WUFI® Passive Version 3.1

Lisa White, PHIUS Certification Manager


I am happy to relay the message that the Fraunhofer Institute for Building Physics (IBP) has released WUFI Passive v3.1! There are many exciting changes with the upgrade from 3.0.3 to 3.1, and below I’ll summarize some of my favorites. In general, I’ve categorized the updates into: Results reports, user friendliness, and technical updates.

New Results Reports

Once you obtain results in WUFI Passive, extremely useful and thorough results reports are generated. In addition to the existing reports, three new shorter reports have been added that specifically cater to different needs and audiences. For example, PHIUS+ Certification has been incentivized by many localized utilities and funding organizations. These 2-3 page reports provide an overview of the predicted building energy usage at a top-level snapshot, which is exactly what most people (who aren’t major energy nerds) want to see.

Site Energy Report (Site Energy Use Intensity or EUI):
This report shows a breakdown of the building site energy. The main categories this is broken out into are shown below:

site energy report

From there, each of the 8 categories of energy use is broken out into their specific components.

This report is especially helpful when comparing monitored data to the modeled results. Of course, the level of detail in the comparison is limited to the number of energy use categories that were monitored.

Knowing the site energy by use type also gives a big picture overview of where the most energy is being consumed in the building. It can help the building owner/occupants get a better feel for where their consumption is coming from, and therefore may influence user behavior.

Source Energy Report (Source Energy Use Intensity or EUI):
This report shows a breakdown of the building source energy broken into the same categories as the site energy report. In addition to the energy use, the source energy factor for each component is specified. This report also specifies if the building has met PHIUS+ Source Zero.

source energy report

REM/Rate Report:
PHIUS+ Projects undergo a comprehensive on-site QA/QC process. As part of this, single family projects and low-rise multifamily units receive a HERS Index, which is determined using REM/Rate software. To streamline this process for PHIUS+ Raters, a new report was developed specifically to output WUFI Passive entries that are applicable to the entries in the REM/Rate software.

User Friendliness

Comment box:
Fraunhofer IBP has implemented a new comment box which allows users to add a unique comment to each input screen in the software. It’s like a sticky note for every individual screen you’re in.

It can be used to remind yourself of a potential assumption that was made for an entry or use it as a log for model updates due to a change in design. If you’re submitting the project for PHIUS+ Certification, you can provide explanation for entries right in the software.

F1 for help files:
Before version 3.1, the WUFI Passive manual was a document external to WUFI Passive. Now, the help files have been expanded and are integrated directly into the user interface! This feature can be accessed for any user input screen at any time using ‘F1’. There is an abundance of guidance here – take advantage of it, especially if you’re a first-time user.

PHIUS+ Certification Tool Tips:
As you navigate the WUFI Passive software and hover over certain entries with your mouse, different tips pop up to guide you through the inputs. These or ‘hover-over hints’ have been expanded to include hints specific to PHIUS+ Certification. These tips are also found in the PHIUS+ Certification Guidebook, but are integrated as hints here to allow for quicker workflow.

To activate these tool tips, go to Options>Usability and check the box for ‘Tool tip PHIUS + Certification’. If you have not already, I also recommend checking the boxes to activate tool tips providing ‘General Info’, ‘Value Range’, and ‘References’.

Other small updates:

calculators and dropdowns“Show edit icons in tables” for drop-downs and calculations:
Many side calculators and drop-downs are built into to WUFI Passive, but you couldn’t see them unless you clicked into the entry. New calculators have been added, and now they’re always visible.

Go to Options>Usability and check the box for ‘Show edit icons in tables’ at the bottom.

Default certificate criteria setting:
If you’re only modeling projects for the PHIUS+ 2015 standard, do yourself a favor and go to Options>Passive and set the default certification criteria to ‘PHIUS+ 2015 Standard’. This also locks in other defaults for PHIUS+ 2015 modeling.

Minimize results:
If you want to maximize the user input screen, you may minimize the results screen while keeping the actual results visible. Numerical results will be displayed, rather than the target bar chart and green checkmark/red X.

The ability to create duplicate cases in WUFI Passive has been in the tool since its inception. This feature is extremely helpful when doing comparison studies, or optimizing the design. Now, there is a new top level view to see all cases you’ve created, and new cases can be created in this screen. If you get carried away with comparison cases (it happens), this will help organize your analysis.

Assemblies show total R-value of each layer:
Units for thermal performance of materials can get confusing. Now, to double check your work, the total R-value of each layer appears when you build an assembly. (Don’t forget, you can also click on the […] box in the conductivity (l) column to input the R/in for each material).

total R-value of layer

Arrow up/down to re-arrange layers in assembly:
Re-arrange layers in an assembly using Up and Down arrows.

Under Options>Usability, set how often you would like data recovery, and the maximum number of files saved per use.

Technical/Calculation Updates

Manual J Method for Cooling Load:
The current static cooling load calculation in WUFI Passive does not include the latent cooling load. Further research is being conducted by the PHIUS Technical committee to come up with more accurate calculation methods. As an interim and more conservative solution to calculating latent cooling load, the Manual J calculation is now implemented in WUFI Passive to prevent under-sizing of cooling systems.

PHIUS+ Source Zero output:
There is now an output in both the ‘Passive House Verification’ and ‘Source Energy’ reports which display when a project meets PHIUS’ new designation: PHIUS+ Source Zero.

PHIUS Heat Pump Protocol Calculators/Devices:
New devices have been added to eliminate the need for external calculators.

  • Air-to-air heat pump: The new device will calculate the annual heating COP based on ratings at two outdoor temperatures. The calculation uses the climate data and monthly heating demand for the specific project to estimate the annual heating COP.
  • Heat Pump Water Heater Device: The new device was added for a HPWH used inside the envelope, in conjunction with a HP used for space heat. Because most heat pump water heaters are not split systems, the HPWH takes heat from the air surrounding it. Therefore, it makes the heat pump for space heat run at a higher capacity, or more often, in the heating season. This new device calculates a de-rated COP for the HPWH, per the same heat pump protocol mentioned above, depending on the number of heating months calculated for the project being modeled.
  • Integrated Cooling COP Calculator: The COP for recirculation cooling from an air source heat pump, as defined in the heat pump protocol, is the average of the SEER and EER, divided by 3.412 BTU/Wh. Now, a built-in calculator allows the entry of SEER and EER to calculate COP.

AHRI calculator for ventilation units:
A new built in calculator which calculates sensible recovery efficiency from an AHRI data sheet, per PHIUS protocol.

Infiltration calculation enhanced:
In WUFI Passive, the infiltration entry includes the option to input cfm50/ft2.envelope area to align with PHIUS’ air-tightness requirement of <0.05 cfm50/ft2. Version 3.1 now includes the area of all components adjacent to attached zones (garage, etc.) and neighboring buildings in this infiltration calculation whereas before they were not included, which then required infiltration to be input in ACH50.


Users of the professional version WUFI Passive 3.x can download the update free of charge. Please log in to your account at the WUFI Web shop, there you can find the update link in the “My Orders” menu.

If you’d like to give it a test drive, Download WUFI Passive Free v3.1 here.

Features you might not know about from v3.0.3:

Assign Data Button:
Along the top of the screen, an [Assign Data] button allows you to assign an entry (window type, shading entries, etc.) to multiple components at once. Huge time saver.

Export into XML File/Import from XML File:
Any user defined entries in your databases can be exported to an XML file and then can be shared with colleagues and friends. This includes assemblies, materials, windows, HVAC devices, climates, etc. that have been created. Go to ‘Database>Export to XML’, and then select all items that you would like to be saved as an external XML file. If you receive an XML file, go to ‘Database > Import from XML’.

Climate Data for PHAUS members:
All PHAUS members have access to a single XML file that contains all 1000+ Climate Data sets, and their respective PHIUS+ 2015 space conditioning targets. Please follow this link to login, download the XML file, and import into your WUFI Passive software. There is also an XML file for each state that may be downloaded rather than for the entire United States and Canada.

Lisa White, PHIUS Certification Manager

Interim adjustments for PHIUS+ 2015 annual cooling demand limits

Graham S. Wright, Senior Scientist & Product Program Manager

The interim cooling demand protocol does not apply to all projects, and can be disregarded for projects that are not challenged on meeting the annual cooling demand target. This temporary protocol was developed specifically to provide an alternative calculation methodology and adjusted criteria for projects that are unable to meet their cooling demand limit, despite all reasonable efforts made to reduce this value. This design limitation typically arises for buildings with high occupant density. The standard-setting optimization studies for PHIUS+ 2018 will incorporate buildings of different size and occupancy, and therefore the interim protocol applies only for PHIUS+ 2015 certifications. This protocol will not apply after the release of PHIUS+ 2018.

As you may know, for building project certification, PHIUS’ standards require that the peak heating and cooling loads and the annual heating and cooling energy demands are limited by design. That is, there are four criteria imposed on space conditioning energy / power, that must all be met. Clearly then, for any particular project, one of these four will be the tightest, the most difficult to meet.

One perspective on this is that whichever criterion is tightest indicates the weak aspect of the design, that is, its greatest “improvement opportunity” as a high-performance passive building. However, certification staff and some Technical Committee members report that projects are more often limited by the Annual Cooling Demand criterion than the other three. This is the case especially for large buildings or those with higher occupant density.

PHIUS and the Technical Committee are currently working on the PHIUS+2018 standard updates. Remember, we committed to updating the standard every 3-5 years as cost parameters change and as we learn more about how specific building typologies behave. Our models are only as good as the assumptions we make in them and these updates, together with measured data, will help us to assure that our modeled predictions will meet measured results as close as possible. We are planning to incorporate buildings of different size and occupancy into the cost-optimization standard-setting studies for PHIUS+ 2018, and thereby come up with adjustments for these factors in a more systematic way.

In the meantime, for certification under PHIUS+ 2015, we introduce the following three adjustments to the criteria and calculation protocol:

1. Lighting seasonality adjustment.

The standard-setting studies for PHIUS+ 2015 used Building America simulation protocol for lighting, which uses lower interior lighting energy in the summer (and therefore lower internal gains). But the monthly-method calculations in WUFI® Passive / PHPP don’t reflect this seasonality. Therefore, for the purpose of calculating the annual cooling demand, the interior lighting energy may be reduced. The lighting energy reduction is latitude-dependent and is calculated using the PHIUS Residential lighting adjustment calculator (downloadable Excel-based tool). This measure applies to all residential projects, but only to the interior lighting energy of the dwelling units.

2. Detailed occupancy sensor credit for multifamily hallway lighting.

Until recently, only a 10% reduction in lighting power density due to occupancy sensors was allowed for multifamily common spaces, as in ASHRAE 90.1 Appendix G. As of March 2017 though, a more detailed calculation can be done that can give larger reductions in many cases, using the PHIUS MF Interior Corridor Lighting Occupancy Sensor Calculator. (see Certification Guidebook section – downloadable via link in sidebar) It is predicated on a daily pattern in which most of the foot traffic is from people leaving the building in the morning and returning in the evening. Therefore, this measure applies to multifamily residential projects, but only to the lighting energy of interior pass-through common spaces i.e. corridors, lobbies, stairwells.

3. Annual-demand criteria adjustment for high internal gains.

Larger buildings appear to have a tendency toward higher internal gains on a per-unit-of-floor-area basis, which tends to increase the annual cooling demand and decrease the annual heating demand. Adjustments to the certification criteria may be made on a climate zone-by-zone basis, up to the limits shown in the table below. If an increase in the annual cooling demand limit is taken, the project must also take the proportional decrease in the heating demand limit. The adjustment limits were determined based on a corridor lighting calculation, but may be used for high internal gain situations of any cause. They allow for up to about a 1/3 increase in specific internal gain, e.g. from 0.9 to 1.2 Btu/h.ft2. This measure applies to multifamily residential, nonresidential, and mixed-use projects.

Table 1. Zone-by-zone adjustment limits for annual heating/cooling demand criteria.

Climate zone AHD difference (% or kBtu/ft2.yr) ACD difference (% or kBtu/ft2.yr)
1 0 +10%
2A -28% +9%
2B -30% +10%
3A -19% +11%
3B -21% +26%
3C -22% +0.23 kBtu/ft2.yr
4A -16% +16%
4B -19% +27%
4C -18% +0.23 kBtu/ft2.yr
5A -16% +28%
5B -14% +0.42 kBtu/ft2.yr
6 -16% +0.42 kBtu/ft2.yr
7 -15% +0.15 kBtu/ft2.yr
8 -11% +0.14 kBtu/ft2.yr

— Graham S. Wright, PHIUS Senior Scientist