Low-energy House in the Alps

by the CADDET Swiss National Team

Click here to view: Shading diagram of the house in Göschenen

Click here to view: Comparison of horizontal solar radiation with and without skyline profile

Introduction

Owing to the varied topography of the Alps, some regions are so strongly shaded by the mountains that, in extreme cases in winter, no sunshine reaches them at all. The construction of a house in such a strongly shaded location, using a minimum of energy and making maximum use of solar radiation, represents a major challenge to the architect and the energy engineer.

The Challenge

The house described in this article shows that even with only 32 minutes of sunshine during a day in December, passive exploitation of solar energy in Alpine regions is feasible.

Solar radiation in the Swiss Alps in winter is considerably greater than in the central plain. This is mainly because of the low stratus cloud typically covering the central plain during the winter months. The higher regions of the Alps offer ideal conditions for active and passive solar applications. Two major problems, however, have to be overcome:

  • In the higher regions, the ambient temperature is usually much lower than in the central plain. Thus, although solar radiation in the winter months is generally higher, more energy is needed to keep the building warm.
  • Owing to the varied topography of the Alps, some regions are strongly shaded by the mountains. In extreme cases, there is no sun at all in winter.

The House in Göschenen

Göschenen lies on the Gotthard motorway and is the last town before the Gotthard tunnel through the Alps. Owing to the low outside temperatures and frequent cold outbreaks in this very mountainous region, the inhabitants are often obliged to heat their houses in summer.

In addition to the very cold weather conditions in Göschenen, the building site suffers from a high skyline profile. In winter, the solar radiation is so strongly occluded, that on the shortest day in December, the sun shines for only 32 minutes.

In constructing a low-energy house under such extreme conditions, a well thought-out energy design concept and a well-conceived architectural design, that also takes account of local conditions, are essential.

Energy Design Concept

The limited solar radiation available in the winter months severely restricts the opportunities for passive application of solar energy. Thus first priority in the energy design concept must be given to minimising energy losses. The roof and wall are designed for a U-value of about 0.14 W/metres squared K, and the windows, which are triple glazed, have a U-value of about 1.1 W/metres squared K. In addition, a mechanical ventilation system with heat recovery from the spent air ensures that ventilation losses are kept as low as possible.

The heating system has been designed to enable solar collectors to be added at a later time. At present, the necessary auxiliary energy during the winter months is supplied by a wood-fuelled boiler.

Passive Solar Design

To keep the auxiliary energy requirements down, great importance was attached to the architectural design of the house. The design must ensure that despite a high skyline, the greater part of the heating energy in the summer months is provided by solar radiation.

The house was constructed on a south-facing slope at an altitude of 1,120 m above sea level. The house has a ground plan of 9 m x 9 m. To avoid having a single facade facing towards the south, the axis of the house was rotated by 45 degrees from due north. This enables the windows facing south-east and south-west to make full use of incident solar radiation at the beginning and end of the heating season. Solar buildings are normally provided with large overhanging rooves to prevent overheating in summer, but here the protrusion of the roof has been kept to a minimum.

The building consists mainly of prefabricated wooden sections. Thus, most of the fabrication work could be done in advance, enabling rapid erection of the building on site. However, in comparison to concrete, wood has the disadvantage of a lower heat storage capacity. For this reason, the floor is designed in the form of a combined wood and concrete structure. This enables building mass to be increased at the point where this is most needed, namely where it can best absorb the incident solar radiation.

By these means, it was possible to ensure that passive solar energy provided a major fraction of the energy needs in the building (about 50%). In combination with the wood needed for auxiliary heating, the building in Göschenen can be heated to 100% by renewable energy. Domestic hot water is heated using the wood-fuelled boiler in winter and by electricity in summer.

Economics

The modular construction and prefabrication have kept down the additional costs resulting from the high standard of insulation. In fact, the additional costs of the energy-saving measures (insulation, recuperation system and triple glazing) amounted to only SFR50,000 (where SFR is the Swiss franc). These costs are balanced out by massive savings in energy consumption. In comparison, total building costs were SFR680,000. Compared with a building insulated according to the standard stipulated in current regulations, 7.9 metres cubed of wood per year can be saved.

Fuel

Maximum allowed by regulations

House in Göschenen

Saving

Wood [metres squared]

10.1

2.2

7.9

Oil [litres]

1,720

370

1,350

For more information contact the CADDET Swiss National Team in Brugg.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.