In was common practice in the inter-war years of the twentieth century, for special large cross- section ducts to be included in residential buildings, in addition to the common ventilation and plumbing shafts, as well as, in the chimneys. In residential houses, such shafts were fitted with small windows that could be opened for inspection and access. These technical features provide identical physical and thermal dynamics and effects to the core principles of a high-tech ground heat exchanger, as used in today’s modern passive houses. Ventilation shaft windows located in the individual apartments in these earlier buildings were designed to provide cool air flow in the hot summer season and warm air throughout the winter months.

In was common practice in the inter-war years of the twentieth century, for special large cross- section ducts to be included in residential buildings, in addition to the common ventilation and plumbing shafts, as well as, in the chimneys. In residential houses, such shafts were fitted with small windows that could be opened for inspection and access. These technical features provide identical physical and thermal dynamics and effects to the core principles of a high-tech ground heat exchanger, as used in today’s modern passive houses. Ventilation shaft windows located in the individual apartments in these earlier buildings were designed to provide cool air flow in the hot summer season and warm air throughout the winter months.