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Rainwater Harvesting Design Methods for Commercial Buildings MATTHEW WILLIAMSON, P.E.
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OBJECTIVES
• CREATE A DESIGN PLAN
• REVIEW EXAMPLES
• OPEN DISCUSSION
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DESIGN PLAN 1. DETERMINE OWNER’S INTEREST
2. DETERMINE REGULATORY REQUIREMENTS
3. RESEARCH PRECIPITATION PATTERNS
4. CALCULATE TRIBUTARY AREAS
5. CALCULATE WATER DEMAND
6. CALCULATE STORAGE REQUIREMENTS
7. DEVELOP TREATMENT SYSTEM
8. DOCUMENT THE DESIGN
9. REVIEW THE SYSTEM
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CASE STUDY
• SINGAPORE CREATE
• 60,000 sq. meter laboratory complex
• Limited site landscaping
• High annual rainfall
• Municipal non-potable system
• Project goal: Greenmark Platinum
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DETERMINE REGULATORY REQUIREMENTS
• SCREENING - YES
• FILTRATION - YES
• DISINFECTION - YES
• COLORIZATION - NO
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RESEARCH PRECIPITATION PATTERNS
MONTHLY RAIN TOTALS DECEMBER = 8.0 in
RAIN FREQUENCY
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CALCULATE TRIBUTARY AREAS
1. HJKK
Collection Area Area (sf) podium roof 20014 Bar Buildings 50540 Canopy 22284 Tower 32334 Plaza areas 37628 Total Tributary Area 162799
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CALCULATE WATER DEMAND
• Irrigation requirements
• Flush Volumes
• Hydronic systems make-up rates
Month Irrigation Demands
Flush Demand
Jan 169,694 473,634
Feb 153,272 473,634
Mar 169,694 473,634
Apr 164,220 496,188
May 169,694 451,080
Jun 164,220 496,188
Jul 169,694 451,080
Aug 169,694 518,742
Sep 164,220 473,634
Oct 169,694 473,634
Nov 164,220 451,080
Dec 169,694 451,080
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CALCULATE STORAGE REQUIREMENTS
• COMPARE COLLECTION AMOUNTS WITH DEMAND AMOUNTS
• DETERMINE STORAGE DURATION (BRIDGING EVENTS)
• COMPARE REGULATORY REQUIREMENTS
• HOW MUCH SPACE DO YOU HAVE?
• HOW BIG ARE TYPICAL STORMS?
Month Rain water
rate (in) Effective RW
available Jan 7.8 672,391
Feb 6.1 526,367
Mar 6.7 577,305
Apr 5.6 482,220
May 6.2 533,159
Jun 5.5 475,428
Jul 5.7 492,408
Aug 5.6 482,220
Sep 7.0 604,473
Oct 6.6 570,514
Nov 9.9 852,375
Dec 8.0 689,371
CREATE = 300 CUBIC METER (80,000 GALLONS)
4 DAYS USE IN STORAGE TANK
TYPICAL STORM = FULL TANK
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DEVELOP TREATMENT SYSTEM
• SCREENING
• FILTRATION
• DISINFECTION
TREATMENT SYSTEM FLOW CHART
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DOCUMENT THE DESIGN
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REVIEW THE SYSTEM • 89% Reduction in potable water
• 47% Reduction in total municipal water used
• 74% of the water used on site is from rain water
• Helped the project reach Greenmark Platinum
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CASE STUDY • CIVIC BUILDING AND PARK IN LOS ANGELES • PROJECT IS TARGETING LEED GOLD
• VERY LARGE SITE (17 acres)
• LARGE IRRIGATION DEMAND
• LOW FLUSHING DEMAND
• WHAT WATER REUSE OPTIONS ARE POSSIBLE?
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THE PLAN
MANY SOURCES OF WATER AVAILABLE FOR THE PROJECT
• MUNICIPAL RECYCLED WATER (1.5 MILES AWAY)
• DRY SEASON FLOW
• WETLAND
• RAIN WATER
• GREY WATER
• GROUND WATER
• WASTE HYDRONIC WATER
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THE PLAN AFTER VALUE ENGINEERING
• MUNICIPAL RECYCLED WATER (1.5 MILES AWAY)
• DRY SEASON FLOW
• WETLAND
• RAIN WATER
• GREY WATER
• GROUND WATER
• WASTE HYDRONIC WATER
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RAIN WATER HARVESTING
ANALYSIS
• Low annual rain
• 5-7 day rain gaps during rainy season
• Large tributary area
• Low demand
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RAIN WATER HARVESTING
FEATURES • 4000 gallon storage tank
• In-line downspout filter
• Booster pump
• Harvested rain water piping throughout the building (purple pipe)
EQUIPMENT ROOM
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EFFECT
• 57% Reduction in potable water used for flushing
• Saves 122,000 gpy
• Saves $3,000 annual in water costs
• Costs $3,100 annual in electrical costs
• Requires an investment of $55,000
• Requires an approved Alternative Means and Methods to exclude disinfection (with chemical disinfection +$10,000 investment and $2000 in annual costs, with UV +$500 in annual energy costs)
• Would earn the project 2 LEED points
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Final Result
• No water collection.
• No rain water harvesting.
• Dual piping to permit future municipal connection of recycled water.
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The End
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OWNER INTEREST
• REDUCE PERPETUAL COSTS
• GREEN DESIGN GOAL
• PUBLIC RELATIONS
• CODE COMPLIANCE
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REGULATORY REQUIREMENTS
• MANDATED FIXTURE EFFICIENCY TARGETS
• DEVELOPMENTAL WATER USE LIMITS
• MANDATORY WATER USE REDUCTIONS
• TREATMENT REQUIREMENTS FOR NON-POTABLE WATER SYSTEMS
• SPECIAL PIPE LABELS
• FIXTURE WARNING LABELS
• COLORIZATION
• DISINFECTION
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RESEARCH PRECIPITATION
AVERAGE MONTHLY • http://www.nws.noaa.gov/
oh/hdsc/currentpf.htm
• http://www.weather.com
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CALCULATE TRIBUTARY AREAS
CLEAN ROOF AREAS
• ACTS AS BIO-FILTER
• CAN CAUSE COLOR
GREEN ROOF AREA
• REDUCES BURDEN ON FILTRATION
• ELIMINATE FOOD WASTES
• ELIMINATE OILY WASTE
USE ONLY HORIZONTAL AREAS
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CALCULATE WATER DEMAND
SYSTEMS • NUMBER OF FULL TIME
EQUIVALENT
• FLUSH RATES
• IRRIGATION RATES
• MAKE-UP WATER DEMAND
REQUIRED INFORMATION
• FLUSH FIXTURES
• IRRIGATION*
• WATER FEATURES*
• COOLING TOWERS*
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CALCULATE STORAGE REQUIREMENTS
BRIDGING RAIN EVENTS
• ACCESS
• EASE OF CONSTRUCTION
• VERMIN CONTROL
WHAT SPACE IS AVAILABLE?
• HOW LONG BETWEEN RAIN EVENTS SHOULD THE TANK LAST?
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DEVELOP TREATMENT SYSTEM
REGULATORY COMPLIANCE
• SCREENING
• FILTRATION
• DISINFECTION
• COLORIZATION
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DOCUMENT THE DESIGN
1. CREATE EQUIPMENT SCHEDULE
2. SPECIFY COMPONENTS
3. CREATE DETAILED DRAWINGS
• TANK
• SCREENS
• FILTERS
• PUMPS
• DISINFECTION
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REVIEW THE SYSTEM
• WHAT ARE YOU GETTING FROM YOUR SYSTEM?
• WHAT ARE THE OPERATIONAL COSTS?
• HOW MUCH POTABLE WATER DID YOU OFFSET?
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PRINCIPLES OF RAIN WATER HARVESTING
• Urban development is expanding faster than municipal infrastructure
• Changing weather patterns
• New understanding of drought patterns
• Aquifer demands are exceeding replenishment rates
Photo by John Lewis, NWS, Little Rock, Arkansas
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POTABLE WATER
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MUNICIPAL NON-POTABLE USE
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SEWAGE GENERATION
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STORM WATER DISCHARGE
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THREE QUESTIONS
• Have we really offset potable water use if we are treating harvested water to potable quality?
• Could the money spent on private systems be better spent on municipal distribution?
• If there’s no energy or money savings, is saving water enough to justify recycling?