rate $0.009Max 58.1 56.1 1,429,502 64,931 1,429,502 1,478,391 2,103,609 1,314,189Total 313.1 303.1 7,716,867 256,159 7,716,867 7,973,027 14,725,069 6,999,011

Diameter Length4 5326 236

Average 999,859 91% 997,755 47% 999,859 88% $11,998 8 133Max 1,314,189 95% 1,301,613 62% 1,314,189 94% $15,770 10 85Total 6,999,011 91% 6,984,284 47% 6,999,011 88% $83,988 12 59

WA DC Dulles


Water Savings



LaundryWash water

Demand Captured

Runoff Retained (Targeted Rainfall)

Water Savings Total Retained(Targetd, Peak, Secondary)

Savings

Stormwater Total: SW + SecondaryRainfall

Cistern Dimensions

Location


ToiletStormwater

ScondaryAC Condensate (ga l lons)Gray Water (ga l lons)

Total (ga l )

ApplicationSource

Cooling MakeupTotal

DemandSupply

Years Modeled


Rooftop Runoff Reduction91%999,000 gal/yr

Water Savings47% Irrigation & Toilet997,000 gal/yr

Potential Savings$12,000/yr

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Scenario 2: Rooftop Runoff, Irrigation and Toilets

Overflow: rare and usually in winter

Option: Stop ‐ this is a viable way to manage rooftop runoff

Suggestion: find more SUPPLY in summer – save even more

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Summary

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Wastewater


2M gal

Commercial Development• 43,000 ft2 roof• 43,000 ft2 parking• 43,000 ft2 landscape• 172,000 ft2 office• 45”/yr

1M gal

Potable100k gal

Toilets

Cooling1M gal

1M gal

Irrigation

Municipal Water

3.1 M gal

Stormwater

45” Annual rainfallRooftop: 1M galSurface: 1M

2M gal

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1.1M gal

Potable100k gal

Toilets

Cooling

1M galIrrigation

1M gal

1M gal

45” Annual rainfallRooftop: 1M galSurface: 1M

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Re‐Use

SW 500k

1.5M gal

900k

800kMunicipal Water

100k


900k gal

Wastewater

Water Management Convergence

Drinking

WasteStormReuse

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QUESTIONS?

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rainwater harvesting: as a runoff reduction practice · total 780,192 0 building sq footage (ft2)...

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