The Passive House
is not an energy performance standard, but a concept to achive highest
thermal comfort conditions on low total costs - this is the correct
House ist a building, for which thermal comfort (ISO 7730) can be
achived solely by postheating or postcooling of the fresh air mass,
which is required to fullfill sufficient indoor air quality conditions
(DIN 1946) - without a need for recirculated air."
This is a purely functional
definition. It does not need any numerical value and it is independend
of climate. From this definition it is clear, that the Passive House
is not an arbitrary standard enacted by somebody, but a fundamential
concept. Passive Houses have not been "invented", but
the conditions to use the passive principle has been discovered.
One could argue about, whether the noun "Passive House"
is adequat to denote this concept. Well - there is no better one.
Thermal comfort is delivered in a Passive House by passive measures
as far as reasonable (insulation,
heat recovery in the temperature
gradient, passive utilized solar energy and internal heat loads).
To use only passive measures might be possible in some climates
- but it will not be reasonable in most of them.
An even better understanding
we get from the following practical considerations:
1) In airtight houses one always needs a ventilation
system (ask the Sweds). All really energy efficient houses have
to be airtight. That means, that with the Passive House concept
the technical component "ventilation system", which one
needs anyhow, will be sufficient to heat (and to cool) the building
without additional ducts, hugher duct diameters, additional ventilators,...
Remark for readers
from America: You are used to have air based heating and cooling
systems (thats why you call it "air conditioning"). But
the systems used in America are almost all just recirculating indoor
air at a quite high rate (> 10 ach, but the air is not "changed",
it is just recirculated). The system discussed here is something
very different: It replaces the indoor air with a very low rate
(0.3 to 0.6 ach) with external air to maintain a good indoor air
quality. There is no recirculated air. The airflows are much lower,
there is almost no noise and no draft at all. Well, the use of such
a system might be very similar to the ones you are used to - but
quite more comfortable.
2) This concept makes it possible, to construct buildings with a
very efficient heat recovery and to do that cost-effective. This
is difficult in other cases, because heat recovery systems form
a quite expensive additional investment to the heating system -
normally it is difficult to have a reasonable pay-back-time. Therefor
it is a good idea to reduce costs of at least one of the two systems:
The ventilation or the heating system. If one reduces costs for
the ventilation systems by choosing e.g. just an exhaust fan ventilation,
then the ventilation heat losses will be quite high and the building
will need a conventional heating system - in this case the result
could be a low energy house. Or the heating part is simplified in
a way, that it can be integrated into the ventilation system - in
that case the building will be a passive house.
The extraordinary low
consumptions of passive houses are just a direct consequence of
the concept given above. To deliver all the space heating just by
heating with fresh air
can only work, if the overall heat losses are very low. Therefor
the insulation of the building
envelope has to be very good - at lest in cold climates. But
the same holds for hot climates, if the fresh air supply has to
be sufficient for airconditioning.
Dr. Wolfgang Feist
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