15 years Passive House in Darmstadt - Kranichstein
Directory of the Informations on Passive Houses
Deutsche Version der Publikation

15th Anniversary of the Darmstadt -
Kranichstein Passive House

Factor 10 is a reality

by Dr. Wolfgang Feist, Passivhouse Institute, 2006 Sept.

The translation of this page was made available by support of Intelligent Energy Europe

1 From Low-Energy Buildings to the Passive House

The highlight of the 1980's was the low-energy building which was a legally required energy standard for new buildings in Sweden and Denmark. At that time, many elements necessary for reducing building energy consumption had been developed, i.e. thick insulation, minimized thermal bridges, airtightness, insulated glazing and heat recovery ventilation. From this basis, the "passive House" concept was developed in May 1988 by the author host Professor Bo Adamson during a research stay (in the field of building construction) at the University of Lund/Sweeden. Bo Adamson continued to pursue this development with the author until his retirement. The photo below shows the two together with Robert Hastings, one of the pioneer American architects, during an evening meeting of the 2nd Passive House conference in 1998 in Duesseldorf.

Left to right: Bo Adamson, Robert Hastings and Wolfgang Feist 1998 / 2. Passive House Conference Duesseldorf

"Passive Houses" were defined as buildings which, in the Central European climate, have an negligible small heating energy requirement and therefore need no active heating. Such houses can be kept warm "passively", using only the existing internal heat sources, solar energy admitted by the windows and by heating the fresh air supply. The theoretical proof for the feasibility of such houses was furnished in the thesis, "Passive Houses in Central Europe" through computerized simulations of the energy balance of buildings [Feist 1993]. In this paper, construction elements which determine the energy consumption of buildings, were systematically varied and optimized based on energy efficiency, installation expense and living value. The results in the following diagram show the influence of window size and glazing qualities as an example.

Simulation results stood at the beginning: Here a calculation of the dependence of the heating energy requirement in a Passive House on the size of the southern window area for different glazing qualities (from [Feist 1993]). It's clear that Triple-Pane low-e glazing is necessary for favorable energy balances in this climate (bottom curve). Dr. Ortmanns, at that time VEGLA, Aachen, helped us create this glazing for the first building project, the Passive House Darmstadt Kranichstein. Since that time such glazings have become market available in Europe.

It was quickly realized that the energy optimization for buildings should not be limited to heating energy: all household energy consumption must be minimized. Otherwise it would be possible, for example, to reduce the heating energy requirement to "zero" by using inefficient electrical devices which create high internal gains (such as incandescent light bulbs). At the time, the exact amount of internal heat gains in a typical house was unknown. Careful measurements of the built Passive House revealed that this amount is approximately 2 W/m² [AkkP 5]. Nevertheless, even today, most national energy standards still count on too optimistic high values (over 5 W/m²).

Photo passive house Kranichstein sun (573 KB) 
Passive House Darmstadt Kranichstein - southern facade  (see more Photos)
Architect: Professor Bott, Ridder, Westermeyer. Photo: H.G. Esch.

2 Research Prior to the Demonstration Project

To prepare for the building of the first Passive Houses in Hessen, a scientific working group was formed, financed by the Hessian Ministry for economics and technology (HMWT). The minister of economics at that time, Alfred Schmidt, brought large interest to the development. The working group performed eight research projects, whose results were used directly in the construction of the first Passive House at Kranichstein. Among other things several architectural drafts were developed, research was done to improve the efficiency of ventilation heat recovery, the proper amount of ventilation for good air-quality was determined, new highly thermaly insulated window frames were developed, design details for the connection of different construction elements with only small losses due to thermal bridges were designed and a waste-water heat recovery concept was tested.

The city Darmstadt promptly stated its interest in the realization of the first Passive House project in the context of "experimental housebuilding Darmstadt Kranichstein K7". Four private owners formed the Passive House owner community and commissioned the architects Professor Bott/ Ridder/ Westermeyer for the planning of a four unit row house with each unit having a floor area of 156m². For this first Passive House the prototype components, whose forerunners had already worked in low-energy buildings, were developed further [Feist 1988]. Only by using all of these components together it was possible to reach the ambitious objective of nearly eliminating the heating load - however, these components were not economical at the time because they had to be handmade. The additional costs compared to conventional construction were offset by 50% by the Hessian Department of the Environment. During construction in 1991, in order to later evaluate its performance, the house was equipped with highly precise, data recording monitoring devices.

Light flooded open areas in the first passive house. Photo: H.G. Esch.

3 The Passive House in Kranichstein

The emphasis of the Passive House design and construction is heat conservation: Thermal Insulation and heat recovery ventilation are the crucial components. That still applies to the Passive Houses built today. Beyond that a solar domestic hotwater system and a ground-coupled fresh air preheater were used. The house has an extremely good thermal insulation, which in the 16 years since occupancy, has worked outstandingly.

Building Element





Grass roof: Humus, filter fabric, root protective membrane,
50 mm formaldehyde-free chip board, wooden I-Joist rafter
(Flange made of dimensional lumber, web mad of high density fiber board), framing, polyelthelene airtightness barrier, gypsum plasterboard 12.5 mm,
wallpapers, painted with emulsion paint, entire cavity (445 mm) filled with blown-in mineral wool insulation.


Exterior walls

Fabric reinforced external plaster;
275 mm of expanded polystyrene insulation (EPS)
     (installed in two-parts, 150+125 mm);
175 mm sand-lime brick masonry;
   15 mm continuous interior gypsum finish; wallpapers, painted with emulsion paint


Basement ceiling

Fiberglass reinforced plaster skim coat;
250 mm polystyrene -insulation;
160 mm on site concrete;
  40 mm of polystyrene acoustic insulation;
50 mm cement floor finish;
8-15 mm of parquet, adhesive; sealing solvent-free



Triple pane glazing with Krypton filling
     Ugvalue 0.7 W/(m2K).
Wooden window with polyurethane foam insulated framework (CO2foamed, HCFC free, handcrafted}



Counterflow air-to-air heat exchanger;
Located in the cellar (approx. 9°C in the winter), carefully sealed and thermally insulated, the first one to use electronically commutated DC fans.

recovery efficiency
of approx.

Table: Design features
of the Darmstadt Kranichstein passive house

A blower door test resulted in an n50value below 0,3 h-1. When the building was tested again in October 2001, we result was that airtightness had not diminished [Peper 2005]. Thermographic photos show that the buildings are free of thermal bridges. A documentation of the construction of the house with numerous photos is in the conference proceedings of the first Passive House Conference [ PHI 1996 ]. A description with first measurement results was published in the paper "Passive House Darmstadt Kranichstein" [ Feist 1997 ].

The hot water is heated using a vacuum tube solar collector (5.3 m² for each household or 1.4 m² per person). Secondary heating is done using natural gas. The solar thermal system provides about 66% of the hot water used in the house. Because domestic hot water represents the highest energy draw of this house, an efficient hot water distribution network is of great importance so the pipe network was designed to be compact, within the thermal envelope, and well insulated.

View of the North side of the passive house at Darmstadt Kranichstein. Photo: Feist.

For the first Passive House at Darmstadt Kranichstein we did not yet dare to do without radiators. However, this and following projects proved that the maximum heating loads in the Passive House during the winter were less than 10 W/m² of floor area. Therefore the heat load can be comfortably supplied using the fresh ventilation air, eliminating the need for seperate means of heat distribution. These results agree with the simulation, however not with typical heat load calculation procedures. This was a reason to systematically revise the heating load calculation during a research project [ Bisanz 1999 ]. The resulting, straightforward procedure is available for planners in the Passive House Planning Package [ PHPP]. The following figure shows the comparison of the heating energy balance calculated in PHPP for a conventional buiding which meets the requirements of the EnEV (existing since 2002), and the Passive House at Darmstadt Kranichstein. The modelled value for the Passive House of 10,5 kWh/(m²a) is in good agreement with the measured value.

Performance of an row-end house meeting the current national energy standard in Germany (EnEV). A heating energy requirement of 58 kWh/(m²a) was computed using PHPP

  This calculation for and end-row unit from the Passive House at Darmstadt Kranichstein was calculated with PHPP. Heating energy was determined to be 10.5 kWh/(m²a) what is very close to the actual measured values.

In 1995 Amory Lovins, the American energy efficiency pioneer [ Lovins 1977 ][ Lovins, Weizsaecker 1995 ], visited the Passive House at Darmstadt Kranichstein. Lovins contributed substantially to the developmnet at this stage, to change the concept of the passive house from scientific experiment to solid reality. He stated, "No, this is not just a scientific experiment, this is the solution. You just need to redesign the details in order to reduce the additional costs - and I'm convinced that is possible."

The very good results formed the basis for the "working group on economical Passive Houses", through which the broadening scope of the Passive House concept began 1996. Within the working group the procedures were compiled into a simplified method of planning Passive Houses - e.g. PHPP, the Passive House Planning Package [ AkkP 13][PHPP]. Pilot projects with larger numbers of Passive Houses were the second generation built initializing the development of components suitable for the passive house. The "working group on economical Passive Houses" plays a key role in the transition between building physics and building practice.

Results of heating load measurements in the passive house at Darmstadt Kranichstein; the heat load has never exceeded 7.4 W/m², not even in the particularly cold winter of 1996/1997 (see also [ Feist 1997b ]).

A Passive House in Central Europe can only function with a controlled ventilation system with very efficient heat recovery. This is because the average annual heat losses due to ventilation are 35 kWh per square meter of floor space, thus more than the double the passive house heating energy requirement. That was well-known due to investigations during the pre-building research project. Thus in Kranichstein we used a balanced (intake and exhaust air masses are equal) ventilation system with an high-efficiency counterflow air-to-air heat exchanger - but this unit had to be outfitted with more efficient fan motors. This project was the first use of DC fans with electronic commutators in ventilation systems (a.k.a. ECM). After being installed and optimized, a heat recovery ratio of over 80% was measured. This continuously operated comfort ventilation system provides a continuous supply of fresh air. In the basic ventilation level, for each dwelling, 100 m³/h of fresh air is supplied to the living and sleeping areas. In the Maxium setting, between 160 and 185 m³/h are supplied. Exhaust air is taken in appropriate quantity from the humid rooms (kitchen and bathrooms). Such high-efficiency ventilation systems had not been available before the Passive House; only beginning in 1997, when the development was initiated by the "working group on economical Passive Houses" did several manufacturers bring units of this quality to the market (heat recovery efficiency of over 80%, electrical consumption of under 0,4 Wh/m³ airflow - see the certified devices at www.passiv.de). The fans by the way provided reliable service in the Passive House for 13 to 15 years, when they were replaced during the course of routine maintenence by newer models from the same manufacturer.

External thermographic photo of the first Passive House. (Image: Feist)

The Passive House in Kranichstein was finished in October 1991 and has been inhabited since then by four families. The interior finish materials were selected to create as little indoor air pollution as possible. The insulating materials are - as it must be from a good building design perspective - isolate from the interior by continuous interior plaster and/or completly airtight membranes. The good air quality was confirmed by an investigation, which polled user acceptance in a sociological study [ Rohrmann 1994 ].

Owing to additional movable airtight sealed insulating panels in front the windows, it was possible to operate one of the housing units from 1994 to 1996 without any heating as "zero-heating energy house" [ Feist 1995].

Exact measurement of the temperatures and heat-flows of the Darmstadt Passive House provided extremely valueable scientific data. Together with an user protocol it was possible to compare measured values from the house with the results of the dynamic simulation [ 1997a Feist ]. Through this, the model basis could be verified; e.g. every detail of the procedures of the instationary thermal conduction, as well as the radiant heat in the rooms and the temperature gradients on the window glass surfaces. Thereby validating, for the first time, dynamical building models for regularly used residential buildings. (diagram: V. Sariri PHI)

Results of the energy consumption measurements in the passive house Darmstadt Kranichstein; not only the heating energy is drastically reduced ( over 90% compared to a "normal" new building of the same vintage), but also the gas consumption for domestic hot water (due to good insulation and a solar thermal collector) and household electricity consumption (by particularly efficient appliances, e.g. the "Low Energy Refrigerator" of Gram after a development by J. Nørgard).

Literature referred to can be obtained from The Passive House Institute. An explanation of the structural details of passive houses is on the internet at the site of the International Passive House Conference: From there click the link called "passive house".

4 Efficient Electrical Energy Use in the Passive House at Darmstadt

The measurements in the Passive House in Darmstadt Kranichstein confirmed: With presently available technology, the electrical consumption for household appliances can be reduced to one third of it's current average value. The additional gas consumption for applications which need heat amounts to less than 15% [ Ebel/Feist 1997 ]. Also these savings due to efficient technology have been historically proven to be stable.

5 Moving Forward: The Economical Passive House

After completion and occupancy of the first four row-houses initial tests (blower door) and continuous measurement (energy consumption, temperatures) showed very quickly that the objectives were actually reached [ Feist/Werner 1994 ]. Thus heating energy consumption amounted to:

  • 19.8 kWh/(m²a) in the first operational year 1991/92 or only 8% of the consumption of comparable dwellings,
  • 11.8 kWh/(m²a) in the second operational year 1992/93 or only 5.5% of the consumption of comparable dwellings.
  • less than 10 kWh/(m²a) on the average all subsequent years

These measured energy consumption values were so unbelievably small that they were wrongly quoted for many years in the professional world: the measured 32 kWh/(m²a) for total final energy consumption inclusive of household energy was falsely interpreted as the heating energy consumption, because this appeared rather plausible to scientific community based on mainstream developments at the time. However, the 32 kWh/(m²a) contained all purchased energy consumption of the four terraced houses including household energy, electricity consumption in the basement and gas consumption for cooking and domestic hot water heating. It is remarkable that the 90% energy conservation was reached soley through improved technology.

Even the icecold winter 1996/9, during which temperatures fell well below normal for several weeks causing comfort problems in many conventionally heated houses, it was always comfortable warm in the passive houses. Not only that, but heating energy consumption remained low (under 11 kWh/(m²a)) [ Feist 1997b ].

The first passive house in Darmstadt Kranichstein had completely fulfilled expectations. Now the focus shifted to whether the additional costs for the envelope could be lowered due to mass production. This led into the next phase of the development: Generation 2, the Economical Passive House.

6 Cost Trends and Market Penetration

Since first Passive House prototypes in Kranichstein structural extra costs for Passive Houses have been reduced by a factor of 7: from over 50,000 Euro to between 6,000 and 15,000 Euro per unit today - with a large apartment building on the lower end and a single family home on the higher end. This means that, today, Passive houses are already affordable for everyone. Thanks to the enormous energy conservation the Passive House "pays itself back" today if one accepts an average future price for heating oil or natural gas of € 6 cent/kWh. Contemporarily these fuels often cost more; the "economic gap" is eliminated and the current financial incentive programs improve the situation even more. For example the KfW bank promotes the building of Passive Houses with a low-interest loan of 50,000 Euro.

Even without the promotion, the implementation of Passive Houses has increased sharply in the last few years. About 300 dwellings were realized by the end 1999 in Germany alone, by the end of 2000 were there already 1000 and by 2006 between 6000 and 7000. Also with the 2nd Generation Passive Houses, the extremely low projected energy consumption values are still reached [Feist 2000]; you may find an additional document on the internet here.

But progress is not just based on quantity, because of the ever increasing number of Passive House components on the market, implementation prices are also shrinking. There is also an ever increasing variety within the realized buildings, showing that the Passive House is a standard and not a special building method. Passive Houses have been built as free standing single family homes, as row-houses and in blocks of flats. In addition, several office buildings and schools as well as a factory building have been completed.

7 Passive Houses: Very Comfortabe Too

Again, theory and practice agree, occupants of Passive Houses are very comfortable because even in a cold climate, interior surface temperatures remain high as a result of very good thermal insulation. Thus the effects of a cold and variable radiant temperature are avoided (see: passive house comfort). This was repeatedly confirmed by measurements in the built houses. The feedback from these houses are positive, statements such as: "we have never frozen", "we would definitely build a passive house again", "we have never been so comfortable" have been the norm.

The sun provides considerable heat (interior thermographic photo with sun shining).
COMFORT is largely written in the passive house. (IR-photography: Feist)

In the case of the passive house, higher efficiency leads to higher comfort. "Saving Energy" should not be viewed as a negative, rather it is a positive solution for increased envrironmental protection and increased prosperity. The time to make key improvements is now. This also applies within other areas of energy use, e.g. transportation. Improved efficiency without sacrificing travelling comfort is the goal of the "Loremo" project, which is working on a marketable solution.

We are pleased that many architects, planners, product developers and owners are following the Passive House concept. If together we accelerate the implemenation, includingh the rennovation of existing buildings,we have a chance to protect the climate, reduce dependency on unstable sources of energy, and improve the local economy through job creation - this above all is particularly important - people will benefit by guaranteed living quality in the short and in the long term future. With the Passive House, sustainable development is possible, as Mark Zimmermann spoke of at the 9th Passive House Conference in 2005 in Ludwigshafen. [Zimmermann 2005 ]

Comparison of measured energy consumption (left) with values determined by the "Passive House Planning Package" (PHPP) for the Darmstadt Kranichstein Passive House. See: PHPP balances.

The contributions of scientists, architects, engineers and other disciplines made the Darmstadt Kranichstein Passive House a success. The author would like to express thanks to all those involved. This project was built on the results of many forerunner projects in the areas of building physics, building engineering and computer-assisted systems analysis.

(most only published in German; if an english translation is available, that is stated)

[ AkkP 5 ] Energy Balance and Temperature Behavior; proceedings NR. 5 of the Working Group on Economical Passive Houses, 1. Edition, Passive House Institute, Darmstadt 1997 (publication list, pdf, 200kB)

[ AkkP 13 ] Energy Balances with the Passive House Project Engineering Package; proceedings NR. 13 of the Working Group Economical Passive Houses, 1. Edition, Passive House Institute, Darmstadt 1998 (publication list, pdf, 200kB)

[ Bisanz 1999 ] Bisanz, C: Low supply Heating load analysis in the passive house; Passive House Institut; Specialized information PHI-1999/2; Darmstadt 1999. (publication list, pdf, 200kB)

[ Ebel/Feist 1997 ] Witta Ebel and Wolfgang Feist: "Electricity Consumption results from the Darmstadt Kranichstein Passive House" in "Saving Electricity in the passive house"; proceedings 7 Working Group Economical Passive Houses; PHI; Darmstadt, 1997.

[ 1988 ] Passive House Research Poject, Feist; Aims of the project - with a comment of the author to 2. Edition 1995, Institute Housing and Environment, Darmstadt, 1. ed. 1988, 2. ed. 1995

[ 1993 ] Passive Houses in Central Europe, W. Feist; Thesis, University of Kassel, 1993

[ Feist/Werner 1994 ] Wolfgang Feist and Johannes Werner: "total energy characteristic value < 32 kWh/(m²a)"; Bundesbaublatt 2/1994

[ Feist 1995 ] Wolfgang Feist (Hrsg.): "Insulated windows in the passive house"; Passive House report NR. 9; Institut Housing and Environment; Darmstadt, 1995.

[ Feist 1997a ] Wolfgang Feist, Tobias Loga: "comparison of measurement and simulation" in "energy balance and temperature behavior"; proceedings NR. 5 Working Group on Economical Passive Houses; PHI; Darmstadt, January 1997.

[ Feist 1997b ] Wolfgang Feist: "Approved: Passive houses in the severe winter 1996/97"; GRE Inform, 12/1997.

[ Feist 1997c ] Wolfgang Feist: "Darmstadt Kranichstein Passive House - Design, Construction, Results", Information PHI 1997/4, 1. Edition, 16 sides, (publication list, pdf, 200kB) - on english version is available

[ Feist 2000 ] Wolfgang Feist: "Objective Experiences: Results of measurement from inhabited passive houses "; in: Conference volume to 4. Passive house conference. Passive House service GmbH, 1. Edition, Darmstadt 2000

[ Lovins 1977 ] Amory Lovins, "Soft Energy Paths"; (english) Harmonsworth 1977

[ Lovins, Weizsaecker 1995 ] Amory Lovins, E.U. von Weizsaecker, L Hunter Lovins: "Factor Four; Double prosperity - halve resource consumption "; Munich 1995, German

[ PH conference 1996 ] conference volume of the 1. Passive House conference, 1. Edition, Passive House Institut, Darmstadt 1996 ( publication list pdf, 200kB)

[ Peper 2005 ] Peper, Soeren; Kah, Oliver; Feist, Wolfgang: The durability of air tightness layers within Passive Houses - field surveys. Research project in the context of the national participation in the task 28 ' Sustainable solar housing' of the international energy agency IEA, 1. Edition, passive house Institut, Darmstadt 2005

[ PHPP 2004 ] W. Feist; Pfluger, R.; Buyer, B.; Schnieders, J.; Kah, O.: Passive House projecting package 2004, Passive house Institut Darmstadt, 2004 (left to the description: PHPP). (english version available)

[ Rohrmann 1994 ] Bernd Rohrmann: "Sociological Evaluation of the Passive House in Darmstadt"; Passive House report NR. 11; Institut Housing and Environment; Darmstadt, Septembre 1994.

[ Zimmermann 2005 ] Mark Zimmermann: "Passive House and 2000-Watt-Society - which are the challenges of a sustainable development?" in the conference volume of the 9. Passive House conference, Ludwigshafen, PHI, Darmstadt 2005

The Passive House concept is freely available. Every homeowner can build a Passive House with a competent architect. Some prefer the notation "Ultra Low Energy Houses", but there is no definition of this standard so far. Others call it "Near Zero Emitting Houses", which is nearer to the concept. The important idea behind the Passive House is, to keep construction costs
low while building a house which can be kept comfortable using sustainable energy - although it is not required that all the energy is produced at the site. Even in future it will be less expensive to generate e.g. electricity by wind power plants or solar power plants placed at otherwise unproductive areas.

Literature can be obtained from the Passive House Institut.
An explanation of further details is on the internet at the site of the international passive house conference:
There click the link to"passive house ".