Construction and function: Passive houses (PH) are a rather simple construction because they are at least nothing else than highly insulated buildings combining a medium insulating thickness of about 30 cm and triple-glazed windows. Heat losses are reduced in so far that the ventilation with integrated heating recovery system transports the remaining inflow of heat. Heaters and a conventional radiator system are no longer required, here cost saving can serve as partly refinancing of higher expenditure for additional insulating and ventilation. The annual heating energy need amounts to less than 15 kilowatt hours per square meter, corresponding to 1.5 litres heating oil. Conventional buildings need on average more than 200 kilowatt hours per square meter and year, low-energy houses still between 30 and 70.
Architecture: In principle no architectural restrictions regarding shape and form or selection of building material are given. A basic requirement is a compact functional style of the buildings with the lowest possible proportion between surface and volume which serves also as a cost saving factor. Passive house standard is also achievable with an unfavourable surface/volume-proportion but then requires better insulating layers. Therefore it is most difficult to achieve the passive house standard for solitary detached family houses with conventional surface/volume-proportion. With an increasing building volume the surface/volume-proportion decreases simultaneously.
Technical equipment of buildings: In principle passive houses are equipped with a comfort ventilation with integrated heat recovery system. Natural earth heat exchangers to increase the temperature of the outer air are additionally required in combination with heat pumps for used air. These kind of ventilation is often part of low-energy-houses, whereas it is only of additional character within passive house technology. All well-known technologies are suitable for passive houses. The very low consumption of heating energy results in high investment expenditure - also for infrastructure like a gas supply system - but on the other hand regular expenses are radically reduced. This fact is worth to be considered for evaluations of economic efficiency and might initiate further developments.
Comfort: The extremely insulated building layer leads to a very balanced temperature increasing the thermal comfort. Normal draught - often arising at large double-glazed windows with corresponding reactions at the cooler inner window panes - is not known. The filtered outer air shows a lower amount of dust and pollen leading to specific advantages for persons suffering from an allergy. The comfort in summer depends on the quantity of glass surfaces and on the efficiency of sun protection. Regarding their comfort passive houses normally outstrip conventional buildings.
Hygiene: Tests of the Freie Universität Berlin prove that the endotoxin content of filtered air (endotoxin escapes during bacteria destruction) is lower than from outer air. Only after a filter has been used for more than 12 months an increase of endotoxin was determined. This proves that a properly maintained ventilation results in better air quality than window airing. Corresponding tests in passive houses confirm this theory.
User habits: Passive houses do not demand a specific habits of the users and the technical equipment is not more extensive than for conventional buildings. The user has to set only room temperature and ventilation intensity. Additional window airing is also possible, e.g. if needed after intensive smoking, but is not useful on cold days because the heating performance cannot achieve a 20°C temperature. Only criticism of some passive house users are rather high temperatures in sleeping rooms in winter because the passive house technology allows only low temperature differences among the interior rooms.
Energetic amortisation period: The primary energy need to build the passive house Darmstadt Kranichstein was determined at 1,391 kilowatt hours per square meter. Out of this only 14% are allotted to insulation and only 2% to ventilation, the lion's share of 51% to the shell of the building. Comparing the additional energetic expenditure for passive house construction with those of low-energy-houses, the former pays for itself after 2 years thanks to heating energy saving.
Hindering factors: Passive houses need a construction without thermal transmitters and a high tightness of the building ensuring a fresh air inflow by means of the ventilation and not via any gaps. Both requires a high carefulness within planning stage and construction. Predominantly the qualification of architects and building contractors, and an adequate quality management are of decisive importance for the further dissemination of passive house technology.
Renovation: First ideas tend to achieve the passive house standard also for conventional buildings in the course of renovation measures. This is theoretically possible but requires more restrictions than within the construction of new buildings. Most of all energy saving technologies are planned for new buildings and only to a small scale for renovated ones. A similar development is to expect in passive house standard. Even if this is not fully achievable within existing buildings it is likely that the insulating standard can be further improved by the development of passive house technology and the corresponding construction parts or -components.
