Sustainability: Water Independence

1. Water
Greenroofs
Resilience
Independence
Gulf Coast Green – Houston – May 2012

2.  to save energy
 to sustain our and our children’s lifestyles
 to inflict less damage on our environment
 to rid our inhabited realm of chemicals, additives and
supplements that harm
 to improve our living environments
 to conserve the most valuable asset on the planet –
water
 Better known as – save the planet!

3.  Evaporation – accounts for the movement of water to
the air from sources such as the soil, canopy
interception and water bodies.
 Transpiration – accounts for the movement of water
within a plant and the subsequent loss of water as vapor
through stomata in its leaves.
 Evapotranspiration – a key element or part of the water
cycle – describes the sum of evaporation and plant
transpiration from the Earth’s land surface to the
atmosphere.

4.  Acre-foot – a unit of measure denoting one acre of
ground (a chain x a furlong – 60’ x 660’) x one foot
depth of water. 325,851.4 gallons. Historically
visualized as the amount of water a suburban family
household will use in a year.
 1 kWh = 3413 btu
 Evaporation – 1 gm of H2O = 580 calories
 1 btu = 252 calories – 1 ton = 72,576,000 calories
 1 gallon = 3783 grams
 1 cf = 7.4805 gallons

5.  75% of the surface is water
 25% of the surface is land
 Of that 25%, 50% is habitable
 Of that 50%, 50% is arable
 98% of the water is in the oceans
 2% of the water is fresh but 1.6% is locked in polar ice
caps and glaciers and .36% is underground in aquifers
and wells
 0.036% is actually found in rivers and lakes
 Water is in a constant cycle – we never lose it

6.  Two (2%) percent of the surface of the earth is
comprised of cities
 Fifty-three (53%) of the population of the Earth lives in
cities
 Sidenote: thirty-five (35%) of those residents live in
slums with minimal or no services – e.g. no running
water, sewage conveyance or storm water controls

7.  Five intensive green roofs constructed
 Roughly 1.40 acres (.6 hectare)
 Design/build approach
 Anticipated - Energy Star and LEED certification
 So far – three Platinum certifications
 Goals
◦ Minimum 50% less energy usage
◦ Unique identity within the community
◦ Control long term costs
◦ Radically lessen impacts by and to water

8.  Firstly
 reduce stormwater run-off
 improve water quality
 decrease overall water use
 reduce the heat island effect
 conserve energy
 reduce sound reflection
 create wildlife habitat
 improve the aesthetics of the roof

9.  Long term investment
 Long term maintenance and operations are crucial
components dwarfing the initial cost of the facility
 Long term utility requirements and energy needs
present a serious case for understanding and pursuing
sustainable design and building
 Greatest water impact opportunities

10.  First, third and fourth buildings – composite framing
 Second building – pre-engineered steel frame + bar joists
with concrete deck
 Fifth building – steel frame + bar joists with concrete deck
 Composite system – reinforced concrete slab diaphragm
with steel girders + shear connectors
 Unanticipated benefit – 24 tons less steel at roof with
composite system at roof
 Our loads – 50 psf live load + 30 psf (saturated) soil mixture
+ 25 psf dead load (the structure)
 All roofs - intensive

11.  Average depth – 9 to 10 inches; maximum depth 12”
 Repeated floor system at roof = minimal cost impact
 Composite system inherently rigid
 Intensive – less complicated wind resistance
 Extensive – wind uplift issues; complicated anchorage
 Intensive – more robust plantings
 Extensive – smaller scale plantings

12. o 15,741 sf green roof (based on Bush rainfall rate)
o 8” soil depth results in run-off of 133,085 gallons
o 8” soil depth results in retention of 329,985 gallons
o 15,741 sf green roof (based on Hobby rainfall rate)
o 8” soil depth results in run-off of 182,355 gallons
o 8” soil depth results in retention of 360,035 gallons
o Bush retention equates to 44,113 cf = 1.013 ac-ft
o Hobby retention equates to 48,130 cf = 1.105 ac-ft
o These quantities never impact the storm system

13.  Texas Water Development Board
 Texas Manual on Rainwater Harvesting
 Texas Rainwater Calculator, Version 2
 Garden Roof Storm Water Run-off/Detention Estimator
 Run-off and Irrigation worksheet
 Innovative Water Technologies

15.  Evaporative cooling off-setting solar radiation
based on month of June
 Average direct solar radiation – 1443 btu/sf/day
 Equates to 363,550 calories/sf/day
 Equates to 626.81 grams/sf/day
 Equates to 2607 gallons/day on total roof
 Resultant required evaporation = 6.7477mm
 Equivalent tons of ac avoided = 78.85
 Power saved = 6655 kWh
 Cost savings at $0.12/kWh = $798.60

16.  Evaporative cooling based on average Eto
(inches/month) again using June (6.57”)
 Equates to 0.219 inches/day
 Equates to 2,149 gallons/day over entire roof
 Equivalent tons of ac avoided = 65.001
 Power saved = 5,486 kWh
 Cost savings at $0.12/kWh = $658.34
 Resultant kBtu/sf (of building/day) = 13.215
 Average resultant kBtu/sf = 8.93
 Resultant cost savings/sf = $0.11

17.  Evapotranspiration data
 ITC – Texas ET Network found at texaset.tamu.edu
 Rainmaster.com – provides evapotranspiration data by
zip code

18.  Roof top retention
 Underground cistern approach
 Above ground cistern approach
 Side benefits – detention system and opportunity to
retain stormwater + reclaim
 Capture condensate
 Filter out/settle out suspended particles and phosphates

20.  Absorb storm events
 Hold 2.52 – 2 year storm events before discharge
 Gulf Freeway cistern system holds 395,000 gallons
 Gulf Freeway facility – 1.0127 acre-feet never leave
the site or enter the storm system thanks to the green
roof
 Total site holds 2.2238 acre-feet (725,000 gallons)
before any impact on storm system

24. • Net Zero Water: One hundred percent of occupant’s
water use must come from captured precipitation or
closed loop water systems that account for downstream
ecosystem impacts and that are appropriately purified
without the use of chemicals.

25.  Ecological Water Flow: One hundred percent of storm
water and building water discharge must be managed
onsite to feed the project’s internal water demands or
released onto adjacent sites for management through
acceptable natural time-scale surface flow, groundwater
recharge, agricultural use or adjacent building needs.

26.  The gaps between our current building design and the
Living Building requirements include the processing of
water for potable use onsite for a true closed-loop
system and some potential minor additional capacity
during dry seasons.

27.  Recreational rooftop garden – 20%
 Productive rooftop garden – 7%
 View onto a green roof – 4.5%
 Adjacent properties – range of 2 to 7%
 Source: Monetary Value of the Soft Benefits of Green
Roofs – Canadian Mortgage and Housing Corporation

28.  Particulate matter removed from atmosphere – 1 square
meter (10.76 sf) absorbs .2kg/year (644#’s)
 Oxygen production – 1.5 square meters (16.15 sf)
produces enough oxygen for 1 person per year. A
person uses 6 pounds of oxygen per day (975 people)
 Sound attenuation – dependent upon roof assembly
reductions can range from 10 db to 40 db.