LEED is the most popular certification for green buildings around the world. It was developed by the US Green Building Council, and the first version was launched in 1998.  The rating system is constantly reviewed and updated, and LEED v4 is the latest version as of mid-2020. 

The LEED certification covers several areas of building performance, including energy efficiency and water conservation. However, many requirements have a similar structure: there is a minimum performance level that is mandatory (Prerequisite), with points available for enhanced performance (Credits). Measurements have a fundamental role in LEED since building owners must demonstrate their project performance.

This article provides an overview of some LEED prerequisites and credits that involve a measured performance level. Only prerequisites are mandatory, but building owners must choose a combination of credits that adds at least 40 points to get the certification.

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Measuring Water Efficiency in LEED Buildings

Since the LEED certification aims to reduce the environmental footprint of buildings, many of its requirements focus on water conservation. There are specific requirements for both indoor and outdoor water consumption.

LEED requires at least 30% water savings for landscaping, using the US EPA WaterSense Water Budget Tool as a baseline. These savings can be achieved with a combination of irrigation efficiency and smart plant selection. Buildings that reduce water consumption by 50% earn 1 point towards the LEED certification, while those with 100% savings earn 2 points.

• This calculation is based on potable water, natural water bodies, and groundwater.
• In other words, alternative water sources count towards the savings percentage.

For indoor water consumption, LEED requires at least 20% savings for the local design baseline. WaterSense plumbing fixtures are required for LEED projects in the US since they guarantee 20% savings based on EPA lab tests. Just like with outdoor water consumption, points can be earned for higher performance:

If a building uses cooling towers, building owners can earn up to 2 points by demonstrating water quality. LEED requires at least the 5 following measurements: Calcium (1000 ppm), total alkalinity (1000 ppm), SiO2 (100 ppm), chloride ions (250 ppm), and conductivity (2,000 μS/cm).

Building-level water metering is mandatory under the LEED rating, and the data must be compiled by month and by year. The owner must also share data with the USGBC for at least five years after getting the certification or opening for occupancy - whichever happens first. One LEED point can be earned by installing dedicated water meters, in at least two of the listed subsystems for the corresponding building type.

Measuring Energy Performance in LEED Buildings

Building-level energy metering is mandatory for the LEED certification, just like water metering. This includes not only electricity and gas but also other fuels like propane and biomass. If the building gets chilled water or steam from an external source, it must also be measured to track energy performance.

Submeters and utility-owned meters are acceptable, as long as they aggregate building energy consumption. This information must also be shared with the USGBC for at least five years after getting the LEED certification or opening the building for occupancy. Energy consumption must be tracked at intervals of one month or less, and electric demand data must also be shared when applicable.

One LEED point is available for advanced energy metering, meeting all the requirements and performance features specified by the USGBC. These requirements include a measurement interval of one hour or less, remote data storage, and local storage for at least 36 months.

Measuring Indoor Environmental Quality in LEED Buildings

The concept of building performance has traditionally focused on energy efficiency, water conservation, and other measures that reduce cost. However, indoor environmental quality is equally important, since it affects health and productivity. Many modern buildings are not healthy environments, and this has been evident during the COVID-19 outbreak.

Adequate ventilation is fundamental for indoor air quality. In the LEED certification, outdoor airflow monitoring is mandatory for mechanical ventilation systems:

• VAV systems (variable air volume) must have a dedicated measurement device for their outdoor air supply. The device must have an accuracy of +/-10%, based on the minimum design airflow. An automatic alarm must activate when the outdoor airflow varies by 15% or more from the setpoint.
• CAV systems (constant air volume) must be balanced to the minimum outdoor airflow and equipped with a monitoring device, such as a current transducer or airflow switch.

On the other hand, naturally ventilated spaces must have at least one of the following devices:

• An exhaust airflow monitor with +/-10% accuracy based on the design exhaust rate, and an alarm to indicate variations of 15% or more.
• Signaling devices for all natural ventilation openings, with automatic alarms when any of the intakes are closed during occupied hours.
• Carbon dioxide (CO2) monitors in each thermal zone, 3-6 feet above the floor, with an audible or visual indicator when CO2 levels exceed the setpoint by over 10%.

One LEED point is available for using CO2 monitors in mechanically ventilated spaces as well. The installation requirements are the same as in naturally ventilated spaces.

Building owners can also earn 2 LEED points for testing the concentration of key air pollutants, according to the methods provided by ASTM, EPA, and ISO. In the case of volatile organic compounds, the laboratory in charge of the tests must be accredited under ISO/IEC 17025. The substance concentrations that must be tested include particulate matter, ozone, carbon monoxide, total volatile organic compounds, and formaldehyde.

Buildings can also earn LEED points if they use daylight to reach an illuminance between 300 lux and 3,000 lux. Projects can earn from 1 to 3 points, depending on the building type and the percentage of floor area with daylight.

LEED also covers acoustic performance, since it influences the indoor environmental quality. The HVAC Applications ASHRAE Handbook provides maximum noise levels in decibels(dBA), based on the type of building. LEED makes HVAC noise reduction mandatory for schools, where the maximum background noise is 40 dBA. Other buildings can earn 1-2 points for meeting their respective background noise limit, and schools earn 1 point for staying below 35 dBA.

Conclusion

Measurements are fundamental in scientific and technical fields, and the LEED certification for buildings is no exception. Accurate measurements serve as proof that a building saves water and energy while offering a healthy indoor environment. Performance levels can be determined by comparing actual measurements with a baseline, ideally, one that uses recognized standards as a reference.