HERS index and PHIUS
harrison55
| Posted in General Questions on
The zero energy ready home (ZERH) certification requires that you have a HERS index that is less than 50% of the HERS index of a model house of the same size and shape. I’m trying to get a rough idea of how this would compare to a house built to passive house standards.
Is there anyone out there who has built to passive house standards and also got a number for their HERS rating? I am curious to know how you fared on the HERS scale.
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This article is 10 years old, but it might be worthwhile to follow up with the author.
https://www.greenbuildermedia.com/buildingscience/hers-rating-a-passive-house
Hi Mark.
This house--Lessons From a Practical Passive House--got a HERS rating of 36. The builder, who has built a bunch of Passive Houses, wrote to me in an email, "We have found that PH's don't tend to get great HERS ratings- I'm not really too sure as to why this is."
Not an energy rater (developer of affordable high-performance homes) here so my experience is anecdotal. I am working on 5 passive homes at the moment and 1 DOEZERH triplex. the passive homes have a 32 on the HERS index and the triplex has a 50Both of these are pre-construction numbers. (I have a 2 MN code-built home that scored a 48, verified after construction).
Getting to the point. I was able to compare the HERS index to the WUFI modeling and the WUFI was reporting Site energy usage per year on average 18% lower than the HERS score. As far as I know, the HERS index does not take into account specific site conditions. shading and solar heat gain through windows. The WUFI modeling is way more in-depth b/c it is looking at more data points as compared to HERS.
There is most likely a new metric needed to compare homes. Maybe energy usage per/sf or occupant? as you can imagine their is no perfect system to compare one house to another.
Because of the simplicity of the way HERS scores are calculated (REM/RATE software), you will need to file for IDR’s (Innovative Design Request) to get a more realistic and lower HERS score. But if all you care about is hitting 50 that should be easy enough.