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Comparing Passivhaus Homes to Other Low-Energy Homes

Some Passivhaus recommendations are impractical and unjustifiably expensive

Posted on Oct 14 2009 by John Straube

[Editor's note: This article originally appeared on the Building Science Web site as "The Passive House (Passivhaus) Standard—A comparison to other cold climate low-energy houses." GBAGreenBuildingAdvisor.com is presenting Straube's article as one of a pair of Pro/Con articles. The response from Marc Rosenbaum and David White is titled "In Defense of the Passive House Standard."]

By John Straube

The Passivhaus (PH) standard is a set of voluntary criteria for an ultra-low energy use home. Originally developed in Germany for houses and low-rise multi-unit residential buildings, the standard has been applied to houses in a range of other countries and to commercial buildings as well. The most interesting aspect of the criteria of the Passivhaus standard may be that it has relatively few mandatory requirements, thereby providing design flexibility, and that it focuses exclusively on energy consumption. There are, however, many recommendations in the PH program that are not likely good decisions for cold climate (DOEUnited States Department of Energy. Climate Zones 5-7) North American housing, and some are very impractical with little or no benefit to the environment or the homeowner.

The unique focus of the PH standard is an exceptional concern for heat loss by conductionMovement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow. and air leakage through the building enclosure and a complete disregard for the climate zone in its recommendations. High insulation values, very high performance windows, and airtightness levels better than any other building program anywhere are the normal result. Very efficient appliances are also practically required to meet the energy consumption targets.

Despite their name, homes built to the Passivhaus standard are not “passive.” All Passivhauses must have an active mechanical ventilation system and all have some type of active heating system, albeit very small ones. The use of passive solar design principles is recommended but not mandatory.

The Passivhaus concept was developed by Dr Wolfgang Feist and Prof. Bo Adamson in the late 1980s and implemented in research in the 1990s. According to Feist, the inspiration of the PH program was the housing of William Shurcliff (a solar house pioneer) and Harold Orr (a superinsulated house pioneer of Saskatchewan House).

Requirements
The primary Passivhaus target criteria are:

  • a total heating & cooling demand of <15 kWh/m2/yr ( 4.7 kBtu1,000 Btus/ft2/yr)
  • total primary (i.e., source) energy of <120 kWh/m2/yr ( 38 kBtu/ft2/yr)
  • airtightness 0.6 ACHACH stands for Air Changes per Hour. This is a metric of house air tightness. ACH is often expressed as ACH50, which is the air changes per hour when the house is depressurized to -50 pascals during a blower door test. The term ACHn or NACH refers to "natural" air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. While many in the building science community detest this term and its use (because there is no such thing as "normal" or "natural" air leakage; that changes all the time with weather and other conditions), ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations.@50 Pa or less

Even some of these requirements may not be actually be mandatory: in a 2008 interview in Energy Design Update [1] Feist himself stated that the heating demand number could be anything. In this interview Feist also stated “As long as you build a house in a way that you can use the ventilation system … to provide heating and cooling it can be considered a Passivhaus.” By this latter definition, thousands of Building America homes that use the heating and cooling system to provide ventilation, are Passivhauses! Of course, if the requirement is for a non-recirculating heating system then this is quite restrictive and not very beneficial for cold climate housing.

Other commonly recommended (or, depending on what you read, required) measures include:

  • peak heating demand should be under 10 W/m2 (3.2 Btu/ft2)
  • total site energy of <42 kWh/m2/yr ( 13.3 kBtu/ ft2/yr)
  • window U-values of <0.8 W/m2K (0.15 Btu/ ft2/F, R-7.1)
  • high-efficiency heat recovery (over 80%)

The floor area is measured by total conditioned area inside the claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. . (The PHPP 2007 states on page 37, that “The dimensions used in the PHPP are always exterior dimensions. Therefore the most exterior layer of the thermal envelope are to be entered.” However, the area is reduced further by about 20% because stairwells, and walls are subtracted, as this is the standard German method of area calculation). The basement is only considered at 60% of its actual area because it is not considered living space in the German standards. Why, I can't understand; perhaps Germans don't build basements you can live in like a modern basement in North America.

Typical Passivhaus Approach
The typical Passive House approach is focused almost exclusively on the reduction of space heating loads, leaving the lighting, hot water, cooling, appliance and miscellaneous electrical loads to fall under the “total primary” requirement. However, it is widely acknowledged that very efficient appliances and lighting must be used to meet the primary/source energy targets in most cases.

Almost all Passivhauses rely on:

  • very heavy insulation, R-40 to R-60 walls, R-50 to R-90 roofs, and often R-30 to 50 sub-slab insulation, triple-glazed low-e windows, and exceptional avoidance of thermal bridges (except for wood framing),
  • ultra-airtight construction (<0.6 ACH@50) which, together with the R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. requirements, usually result in designers needing to choose simpler shapes,
  • passive solar gain for a portion of the heating by orienting the house to the south and using a window SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of around 0.5 (or higher if possible),
  • heat recovery, in the past with earth tubes and more recently with dual core HRVs to reach high 80% to low 90s efficiency, but essentially always with supply air to each space with return air pathways, and
  • heating of the ventilation air to provide space heating, although many homes use radiant floors, walls, ceilings, and radiators.

The diversity of solutions is, however, large, and could be considered a strength of the program. There are Passivhauses that use gas boilers to provide heating, and those that include solar hot water and/or PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow., and wood stoves. Cooling on the other hand, is rare, largely because of the geographic areas in which the program has been more widely adopted.

Insulation and Airtightness
Insulation levels of walls of Passivhaus’s are generally in the range of R-40 to R-60 for walls, R-60 to R-90 for roofs, and R-30 to 50 for slabs. Perhaps just as importantly, thermal bridges are rather accurately accounted for in the calculation methodology.

Window specifications are also demanding. A common specification is for U=0.15 (0.8 W/m2 K) or less for windows. It is not clear how to translate these values to North America, as the NFRC testing methods generally result in about a 10% increase in heat flow for the same window as compared to European standards. However, to approach these targets windows certainly need to have non-conductive frames (vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate)., wood or fiberglass) and triple-glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill., low-e coatings and gas. In fact, it is very difficult to find commercially-available operable windows that can achieve these specifications, and imported PH-certified windows reportedly cost about twice as much ($90-100 per square foot) as much more readily available triple-glazed fiberglass windows (R6 at $50/sf).

The airtightness level of <0.6 ACH@50 is also extraordinary. It is achieved in North America by very few homes, and always when built as special custom houses, usually with a very simple plan form and simple roof lines. One Swedish prefabricated house exporter [2] states that it does not recommend Passivhaus standards for any of its house plans other than single-storey ranches because of its experience with the difficulty of reliably meeting the stringent airtightness target with other than the simplest of building shapes.

Ventilation and Heating
Although it is recommended that the peak heating demand be kept to under 10 W/m2 (3.2 Btu/ft2) this is not mandatory and is based on the desire to heat the house with ventilation air only. However, based on our analysis at BSC, this recommendation is both very difficult to achieve in cold climates (using standard calculation methods), and unnecessary for achieving low annual energy consumption. By using extreme insulation and eliminating safety factors such as thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. and internal gains it is possible to reach this low of a heat demand.

In Europe, higher ventilation rates are often specified, likely because there is not a long history of providing mechanical ventilation, and past systems did not distribute air to each room. The 2007 Passive House Planning Package (PHPP 2007) recommendation is 30 m3/hr, which is 17.5 cfm/person, whereas ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. requires 7.5 cfm/person+0.01 cfm/ft2. The PHPP 2007 also states that the “average air change rate should not fall below 0.3 ACH.” For a 3-bedroom 2000 square foot single family home, this results in a PH ventilation rate of 80 cfm versus 50 cfm (25 l/s) for ASHRAEAmerican Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). International organization dedicated to the advancement of heating, ventilation, air conditioning, and refrigeration through research, standards writing, publishing, and continuing education. Membership is open to anyone in the HVAC&R field; the organization has about 50,000 members. 62.2-2007. Although this 60% difference is not too large, so many PH have been ventilated at much higher rates that the PHPP 2007 (page 81, section 14.1) warns users not to over-ventilate.

The PHPP 2007 also sets the maximum temperature of air delivery be less than 52 °C (126 °F). This limits the heat delivery rate to about 60 Btu/hr per cfm of airflow (126 supply less 70 F return times 1.08 Btu/hr/cfm/F = 60). If the 50 cfm of ventilation air from the 2000 ft2 home were heated to the maximum of 126 °F (52 °C), it could deliver a maximum total of 3000 Btu/hr, or about 15 times less heat than a standard small furnace! This works out to a heat delivery of just 1.4 Btu/ft2 (4.3 W/m2). To deliver the PH maximum heating intensity of 10 W/m2 (3.2 Btu/ft2) with ventilation air would require a ventilation rate of 115 cfm (60 l/s), which is 2.3 times the ventilation rate of ASHRAE 62!

If one were to apply such an approach, the over-ventilation would impose a very significant energy penalty for a low-energy house as it is tantamount to using a mechanical system to impose air leakage. It is likely for this reason that the Passivhaus Institut recommends very high efficiency (eg 75-85%) heat recovery ventilators with high efficiency fans. Although the standards for measuring HRV efficiency in Europe are different than North America, it should be clear that a standard 65% efficiency HRV (a typical specification in North America) operating at 50 cfm and 0.6 W/cfm, will use less energy than a very expensive 75% efficient HRV operating at 80 cfm and 0.75 W/cfm. Hence, North American houses ventilated to ASHRAE 62.2 with a standard efficiency (>60%) HRV and efficient fan motors (>1.5 cfm/W) will consume less energy than most Passivhaus-approved ventilation systems. Such HRV/ERV units have been installed in numerous Building America, Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners., R2000, and just better homes. The energy savings of an HRV relative to a central fan-integrated ventilation system (i.e. FanCyclers) are small, but for very low-energy buildings in cold climates, an HRV with the specification recommended above can usually reduce primary energy consumption.

It should be noted that many North American HRVs consume excessive amounts of electrical energy and should be avoided. Energy Star will soon be limiting the electrical energy draw of HRVs but these requirements will not come into force for several years. Numerous right-sized HRVs (meeting ASHRAE 62.2) with efficient fans (i.e., 0.5 to 0.75 W/ cfm) are available and can be purchased for $500 to 700. In more moderate climates, central fan-integrated ventilation systems (i.e., without heat recovery) consume only very little additional energy than a high performance HRV, but provide equivalent quality ventilation at a fraction of the capital cost.

Given the standard rates of ventilation and the occurrence of design temperatures of 0 °F (-18 °C) or lower in parts of the United States and Canada, increasing ventilation rates to allow the use of ventilation air as the only means of heating is at best highly restrictive to a design and at worst simply impractical and antithetical to a low-energy house.

There also appears to be an almost dogmatic avoidance of using radiant floors or air-based heating with re-circulating airflows (the two most commonly available heating systems in most parts of North America).

Although radiant floors provide “too much” heat in a low energy house, they may be desirable from a comfort perspective, particularly if they are applied to small areas of the home (e.g. under tiled floors in bathrooms and kitchens). That said, radiant floors are rarely the lowest cost approach to space heating.

One of the Passivhaus recommendations is that duct air velocity be kept below 3 m/s (588 fpm). In all of our projects, BSC recommends trunk velocities should be kept between 500 and 750 feet per minute and runout / branch duct velocity should be under 500 fpm. These limits save fan energy and reduce noise.

Another recommendation common to both Passive Houses and BSC Building America houses is the requirement for defined return air pathways, and the specification of transfer grilles. PassivHaus describes a target pressure drop of 1 Pa, whereas BSC allows up to a 3 Pa pressure drop across grilles. The Passivhaus standard makes no mention of ducts outside the enclosure as this risky practice is almost unknown in Europe.

Typical BSC BA low-energy house
Numerous BSC-designed Building America prototype homes have been built in cold climates (Zone 5 and higher) that compare well to the Passivhaus standard in terms of their primary/source energy consumption. That is, they consume perhaps 40 to 60% more than a Passiv Haus, but are more cost-effective. Typically, these houses use a minimum of R-5 (U=0.2) windows (triple-glazed, low-e coated, warm edge spacers), R-10 sub-slab insulation and R-20 wall insulation in a conditioned basement, R-40 above-grade walls and R-60 ceilings (the "5/10/20/40/60" approach). All thermal bridges in these BSC houses are controlled by using insulation on the exterior of the framing. These R-values are comparable, if on the low-end, of the range that PH use.

Airtightness levels of 3 ACH@50 Pa can regularly be achieved by production builders if airtightness details are tested, and some training and airtightness testing is undertaken. In our experience, and that of others, airtightness levels of 1.5 ACH@50 Pa can be reliably achieved if significant effort is taken in designing details for airtightness, and on-going training, testing, and inspection is employed. In the experience of the Building America and the Canadian R2000 program, such airtightness levels are achievable, but with some effort. The biggest obstacle to achieving lower air leakage may be complexity in building shape. Given the state of practice of air barriers and trade skills, the 0.6 ACH@50 level demanded by PH is too difficult to achieve for production homes (although achievable in custom homes), and hard to justify in any case given the small incremental benefit to energy, air quality or durability.

The BA program expends a significant amount of effort to ensure that a BA house is more durable and healthier than equivalent housing. There is essentially no discussion of durability and little on IAQIndoor air quality. Healthfulness of an interior environment; IAQ is affected by such factors as moisture and mold, emissions of volatile organic compounds from paints and finishes, formaldehyde emissions from cabinets, and ventilation effectiveness. in the PH standard: the effect on the durability of exterior building materials when the insulation levels rise to the levels used is not discussed, nor is the need for heightened rain control requirements, although damaging air leakage condensation is likely controlled by the very low acceptable air leakage.

Energy Consumption Compared
Measurements (not the Building America Benchmark assumptions) show that electricity use for appliances and miscellaneous loads can be held to 3000-4000 kWh/year per household in a modest sized, typical home. This can be reduced further by very efficient appliances, exceptional lighting, and by better controls. The reported values for Passivhauses tend to be lower, in the range of 2500 to 3000 kWh/year. These lower levels can be achieved in North American homes, but depend on occupants operating and maintaining the home in a low energy manner.

Domestic hot water energy consumption is approximately 3000 - 4000 kWh/year per household in American homes.3 Large variations depend on the lifestyle of the occupants, but this energy use appears to be similar in Passivhauses. If a basement is available, this energy use can be reduced (perhaps by 10-20%) by drainwater heat recovery and reduced (perhaps by 10-20%) by choosing the very lowest hot water use appliances. Again, occupant behavior is critical: a retired couple may use half this energy, whereas a family of five with teenage children can use 50% more. A reasonably priced two-panel flat-plate solar hot water system can provide about 2000 kWh/yr of preheated water to the domestic hot water appliances even in cold climates.

Space conditioning and ventilation energy demand for houses built to the low energy standard described above in DOE Climate Zones 5-7 tends to be 10000 to 15000 kWhe for a house with 2000 ft2 living space (54 to 80 kWhe/m2/yr). An upgrade from double to triple-glazed windows (R3.3 to R5 or R6), and the addition of an efficient HRV drops these values by 2000-3000 kWh/yr, and if a south-facing exposed solar lot is available, another 1000-2000 kWh can be reduced. Hence space heating energy values can be reduced to the range of 7000-11000 kWh/yr by some combination of measures that may be available on some lots (full south exposure is often NOT available) and may be cost effective in some situations (triple-glazed windows are not always cost effective).

Using a site-to-source (site-to-primary energy to use PH terms) conversion of natural gas to electricity of 3 (which is about mid-way between the German 2.7 value and the US Department of Energy gives as a 3.365 value), the following general energy use profile can be developed for a 25 by 40 ft raised ranch home with a fully finished basement (e.g., a home with 2000 ft2 of conditioned, useable space).

The table [See Table 1 below — click image to enlarge] takes mid-range values for energy consumption and converts this energy demand to primary (source) energy use. It assumes the smallest available standard condensing natural gas two-stage furnace with an ECM motor (e.g. Goodman GMH95), a condensing sealed-combustion hotwater heater (such as an AO Smith Vertex, Navien, Quietside, or Viessman VitoDens), an efficient HRV (such as a Fantech VHR704 with an AirCycler controller), Energy Star appliances and all CFLCompact fluorescent lamp. Fluorescent lightbulb in which the tube is folded or twisted into a spiral to concentrate the light output. CFLs are typically three to four times as efficient as incandescent lightbulbs, and last eight to ten times as long. CFLs combine the efficiency of fluorescent light with the convenience of an Edison or screw-in base, and new types have been developed that better mimic the light quality of incandescents. Not all CFLs can be dimmed, and frequent on-off cycling can shorten their life. Concerns have been raised over the mercury content of CFLs, and though they have been deemed safe, proper recycling and disposal is encouraged. lighting.

As can be seen, the source energy consumption, at 158 kWh/m2/yr, exceeds the Passivhaus requirement of 120 kWh/m2/yr (because the German method of floor area calculation is different than that used in North America, the whole house comparison is more accurately 29300 vs 17800 kWh). However, for a further unsubsidized investment of under $20000, a 2.5 kW PV array (which can generate 3250 kWh/yr) can be installed that reduces primary energy consumption by 9750 kWh to close in on the arbitrary (and laudable) Passivhaus energy target. The PV was chosen in this case as it was the least cost approach to achieving the target. In many cases triple-glazed windows and ERV (at an upcharge of $4000-5000 these measures may save 2000-3000 kWh/yr) may be a less expensive approach in conjunction with a 2.0 kW array. PV is currently the most expensive un-subsidized form or renewable energy, often at a cost of 50 to 70 cents per kWh. Many renewable and/or no-carbon sources of electricity (such as wind, bio-mass, tidal, etc) can be produced for 1/2 to 1/3 this cost (see also BSI-026).

Some of the PH recommendations require designers to spend more limited resources on conservation that are even more expensive that producing the energy at the very high bar of current PV prices. For example, in a 6000 HDDThe difference between the 24-hour average (daily) temperature and the base temperature for one year for each day that the average is below the base temperature. For heating degree days, the base is usually 65 degrees Fahrenheit. For example, if the average temperature for December 1, 2001 was 30 degrees Fahrenheit, then the number of heating degrees for that day was 35. F climate, switching from a 0.6 W/cfm, 63% efficient Fantech HRV to a PH-certified 80% efficient, 0.75 W/cfm HRV will, even if one uses the same ASHRAE 62.2 50 cfm ventilation rate, saves $11 per year in heating energy at $1.65/therm gas and 15 cent/kWh prices. Even if gas and electric prices triple in the next ten years, it is not feasible that the $1000-$1200 premium commanded by a PH-certified HRV can ever be recouped. Upgrading the 200 square feet (10% of floor area served) of R6 windows (such as Inline fiberglass with argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. -filled dual low-e coatings) to R7.1 PH-certified windows (superior performance) might save 250-400 kWh/yr in a 6000 HDD climate, but would command a $10000 premium at current prices. Increasing the R-value of sub-slab insulation from R20 to R40 is another measure that is very expensive.

Doubling the insulation levels of the proposed home (i.e., changing the specs to R-10 windows, R-80 walls, R-120 roof, 0.6 ACH@50, and a 100% HRV) and increasing airtightness would not necessarily reduce primary energy demand enough to meet the PH energy target. Increasing the insulation, window, and airtightness values to these levels is not only quite expensive, but very architecturally constraining, i.e., dormers, bay windows, etc all become challenging to incorporate and maintain low surface-volume ratios. Even with all of the measures to halve the heating energy demand, the primary energy demand intensity would barely drop below 120 kWhe/m2/yr (the PH energy target).

In DOE Climate Zone 6 or 7, the peak heating demand of the extreme R-10/R-80/R-120 specification would remain above the 10W/m2 (3.2 Btu/ft2 or 6400 Btu/hr) PH recommendation without relying on occupant producing average heat (eg not below average, with one person at home) and thermal mass, and 50 cfm of ventilation airflow would not be sufficient to provide space heating on a design 0 °F or -10 °F night (that is, the heat loss would need to be lowered to 3000 Btu/hr for ventilation air to provide heating). As the cost of an efficient furnace (described above) is less than about $2500 installed (plus ductwork, which is largely needed for ventilation anyway), and smaller capacity furnaces cost no less, there are essentially no capital cost savings to reducing space heating energy demands.4

From a point of view of the wise use of capital, the Passivhaus approach in cold-climate zones of North America can lead to more expensive, less architecturally flexible, and even potentially more energy intensive houses than a more flexible approach that focuses only on the least cost, most durable means of achieving a primary energy use per area target value. Perhaps the most important contribution made by the PH standard to low-energy North American housing is that one cannot simply buy $200 000 worth of PV panels to meet the target, as too many net zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. homes have done.

Conclusions
Homes in cold climates (DOE Zones 5-7) that employ:

  • minimum R-5:10:20:40:60 enclosure,
  • 1.5 ACH@50 airtightness or better,
  • condensing (>95%) gas furnaces with ECM fan motors,
  • right-sized (ASHRAE 62.2) efficient (> 65%, <0.6 W/cfm) HRVs
  • condensing (>92%) hotwater natural gas water heaters
  • appliances in the top 10% of Energy Star combined with CFL lighting

deliver total energy and environmental performance that approaches the Passivhaus standard in cold climates. Such houses depart in relatively minor ways from standard North American construction, accommodate a broader range of architectural styles, can be modified easily for different climate zones, and can even be built by production builders.

Achieving the specific Passivhaus target of 15 kWh/m2/yr for heating on site energy use, results in investment of materials and money that often will exceed other less costly and environmentally impactive solutions. Achieving the equally arbitrary 120 kWh/m2/yr has more direct environmental benefits than the heating target, but may best (i.e., with least cost and environmental damage) be achieved using some on-site or renewable off-site power generation.

As new clean, local, and renewable energy sources come on line over the next 25 years and become more affordable than current PV prices, it is unlikely that the extreme conservation measures taken by Passivhaus to meet the specific requirements will be considered an optimal deployment of resources for cold climate housing.

Read a response to this article by Marc Rosenbaum and David White.

References
“An Interview with Wolfgang Feist”, Energy Design Update, Aspen Publishers, Vol. 28, No. 1, January 2008.

Passive House Planning Package 2007/1-E, Passivhaus Institut, Darmstadt Germany, 2007.

“Certification as Quality Approved Passive House: Criteria for Residential-Use Passive Houses”, June 18, 2007, Passivhaus Dienstleistung GmbH.

The best source of information is the official website of the Passivhaus Institut, www.passiv.de and www.Passivhaus-info.de

Footnotes
1. Energy Design Update. “An Interview with Wolfgang Feist” Aspen Publishers, Vol. 28, No. 1, January 2008.
2. Scandinavian House accessed from www.scanhome.ie 2009.0717
3. kWh is used as the unit of energy in this article. One kWh = 3412 Btu. One therm of gas = 29.3 kWh.
4. European quality boiler heating systems are quite different as the typical cost is over $20,000 installed, and thus avoiding their use is a major capital cost saving.


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Image Credits:

  1. Green Line Architects, Carbondale, Colorado
  2. John Straube

1.
Wed, 10/21/2009 - 11:40

passive house pro-con
by Michael Hindle

Helpful? 0

I find it dismaying when people assert that Passive House shows a "a complete disregard for the climate zones" in critiques. It is true that the energy performance standards are consistent, and some climate zones are more demanding than others, but going through the passive house training I can attest to the fact that we spoke about climate zones and strategies particular to different climate zones pretty much the whole time.
If Passive House design demands more of people in challenging climates that is more a reflection of the realities that we all face as we, as a global society struggle to meet the demands of climate change and avert catastrophe. Since when has good design meant "give yourself an easier standard if you meet challenges"?
It is also not true that Passive House is not cost effective and does not consider cost benefit. All I have heard at Passive House Training is that we accomplish nothing if we do not make such houses available at competitive costs. Low cost projects have been completed in the challenging climate of Illinois and the Passive House concept is very popular and competitive in Europe.
Even issues that caused me serious concern about Passive House, such as the extensive use of foam insulation, were addressed in full during our training session. The folks at Passive House are very sharp and are doing everything they can to account for the effects of everything from the green house effects of foam blowing agents to embodied energy of insulation.
I would suggest that we all aspire to the most rigorous standards possible and design to meet the challenges. If we all got even close to the Passive House Standards we would be doing a great service to the future. I am concerned that dismissal of such efforts will create an easy out for those who really do not wish to address our profligate national energy consumption.


2.
Thu, 10/22/2009 - 11:51

floor area
by Dave Brach

Helpful? 0

I'm happy to see that Dr. Straube has clarified the way PH determines floor area, but he is still slightly off the mark. This is extremely important, since all energy comsumption numbers are expressed per unit area and even small inaccuracies distort results. It has already been pointed out elsewhere that the statement "The floor area is measured by total conditioned area inside the cladding" is not correct. I'm surprised to see it resurface in this text. By way of explanation Dr. Straube make this citation from the PHPP: "The dimensions used in the PHPP are always exterior dimensions. Therefore the most exterior layer of the thermal envelope are to be entered" but this is taken from the section explaining the dimensioning of walls, roofs, and floors as elements of the thermal envelope, not the floor area. The floor area is explicity described in another section of the PHPP, and it is (logically) a completely separate calculation from the areas that determine energy loss/gain.

He does state this area is further reduced by the subtraction of walls, stairs and 40% of basement and utility areas, estimating these reductions to be about 20%. As a concrete example of this, I am presently completing a Passive House and have calculated the floor area per ANSI Z765-2003 to be 3640 sqare feet. The same house has a treated floor area (PH) of 2723 square feet, 25% less. I suspect that this 25% difference is probably closer to what is typical.


3.
Mon, 11/30/2009 - 05:39

floor area
by Interested Onlooker

Helpful? 0

How many occupants is the 3640/2723 sq ft design for?


4.
Tue, 03/30/2010 - 14:28

cost benefit
by ben graham

Helpful? 0

I am not sure how we can so easily dismiss anything that costs more in an economy whose value system is subsidized and largely developed by the manufacturers of the very crises we are working on. Especially when the effort is towards solutions to the crises are in a determined and effective fashion. Rosenbaum and White, in their response to this article show how the PH incentive has actually developed the German market in a positive direction. Perhaps there is more interest over there in efficiency, but I diverge. It is clear, and history shows that "common good" market changes typically require incentive, as the control of markets are based in the control of capitol, which we also know is with a whopping 4%. This 4% is more concerned with profit than people or the environment.
We can do better.
It is also not clear to me the the Building America program is effective enough in terms of real carbon savings.

Thanks for the discussion. It is an important one.


6.
Sat, 12/04/2010 - 15:12

General Comments
by John Straube

Helpful? 0

To repeat for the 100th time, I dont think the PH standard is completely broken or wrong spirited or etc. I do think it is dangerous to apply German-developed (or Canadian or Mexican) guidelines as dogmatic rules without understanding them. A few of the PH recommendations seem on my analysis to result in less than optimal results.
The "complete disregard for climate" comment is based on the targets of heating energy (15 site), total energy (120 source) and 0.6 ACH@50. It is trivial to achieve the heating target in Berkeley and exceedingly difficult to the point of insanity in Edmonton. The environment does not benefit from achieving this target. Expending much effort and resources achieving 0.6 ACH@50 is also not sensible in mild climates, and there is little to no understandable reason why 1 ACH@50 would not be just as good for the environment in Minnesota if the total primary energy number was achieved. One should also question the metric of "ACH" which punishes small houses, much like the "energy/floor area" does: both targets are much easier to achieve in all climates by building a larger house, something that seems to defy the implied goals of PH.
Building America is NOT a fixed set of targets or standards: it is a research program that is trying to develop cost effective low-energy houses that can be rolled out across the country in scale. One of the ultimate targets in the past has been Net Zero Energy use: for those prototype homes built to achieve NZE, the environmental footprint is significantly less than a PH house. For those homes that targeted 50% below code for $5000 incremental cost, the environmental footprint of a BA project would be more than a PH in cold climates, but still less than many PH projects in mild California.
Although the "energy/area" metric is highly flawed from an environmental point of view, there is no reason to use a different area measure than commonly used in north America: all it does is confuse, which is my critique of the PH standard. The difference between ANSI and DIN will vary with the type of house, and your definition of below-grade. to make PH work in North America it would probably make sense to simply reduce the target values by 25% to get closer to everyday understandings of square feet (which makes the heating number even more insane in cold climates). German window test standards and HRV test standards in the PH are both based on milder temperatures than Zone 5-7 US climates. I know of one German HRV that is having a hard time passing the Canadian test, since the unit fails to work at all at the required minimum temperature of -25C. But it is a PH certified product.
An interesting point to ponder: a house of 4750 square feet that used the average source energy of the current stock of American homes would meet the PassivHaus standard of 120 kWh/m2/yr primary.
energy.
I too think this is an important discussion. One that should be based on facts and understand, not dogma or blind following of rules. Getting our building stock built right is too important.


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