Water Balance Analysis
ASHRAE Headquarters, Atlanta GA
March 28, 2019
17 April, 2019
Water Conservation Goals and Opportunities
ASHRAE Headquarters
PROJECT GOALS Net Zero Water Definition
Achieve All 11 LEED Water Efficiency Points (ASHRAE OPR):
(2 pts) No Permanent Irrigation
(6 pts) 50% Reduction in Indoor Water Use
(2pts) Optimize cooling tower water cycles (>10 CoC) or use minimum
20% recycled water (If applicable).
(1pt) Install permanent water meters for 2+ water subsystems
Recover/Reuse water to the greatest extent possible (ASHRAE OPR) :
Investigate opportunities to reuse for non-potable uses recovered water
from HVAC condensate, rooftop stormwater. Potential non-potable uses
include cooling tower make-up, toilet flushing, irrigation.
Optimize Use of Existing stormwater Pond (ASHRAE OPR)
Zero Water Waste (Target Project Goal)
No potable water use for non-potable demands “Net zero water creates a water-neutral building where the amount of
alternative water used and water returned to the original water source is
equal to the building's total water consumption”
LEED Zero Water (Net Zero Water)
https://www.energy.gov/eere/femp/net-zero-water-building-strategies
Treat and Return water from building systems (green infrastructure for
stormwater, on-site wastewater treatment, etc.)
17 April, 2019
Business-As-Usual Water Flow Diagram
ASHRAE Headquarters
SUPPLY DEMAND DISCHARGE
What can be done to minimize Potable Water Demand,
manage Stormwater On-site with green infrastructure, and
Recycle and Clean Water Discharge?
17 April, 2019
Potential Best Practice - Water Flow Diagram
ASHRAE Headquarters
SUPPLY STORAGE / TREATMENT 1 DEMAND DISCHARGE
5,000-10,000 GAL.
CISTERN WITH
TREATMENT
(ASSUMING REUSE
FOR FLUSHING ONLY)
1 Minimize Water Consumption:
Water Efficient Fixtures
Drought- Tolerant Landscaping
Water-Efficient Heat Rejection
17 April, 2019
Potential Best Practice - Water Flow Diagram
ASHRAE Headquarters
SUPPLY STORAGE / TREATMENT DEMAND DISCHARGE
5,000-10,000 GAL.
CISTERN WITH
TREATMENT
(ASSUMING REUSE
FOR FLUSHING ONLY)
2 Recycle Water For Non-potable Uses (No Potable Water For Non-
potable Demands). Options Include:
Option 2A: Rainwater Reuse For Flushing & Cooling Towers
Option 2B: Composting Toilets, No Cooling Towers
Option 2C: Blackwater Treatment (Living Machine) and Reuse for
Toilet Flushing
17 April, 2019
Potential Best Practice - Water Flow Diagram
ASHRAE Headquarters
SUPPLY STORAGE / TREATMENT DEMAND DISCHARGE
5,000-10,000 GAL.
CISTERN WITH
TREATMENT
(ASSUMING REUSE
FOR FLUSHING ONLY)
3
3 Minimize Discharge From Site:
On-site Stormwater Management &/or wastewater treatment to
minimize wastewater discharge and return clean water to the
local watershed
17 April, 2019
Monthly Water Balance Analysis
ASHRAE Headquarters
MONTHLY ANTICIPATED WATER SUPPLY & DEMAND
Monthly Supply vs. Demand:
• Water Demands: the major anticipated
water demands are toilet flushing followed
by water use for flow fixtures including
showers and lavatory sinks. There is no
anticipated permanent irrigation demand and
cooling towers are one of many heat
rejection options being evaluated.
• Recycled Water Supply: By far, the greatest
Potential
potential recycled water source is rooftop Cooling
rainwater, followed by blackwater, greywater, Tower
Demand
and HVAC Condensate. (TBD)
Flush Fixture
• Based on current anticipated demands, there Demand
is sufficient rainwater from the building roof
Rooftop
to offset most, if not all water consumed for Rainwater
toilet flushing with a 5,000-10,000 gallon Collection
cistern. A larger cistern will be required if
cooling towers are included in the project.
17 April, 2019
Indoor Water Savings Potential
ASHRAE Headquarters
Key Findings:
• Option 3 (LEED 50% Reduction): : Assuming that
there is no cooling tower make-up or irrigation
demand, the project could potentially reduce indoor
water use by over 50% with the use of ultra-low-flow
fixtures. While technically possible, we do not
recommend the Ultra Low Flow Fixture rates case
due to maintenance concerns with waterless urinals
and ultra low-flow toilets.
LEED
TARGET
(50%) • Option 4 (Stretch Goal): Target a 35% reduction in
indoor water use with Standard Low-Flow Fixtures
and offset the remaining non-potable demand with
STRETCH GOAL recycled rooftop rainwater and HVAC Condensate.
(NO POTABLE Catchment area, cistern location, and treatment
requirements to be determined.
WATER FOR NON-
POTABLE USES)
• As an alternative to Option 4, ASHRAE could also
consider foam-flush composting toilets to
significantly reduce water use for toilet flushing
WC 1.6 1.28 1.1 0.9 while also reducing sewage discharge.
Urinal 1 0.125 0.125 waterless With a 5,000-
Lavatory Faucet 0.5 0.4 0.35 0.35 10,000 gallon • Another alternative is to include blackwater
Shower 2.5 1.5 1.5 1.5
cistern recycling, such as a “living Machine” or packaged
Kitchen Sink 2.2 1.5 1.5 1
blackwater treatment system.
17 April, 2019
Key Water Balance Analysis Assumptions
ASHRAE Headquarters
PRECIPITATION % FLUSH DEMAND OFFSET – 49 INCH
ANNUAL RAINFALL (TYPICAL YEAR)
6
5 % FLUSH DEMAND OFFSET – 30 INCH
PRECIPITATION [INCHES]
ANNUAL RAINFALL (YEAR 2012)
4
3
4.65 4.85 5.11
2 3.67 4.19 4.22 3.69 3.74 4.10 4.21 4.15
3.11
1
-
SEP
NOV
AUG
FEB
MAR
MAY
JUN
JUL
APR
OCT
DEC
JAN
KEY ANALYSIS INPUTS
Rooftop Rainwater Collection Area 30,000 Ft2
Rooftop Runoff Coefficient 0.95
Average Annual Rainfall (2006-2018
49.7 Inches
Dekalb-peachtree)
INDOOR WATER USE
# Full-time Occupants 124 PEOPLE, 260 DAYS/YEAR (Source: OPR)
3 Visitors 100 People, 2 Weekend Days Per Month (To Be Verified)
FIXTURE FLOW RATES EPA BASELINE STANDARD LOW-FLOW
Toilets [gpf] 1.6 1.28
Urinals [gpf] 1 0.125
Lavatory faucet [gpm] 0.5 0.4
Shower [gpm] 2.5 1.5 88-91% Reduction in 97-100% Reduction in
potable water use for potable water use for
Kitchen sink [gpm] 2.2 1.5
flushing with a 5,000 flushing with a 10,000
ADDITIONAL RESOURCES gallon cistern gallon cistern
https://www.dca.ga.gov/sites/default/files/2009_ipc_appendixi_rainwater.pdf
17 April, 2019
Georgia Rainwater Harvesting Guidelines
ASHRAE Headquarters
Next Steps – Rainwater Reuse:
1. Determine roof catchment area feeding into
rainwater harvesting system. Collecting
rainwater from only one or the two rooftops
may be sufficient to meet flushing demands
while reducing piping runs.
2. Locate space for a 5,000- 10,000 Gallon
Storage Tank
3. Incorporate filtration and disinfection as
required by the local plumbing code
4. Consider incorporating a “Day Tank” for the
storage of a limited supply of filtered water
to potentially reduce pump run-hours.
17 April, 2019
