Water Greenroofs Resilience IndependenceGulf Coast Green – Houston – May 2012
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!
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.
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
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
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
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
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
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
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
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
o 15,741 sf green roof (based on Bush rainfall rate)o 8” soil depth results in run-off of 133,085 gallonso 8” soil depth results in retention of 329,985 gallonso 15,741 sf green roof (based on Hobby rainfall rate)o 8” soil depth results in run-off of 182,355 gallonso 8” soil depth results in retention of 360,035 gallonso Bush retention equates to 44,113 cf = 1.013 ac-fto Hobby retention equates to 48,130 cf = 1.105 ac-fto These quantities never impact the storm system
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
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
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
Evapotranspiration data ITC – Texas ET Network found at texaset.tamu.edu Rainmaster.com – provides evapotranspiration data by zip code
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
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
• 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.
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.
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.
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
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.