LEED v.4.1 - A Comparative Analysis

Date Published

8th Feb 2021

Edward Keyrouz
Senior Project Consultant

LEED v.4.1:

Twenty years ago, the U.S. Green Building Council (USGBC) introduced LEED to the building and construction world to help define what it means to create a green building. Today, the rating system has become the de facto leadership standard and an international symbol of excellence.

LEED v4.1 is the next generation standard for green building design, construction, operations and performance

LEED v4.1, the most recent version, raises the bar on building standards to address energy efficiency, water conservation, site selection, material selection, day lighting and waste reduction.

LEED v.4.1 (O+M, BD+C, ID+C) is now available for registration in LEED Online. In addition to registering a new LEED v.4.1 project, project administrators have the flexibility to use any and all the LEED v.4.1 prerequisites/credits on a LEED v.4 project.

ASHRAE 90.1-2010 vs. ASHRAE 90.1-2016:

Firstly, looking at LEED v.4 EAp.2 Minimum Energy Performance compliance using the whole building energy simulation where new buildings have to demonstrate a cost improvement of 5% compared with the baseline building performance according to ASHRAE 90.1-2010, Appendix G. 

Whereas in LEED v.4.1, using the Normative Appendix G Performance Rating Method with ASHRAE 90.1-2016, it uses the Performance Cost Index (PCI) which has to be less than or equal to the Performance Cost Index Target (PCIt), the percentage improvement is documented using cost or Greenhouse Gas (GHG) emissions.

When using Appendix G, the Performance Cost Index (PCI) has to be less than or equal to the Performance Cost Index Target (PCIt) when calculated in accordance with the following: 

PCIt = [ BBUEC + ( BPF x BBREC )] / BBP
  • BBUEC = Baseline Building Unregulated Energy Cost
  • BBREC = Baseline Building Regulated Energy Cost
  • BPF = Building Performance Factor
  • BBP = Baseline Building Performance

This results in a PCI of 1.0 for a building designed at the energy cost level of 90.1-2004, and a PCI of zero for a net-zero energy cost building. 

The maximum PCI (PCI target) required for compliance with any edition of Standard 90.1 can be determined based on the energy cost of a typical building designed to the mandatory and prescriptive requirements of that standard compared to a similar building designed to the mandatory and prescriptive requirements of 90.1-2004.

Going forward the stringency of the baseline will not change with subsequent versions of the standard. Instead, compliance with new versions of the standard will simply require a reduced PCI (a PCI of 0 is a net zero building). Using this approach, buildings of any era can be rated using the same method. The intent is that any building energy code or beyond code program can use this methodology and merely set the appropriate PCI for their needs.

With a fixed baseline USGBC can now evaluate projects across time the same way. In short, an XX% savings generated now and an XX% 5 years from now are one the same scale and can be compared. 

Proposed vs Baseline [2010,2016] and their impact on EAc.2:

A typical 7 storey office building located in climatic zone 4A [Paris] with a floor area of approximately ~10,000m2  is examined and 2 baseline buildings are generated, one compliant with ASHRAE 90.1 - 2010 and another compliant with the 2016 standard. This exercise aims to compare baseline annual energy consumption and see their impact on number of awarded EAc.2 credits.

CASE 1: ASHRAE 90.1-2010 Energy comparison Proposed vs. Baseline using the Normative Appendix G Performance Rating Method.

Proposed Building Total Annual Energy Consumption 1086.7 MWh
Baseline Building Total Annual Energy Consumption 1426.2 MWh
Energy Reduction (%) 23.8%

CASE 2: ASHRAE 90.1-2016 Energy comparison Proposed vs. Baseline using the Normative Appendix G Performance Rating Method. 

Proposed Building Total Annual Energy Consumption 1086.7 MWh
Baseline Building Total Annual Energy Consumption 1739.4 MWh
Energy Reduction (%) 37.5%

Does the proposed building design comply with 90.1-2016?

In order to check compliance for our 7 storey building, we have to calculate the following:

  • Proposed Building Performance = 1,086,664.2
  • Baseline Building Performance (BBP) = 1,739,404.2
  • Baseline Building Regulated Energy Cost (BBREC) = 1,242,848.1
  • Baseline Building Unregulated Energy Cost (BBUEC) = 496,556.1

Step 1. Determine Performance Cost Index from Equation 1:

π‘ƒπ‘’π‘Ÿπ‘“π‘œπ‘Ÿπ‘šπ‘Žπ‘›π‘π‘’ πΆπ‘œπ‘ π‘‘ 𝐼𝑛𝑑𝑒π‘₯ = (π‘ƒπ‘Ÿπ‘œπ‘π‘œπ‘ π‘’π‘‘ 𝐡𝑒𝑖𝑙𝑑𝑖𝑛𝑔 π‘ƒπ‘’π‘Ÿπ‘“π‘œπ‘Ÿπ‘šπ‘Žπ‘›π‘π‘’ / π΅π‘Žπ‘ π‘’π‘™π‘–π‘›π‘’ 𝐡𝑒𝑖𝑙𝑑𝑖𝑛𝑔 π‘ƒπ‘’π‘Ÿπ‘“π‘œπ‘Ÿπ‘šπ‘Žπ‘›π‘π‘’) = 0.62

Step 2. Determine Building Performance Factor

Table 1- Building Performance Factor (BPF)

𝐡𝑒𝑖𝑙𝑑𝑖𝑛𝑔 π‘ƒπ‘’π‘Ÿπ‘“π‘œπ‘Ÿπ‘šπ‘Žπ‘›π‘π‘’ πΉπ‘Žπ‘π‘‘π‘œπ‘Ÿ = 0.58

Step 3. Determine Performance Cost index Target

𝑃𝐢𝐼𝑑 = (π΅π΅π‘ˆπΈπΆ +(𝐡𝑃𝐹 Β· 𝐡𝐡𝑅𝐸𝐢)) / 𝐡𝐡𝑃 = 0.7

Answer: Yes, our building complies with ASHRAE 90.1-2016, PCI < PCIt (0.62 < 0.7)

LEED v4.1 splits the energy modelling output into two separate points thresholds - Performance Cost Index (PCI) & greenhouse gas emissions (GHG). Up to 9 points for reducing energy cost and up to 9 points for reducing GHG, while in LEED v4, the 18 points are awarded based on either energy reduction, cost reduction or GHG reductions. 

The total GHG, in terms of carbon dioxide equivalents, shall be calculated for the baseline and proposed building performance ratings and the percentage improvement determined using carbon dioxide equivalent emissions.

LEED points are then calculated based on the tables below:

Table 1. Points for percentage improvement in energy performance – % Cost PCI below PCIt

Table 2. Points for percentage improvement in energy performance – % GHG PCI below PCIt

For this particular sample case study, the national grid mix coefficients from the International Energy Agency CO2 Emissions were used to calculate GHG emissions by energy source.

The overall points awarded for the project under v.4.1 is a total of 4 points compared to 9 points under LEED v.4.

What to Expect?

It is clear that the new V.4.1 requirement is more stringent and would require more effort to achieve the expected level of savings. Project team members would have to consider approaching this credit from the early design phase to optimize the building massing and envelope, reduce heating and cooling loads and maximize daylighting opportunities. Modelling from early design stages would also allow better predictions on building energy consumptions, CO2 emissions, peak demands, energy cost and renewable energy production.

Design teams will also need to consider managing energy usage and shifting away from a dependence on oil and electricity to renewable energy sources like solar and wind as well as calculating the buildings’ GHG emissions from early design stages.

Following these steps will impact the long-term operational cost-savings across your building, as well as contribute to a significant increase in number of points for LEED.

How can we help?

The VE includes easy to use step-by-step guidance from model setup, to data assignment to simulation. IES recently released VE 2021 that now includes the VE-Navigator for ASHRAE 90.1-2016 version enabling you to undertake this study more easily.

IES expert consultants are immediately available to perform this calculation on your projects. Alternatively, should you be looking to expand your skills then take advantage our of our VE mentoring service where our consultants guide you through the steps to successfully model the LEED and HVAC intricacies. We have performed over 3000 simulation projects and tailor our services to suite the individual needs of our customers so you will always benefit from the unparalleled experience of our expert consultants. Contact us today to get started by emailing consulting@iesve.com with details of your project.

EQ credit: Daylight

LEED 4.1 has made changes to make certain credits more achievable. After reassessment their threshold requirements were reduced. One example of these is the EQ credit: Daylight where a singular credit is now available making analysing Daylight more attractive.

Compliance is achieved by following either of these 2 options:

How can we help?

IES can help you explore the opportunities for daylight optimisation at the design stage. We can work with you right from concept using the latest in analysis technology to communicate visually and statistically the impact of a potential design strategy.

We can provide Climate Based Daylight modelling (CBDM) for LEED v4 and v4.1 , and WELL to reveal the true daylight performance for the building. Our daylighting services also cover:

  • Solar intensity
  • PV Feasibility
  • Daylight Controls
  • Glare
  • WELL

Find out more about our services by visiting www.https://www.iesve.com/consulting and contact us today by emailing consulting@iesve.com to get started. 

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