Carbon Neutral Design Metrics
Michael D. Utzinger
School of Architecture & Urban Planning
University of Wisconsin-Milwaukee
utzinger@uwm.edu
Consider the well-designed high performance buildings recognized annually in the AIA COTE Top Ten Awards. Why do these buildings perform well? What aspects of design and system integration, knitted with response to climate and program result in solutions that require a fraction of the resources compared with buildings designed just to meet code?
PLEASE NOTE:
The following metrics for designing a building to Carbon Neutral ARE A WORK IN PROGRESS. Their development began with the design of the Aldo Leopold Legacy Center. Although that building was completed in 2008, the metrics continue to evolve, as post occupancy analysis, ongoing, is revealing additional information and concerns that we feel must feed back into the design process. Designing a building to emit no carbon as a result of its operation and occupancy. These metrics feed into a spreadsheet tool that is being developed to assist in the detailed design of a Carbon Neutral Building. It is the tool that was used to design the Aldo Leopold Center. It is anticipated that the spreadsheet tool will be complete and issued for use in late summer 2009. In the interim, the Metrics are being provided for their informational value only.
The Metrics, and Spreadsheet Tool, in their current forms, have been used to develop the Case Studies within this web site. Any values currently posted in association with these Case Studies are intermediate values, and will be refined and reposted in late summer 2011.
NEW: CND METRICS REPORT LINK
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Level I Metrics
The Level I Metrics generally correspond to data collected and metrics reported from most high performance building databases. These metrics are based on whole building values including size, cost, occupancy, energy consumption, energy production and water consumption.
Measurements |
Gross Floor Area [SF] |
The total floor area of the building measured to the outside face of the enclosure walls. |
Construction Cost [$] |
Total building construction cost. |
Occupancy [FTE] |
Full time equivalent building occupancy including staff, visitors, students, etc. |
Water Consumption [ccf/yr] |
Annual water consumption in the building reported in hundred cubic feet per year. |
Electrical Consumption [kWh/yr] |
Annual electrical energy purchased from the grid. |
Solar Electricity Produced [kWh/yr] |
Total annual electricity produced on site from photovoltaic panels. |
Electricity Sold [kWh/yr] |
Solar electricity sold to the electric utility per year |
Fossil Fuel Combustion [kBTU/yr] |
Total annual consumption of fossil fuels in the building including natural gas (reported in therms), heating oil (reported in gallons) and propane (reported in ccf). |
Biofuel Combustion [kBTU/yr] |
Total annual consumption of biofuels in the building including biogas (reported in therms) and wood (reported in pounds) |
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Level 1 Metrics |
Unit Cost [$/SF] |
Construction cost per gross square foot of building. |
Occupant Density [SF/FTE] |
Building gross floor area per full time equivalent occupant |
Energy Utilization Intensity [kBTU/sf/yr] |
Annual building energy consumption per unit floor area. The building energy consumption is equal to the sum of the biofuel combustion energy, fossil fuel combustion energy, grid electricity consumed and solar electricity produced minus solar electricity sold. |
Occupant Energy Utilization [kBTU/FTE/yr] |
Annual building energy consumption per full time equivalent occupant. Given as the product of the Energy Utilization Intensity (EUI) and the Occupant Density. The Occupant Energy Utilization Intensity may be a better measure of the true energy impact of the building. |
Site Renewable Energy Fraction [%] |
Fraction of the total building energy consumption met by renewable energy produced on site. Equal to the sum of solar energy produced on site and any biofuel energy produced on site divided by the product of energy utilization intensity (EUI) and building gross floor area. |
Scope 1 Emissions - Fossil Fuel [CO2e/SF/yr] |
Carbon Dioxide equivalent emissions per year per unit gross floor area due to combustion of fossil fuels in the building. |
Scope 1 Emissions -Biofuel [CO2e/SF/yr] |
Carbon Dioxide equivalent emissions per year per unit gross floor area due to combustion of biofuels in the building. |
Scope 2 Emissions [CO2e/SF/yr] |
Carbon Dioxide equivalent emissions per year per unit gross floor area due to production of net grid electricity consumed in the building. Net grid electricity is total grid electric consumption minus solar electricity sold. |
Total Emissions due to Fossil Fuels [CO2e/SF/yr] |
Total equivalent carbon dioxide emissions due to fossil fuel produced per year per building gross floor area. Equal to the sum of Scope 1 emissions – fossil fuels and Scope 2 emissions. |
Water Utilization Intensity [gal/SF/yr] |
Water consumption per building gross floor area per year. |
Level II Metrics
The Level II Metrics are based on a number of building design parameters and more detailed energy consumption values. While Level I metrics generally measure building performance (e.g. Energy Utilization Intensity), Level II metrics measure building design variables (e.g. Enclosure Heat Transfer Rate per Unit Floor Area). Building performance is, in part, a function of building design. A goal for measurement of Level II metrics is to determine which design variables strongly influence building performance.
Building Design Variables |
Enclosure Heat Transfer Rate [BTU/°F/SF/hr] |
Total heat transfer rate between the building and the environment including all exterior surfaces, heat transfer through the ground and infiltration divided by the building gross floor area. |
Enclosure Transparency [%] |
Total enclosure glazed area (windows and skylights) divided by the building gross floor area. |
Natural Ventilation Factor [%] |
Total opening area in the enclosure divided by the building gross floor area. |
Net Occupied Area [SF] |
Occupied area of the building measured to the interior surface of the exterior enclosure. |
Daylit Fraction [%] |
Daylit Area of the building divided by the net occupiable area. |
Light Power Density [W/SF] |
Total installed light power divided by the building gross floor area. |
Solar Electric Intensity [Wp/SF] |
The installed peak power of the photovoltaic system per building gross floor area. |
Solar Thermal Intensity [SF/SF] |
Total solar thermal collector area per building gross floor area. |
Minimum Outdoor Air Ventilation [cfm/SF] |
Minimum required outdoor air ventilation rate divided by building gross floor area |
Maximum Outdoor Air Ventilation [cfm/SF] |
Maximum provided outdoor air ventilation rate divided by building gross floor area |
Maximum Building Ventilation [cfm/SF] |
Maximum installed air ventilation rate (outdoor plus return air) divided by building gross floor area |
Total Installed Fan Power [W/SF] |
Total fan power installed in the building divided by building gross floor area. All supply and exhaust fans should be included in the calculation. |
VFD Fan Fraction [%] |
Percent of total installed fan power that is either variable or VFD drive. |
Unit Heating Capacity [Btu/SF] |
Installed heat production capacity per unit building gross floor area. |
Cooling Intensity [SF/Ton] |
Building gross floor area divided by total building cooling capacity. |
Pump Power Density [W/SF] |
Total installed pump power per unit building gross floor area. |
VFD Pump Fraction [%] |
Percent of total installed pump power that is either variable or VFD drive. |
Level III Metrics
The Level III Metrics explore at a very detailed level two aspect of building performance: glazing systems and material environmental impact. Each glazing design in the building (up to 40 unique orientations and geometries) is evaluated in terms of incident solar radiation, reduction of solar radiation due to shading, reduction of solar radiation due to glazing transparency, and net admitted solar radiation. Values are calculated for the average hour of the average day of each month. TMY 3 weather data is used to calculate the average solar radiation incident on each unique glazing system in the building. A single graph for each glazing system plots average daily solar radiation per unit window area blocked by shading, reduced by glazing and admitted into the building for each month of the year.
A REVIT model of buildings provides a database of the volume of major materials used in the building (concrete, steel, wood, insulation, glass, etc.). With the volume of materials known, the embodied energy and carbon dioxide emissions per building gross floor area are calculated.
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