Project teams may demonstrate compliance with the Minimum Energy Performance Prerequisite, and EA Credits 1.1 through 1.4 by a tenant-level energy simulation. If this path is selected, this compliance path must be used in its entirety to replace EA Prerequisite 2: Minimum Energy Performance, and EA Credit 1.1 through 1.4: Optimize Energy Performance.
Demonstrate an improvement in the proposed performance rating compared with the baseline performance rating for portions of the building within the LEED project boundary. Calculate the baseline according to ANSI/ASHRAE/IESNA Standard 90.1–2007, Appendix G, with errata (or a USGBC-approved equivalent standard for projects outside the U.S.), using a simulation model for all tenant project energy use.
The proposed design must meet the following criteria:
- compliance with the mandatory provisions of ANSI/ASHRAE/IESNA Standard 90.1–2007, with errata, (or a USGBC-approved equivalent standard for projects outside the U.S.);
- inclusion of all energy consumption and costs within and associated with the tenant project; and
- comparison against a baseline tenant project that complies with Standard 90.1–2007, Appendix G, with errata but without addenda (or a USGBC-approved equivalent standard for projects outside the U.S.).
Percentage Improvements Required to Achieve EA Prerequisite 2: Minimum Energy Performance, and points under EA Credit 1.1 through 1.4: Optimize Energy Performance are as shown in the Related Resource "ASHRAE 90.1-2007 Point Scale for LEED-CI v2009 Tenant-Level Energy Models".
Document the energy modeling input assumptions for unregulated loads. Unregulated loads should be modeled accurately to reflect the actual expected energy consumption of the tenant project.
If unregulated loads are not identical for both the baseline and the proposed performance ratings, and the simulation program cannot accurately model the savings, follow the exceptional calculation method (ANSI/ASHRAE/IESNA Standard 90.1–2007, G2.5). Alternatively, the following exceptional calculation methods are approved for unregulated loads:
- use the COMNET modeling guidelines and procedures to document measures that reduce unregulated loads;
OR
- for equipment that is classified as eligible by ENERGY STAR, complete the appropriate ENERGY STAR savings calculator. The baseline design energy consumption for ENERGY STAR-eligible equipment shall be the average annual power consumption for the equivalent Conventional equipment as determined by the ENERGY STAR savings calculator. The proposed design energy consumption may be either the average annual power consumption for ENERGY STAR equipment as determined by the ENERGY STAR savings calculator, or manufacturer reported average annual power consumption that has been calculated in accordance with the appropriate ENERGY STAR product specification.
Modeling the Baseline Case:
The baseline HVAC system type must be based on the building’s area and number of floors (not the project’s area and number of floors).
Existing conditions for lighting and HVAC systems must be modeled as new construction in the baseline case, following Appendix G, for all components and systems.
If appropriate, apply Section G3.1.1 exceptions (a–f) to the model. More specifically, if the building heating source (fossil fuel or hybrid versus electric) or building type (nonresidential versus residential) varies from the predominant conditions of the building for an area exceeding 20,000 square feet, an alternative system type should be modeled for the space where exception (a) applies. Additional systems should be modeled in any portions of the space where exceptions (b) through (d) apply.
Allocation of Central HVAC and DHW systems to the project space:
In many projects, a portion of a base building HVAC or service water heating system serves the project’s tenant space. To allocate a percentage of that HVAC or service water heating system to the tenant area, use whichever of the following two methods is more appropriate. (Note: for air handling units, this method should be consistent with the method used for IEQ Prerequisite 1: Minimum Indoor Air Quality).
Method 1:
Method 1 is applicable when the additional spaces served by the HVAC or service water heating system have similar occupancies to the project space, provided the resulting unmet load hours for the proposed design do not exceed the amount allowed by ASHRAE 90.1.
- Determine the total square footage (square meters) served by the HVAC or service water-heating system.
- Determine the project floor area served by the HVAC or service water-heating system.
- For air-handling units, determine the design supply airflow, design fan power, design heating capacity, design cooling capacity, and outdoor airflow. For central service water heaters or thermal energy plants (e.g., steam, hot water, or chilled water) located in the building, determine the chiller or boiler quantities and capacities, storage tank volumes as applicable, pump design supply volume for each pump as applicable, heat rejection fan power, and any other pertinent parameters relative to HVAC system capacities.
- Determine the relative contribution of the HVAC or service water-heating system to the project floor space by applying the project floor space ratio to each design parameter (design supply airflow, design fan power, design heating capacity, design cooling capacity, outdoor airflow, chiller capacity, service water heating storage volume, or pump capacity):
Adjusted parameter = Parameter x Project area served by system / Total area served by system
- Model the HVAC or service water-heating system based on the actual design conditions and sequence of operations, but use the adjusted parameters as calculated above.
- For chilled water, hot water, or steam central plants, the District Energy Guidance may be used in lieu of the method above to determine average efficiencies for the central plant equipment.
Method 2:
Method 2 is applicable when the other spaces served by the air-handling unit have dissimilar occupancies to the project space.
- For air-handling units, determine the design supply airflow, design fan power, design heating capacity, design cooling capacity, and outdoor airflow. For central thermal energy plants or service water heaters located in the building, determine the chiller or boiler quantities and capacities, storage tank volumes as applicable, pump design supply volume for each pump as applicable, heat rejection fan power, and any other pertinent parameters relative to HVAC system capacities.
- Determine the percentage allocation of HVAC or service water heating capacity to the project space, using the following equations:
% allocation = Airflow allocated to project space / Total design supply airflow
% allocation = Chilled water capacity allocated to project space / Total chilled water capacity
Example: A dedicated outside air system supplies the entire building, and VAV boxes distribute the outside air to each tenant space. The team makes the calculation as follows:
% allocation = [AHU design supply flow] / [Sum of all VAV box peak design flows] x [VAV box peak design flow for project space]
- Provide documentation from the base building’s owner identifying the airflow and/or thermal capacity allocated to the project space versus the total design supply airflow and/or thermal capacity. Justify this percentage allocation in a narrative.
- Identify the different occupancies, by type and square footage (square meters), served by the air-handling unit or thermal energy system.
- In ASHRAE 90.1 User’s Manual or ASHRAE 62.1, look up default assumptions for the other occupancies’ lighting loads, ventilation, occupancy, etc. Use these values to determine (per square foot or square meter) the peak heating and cooling loads, design supply air volume, and design outside air volume for the other occupancies:
Total load = Sum [(Design load/ft2) x (Area)]
Adjusted parameter = Parameter x Total project area served by AHU or thermal system / Total area served by AHU or thermal system
- Model the air-handling unit or thermal energy system based on the actual design conditions, but use the adjusted parameters as calculated above.
- For chilled water, hot water, or steam central plants, the District Energy Guidance may be used in lieu of the method above to determine average efficiencies for the central plant equipment.