Introducing the PHIUS+ 2015 Rating System, by Steven Gray By: greening homes

October 5, 2015
Community, Passive House, Resource Efficiency

I had the good fortune of attending an all-day pre-conference workshop on WUFI Passive; for which I am grateful to Greening Homes for its dedication and commitment to the ideals of Passive House (and my own continuing professional development)!

The Passive House standard originated in Germany and has been enthusiastically adopted by high-performance builders and designers in North America. However, the standard is based on the central European climate, and while its requirements are simple and theoretically achievable anywhere, the feedback from the North American building community was the need for a rating system that reflects the diverse climates and regional economics of this continent (from tropical humid Florida to the deep freeze of northern Canada).

To address this need, PHIUS (Passive House Institute US) has released a revised rating system – PHIUS+2015. Below are some highlights of the pre-conference workshop and PHIUS+ 2015.  A project by Richard Pedranti, an architect in Pennsylvania, was used as a case study for the workshop.  His Passive House drawing set was truly amazing, communicating the complex details and information required to construct a Passive House so concisely and with exceptional clarity.

Richard Pedranti Shading Study.

1) Modelling Software: WUFI Passive replaces the spreadsheet-based PHPP energy modelling software for project certification. WUFI Passive has a more user-friendly and graphical interface, allowing users to import geometry from SkethUp or Revitt (other plug-ins coming soon). There is a static side, based on the monthly method (generally used for modelling small buildings), and a dynamic side which incorporates the sophisticated hygro-thermal modelling capabilities of WUFI including thermal and moisture storage properties of materials and effects over time.

PHIUS+ 2015 Climate Specific Requirements.

2) Airtightness. The 0.6ACH @50/Pa benchmark has been revised. The problem with this metric is that it ignores the fact that as buildings get larger, their surface-area-to-volume ratio decreases making it possible for relatively leaky larger buildings to meet the airtightness requirements. Conversely, for smaller buildings, there is much more building envelope area per unit volume enclosed, making the requirement difficult to achieve even with a well-sealed envelope. The new metric measures air leakage per unit area of envelope, levelling the playing field across buildings of all sizes, and requires equal airtightness from any building envelope. The new benchmark is 0.05CFM/SF of building envelope @50Pa and 0.08CFM/SF of building envelope @75Pa.

3) Space Conditioning Energy. In adapting the standard to the North American market, PHIUS’ goal was to create climate-specific space conditioning requirements that “represent the sweet spot where aggressive carbon and energy reduction overlap with cost-effectiveness.”

WUFI Passive

Projects will now have to meet heating and cooling annual demand and peak load requirements, as opposed to either heating demand or peak load.  For Toronto, this means that the annual heating demand target has been increased from 4.75kBtu/SF/year to 6.4kBtu/SF/year. This is supposed to account for the diminishing returns of increasingly thick walls and yield an acceptable economic payback relative to operational energy savings.

4) Source Energy Limit (Primary Energy).  PHIUS has changed this requirement to a per-person rather than area-based metric. As a “small is sustainable” advocate, this is definitely a step in the right direction. The number of occupants is calculated as the number of bedrooms plus one; this rewards households that accommodate more people in less space and discourages large homes with few occupants.

5) Solar PV. Previously no credit was given for PV generation. Now PHIUS is crediting concurrent PV generation; in other words, the electricity you generate from an on-site PV array can be deducted from any consumption occurring at the same time. This is encouragement toward net-zero and energy-positive buildings.

Hopefully we’ll be hope to apply this new knowledge to a Passive House project in Toronto soon!

PE Requirement Comparison

By Steven Gray, Construction Manager at Greening Homes