What is a Passive House
The Origins of the Passive House
In 1988 Professors Bo Adamson of Lund University in Sweden and Wolfgang Feist from the Institute for Housing and the Environment in Germany developed the idea of the Passivhaus or Passive House. In 1990 they designed and built 4 Passive Houses in Darmstadt in Germany.
In September 1996 the Passivhaus Institute was set up in Darmstadt to help develop standards and improve techniques for building Passive Houses. Since then, over 25,000 certified Passive Houses have been built.
Principles of a Passive House
Concept
The main concept behind the Passive House is to design a house that does
not need to be ‘actively’ heated (or cooled) by a HVAC system such as
central air, hot water or gas. As with sustainable design and green
interior design, the motivation is to make environmentally friendly
houses that have a low carbon footprint and that reduce the use of
electricity to a minimum and thus reduce carbon emissions from power
stations.
The difference between a Passive House and a Zero Energy Building is
that the Zero Energy Building does not seek to replace heating/cooling
systems with alternative technologies. Rather the electricity for the
house is generated from alternative energy sources such as photovoltaic
panels. The aim of the Zero Energy Building is to make a building that
produces more electricity than it consumes. The aim of a Passive House
is to design a house that doesn’t need heating and cooling by heat
pumps, furnaces, air-con units etc.
Passive Houses have worked very well in Central Europe and Northern
Europe. Most of the certified Passive Houses have been built in Germany,
Austria and Scandinavia. Typically, a passive House loses less than 0.5
°C (1 °F) per day (in winter), stabilizing at around 15 °C (59 °F) in
the central European climate. This is an incredible achievement and
obviously makes Passive House technologies key to formulating strategies
for making buildings independent of fossil fuel energy.
Passive House in Germany
Read More About Passive House Technology
How Does a Passive House Work?
One of the key components to designing a Passive house is the use of
superinsulation. Superinsulation is what it sounds like – insulation of a
much higher specification than normally found in buildings. One of the
key components to Passive House construction is to build walls with much
bigger insulation gaps than normal houses. Much more insulation is
used. Although Passive Houses are normally built from scratch it is
possible to retro fit a house to conform to Passive House standards.
Insulation is also used in the roof and the gaps between the walls and
the roof and the walls and the flooring are firmly sealed to prevent
loss of heat. All holes for wiring, ventilation etc. are also carefully
sealed to remove any holes where heat can be lost. Also the doors and
windows are made with air-tight seals. Typically for a Passive House the
walls are Rip40 and the roof is Rip60. These figures are measures of
thermal resistance.
Another key component of superinsulation is the window design. Windows
are made smaller and often use tree cover and awnings to reduce heat
transfer. The windows themselves are triple glazed with a low e finish
to further minimize heat loss/gain.
Instead of using standard HVAC equipment such as central air, air-con
units, gas, hot water etc. a Passive House instead uses a dual purpose
800 to 1,500 watt heating and/or cooling element integrated with the
supply air duct of the ventilation system. Normally the heater will not
be used as the house is so well sealed and insulated that the waste heat
given off from electrical appliances such as fridges, washing machines,
light bulbs etc. combined with the body heat given off from the human
inhabitants of the house is enough to keep the house warm.
It is, however, important to use electricity to keep the house properly
ventilated. Because the house is sealed it is not easy for air to
circulate around the house. Without air circulation the indoor air
quality deteriorates. To solve this problem as efficiently as possible,
using as little electricity as possible a heat recovery ventilation
system is used. The heat recovery ventilation system has a heat recovery
rate of over 80%. The system uses high-efficiency electronically
commutated motors (ECM) to maintain air quality. When the weather
permits natural ventilation is used such as a small opening or a more
effective stack effect (smaller ingress and larger egress windows).
To power the heat recovery ventilation system photovoltaic panels can be
put on the roof. Because the system uses much less electricity than
normal HVAC systems and because it is often not used in the summer and
spring the electricity generated can be deployed for running other
electrical appliances. Often a Passive House will also use solar gain
technologies to heat water.
Cost / Pros and Cons
A Passive House costs 14% more to build than a conventional house. The
extra expense is soon paid for by the huge savings to be made on heating
bills.
Passive Houses have performed excellently in the colder climes of
Central and Northern Europe. Only a few Passive Houses have been
certified in hot and tropical climates. Obviously in hot and humid
conditions the challenges to the green designer are different. There is a
danger of the insulation in the walls and roof becoming covered in
mold. There is a house in Lafayette, Louisiana, USA, which is a
certified Passive House The house uses Energy Recovery Ventilation
instead of Heat Recovery Ventilation. This removes excess humidity and
transfers excess heat to the hot water tank. Still much of the
literature and technologies associated with Passive House design and
architecture are concerned with replacing conventional heating not
conventional cooling systems.
Finally, Passive House design tries to limit surface area and window
size. Not everyone will be happy about living in a smaller house with
small windows. Still overall, the Passive House is an impressive
achievement and a testament to the efficiency of superinsulation. It is
also a testament to how inefficient conventional homes are.
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