Warm homes bring winter cheer

Collaboration between the Fraunhofer Institute for Solar Energy Systems ISE and several other industrial partners has led to the development of habitable ‘passive’ solar housing.

‘Passive’ solar houses are designed to supply a large part of their energy requirements with the solar power they capture; whilst the rest is provided by an innovative and compact technical system.

Passive solar houses are built in such a way that as little heat as possible is lost through walls and windows. In addition to the thermal insulation incorporated in the construction of the house, this also calls for controlled ventilation of the building.

The passive use of solar energy alone is said to be enough to reduce a home’s annual heating requirements – in the temperate climate of central Europe – from an average of ten litres of oil per square meter to the equivalent of one litre.

In order to generate the remaining requirements, the company Maico HaustechnikSysteme provided a new and compact ventilation device.

‘The system recovers heat from the exhaust air in combination with a heat pump. In this way it provides an intake of fresh, warm air and – as a backup to the solar collectors – serves to heat household water,’ said Dr. Christel Russ. ‘There is no need for other forms of space heating, such as hot-water radiators.’

Heat is distributed throughout the buildings together with the fresh air brought in by the ventilation system and an acceptable temperature is attained in three stages.

First, the air is led through pipes buried in the ground, which raises the temperature slightly. A further increase in temperature is provided by a plate heat exchanger: the air extracted from rooms passes on a large part of its energy to the pre-warmed fresh intake air. On cold days, the required temperature is reached with the help of a heat pump, which extracts further energy from the exhaust air.

Tests on seven houses during the winter of 1999 showed that total energy consumed amounted to a tenth of the value recorded for so-called ‘low-energy’ homes.

More on the web at www.ise.fhg.de/