TOOLBOX of a CERTIFIED PASSIVE HOUSE CONSULTANT So what is a Certified Passive House Consultant and what do they do. PHPP, Solar Pathfinder, WUFI, THERM

1) Energy Model, The Passive House Planning Package Firstly a Consultant models the energy using the Passive House Planning Package. The Passive House Planning Package is an Excel spreadsheet based computer program that models the energy use of building design. Areas, R-values, climate data and mechanical systems are entered into the spreadsheet and the PHPP calculates the heating energy demand per square foot per year, the hourly heating and cooling load per square foot and the primary energy usage.

2) Shading Analysis, the Solar Pathfinder I passive house doesn’t require a certain of site but the shading condition need to be determined for an accurate energy model. In complex shading situation a Solar Pathfinder can be used. Not necessary in relatively flat location with a only a few obstruction as these can be accounted for in the PHPP. In hilly or forested location a shading study is recommended. A plastic dome is placed over a sun path chart. A picture is taken or the tree line is traced on the sun path chart. The summer and winter condition are determined by adding the numbers on the chart to determine a percentage for shading reduction.

3) Moisture/Mold Risk, WUFI-ORNL Here we have WUFI, which is a moisture mold risk determination computer program. This is a free version that the Oak Ridge National Lab produced in collaboration with Fraunhofer. Super-insulated wall and roof constructions are more suscesptable to moisture and mold risk because their are more temperature differentials. A Passive House consultant should use WUFI to compare different assemblies to determine which ones appear to be more safe.

4) Thermal Bridge Analysis, THERM A Passive House wants to be thermal bridge free. However there are many situation where this isn’t possible. In these situations to get an accurate thermal bridge number a 2 dimensional thermal conductance program such as THERM must be used. THERM was developed by the Lawrence Berkley National Laboratory for window manufacturers to determine thermal performance of window products for NFRC ratings. A Passive House Consultant uses it to analyse problem areas. It is free and frustrating to learn but essential for certain situations.

OUR PROJECT Our Project consisted of a DIY architect/homeowner, a dedicated contractor and myself passive house consultant. The homeowner was interested in a very well insulated home and we helped push them in the direction of Passive House. There isn’t anything particularly difficult of about designing a passive house, everything just need to be accounted for and entered into the PHPP with the goal of

A Passive House = 4.75 kBTU/ft.2/yr The whole design process centers around this number. Everything from where the windows are placed to the thickness of the walls effect this number. In our project we decided to maximize solar gain instead of insulation by placing many windows to the south. Before we decide that we are going to do a Passive House I put together a feasibility PHPP. I quickly breeze through the PHPP using rough numbers to see if we are in the ballpark. This takes about a day. In our case we were at something like 5 kBTU/ft.2/yr. The original design was an EPS box but me and Chris are both big proponents of cellulose for environmental reasons so we were able to show that it was going to be just as easy to achieve this goal with cellulose.

1) The Whitchurch PH Cottage, 4.35 kBTU/ft.2/yr After many revisions our final design comes in well below Passive House standard at 4.35 kBTU/sq.2/yr

Conventional Build, same design 90.94kBTU/ft.2/yr Once all the areas and climate data are entered into the PHPP it is fairly easy to change individual components to determine how different things affect over all energy demand. This makes it pretty easy to compare different assemblies. I take this opportunity to model the building using conventional insulation levels and windows. In our case the design with typical double pane windows and 2x6 walls came in at 90.0 kBTU/sq.2/yr. The tag line for Passive hOUses is that they use a 1/10 of heating energy as a code built home. In our case we are well below that.

Heating load on coldest days= 5,096BTU/hr= 1494 Watts= Heating system equivalent to 15, 100W light bulbs Our heating system will be equivalent to 15 100W light bulbs. This is based on coldest conditions of the year from Montpelier climate data.

THE CERV

2) Use the solar pathfinder to determine shading conditions at future location of windows Before you get to far into the design process and thorough shading study is required for complicated shading situations. Our site was fairly complicated so I did full solar pathfinder study. Shading can have a huge effect on the over all energy demand and potential overheating in summer. Here I am getting a reading for an upstairs windows.

Proper Orientation The building must be laid out in the proper orientation for the shading analysis to be useful. The orientation can be easily changed in the PHPP but you want the building to be oriented to solar south.

-16 Degrees from magnetic north Magnetic north is 16 degrees different from solar north for our location. This is a map showing Declination for entire US. You can see that magnetic north can be significantly different from true north. Compass must be set accordingly. The importance of being to able to accurately determine the amount of solar radiation that can be gained from the windows is dependant on getting the building oriented the same way as designed in the PHPP.

3) WUFI Hygrothermal Analysis Before assemblies are settled on, it is a good idea to do a WUFI analysis. A free version is available from ORNL. This page shows your assemblies. Basically what you do is add your materials from the material library and adjust for your thicknesses. Initial condition and climate conditions are then specified and program runs and moisture risk analysis for a given period of time. Can be predicted for any number of years you want to know.

WUFI-ORNL, vented roof 7 yr. In our case I had some question about our roof assembly because it is vapor closed to the outside. I wanted to compare a vented roof assembly to ours as designed. This slide shows the vented assembly As we can see, the vented roof shows a good drying potential. This was modeled with 1 ACH in the ventilation plane. I used 3 layers of 15# felt to simulate Intello as new materials can’t be added in free ORNL version. 15# felt has variable perm as does Intello. Multiple layers brings dry perm down to class II vapor retarder. Overall water content drops by almost 2/3.

WUFI-ORNL, unvented 7 yr. Here I used the same assembly but omitted the 1 ACH back venting. The results are dramatic. Instead of drying by a 2/3 over 7 years the assembly is actually taking on water slowly. This analysis caused caution for me and for PHIUS. PHIUS actually refused to certify this building for fear that this was an unsafe assembly unless an engineer took responsibility for the roof design from a moisture management perspective. Thanks to Bill Root for providing this service and giving us a thorough report referencing a study that shows cellulose dense pack roofs perform better than other air-permeable insulation if extreme caution is taken to air seal completely on the inside of assembly.

WUFI Pro 10-Year Initial Dry-out The suppliers of Intello provided this WUFI analysis for us as well showing assembly would dry out by less than half over 10 years. This analysis had over 2,000 convergence failures which causes me to caution their validity. A convergence failure happens when the program can’t solve the calculation in the amount of time it gives itself, so it skips that time and moves on. Better than my WUFI-ORNL unvented analysis but not better than the vented assembly. Venting this assembly would still be safer based on these results. Homeowner decided to go unvented for fear of summer humidity making it into the assembly and other reasons. Consultants job to advise, and let others make whatever call they see fit.

Shows Over 20% Moisture Content In Winter Of 1st Year This shows moisture content of outer layers of assembly as provided by supplier of Intello. WUFI shows spike in first winter followed by gentle decline. 20% moisture content is generally considered to be the point at which mold and rot issues begin to arise. Over 20% only appears to take place for a few months so may not be an issue. As you can see, moisture still builds up each winter and then is baked out during the summer months as vapor drive is reversed.

Thermal Bridge Free= <.006 BTU/hr.ft.F In a Passive House we try to design it to be completely thermal bridge free. This slide shows a continuous thermal envelope and air barrier. Typical thermal bridge connection are at the slab and foundation, the band joist of the first floor, the wall to roof connection and the window installation. Continuous thermal envelope

4) Thermal Bridge= 2D Thermal transmittance modeled in THERM minus 1D Thermal Transmittance as modeled in PHPP How a thermal bridge is determined is by modeling the area in question with a 2D Thermal transmittance program such as THERM and subtracting what was entered for that section in the PHPP. If basic principles of Thermal Bridge free construction are adhered to, thermal bridges don’t need to be specifically calculated. For instance, a TJI in a cellulose bay is close enough and specific thermal bridge values don’t need to entered for the TJI chord. Each material and its conductance is entered in the R-values tab however. Anything greater than .006 BTU/hr. ft.2. F. need to be entered as a thermal bridge in PHPP

Foundation Foam=TB? In our construction we were fairly confident that we were thermal bridge free but someone asked us about our foundation detail wondering if it was thermal bridge free.

Foundation Foam in THERM Chris West of Eco Houses of Vermont did this analysis for us. Our construction turned out to be a negative thermal bridge of .003 in comparison to what was entered in the PHPP. So that made us feel better about our other connections as well. By Chris West, Eco Houses of Vermont

Window connection Mullion= Giant piece of metal= Giant thermal bridge One thing I missed was this window mullion. The large southern windows of our house are connected with these curtain wall mullions from Intus. When these arrived on sight I realized they were a significant thermal bridge.

Plan View of Window Jointing Mullion In THERM This is THERM model of the window frames and joining mullion.

Thermal Bridge=0.16 BTU/hr.ft.F Temperature=42.6 F THERM provides a Infrared view of what the assembly will probably look like. Each color relates to different temperatures. The inside surface shows a possible temperature of 42.6 degrees. This is certainly a possible condensation risk. Unfortunately there is not much we can do about this area. The thermal bridge of 0.16 BTU/hr. ft. F brought our total energy demand from 4.09 to 4.3 kBTU/sq. Ft./yr. So these seemingly little things make a big difference when you are designing such a low energy house.

Thermal Bridge=.043 BTU/hr.ft.F Temperature=49.4 F We also have this half mullion for some of the windows where the metal doesn’t go all the way through the frame to the inside. Much smaller Thermal bridge of .043 BTU/hr.ft. F. Inside temperature of 49.4 degrees. Passive House suggests wall and window surfaces not be more than 7 degrees different from internal design temperature of 68 degrees. So we were not successful in that aspect.

Exterior Trim w/ EPS Thermal Bridge=.039 BTU/hr.ft.F

Performance based design So that is the design process of a Passive House. It is essentially performance based design. How will the house in these specific conditions perform and what can be done about it. We let the functionality of the energy model drive many of the design decisions.