Summary and critique of "LEED" 2009 Green Building Design & Construction Reference Guide

Jonathan Ochshorn

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Following is my summary and critique of the Green Building Design & Construction Reference Guide, 2009 Edition. Commentary on the Reference Guide can be found in these red boxes, sometimes within each of the chapter links immediately above, but mostly in my summary and critique of the prior version: Version 2.2 NC.

3. Water Efficiency (WE)

Overview

WE Prerequisite 1 Water use reduction

Intent: Use less water (benefits on both ends -- less strain on local supply, plus less impact on local wastewater systems).

Requirements: Use 20% less water (in WCs, urinals, lavs, showers, kitchen sinks, and "pre-rinse spray valves") than a "baseline" building with the following "baseline" limits:

Fixture typeCommercial baselineResidential baseline
Toilets1.6 gpf (or 3.5 gpf for "blow-out" types)1.6 gpf
Urinals1.0 gpfn/a
Lavatory faucets
  • 2.2 gpm at 60 psi (hotel/motel/hospital)
  • 0.5 gpm at 60 psi all other non-private
  • 0.25 gallons per cycle for metering faucets
2.2 gpm at 60 psi
Pre-rinse spray valves
(food service)
1.6 gpmn/a
Kitchen faucetsn/a2.2 gpm at 60 psi
Showerheadsn/a2.5 gpm at 80 psi

Note that this prerequisite does not limit commercial steam cookers, dishwashers, ice makers, clothes washers.

1. Benefits/issues. Same as "intent": less water use preserves natural hydrology, saves money on the supply and return end, and causes less contamination and stress on wastewater plants, as well as using less energy (especially hot water heating).

2. Related credits. Yes.

3. Referenced standards. For baselines, refer to Energy Policy Act (EPAct) of 1992 and 2005; plus ANSI UPC 1-2006 Uniform Plumbing Code 2006, Section 402.0) and ICC, International Plumbing Code 2006, Section 604.

4. Implementation: Use flow restrictors, sensors and metering controls, low-flush fixtures, nonwater fixtures, and capture rainwater. "WaterSense" fixtures (EPA sponsored) exceed baseline requirements.

Fixture typeWaterSense Standards
Toilets1.28 gpf
Urinals0.5 gpf
Lavatory faucets1.5 gpm
Showerheads1.5-2.0 gpm

5. Timeline and team.

6. Calculations. As described above. Use "fixture usage groups" (facilities used by different types of occupants). For "design case," any nonpotable supply (e.g., captured water) may be subtracted. Find typical usage for fixtures based on occupant groups.

Step 1: Determine FTE occupants, divided into usage groups if appropriate (e.g., customers versus staff). Then add up fixture use per day, as follows:

FixtureFTEStudent/visitorretail customerresident
WC female30.50.25
WC, male10.10.15
Urinal, male20.40.1n/a
Lav faucet130.50.25
Shower20.1001
Kitchen sink31004

Notes:
  1. 15 sec. duration typical, except 12 sec. if autocontrol; and 60 sec. residential
  2. 300 sec. duration typical, except 480 sec. residential
  3. 15 sec. duration typical, except 60 sec. residential

Step 2: Calculate total annual water use by summing for each fixture the product of occupants (or subdivided occupants = usage groups) x daily fixture use x flow/flush rate per fixture x number of days per year used. This is done for design fixtures and again for baseline fixtures.

7. Documentation guidance.

8. Examples.

9. Exemplary performance. N/A

10. Regional variations.

11. Operations/maintenance.

12. Resources.

13. Definitions: aquifer; automatic fixture sensors (motion detectors); blackwater = wastewater from toilets, urinals and (under some definitions) kitchen sinks, showers, bathtubs; metering controls (limit flow time, mostly user-initiated "on" with automatic "off"); nonwater (composting) toilet use microbiological processes to treat human waste; nonwater (dry) urinal uses trap with buoyant liquid blocking sewer gas; on-site wastewater treatment; potable water; process water is used in industrial processes and building systems (e.g., cooling towers) but can refer also to uses in dishwashing, ice making, etc.

WE Credit 1 Water efficient landscaping (2 points for option 1; 4 points for option 2)

Intent: Reduce use of both potable, and near-site natural water, for landscape irrigation.

Requirements: 2 options. Either (1) Reduce potable water for irrigation (mid-summer baseline measured in July) by 50% based on plant species, efficiency of irrigation, captured rainwater (including groundwater pumped away from foundation walls), recycled wastewater, or use of public nonpotable water; or (2) Do not use potable water for irrigation or do not use irrigation at all (and meet the requirements for Option 1: this last requirement seems redundant since using no potable water means that a reduction of at least 50% from a baseline must be met). Note that the "calculations" clarify the requirement for Option 2: that the total use of water for irrigation be reduced by 50%. That is, even if all irrigation water used is captured, it still must be 50% less than the baseline use.

[From Version 2.2 critique] It seems strange to award these points in climate regions where no irrigation is necessary. It's also not clear why a 50% reduction of water use is required to achieve the second "bonus" point, when all of the water used could conceivably be harvested from the roof (i.e., have no impact on the use of potable water).

1. Benefits/issues. Irrigation for landscaping uses most of 30% of 26 billion gallons of water used daily in the US (not clear bow this 26 billion gallon number compares with the 43.3 billion gallon number used in the overview). Better to use native plants that require less irrigation, fertilizer, or pesticides.

2. Related credits. Yes.

3. Referenced standards. n/a

4. Implementation. Minimize conventional turf grass. Use drip, micromist, subsurface irrigation strategies if necessary, with no irrigation between Nov and April (no shrub irrigation between Sept and June). Keep irrigation water away from buildings and air intakes. No outdoor plants? No problem: the points can still be earned by applying the requirements to roof/courtyard gardens, planters, etc. if they "cover at least 5% of the building site area." Hose bibs can be used in an ad hoc manner, and irrigation can be used for up to a year to get things started. Reducing the planted (irrigated) area cannot be used for this credit.

Use hi-tech devices to limit irrigation water use: drip systems, high-efficiency nozzles, rain sensors, and so on. Capture rainwater in cisterns, ponds, tanks. Use metal, clay, or concrete roofing rather than asphalt-based products.

5. Timeline and team.

6. Calculations.

Step 1: First establish the baseline irrigation use in July based on these factors:

Step 2: Tabulate values for the designed landscape, based on the following recommended values (Table 1):

Typeks (species factor)kd (density factor)kmc (microclimate factor)
 lowav'ghighlowav'ghighlowav'ghigh
Trees0.20.50.90.51.01.30.51.01.4
Shrubs0.20.50.70.51.01.10.51.01.3
Groundcover0.20.50.70.51.01.10.51.01.2
Mixed0.20.50.90.61.11.30.51.01.4
Turf grass0.60.70.80.61.01.00.81.01.2

 

Step 3: Find ET0 = local reference evapotranspiration rate (water needed to grow a "reference plant") in units of inches or mm, found in regional agricultural resources, and measured in July for this LEED chapter.

Step 4: Calculate ETL = evapotranspiration rate specifically for each landscape project area by multiplying ET0 x KL = ET0 x ks x kd x kmc. In other words, this evapotranspiration rate for a particular project area equals the "generic" rate for the reference regional plant multiplied by factors that adjust this value for the specific qualities of the species, its density, and the microclimate found on site.

Step 5: Find IE = irrigation efficiency (0.625 for sprinkler; 0.9 for drip) for each area; CE = controller efficiency (manufacturer or other documentation) for each area; amount of reused water (harvested, graywater, treated wastewater) and storage capacity (must figure out how much "extra" water is available for the month of July based on capture and storage modalities) in order to calculate the TWA (total water applied) and TPWA (total potable water applied) as follows:

TWA (gal) = area x (ETL/IE) x CE x 0.6233 where area is sq.ft., ETL is inches, and 0.6233 is a conversion factor (gal/sf/in.); and

TPWA (gal) = [sum of all] TWA (gal) reuse water (gal).

Step 6: Baseline: use average/conventional values for ks, kd, and IE, with the same (design) values for ET0 and kmc. Reallocate areas if species type change, but keep total area the same; and use typical regional reference values for species (e.g., typical areas of trees, grass, and shrubs rather than just turf grass). The total water applied (baseline) is:

TWA (gal) = area x (ETL/IE) x CE x 0.6233 where area is sq.ft., ETL is inches, and 0.6233 is a conversion factor (gal/sf/in.).

Step 7: Finally, the reduction in total irrigation water use (including reused water) and in potable water use for irrigation is found:

For Option 1: Reduction in potable water (%) = (1 - TPWA/TWAbaseline) x 100 must be at least 50%.

For Option 2: TPWA must equal 0 (so that reduction in potable water = 100%) and the use of any water for irrigation (i.e., reused water in the design case) must be cut in half (this is not mentioned in the requirements above), that is:

Reduction in total water (%) = (1 - TWAdesign / TWAbaseline) x 100 must be at least 50%.

Doesn't seem to account for actual rainfall used directly by the vegetation.

7. Documentation guidance.

8. Examples.

9. Exemplary performance. N/A

10. Regional variations. N/A

11. Operations/maintenance.

12. Resources.

13. Definitions: adapted (introduced) plants are low maintenance, non-invasive; aquifer; conventional irrigation (mainly pressurized water delivered via sprinklers); drip irrigation (low-pressure delivery through buried pipes); evapotranspiration rate (ET = water lost per unit time in mm or inches); graywater = untreated water from household waste (baths, showers, bathroom lavs, clothes-washers no kitchen sinks/dishwashers or toilets, although kitchen sinks are sometimes included); IPM = integrated pest management uses environmental knowledge to control pests with minimum hazard to people, environment; landscape area = total site minus hardscape, water bodies, and buildings; micro-irrigation = apply small amounts of water strategically; native plants; potable water; xeriscaping = method of landscaping with no irrigation.

WE Credit 2 Innovative wastewater technologies (2 points)

Intent: Reduce both wastewater and potable water demand.

Requirements: 2 options. Either (1) reduce potable water use by 50% through water-conserving (flush) fixtures or by using nonpotable water; or (2) treat half of wastewater on-site to "tertiary" standards, which is then used on site (or allowed to infiltrate).

1. Benefits/issues. Graywater comes with a price (extra piping, etc.) and has code issues; whereas capturing rainwater is easier from that standpoint.

[From Version 2.2 critique] The idea that profitability is the driving force for implementation of these guidelines is constantly reiterated in the LEED commentary. For example, building owners are warned here that reusing graywater might not be a realistic strategy: "While graywater collection and storage may not be a water reduction method that many owners and designers have the opportunity to include in their projects [presumably because of high cost and/or local code restrictions], high-efficiency plumbing fixtures are."

2. Related credits. Yes.

3. Referenced standards. same as for Prerequisite 1.

4. Implementation. A "purple pipe" system is a municipally-supplied nonpotable water.

5. Timeline and team.

6. Calculations. The credit is based on blackwater (flush fixture generated water): compare design to baseline case. See Prerequisite 1 for tabular information.

The designed annual water use = sum of annual use for each fixture minus nonpotable supply, if any. Detailed flush fixture data follows:

FixtureFlush data (gpf)
Conventional toilet1.6
HET (high-efficiency toilet) single-flush gravity1.28
HET, single-flush pressure assist1.0
HET, dual flush (full-flush)1.6
HET dual flush (low-flush)1.1
HET foam flush0.05
Non-water toilet or urinal0.0
Conventional urinal1.0
HEU (high-efficiency urinal)0.5


 

7. Documentation guidance.

8. Examples. On-site treatment example uses the following parts in series: waste from building -> anaerobic septic tank (below grade) -> closed aerobic reactor -> open aerobic tanks -> constructed wetland.

9. Exemplary performance. Yes: extend compliance from 50% to 100% for either option.

10. Regional variations. N/A

11. Operations/maintenance.

12. Resources.

13. Definitions: same as before, plus tertiary treatment = highest level of wastewater treatment, reduces contaminants to 10 mg/L biological oxygen demand (BOD) and 10mg/L TSS (total suspended solids).

WE Credit 3 Water use reduction (2-4 points)

Intent: Reduce water in buildings (helps at both ends: potable water supply and wastewater reduction) just like Prerequisite 1, but more.

Requirements: Use 30% less water (2 points), or 35% less (3 points), or 40% less (4 points) than the baseline use. See Prerequisite 1 for nominal (baseline) fixture water use and exclusions (steam cookers, etc.).

1. Benefits/issues. See Prerequisite 1.

2. Related credits. See Prerequisite 1.

3. Referenced standards. See Prerequisite 1.

4. Implementation. See Prerequisite 1.

5. Timeline and team. See Prerequisite 1.

6. Calculations. See Prerequisite 1.

7. Documentation guidance. See Prerequisite 1.

8. Examples. See Prerequisite 1.

9. Exemplary performance. Yes: Extend compliance to 45% for 1 more ID point.

10. Regional variations. See Prerequisite 1.

11. Operations/maintenance. See Prerequisite 1.

12. Resources. See Prerequisite 1.

13. Definitions: See Prerequisite 1.

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