Are most homebuyers interested in purchasing a home that saves 90% over a traditional home on heating and cooling costs and requires only a small active heating system the size of a hairdryer? The Passivhaus movement is an exciting building design concept that offers tremendous energy savings due to reliance on passive heating systems. Europe is embracing the concept with between ten and fifteen thousand houses already built and governmental support of mandating the standard. The Passivhaus Institut in Darmstadt was formed in 1996 to promote and control passive house design and the group only recently formed the Passive House Institute US (PHIUS) to reach out directly to the US building market. It is slow to gain momentum, but holds promise for the US market in the future.
What is a Passive House?
The PHIUS defines a passive house as a fundamental design concept, not a rigid energy performance standard, although it does outline a few basic performance characteristics. The basic concept is that thermal comfort (ISO 7730) is achieved through post-heating or post-cooling of fresh outside air through thermal transfer from the warm air leaving the building as exhaust. Air leaving the building is not recirculated, which leads to outstanding indoor air quality. The building is designed to be virtually air-tight and primarily heated by passive solar gains and by internal gains from people, electrical equipment, hot water, etc. A widely-praised flexible software package, Passive House Planning Package (PHPP) projects detailed heat load, heat loss, and primary energy usage for individual building parameters.
The energy consumption statistics are impressive: PHIUS widely claims a 90% improvement in heating energy consumption and overall energy savings of 60-70%. Further, these energy gains are achieved without implementing expensive active technologies such as photovoltaics or thermal hot water systems. Most passive houses do have some source for additional heating, but the typical system is far smaller than a traditional HVAC system and may use as little energy as a hair dryer.
The primary design components of a passive house are:
Ventilation and Heat Exchanger:
At the heart of passive house design is a ventilation system which employs a heat exchanger to transfer the warmth of the exhaust air to the fresh outside air entering the building. Using a geothermal system to cool or warm air by forcing it through earth-buried ducts provides an additional opportunity to increase the efficiency of the ventilation system. PHIUS touts this design as providing superior indoor air quality compared to traditional buildings, although as I’ll discuss later, some American builders believe this claim is overstated.
To read more about the really exciting potential for Geothermal Heat Pumps (GHPs), which also known as ground-source heat pumps read our post Geothermal Heat Pumps: Good for the Bottom Line, Good for the Nation and Good for the Earth that discusses this very promising and widely applicable energy saving technology.
Passive Solar Gains:
A concept widely-embraced by the US green building market already, passive solar strategies such as, building orientation, shading, and window placement are critical to the design of a passive house.
A passive house requires an airtight shell, preventing heat from escaping or cold from seeping inside. The PHPP software calculates R-values for insulation in a building taking into consideration may factors, including climate.
Internal gains or inner returns refer to sources of heat generated that are not normally considered active heating systems, such as cooking, showering, appliances and human activity. Humans emit around 100 Watts of heat energy per person.
In addition to being oriented to reduce solar gain in the warm summer months, a passive house requires high performance triple-glazed windows. These windows are costly and more difficult to find in the US than in Europe.
Major Barriers to Widespread Passive House Adoption in the US
Should builders, architects, and suppliers in the US gear up to support demand for passive houses or is this a trend that will fall flat on American soil? At this time there are only a few passive houses in the US, although markets such as California and the Northwest US are beginning to gain momentum. While not insurmountable, there are currently several major barriers to large-scale adoption of passive house standards:
In Germany, passive houses cost only about 5 to 7 percent more to build than conventional houses. PHIUS estimates an additional upfront investment of approximately 10 percent over a code compliant home in the US. Estimates of actual costs in US construction range widely and are difficult to nail down due to the few houses actually constructed in the US.
The two primary cost issues related to passive houses are the long-term energy cost savings and the availability and cost of passive construction materials in the US.
In terms of long-term energy savings, passive houses seem very likely to create a significant cost savings. Once the ventilation systems and insulation are in place, the only costs outside of basic maintenance are the small, in some cases unnecessary, active heating systems. No one is seriously challenging the claim of a 90% reduction in energy costs related to heating – that’s the beauty of a passive system. US green building groups such as the LEED certification system have recently suffered criticism that certified buildings do not always lead to energy savings, particularly if staff and tenants are not properly trained on using the systems. Passive houses may be able to avoid this pitfall with the strength of the passive design.
While passive houses will very likely exhibit long-term energy savings, it is not clear if the initial construction costs will prove too high. Currently, the availability of certain items, primarily the heat-exchange ventilation system and sophisticated windows, is challenge in terms of construction cost. I believe if the PHIUS and others are able to demonstrate actual long-term energy savings in the US (and associated reduction in carbon footprint) consumer demand will drive down the costs of equipment specific to a passive house. Passive house design will be primarily limited to new construction; retrofitting a building with the new ventilation system and insulation is cost prohibitive for the average homeowner.
It is not clear yet if passive houses are desirable in every climate, most notably in extremely cold or warm, humid climates. One reason why passive houses thrive in Europe is the relatively stable temperate climate. One barrier to large-scale adoption in the US is that passive houses will require very different insulation and ventilation based on the many different climates throughout the US. It is no surprise that California’s mild climate has drawn the initial support of US passive house adopters.
PHIUS’s PHPP software will calculate requirements for a passive design, taking into account different climates. Yet, is a passive house really cost-efficient in certain extreme climates? For instance, in very cold climates even the cost of very thick insulation can be quite high, possibly higher then just adding an active system, such as a photovoltaic cell to provide heat for the home.
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3. Lack of Controls
There are a few attributes of a passive house that are different than a traditional home and may cause some resistance to the idea of a passive house, at least initially. The biggest adjustment for the homeowner will be the lack of adjustment; passive houses are designed to operate passively and without input from humans. Although this makes the system very easy to use, it limits the control a homeowner can exert over the environment. The entire house is the same temperature, so you can’t keep the bedrooms several degrees colder than the living room. You can open a window for some short-term extra coolness, but the air will quickly return to the “normal” temperature when closed. While technically unnecessary, most architects install a switch with three settings so it is possible turn down when no one is home, or to increase the air circulation during a party.
4. Overcoming misconceptions and marketing challenges
The passive house movement in the US has been a bit rocky and hampered by lack of a consistent message in a few key areas. PHIUS needs to work to design a better US marketing message for builders and homeowners. Most notably, passive house experts from Europe keep saying that no additional space heating is necessary in a properly designed passive house. While that may be a theoretical ideal, the fact is that most passive houses, even in Europe, do have a small active system.
Also, US builders have been frustrated by Passivhaus advocates’ claim that passive houses deliver better air quality then traditional US homes. One of the great qualities of a passive house is the fresh air ventilation system, but US homes must conform to the air quality standard ASHRAE 62.2 and good ventilation is already essential to energy-efficient homes in the US.
5. American disinterest in “passive” systems
A few critics theorize that the passive house design will not prove marketable in a nation that loves gadgetry and that the concept of a passive system runs counter to US culture. Americans thrive on the idea of active systems – something to tack onto a home, such as an active solar energy panel. Certainly Americans are enamored with fancy devices, many useless, that track and claim to reduce energy use. However, I believe this criticism doesn’t have any long-term merit. Americans are seeking energy savings and the unique nature of this home will appeal to many US homebuyers hoping to reduce energy costs and shrink their carbon footprint.
© 2009, Jessalyn Dingwell. All rights reserved. Do not republish.