Rainwater Harvesting Design Methods for Commercial Buildings MATTHEW WILLIAMSON, P.E.

OBJECTIVES

• CREATE A DESIGN PLAN

• REVIEW EXAMPLES

• OPEN DISCUSSION

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

CASE STUDY

• SINGAPORE CREATE

•  60,000 sq. meter laboratory complex

•  Limited site landscaping

• High annual rainfall

• Municipal non-potable system

•  Project goal: Greenmark Platinum

DETERMINE REGULATORY REQUIREMENTS

•  SCREENING - YES

•  FILTRATION - YES

• DISINFECTION - YES

• COLORIZATION - NO

RESEARCH PRECIPITATION PATTERNS

MONTHLY RAIN TOTALS DECEMBER = 8.0 in

RAIN FREQUENCY

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

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

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

DEVELOP TREATMENT SYSTEM

•  SCREENING

•  FILTRATION

•  DISINFECTION

TREATMENT SYSTEM FLOW CHART

DOCUMENT THE DESIGN

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

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?

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

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

RAIN WATER HARVESTING

ANALYSIS

• Low annual rain

• 5-7 day rain gaps during rainy season

• Large tributary area

• Low demand

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

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

Final Result

• No water collection.

• No rain water harvesting.

• Dual piping to permit future municipal connection of recycled water.

The End

OWNER INTEREST

• REDUCE PERPETUAL COSTS

• GREEN DESIGN GOAL

• PUBLIC RELATIONS

• CODE COMPLIANCE

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

RESEARCH PRECIPITATION

AVERAGE MONTHLY • http://www.nws.noaa.gov/

oh/hdsc/currentpf.htm

• http://www.weather.com

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

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*

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?

DEVELOP TREATMENT SYSTEM

REGULATORY COMPLIANCE

•  SCREENING

•  FILTRATION

• DISINFECTION

• COLORIZATION

DOCUMENT THE DESIGN

1.  CREATE EQUIPMENT SCHEDULE

2.  SPECIFY COMPONENTS

3.  CREATE DETAILED DRAWINGS

•  TANK

•  SCREENS

•  FILTERS

•  PUMPS

• DISINFECTION

REVIEW THE SYSTEM

•  WHAT ARE YOU GETTING FROM YOUR SYSTEM?

•  WHAT ARE THE OPERATIONAL COSTS?

•  HOW MUCH POTABLE WATER DID YOU OFFSET?

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

POTABLE WATER

MUNICIPAL NON-POTABLE USE

SEWAGE GENERATION

STORM WATER DISCHARGE

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?