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Many subjective perceptions determine living comfort, even the colour of the surroundings plays a certain role – particularly for the mood of person who thereby expresses his or her perceptions. Living comfort mainly depends on the “thermal comfort”. This has been well-researched and the results have been incorporated into international standards (DIN ISO 7730). A large part of the information available to us today is due to the work of the Danish scientist P. O. Fanger (Wikipedia Seite).
Fig. 1 Air movement near to a Passive House window: Due to the small temperature difference between window surface and room air, the speed of air sinking at the window is small. At the floor, approximately 10 cm horizontally from the passive house window (U=0.8 W/(m²K)) the maximum air speed is a barely noticeable 0.11 m/s. If the insulating value of the window is worse, then air speed rises to disturbingly high values. Therefore it is recommended, with “normal windows”, to position a heating element under the window.(CFD simulation: J. Schnieders, PHI)
Fig. 2 Stratification: The temperature stratification of air is also imperceptible with the passive house window. Therefore the heating element can be placed also at an inner wall while still reaching optimal comfort in accordance with ASHRAE Comfortclass “A”. (computation: J. Schnieders, PHI).
Optimal thermal comfort is established when the heat released by the human body is in equilibrium with its heat production. Fanger's comfort equation is derived from this fact. It creates a relationship between the activity (e.g. sleeping, running…) and clothing as well as the determining factors for the thermal surroundings, which are as follows:
There is a complete range of combinations of these four comfort factors where the level of comfort is very good, this is known as the comfort range. It can be determined by Fanger’s equation, documented in ISO 7730. Furthermore, according to this standard it is essential that
Regarding the last point, P.O. Fanger writes: “the more irregular the thermal field in a room is, the greater the expected number of dissatisfied people.”
It is exciting that by the requirements of the passive house standard all comfort criteria are automatically optimally fulfilled - substantially improving the thermal insulation simultaneously improves thermal comfort. This can be understood as follows:
The practical consequence: With highly insulating external construction components, the temperature of the interior surface is only slightly different from the other temperatures in the area; this applies both in summer and winter. In the winter, the interior surfaces of the external construction components are comfortably warm (external walls, roofs etc. at the most 1 °C under the ambient temperature, window surfaces maximally 3 to 3.5 °C under it [ 1 ]). The definition of “Passive House quality” windows is straightforward: The insulating efficiency of a window suitable for Passive Houses must be so good that under the coldest design conditions, the equation:
θ area - θ Oberfl ≤ 3.5 °C
still holds true. These small temperature differences have the following affects on the comfort criteria:
Because all of the comfort criteria are fulfilled, without the need for a compensatory radiation heating surface, everythere in the Passive House there is “automatically” a radiant heat climate, independently of how the heat is supplied. More still: since there are no large temperature differences, air movement remains small. The results represented here are documented in the publication [ 1 ].
The comfort characteristics of well insulated buildings can be observed in practice and is confirmed by three independent research results: