Energy Efficiency Comparison Between LEED v2.2 and v3
As illustrated by the new ThedaCare Clinic in Darboy, WI
Evaluation of the two LEED rating systems, New Construction v2.2 and v3 is important, not only in the determination of which rating system to submit the project under, but also in order to ensure that we’re achieving the energy efficiency goals that we based the design on. We are fortunate enough to have a knowledgeable partner in August Winter & Sons, Inc. as our HVAC subcontractor on the ThedaCare Darboy project. With the help of Wes Pohlman and Rick Verstegen of August Winter we can take a more in depth look at the differences in the energy efficiency section of these two rating systems.
One of the changes to v3 in the Energy and Atmosphere category is the increase in available points for Credit 1 - Optimize Energy Performance. There are now up to 19 points available for this credit as opposed to 10 points available in the previous version. However, as part of the new credit, the standard used is now ASHRAE 90.1 – 2007 without addenda. The previous standard used was ASHRAE 90.1 – 2004. The new ASHRAE standard raises the minimum efficiencies and standards required for the Building Envelope and HVAC. The following are building envelope examples of changes to the ASHRAE standard for Climate Zone 6 (all but 15 counties in the state of Wisconsin):
For a roof with insulation entirely above deck, the minimum insulation R-value increases from an R-15 to R-20 (a 25% increase in required performance) with the overall assembly u-value changing from U-0.063 to U-0.048 (a 31.25% increase in performance).
A steel framed wall above grade performance changes from an R-16.8 to an R-20.5 for insulation minimum (an 18% increase) with an assembly u-value change from U-0.084 to U-0.064 (a 31.25% increase in required performance).
The standards for vertical building fenestration have also changed. In some cases, values have increased. For example, in the 2004 standard, a building with 20.1 – 30% vertical glazing and operable windows required a u-value of 0.67 and a Solar Heat Gain Coefficient (SHGC) of 0.49. The 2007 standard is now identified by vertical glazing type with Non-metal framing requiring U-0.35, Metal framing (curtain/storefront) requiring U-0.45, Metal framing (entrance door) requiring U-0.80, and all other Metal Framing requiring U-0.55. The required SHGC changes to 0.40. Comparing a Non-metal framing vertical glazing to the previous standard shows an increased performance requirement of 22.5% for the SHGC (0.49 to 0.40) and 91.4% for the u-value (0.67 to 0.35).
An example of this is shown in the energy model created for the ThedaCare Physicians – Darboy Clinic project. Two energy models were created to compare both standards. In the first energy model, comparing the building design to the ASHRAE 90.1 – 2004 standard (LEED NC2.2) showed an increased energy performance of 30.5% which provided 6 LEED credits for EA-C1. The second energy model showed an increased energy performance of 25.4% compared to ASHRAE 90.1 – 2007 (LEED 2009) which provided 7 LEED Points for the EA-C1 credit.
As illustrated, even with the higher minimum performance standards required in the new v3 LEED rating system, energy saving measures are better rewarded.
