All — thanks for all of your contributions and comments about fine-tuning the standard. It’s going to be an exciting process. Continuing that discussion, let’s look at a few really good examples of certified Passive Houses that were modeled for various North American climate zones, and for which we have good monitoring data. The graphic below makes clear that generally, the climates of North America and Central Europe are not directly comparable. One small region–running from the northwest U.S. Coast into Canada–matches the Central European conditions.
Therefore, we’ll look first at a certified project in Salem, Ore., and evaluate how accurately the PHPP modeled the actual monitored experience.
Again — as stated in the inaugural blog post, the core principles behind the Passive House concept, some of which date back to the early 1970s — are not in question. Minimizing the peak loads to a point when balancing the ins and outs (losses and gains) produces a building that nearly reaches equilibrium. Such a building needs very little active energy input — and this only a few months of the year — to maintain comfort.
If the space conditioning meets our 1 W/sqft peak heating load and 0.8 W/sq peak cooling load requirements, then we get the icing on the cake: For mechanicals, we can either use point sources throughout the space or integrate the space conditioning in the ventilation air. In the Northwest, with next to no cooling requirement and lots of passive cooling potential, integrating conditioning and ventilation could prove to be the most cost effective solution.
Let’s look at how one Passive House project played out in Salem, Ore. The 16th & Nebraska project (also known as the Rue-Evans House, named for its owners) was built by Blake Bilyeu and his father. Blake Bilyeu is a pioneer — he took one of the first PHIUS Certified Passive House Consultant training courses offered. And by 2010, he had completed the 16th & Nebraska project. It became one of the first projects certified by PHIUS.
By U.S. Department of Energy climate zone definitions, Salem is considered a marine climate, characterized by:
- mean temperature of coldest month between 27-65 F
- warmest month mean of less than 72 F
- at least four months with mean temperatures over 50 F
- dry season in summer (month with heaviest precipitation at least 3x of driest month)
Here’s the Salem climate data at a glance:
And data for Bonn, Germany.
The climates are very similar: Average temperatures in Salem are a little higher by 4.6 F in winter in Salem, summer highs are the same, and precipitation is generally higher in the Pacific Northwest. Both locations have limited solar availability.
The project’s PHPP data at a glance confirms that both Passive House criteria are met: the annual heating demand criterion with 4.02 kBTU/sqft yr as well as the peak heat load with 2.9 BTU/hr.sqft. There is no need for cooling.
The general specifications of the exterior envelope components are:
- R-45 in the wall, the roof has R-96, the floor over crawl space has R-51.
- The average window installed U-value is 0.226 BTU/hr.sqft.F with orientation specific SHGC of 0.23 for E-N-W orientations and 0.46 SHGC for the South
Note: The window figures are unadjusted NFRC values. Passive House window calculations will result in slightly adjusted values. The PHIUS Technical Committee is developing a method for converting values and/or a protocol to more accurately calculate the window values needed for PHPP. The Tech Committee will make it available for comment in an upcoming PHIUS e-Newsletter. Many thanks to Graham Irwin, John Semmelhack and Graham Wright, who already have devoted a lot of hours to this project!
Energy consumption at the project was monitored for a full year. Over that period, the home was occupied by its new owners (a young couple and a dog, and eventually the couple’s newborn baby. The owners blogged about their early experience — check it out.)
A detailed monitoring report on the first year was prepared by the company Ecotope. (Many thanks to the Ecotope team that graciously gave PHIUS permission to make the information available to the Passive House community. PHIUS plans to share more monitored data from other projects soon—stay tuned.)
Download the full report here. From the executive summary:
The 16th and Nebraska Passive House project located in Salem, Oregon is an impressive example of an energy efficient home. The home is built to the stringent requirements of the Passive House (PH) program. The home’s energy use for the first year post-construction place it in the top tier of the most energy efficient single family homes in the Pacific Northwest. The first-year stats for the project are listed below:
- First Year Total Annual Energy Use: 5,413 kWh/yr
- Electric Utility Cost per Year: $700
- Energy Savings estimate over Oregon Code: 9,064 kWh/yr
- EUI (using gross sq ft of 1,885 sf): 9.8 kBtu/sf/yr2
The Salem Passive House home blows away today’s code homes, and nearly meets — right now — Ed Mazria’s Architecture 2030 Challenge for 80% reduction:
Back to the original questions: how do actual results compare to what was modeled in the PHPP, and what conclusions can be drawn from potential deviations of the measured results to the modeled results?
To start, some of the results are rather unexpected:
The actual first year’s energy use came in between what was predicted and what is allowed in the Passive House program, 5,413 kWh/yr. This results in a 63% energy use reduction over an electrically heated home built to the Oregon 2008 Code. This represents a savings of $750/yr in utility costs.
The DOE Building America Program aims for 70% in overall energy reduction. With 63%, this is below what one might have expected. If the modeled results had actually been met the building would have been saving 73% over the code home. Reading on:
This home represents the upper limits of conservation that can be controlled by the designers and builders; or what can be achieved by applying most of the energy efficiency measures currently available. Space heating and DHW represent 13% of the home’s total energy use. The remaining loads are plugs, appliances, lights, cooling, and energy recovery ventilator (ERV) fans. Since PH is a modeled certification program, there is no guarantee that a home modeled to meet the PH standard will actually perform to the PH standard once built. It is clear that maintaining the PH energy use levels is a function of occupant behavior and lifestyle choices. More research and development of tools for modeling plugs and appliances in the PHPP program should be made available to the PH community.
The report points out higher plug loads and attributes this to the American lifestyle. As we have compared electrical loads modeled in PHPP and actual consumption, we find a large discrepancy between what’s modeled and actual results throughout many North American projects which seems to confirm the author’s explanation.
Conclusion: We need more accurate protocols for the American household. We need to identify realistic stringent savings recommendations and adjust the initial assumptions in the household electricity sheet accordingly. This measured result also points to the potentially higher importance of the source energy criterion rather than the focus on annual heating demand.
The measured space heating demand constitutes only 1/4 of what was actually predicted. Once the additional household consumption is taken into account, though, in the internal heat gains the results once again are pretty close to what PHPP predicted. The modeled kWh amount for space heat in the diagram is reflecting the assumed 3.2 COP of the heat pump; if provided through direct resistance that would amount to 3.2 times 694 kWh, equaling a little over 1800 kWh/yr. The discrepancy is roughly the additional kWh use for the DVR and server, which is direct electric internal heat gain (no bonus through COP). That explains the total higher energy consumption.
In short, the predicted space heat demand result is indeed very close to the modeled prediction. On the flip side though, there is talk about energy used for cooling in the report and the PHPP modeled 0 energy use for cooling. Additional household consumption can be used to replace heating needs in winter, in summer it adds to the energy used for cooling needs.
The report concludes:
This 16th & Nebraska Passive House home represents the leading edge of current energy conservation. Insulation has been maxed out, the envelope is extremely air tight, and the glazing percentage has been reduced to 15%. The solar water heating system is providing 69% of the hot water energy, the home uses highly efficient appliances, low lighting levels, and a very efficient ERV. The remaining loads are a product of the American lifestyle and are the hardest loads to control without major impacts to lifestyle.
For the Northwest, the Salem example indicates that the PHPP is, as expected, reasonably accurate in predicting the annual space conditioning. Assumptions for household and plug loads need to be revisited and entered as correctly as possible, but this is not a climate but rather a market issue.
Just as in Germany, the Salem project proves Passive House is a good basis for net zero. From the report:
This project is a great example of what is possible with the PH program and represents one path to achieving net zero energy use. A 6-7 kW PV array on the roof with the current 3 people living in the home would take this project to a net zero energy status.
That’s a sizable PV installation, but, just like in Germany, forgoing active energy in favor of conservation is more cost-effective.
So we’ve seen what happens when we apply Passive House in a climate very close to the European climate. To predict space conditioning it works very well. American life style and market, we have some work to do.
Applicability in regards to humidity, hygrothermal concerns and the impacts on airtightness recommendations for this climate will be addressed separately at a later time.
Next, we’ll venture into more extreme North American climates to evaluate that experience. Stay tuned for more!