Civil Engineering Reference
In-Depth Information
standard, this ventilation is most likely provided by a mechanical system with very
efficient heat recovery (PHi n.d.).
This definition has been the basis for the development of the Passivhaus
standard for residential buildings in central Europe, and the setting values are
based on that definition, especially the heat demand to allow heat distribution with
the ventilation system. The extension of application of the standard to other types
of buildings and other climates has implied that the definition does not fit to the
reality of use of the standard, and often the ventilation system is not sufficient to
provide heating or cooling and simple heating or cooling sources are installed in
the buildings. This is especially true for retrofitted buildings for which a specific
standard has been later developed.
The PHI is an independent research institute into the field of highly efficient use
of energy in buildings. It was established in 1996 and is headed by Professor
Dr. W. Feist. The Passivhaus standard is studied widely through diverse approa-
ches, for example, IEA and EU international projects, and scientific articles and
practices in different countries. Historically, the concept was developed in an
academic environment (Lund University, Sweden). Later work, if not always
within a formal academic world, is not the only output from the PHI; research and
development workshops are regularly organised and a large number of dedicated
scientific conferences have taken place.
The Passivhaus standard focuses on reducing heat losses, securing air tightness
and providing ventilation with an efficient heat recovery. Significant characteristics
are good indoor climate and low-energy costs. Meeting the standard means com-
plying with three requirements validated by calculations made using PHPP (in
addition, several recommendations are provided to help achieve these requirements):
1. The first requirement is that the yearly heating demand of the treated area is a
maximum of 15 kWh/(m
2
.y) or the heating power needed is at a maximum of
10 W/m
2
. The latter condition exists to ensure that enough heating power is
available for the worst weather conditions. Both these values have to be cal-
culated with PHPP for the local climatic conditions.
2. The second requirement is the air tightness of the envelope of the conditioned
space, which is required to be measured as less than 0.6 Air Changes by Hour
(ACH) at n50 (measured on site for a pressure difference of 50 Pa). PHPP also
uses the unit h
-1
or 1/h.
3. The third requirement limits the total weighted primary energy to be less than
120 kWh/(m
2
.y) when calculated with PHPP.
Reducing heat loss is firstly achieved by improving the thermal envelope with a
special thermal bridge-free construction. Secondly, sufficient air tightness limits
heat loss from uncontrolled air exchanges between indoors and outdoors. These
two aspects need to be solved at the envelope level of the building. Increased
insulation of the opaque elements is usually achieved by thicker insulation layers
or the use of material with better thermal resistance, and by a thorough treatment
of structural features to reduce, or preferably to eliminate, thermal bridges.
