continued

The construction concept permits a full basement, offering common cellar rooms and 14 parking spaces. This increases the quality of exterior open spaces and allows room for a playground, generous bicycle storage, and guest parking without reducing the size of the individual gardens.

The structure consists of massive steel-reinforced concrete slabs on steel supports. The outer walls are made of prefabricated wooden elements; the inside walls are of gypsum plasterboard, except for one living unit. That unit is finished with loam plaster layered over reed mats and a wooden substructure.

Additional ecological construction measures that were selected by the contracting families are solid wood floors in all rooms, natural-resin, water-based paint, untreated larch wood shingles on the exterior, Douglas Spruce wood windows with immersion waterproofing, and untreated larch wood slat grids on all terraces.

Typical of passive houses, the well-sealed buildings have high thermal insulation values with construction details to minimize thermal bridges.

The outer wall displays two wall constructions and differing widths between windows reflecting the varying uses of the respective rooms. Architecturally, function manifests in the shape of the facade.

Ventilation Concept and Heat Supply

Virtually nothing of the heating and ventilation system is visible inside. The ventilation ducts are either suspended from the roof or floors or imbedded in the ceiling. The only reminder of the heating is a radiator in the bathroom, which the residents did not want to do without. The main advantage of a heating element in the bathroom is for quickly drying wet towels and clothing that is damp from snow. This comfort could also be achieved by electrically generated infrared heat.

All apartments have their own ventilation devices, which have been set up in niches in the stairwell. Their already minor sound emission is therefore outside the apartment. Maintenance can be performed at any time.

Filter changes are prompted by a saucer-sized control terminal in the living room. A red light starts blinking, and the "exchange filter" text is displayed. All the residents have to do, two to three times a year, is open the flap, remove the old filter, and put in the new one.

In the heat distribution system, the living, dining, work, and bedrooms are all air supply rooms. Normally, the air vents are located over the doors. In some cases, the vents are embedded in the ceiling. The halls and stairwells are upwind plenums, meaning that the air flows from the doorway, over the room, to the outside. The bathrooms and kitchen are exhaust rooms, with exhaust vents to the outside.

The outside air is brought in from a central "fresh air well" in the garden area. The air filters are easily accessible in the stairwell close to the garden. From there, the fresh air moves around the house via geothermal heat lines. The insulated fresh air ducts then branch out into three installation shafts, which lead to the ventilation devices.

In keeping with the fundamental ideas behind the passive house concept, the ventilation device used has the best characteristics with regards to insulation, electricity consumption, and ease of maintenance and operation.

The Heating System

The heat comes from a "solar twin pack": a centralized wood pellet furnace and solar collectors used mainly for water heating. This system — if equipped with a heat pump — could have handled the entire job of room and hot water heating.

Based on a parametric study of investment costs, operational costs, and primary energy consumption, the builders surprisingly chose the most expensive option. Wood was more appealing than the other two energy supply sources for heat generation: electricity and gas.

The pellet furnace is small, as if for a small single-family house, and is located in a little boiler room under one of the two houses. It delivers heat to a buffer storage tank with a volume of 660 gallons (2,500 liters). These storage tanks, one per house, are also storage for the solar-generated heat.

Solar energy is delivered from 335 square feet (31 square meters) of collectors. Their efficiency is not as good as was hoped for, and this has been attributed to faulty execution and shortcomings in construction supervision.

The thermal properties of the building were documented with detailed measurements in the 2000/2001 winter, the first time the building was lived in over the entire period from October to the end of March.

The measurements show that, with one exception, it was never colder than 68 degrees Fahrenheit (20 degrees Centigrade). The average temperature lay at 72.9 degrees F. (22.7 degrees C.) throughout the measurement period.

However, there is a discrepancy between the predicted and actual energy consumption. Possible reasons are the low efficiency of the boiler, a central heating distribution system with long lines, and increased storage losses as a result of positioning the storage tanks outside the heated area.

Other reasons for the discrepancy could be the insulation of lines that do not comply with construction guidelines and losses due to uninsulated valves and pumps. Still, the primary energy value for heating warm water and all electrical applications is over 50 percent lower than the passive house standard.

All in all, the designated goal of creating a low-energy structure for a multifamily dwelling was achieved well. It should be noted, however, that the energy efficiency potential was not fully realized. Insights from subsequent projects show that this efficiency can easily be reached with better construction quality control.

Helmut Krapmeier is an architect on the faculty at the Energy Institute and the International Solar Building School, both in Vorarlberg, Austria. He is the 2000 winner of the European Solar Prize for Architecture and Urban Building. Eckart Drössler heads an engineering office that focuses on marketing low-energy building methods. He is winner of the 2000 Austrian Environmental Prize in Research and Technology Development.

This article is excerpted from CEPHEUS: Living Comfort without Heating copyright © 2001, available from Springer Verlag and from Amazon.com.

Window Construction: Sigg GmbH, Hörbranz

Low-energy multifamily housing in Austria. Photo: Ignacio Martinez Underground parking has ensured greater open space for gardens and playground. Photo: Ignacio Martinez Lower floor plan. Image: Gerhard Zweier upper floor plan. Image: Gerhard Zweier The central stairwell also serves as air plenum. Photo: Ignacio Martinez Window detail. Image: Gerhard Zweier CEPHEUS: Living Comfort without Heating, published by Springer Verlag. Photo: Ignacio Martinez   Click on thumbnail images to view full-size pictures.