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  • R. Alex Giordano, PE

Maximizing LEED Points: Choosing the Ideal HVAC System


Introduction

In the quest for environmentally responsible and sustainable building design, the Leadership in Energy and Environmental Design (LEED) certification has emerged as a widely recognized standard worldwide. LEED aims to promote sustainable practices in the construction industry, rewarding projects that incorporate eco-friendly features and technologies. One critical aspect of earning LEED points involves selecting the appropriate HVAC system type based on the ASHRAE Std 90.1 baseline system to which it will be compared. Failure to choose the right system can significantly impact a project's eligibility for LEED certification. In this article, we explore the importance of selecting the right HVAC system type and its implications for LEED points.


ASHRAE Standard 90.1

ASHRAE Standard 90.1 provides two approaches to demonstrating compliance: The prescriptive path and performance path. Within the performance path approach, there are two sub-approaches, the Energy Cost Budget (ECB) method and the performance Rating Method (PRM). The main difference between the ECB and PRM is how the baseline building performance is defined. See the Appendix for definitions of the ECB and PRM methods.


When either of these two performance compliance paths are used, ASHRAE Std 90.1 provides guidance for the energy-efficient design of buildings. Appendix G, Table G3.1.1-3 outlines the Baseline HVAC System Types based on the building area type, number of stories, and combined floor area. Entering the table for the general building area type, number of floors, combined floor area, and Climate Zone, the table specifies a baseline HVAC system type which serves as a reference for comparison with the proposed design.


The purpose of Table G3.1.1-3 is to establish a baseline for energy performance that reflects typical or conventional HVAC systems used in buildings of various types and sizes. The baseline HVAC systems are determined based on standard practices and equipment availability at the time the standard was developed.


When designing a building to comply with ASHRAE 90.1, the proposed HVAC system should be compared to the corresponding baseline system specified in Table G3.1.1-3. The proposed system should demonstrate energy performance that is at least as efficient as the baseline system for the given building type, area, and number of floors.


It is important to understand that the actual HVAC system chosen for a building project is not required to be identical to the baseline system, the proposed design just needs to meet or exceed the energy performance of the baseline to which it is compared. The standard allows for flexibility in selecting energy-efficient technologies and approaches, provided that any innovative technology achieves the necessary energy savings when compared to the baseline.


Designers and engineers typically use energy modeling software or methodologies to determine the energy performance of both the proposed and baseline HVAC systems. This allows for a fair and accurate comparison to ensure compliance with ASHRAE Standard 90.1’s energy efficiency requirements.


Keep in mind that ASHRAE Standard 90.1 may receive updates over time, so it is essential to consult the latest version of the standard for the most up-to-date information and requirements.


The Importance of HVAC System Type for LEED

The HVAC system type plays a significant role in determining a building’s overall energy efficiency and environmental impact. As such, LEED places considerable importance on selecting an HVAC system that compares favorably with the appropriate ASHRAE Std 90.1 baseline system. At the time of this writing, in LEED v4 and LEED v4.1, the points for carefully chosen baseline HVAC systems based on building type, area, and number of floors are not awarded as a standalone credit. Instead, they are addressed within the “Energy and Atmosphere” (EA) credit category, specifically under the credit named “Minimum Energy Performance.” These sections focus on optimizing energy performance and reducing greenhouse gas emissions.


The Minimum Energy Performance credit focuses on demonstrating a minimum level of energy efficiency for the building’s HVAC and lighting systems. It requires the project to achieve a certain level of energy cost savings compared to the ASHRAE Standard 90.1-2010 (for LEED v4) or ASHRAE Standard 90.1-2016 (for LEED v4.1).


To earn points under this credit, it is important for the design team to choose a proposed system that is at least equal or similar to the proposed system in Table G3.1.1-3. For example, in a project with a nonresidential area larger than 150,000 square feet and a building that has five stories or more in Climate Zone 5, the table specifies a baseline system named 'System 7 - VAV with reheat.' Table G3.1.1-4 further defines this system as utilizing chilled water and a hot-water fossil fuel boiler. If the design team instead chooses a centralized air-cooled package system, they run the risk of the proposed system not meeting or exceeding the overall energy efficiency of the baseline system. However, if the design team has confidence that their proposed system, regardless of being different from the baseline system, can meet if not exceed the baseline system's efficiency, then there should not be any issue.


The project team must perform energy modeling and demonstrate that the proposed building design exceeds the energy performance of the baseline building design, which is developed in accordance with the requirements of ASHRAE Standard 90.1. The baseline building represents the building’s energy performance if it were designed to meet the minimum requirements of the standard without any additional energy-efficient measures.


The specific number of points awarded in the “Minimum Energy Performance” credit depends on the percentage of energy cost savings achieved by the proposed building compared to the baseline building. The more energy cost savings, the higher the number of points earned under this credit.


The energy modeling and compliance documentation required for this credit can be complex and may require the involvement of experienced energy modelers and building design professionals. Additionally, the specific requirements and point allocation for LEED credits may evolve over time with each version update, so it is essential to refer to the latest version of the LEED rating system and specific credit requirements for accurate information.


For both LEED v4 and LEED v4.1, the “Minimum Energy Performance” credit emphasizes the importance of energy-efficient HVAC system design and its impact on achieving the project’s overall energy performance goals. By using the ASHRAE Standard 90.1 as the reference standard for baseline building performance, LEED ensures a consistent and recognized method for evaluating energy efficiency in building designs.



Conclusion

In conclusion, the choice of the right HVAC system type based on the respective baseline system to which it will be compared in ASHRAE Std 90.1 is a critical factor in achieving LEED certification. By understanding the building’s needs, prioritizing energy efficiency, and considering renewable energy sources, project teams can ensure their projects align with LEED’s sustainability goals. Properly designed HVAC systems not only contribute to LEED points but also result in reduced operational costs, improved indoor comfort, and a more environmentally friendly building.



APPENDIX


Energy Cost Budget (ECB) Method: In the Energy Cost Budget Method, the baseline building's performance is defined based on a specific energy cost budget. The energy cost budget represents the amount of energy a baseline building of comparable size, shape, and occupancy would consume to meet the minimum requirements of ASHRAE Standard 90.1. The proposed building's estimated energy costs must be lower than or equal to this budgeted energy cost to comply with the standard.


Performance Rating Method (PRM): In the Performance Rating Method (PRM), the baseline building's performance is defined through a performance rating based on whole-building energy simulation. The PRM establishes a rating that represents the energy performance of a baseline building designed to meet the minimum requirements of the standard. The proposed building's simulated energy performance must achieve an equivalent or better rating than the baseline building to comply with the standard.


To summarize, the characteristic difference in baseline building performance between the Energy Cost Budget (ECB) Method and the Performance Rating Method (PRM) lies in the method used to represent the baseline building's energy performance. The ECB method uses a specific energy cost budget, while the PRM relies on a performance rating obtained through whole-building energy simulation. The goal in both cases is to ensure that the proposed building's energy performance is at least as efficient as the baseline building, which is designed to meet the minimum requirements of ASHRAE Standard 90.1.

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