The beginning of the 20th century

At the beginning of the 20th century, houses were typically not heated: individual rooms were heated. The most common heat source in cities was an oil or kerosene stove. Some urban houses had the luxury of coal-fired central heating, though here, too, for reasons of economy, not all rooms were necessarily heated. At this time, however, much of the population lived in rural areas (agrarian society) and wood was the most common heating source. Hot water was heated on the stove top, or in a compartment in the stove, and carried to a big tin basin set in the kitchen each Saturday night (whether one needed a bath already or not).

Relative to salaries fuel was expensive and heating laborious. Fuel had to be carried to the stove. The coal furnace had to be stoked each morning and ash removed. Firewood had to be harvested, split, dried, the stove fed and ash removed. Given the cost and effort of heating, it is surprising that houses were so badly constructed. They had minimal or no insulation and were draughty. To minimize losses from leaky single-glazed windows a 'snake' pillow was laid on the window sill or 'storm windows' were hung over the primary window each autumn and removed each spring. It was a laborious attempt to slow the loss of precious heat out of the house.

These were ideal circumstances for the introduction of a means to produce hot water which required no fuel, needed no cleaning and operated with no maintenance - a solar system. American entrepreneurs took European know-how and developed the first commercial roof solar water systems. Clarence M. Kemp from Baltimore brought his Climax Solar Heater onto the market. Frank Walter improved the concept and marketed a roof-integrated system. A solar water heating industry boomed, particularly in California. Then, in the 1930s, enormous natural gas reserves were discovered, crippling the young, active solar industry (Butti and Perlin, 1980).

Passive solar energy use became a popular topic when Libbey Owen-Ford introduced insulating glass in 1935. It became possible for windows to become net energy producers in cold climates. Architects such as George Fredrick Keck from Illinois built houses with large south-facing windows and high thermal mass interiors. Measurements of the Duncan House showed that by ambient temperatures of -20°C no heating was required between 08:30 and 18:30. This was a sensation for the press.

During World War II house building went through a dormant phase. After the war energy prices fell to record low prices. Central air conditioning led to a decoupling of architecture from climate. Low energy buildings were no longer a topic.

Source: Pilkington North America, Inc

Figure I.1 House interior by George Fredrick Keck

The 1972 oil crisis renewed interest in renewable energy as a means to reduce oil dependency. The US Energy and Research Development Agency initiated a massive research and demonstration programme. Passive and active solar housing was instantly a national priority! National competitions were held, test houses and test cells were built to validate computer models, and handbooks were written. This solar movement quickly crossed the Atlantic to Europe.

At the same time, numerous pilot projects demonstrated that even zero-energy housing was possible. One famous example is the Nul-Energihus built in 1974 in Lyngby, Denmark, by Vagn Korsgaard. It combined a large active solar system with a highly insulated building envelope. At this time, windows were still a weakness compared to the thick insulation walls. The solution was movable exterior window insulating panels. During this era the solar collector industry boomed again, thanks to numerous and generous subsidy programmes.

By the 1990s, Europe had become the leader in advancing the state of low energy housing design. The topic again lost priority in the US, and as subsidies were cut off, the solar collector industry nearly disappeared while countries such as Austria achieved world records for the collector production per capita. Fascination with zero-energy houses continued. The Solar House Freiburg, built in 1992, achieved total energy autonomy through its highly insulated transparent insulation envelope, extensive area of active solar thermal and photovoltaic (PV) collectors and production of hydrogen for energy storage (City of Freiburg, 2000). This house, like all zero-energy houses of the past, was a pioneering success but not intended to be affordable in the near future. A more plausible approach was conceived by a German physicist (Wolfgang Feist) and Swedish engineer (Bo Adamson).

Source: S. Robert Hastings, NIST (1978)

Figure I.2 Test house facility

Their 'Passivhaus' prototype row houses were extremely well insulated, tightly constructed and heat was efficiently recovered from mechanical ventilation. During much of the year, these houses were self-heating. It is this very simple but effective concept which is the basis for the approach presented in this reference book.

Now, in the beginning of the 21st century, there is a growing recognition that using a non-renewable energy source will result in its depletion. In the meantime, there are now over 4000 Passivhaus projects built across middle Europe and as far north as Gothenburg, Sweden. High-performance components, formerly custom made, are now readily available on the market, including super windows, high-efficiency ventilation heat exchangers, package do-everything mechanical systems and optimized solar thermal systems. Subsidies for photovoltaic systems have resulted in their explosive growth and they are now commonplace as an architectural element.

In the near future, the most noteworthy development is likely not to be a technical breakthrough, but a market breakthrough. Some currently prototype technologies may become standard, such as vacuum insulation. Home automation systems will allow homeowners the same degree of programming control taken for granted in automobiles today. However, the biggest breakthrough is likely to be in the massive penetration in the housing market of this new generation of high-performance housing. Several influences will have to be accommodated in this process - for example, the special requirements of an aging but still active senior population. Comfort expectations will increase (particularly cooling), along with sensitivity to the energy costs of a house.

It is now a good time to plan low energy houses. The topic of sustainability is part of the public consciousness. Substituting renewable energy for expensive fossil fuel-produced energy will help to sell houses as energy prices continue to rise.

Source: W. Feist, PHI, Darmstadt

Figure I.3 The 'Passivhaus' row houses

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