The very first zero-energy houses which were built in the 1970s required complicated and costly technical systems. Today however, experience with low-energy houses has shown a more practical and easier approach: cost-efficient highly insulated houses without any heating systems, called Passive Houses, constitute the standard of the future.
Passive Houses are simple, reliable in operation, user friendly and comfortable. Until recently, even experts didn't expect that the solution to the environmental problems relating to energy use for space heating could be so simple. Against this background, the energy-autarchic house has also become feasible - although the effort is still very high, further advancements are expected.
Considerable progress has been made in the short time since the first Passive House prototypes were built in the early 1990s, especially in relation to windows and ventilation technology. Further developments are under way. The energy-autarchic house is still too expensive and complicated for implementation in areas with an electricity supply and its ecological benefit is dubious.
Since the 1970s some architects and scientists have been trying to achieve the objective of a “zero-energy house” [KORSGAARD 1976] , [HÖRSTER 1980] , [SHURCLIFF 1981] . The task of reducing all of the energy consumption of a house down to zero is a very demanding one, and up till now it has only been achieved in a few costly pilot projects. Although the zero-energy house is technically possible, it is not yet implementable in terms of affordability.
Experience has led to a relatively modest objective: the low-energy house (LEH) proved to be a more cost-effective and simpler standard which could be implemented quickly. Low-energy houses have an annual heating demand of less than 70 kWh/(m²a) based on the living space. Their heating energy consumption is thus about two-thirds less than that of an existing building.
In Sweden at the beginning of the 1980s numerous low-energy houses had already been built for research and demonstration projects. This standard was so successful there that in overfulfilment of the construction standard, mainly low-energy houses were being built even up to the mid-80s. With the “Nybyggnadsregler” in 1991 the low-energy standard became compulsory. For many years already it has been a political objective of the country to achieve independence from fuel oil.
The Energy Saving Regulation (EnEV) of 2010 that is currently valid in Germany corresponds roughly with the standard for low-energy houses. However, in Germany too, the standard of construction today is better than that required by the government regulations.
| The stacked columns shown for the Passive House represent
the measured values of the Passive House in Darmstadt
These values are typical for today's third-generation Passive
Houses too if energy-efficient household appliances are used.
See also Primary energy – quantifying sustainability
|Comparison of the primary energy demand for various energy standards.|
The annual heating demand in Passive Houses is only 15 kWh/(m²a). They should be planned using established methods and built cost-efficiently; excellent thermal insulation, prevention of thermal bridging, airtightness, triple-pane low-e glazing and controlled home ventilation with heat recovery are all very essential. This makes it possible to dispense with a separate heating system. The existing ventilation system can be used for the distribution of heat which can be provided simultaneously by the hot water supply system.
The maximum annual demand for primary energy in the Passive House is also fixed; this includes the power for pumps, ventilators, lighting and household appliances, as well as the energy required for heating and hot water. Currently, the limit for residential housing is 120 kWh/(m²a).
For the implementation of the Standard on a wide scale it is essential for architects, specialist enegineers and trades professionals to acquire qualitatively high-level advanced training. In order to achieve this, the Passive House Institute has developed opportunities for advanced training for certified PassivhausPlaner in cooperation with other European partners.
The range of innovative building products (glazing with low U-values, insulated window frames, prefabricated building components for the prevention and reduction of thermal bridges) facilitates the rapid implementation of this Standard. Products that meet these requirements are awarded a certificate (see Certification -> Certified products) by the Passive House Institute.
By applying additional measures, the Passive House can be further developed into a “zero-heating house”:
A zero-heating house is a building that has an annual heating demand of 0 in an average year. Even on the coldest of days there should be no need for auxiliary heating in such a house.
Advanced development is associated with increased effort
According to experience, continuing energy conservation through improved standards is becoming increasingly complex.
- based on an ordinary new construction (70 kWh/(m²a)), it is comparatively easier to achieve the Passive House Standard with 15 kWh/(m²a).
- However, the last 15 kWh/(m²a) require so much expenditure, that in the Central European climate this is financially unjustifiable: it is not possible to recover any further investments any more because the Passive House already dispenses with the need for a separate heating system.
Nevertheless, for the first time, the Passive House in Darmstadt-Kranichstein demonstrated that it is already possible to realise the zero-heating house today with justifiable extra costs, just by implementing further passive measures. In 1994, in one of the accommodation units, insulated sliding shutters were additionally built in, which could be closed at night in the winter and thus reduced the window U-value to below 0.3 W/(m²K).
Due to this additional reduction in the heat losses, the auxiliary heating could be switched off completely, thus the house was “heated” solely through the passive use of solar energy and the few existing internal heat sources [FEIST 1995] . With a further reduction in the internal heat sources, e.g. due to more efficient lighting with the latest generation of LEDs, this option becomes less relevant. In any case, the use highly efficient electrical appliacnes and lighting is crucial, as both are in use year-round, including during periods when extra sources of internal heat are undesirable.
With progressing development of the Passive House components it will become easier to build zero-heating houses in the future. This progress can easily be associated with the Passive House standard. Admittedly, one can ask whether the further reduction of the almost insignificant 15 kWh/(m²a) to “exactly” zero has any economical or ecological significance. The house still requires an electrical connection - today, no-one wishes to be without a refrigerator, washing machine, dishwasher, lights and the internet.
The question of cost-efficiency arises even more acutely for the most demanding of the standards being dealt with here: the “energy-autarchic house”.
An energy-autarchic house doesn't require any supply of energy from outside the premises - apart from the naturally occurring energy flux (solar radiation, wind, ground water if applicable).
Energy-independence does not only relate to heating but also to all energy applications in the building, therefore hot water provision, ventilation, and household electricity also have to be provided autarchically. There is no mains connection or fuel delivery.
That such a building is technically possible today was proved by the Fraunhofer-Institute for Solar Energy Systems in Freiburg with its energy-independent solar house [STAHL, VOSS 1992] . This house obtains its remaining energy demand for the provision of hot water via solar collectors and its electricity from a photovoltaic system; in winter this is obtained from fuel cells that burn hydrogen which has been electrolytically generated in the summer and stored.
|Energy-autarchic house of the ISE in Freiburg|
Even if – as shown – energy-independent houses are technically possible today, it is doubtful whether they will be practicably relevant in the foreseeable future. Whatever methods of energy provision from fully regenerative sources on the premises are used, it is necessary to over-dimension the energy generation and seasonal storage. In both cases, this is not only financially unjustifiable, but also ecologically dubious, because a significant initial investment in terms of energy is still necessary for all additional systems.
This applies as long as it is possible for a building to connect to an energy network (e.g. electricity mains) with justifiable effort. The mains network can deal easily and cost-efficiently with many of the tasks which, if autarchically achieved, are only possible with unreasonably great effort:
- the mains network compensates for fluctuations in energy demand by a statistical distribution of consumers;
- the mains network can accommodate excess supply and transmit it to other consumers or storage with frequent cycles;
- regenerative electricity generators can be operated in economically meaningful units in the mains network (e.g. 1 MW wind power stations, biomass combined heat and power plants);
- for single houses, seasonal storage in large storage units is more cost-effective than in small units.
It therefore seems to be more reasonable, even in the more distant future, that houses should be grid-coupled and not autarchic, so that if necessary, any surplus regenerative energy that is produced can be fed into the mains network.
This trend is expected to intensify in the future, that is why hardly any energy-autarchic houses were built; instead “plus energy houses” were built which generate energy on the premises (e.g. through photovoltaic systems) and feed it into the mains network and from time to time also draw energy from it; but during the course of the year, more energy is fed into the network than is taken from it. See also this technical paper on Primary energy input.
It is noteworthy that total consumption values achieved with the Passive House Standard are so low that the supply of regenerative energy is technically possible and can even be economically justifiable thanks to the feed-in compensation for regeneratively-produced electricity.
This has been demonstrated many times: the carbon neutral Hannover Kronsberg Passive Houses settlement (german abstract) in Kronsberg has bought shares in a wind power station at a price of about 2500 € for each house in addition. The total (mean annual) energy consumption of the houses is compensated for by the generation of renewable energy. Data monitoring for this housing development has shown that the energy supply really is climate neutral.
A high level of energy-efficiency is a prerequisite for the use of regeneratively produced energy. Because this can be improved even more with regard to the electricity consumption even in the Passive House, the opportunities for renewable energy will continue to increase in the future.
It is expected that low-energy houses will become the general minimum standard for new constructions in Germany in a few years. For their widespread implementation it is essential that further training opportunities are provided for all those who are involved with construction. The Passive House is an extreme version of the low-energy house in which a separate heat distribution system is no longer required due to the excellent thermal protection (15 kWh/(m²a)). An increasing proportion of new constructions in the next few years are expected to be realised as Passive Houses.
Zero-heating houses require considerably more constructional effort compared with Passive Houses, without significantly lessening the impacts on the environment. In the future, this effort can be reduced due to progress in development, especially of windows. However, in the foreseeable future, energy-autarchic houses will have no obvious environmental advantage over concepts which draw their remaining requirement from the existing supply network and feed regeneratively-produced energy back into the network. The better the energy efficiency of the utilisation systems and buildings is, the more opportunities for renewable energy carriers there will be.
[ELMROTH, LEVIN 1983] Elmroth, A.; Levin, P.: Air Infiltration Control in Housing - A Guide to International Practice; Swedish Council for Building Research, Stockholm D2:1983
[FEIST 1988] Feist, Wolfgang: Forschungs- und Demonstrationsgebäude Niedrigenergiehaus Schrecksbach; Institut Wohnen und Umwelt, 1988
(Research and Demonstration buildings – Low-energy house in Schrecksbach; Institute for Housing and Environment, 1988)
[FEIST 1994] Feist, Wolfgang: Forschungsprojekt Passive Häuser; Institut Wohnen und Umwelt,1. Auflage 1989, 2. Auflage 1994
(Research Project Passive Houses; Institute for Housing and Environment ,1st Edition 1989, 2nd Edition 1994)
[FEIST 1994] Feist, Wolfgang; WERNER, Johannes: Gesamtenergiekennwert < 32 kWh/(m²a); Baubl, Februar 1994, S.106-110
(Total heating demand < 32 kWh/(m²a); Baublatt, Februar 1994, pages106-110)
[FEIST 1995] Feist, Wolfgang: Erfahrungen mit Häusern ohne aktives Heizsystem; in: IBK, Jubiläumstagung 200, “Stahlbeton” ohne Stahl? Wärmedämmung “statt” Heizung?; Darmstadt 1995
(Experiences with houses without an active heating system; in: IBK, Jubilee Conference 200, “steel-reinforced concrete” without steel? Thermal insulation “instead of” heating? Darmstadt 1995)
[FEIST 1996A] Feist, Wolfgang: Grundlagen der Gestaltung von Passivhäusern; Verlag Das Beispiel, Darmstadt,1996a
(Fundamentals of Passive House Design; Publisher: Das Beispiel, Darmstadt,1996a)
[FEIST 1996B] Feist, Wolfgang (Hg.): Das Niedrigenergiehaus; Karlsruhe, 4. Auflage 1996b
(The low-energy house; Karlsruhe, 4th Edition 1996b)
[FEIST 1997] Feist, Wolfgang: Messergebnisse zur Nutzerstreuung des Energieverbrauchs bei ausgewählten Bauprojekten; in: Protokollband Nr. 9 des Arbeitskreis kostengünstige Passivhäuser, Darmstadt, PHI, 1. Auflage, November 1997
(Measurement results for user distribution of the energy consumption in selected building projects; in Protocol Volume No. 9 of the Research Group for Cost-efficient Passive Houses, Darmstadt, PHI, 1st Edition, November 1997)
[FINGERLING 1995] Fingerling, Anne: Eine neue Fenstergeneration; glas+rahmen 18/1995, S. 970-972
(A new generation of windows; Glazing+frames 18/1995, pages 970-972)
[HESSISCHES MINISTERIUM FÜR UMWELT 1991], [HESSISCHES MINISTERIUM FÜR UMWELT 1993] Energie und Bundesangelegenheiten; Institut Wohnen und Umwelt: Passivhaus Darmstadt Kranichstein; Dokumentation, Wiesbaden, 1. Auflage 2/91; 3. Auflage 10/93
(Hessian Ministry for the Environment; Institute for Housing and Environment: The Passive House in Darmstadt-Kranichstein; Documentation, Wiesbaden, 1st Edition 2/91; 3rd Edition 10/93) see also in Pasipedia The world’s first Passive House
[HÖRSTER 1980] Hörster, H. (Hg.): Wege zum energiesparenden Wohnhaus, Hamburg 1980
(The way to an energy-efficient home, Hamburg 1980)
[KORSGAARD 1976] KORSGAARD, V.; BYBERG, M.R.; ESBENSEN, T.V.; BILDE, K.; HARBOE, K.P.; HELWEG-LARSEN, K.; NYGAARD, I.; KJERULF-JENSEN, P.: DTH-Nul-Energihus; Danmarks Tekniske HOjskole 1976
(The zero-energy house; Technical University of Denmark 1976)
[LOGA 1996] Loga, Tobias: BHKW für Niedrigenergiehäuser - das Beispiel Niedernhausen; Institut Wohnen und Umwelt, 1996
(Combined heat and power stations for low-energy houses - The Niedernhausen Example; Institute for Housing and Environment, 1996)
[RASCH & PARTNER 1995]: Ökologischer “Weitblick” am Rheinhöhenweg; Rasch & Partner, Steubenplatz 12, Darmstadt, 1995
(Ecological “farsightedness” at Rheinhöhenweg; Rasch & Partner, Steubenplatz 12, Darmstadt, 1995)
[ROHRMANN 1994] Rohrmann, Bernd: Sozialwissenschaftliche Evaluation des Passivhauses in Darmstadt; Institut Wohnen und Umwelt, Darmstadt 1994
(Socio-scientific evaluation of the Passive House in Darmstadt; Institute for Housing and Environment, Darmstadt 1994)
[RUDOLF, RUDOLF 1994] Rudolf, H.; Rudolf, R.: Haus ohne Heizung; Deutsche Bauzeitung (db) 128 (1994) Nr.12, S. 122-126
(The house without heating; Deutsche Bauzeitung (db) 128 (1994) No.12, pages 122-126)
[SHURCLIFF 1981] Shurcliff, William A.: Super Insulated Houses and Double Envelope Houses; Andover, Massachusetts,1981
(Super Insulated Houses and Double Envelope Houses; Andover, Massachusetts,1981)
[STAHL 1992] Stahl, Wilhelm; VOSS, Karlo: Das Energieautarke Solarhaus; Institut für Solare Energiesysteme, Freiburg 1992
(The energy-autarchic Solar House; Institute for Solar Energy Systems, Freiburg 1992)