Primary energy use worldwide breaks down approximately as follows: 42% for construction, 32% for transport, 24% in industry, 2% for agriculture. In buildings in Belgium, about 50% of the energy is used for heating. The need for heating comes from: the need to compensate for heat losses by conduction through walls, floor and roof ; the need to heat fresh air, continuously entering the building. To reduce the part of the energy consumption associated with heating, buildings must first be better insulated. However, this insulation generally leads to an increase in the tightness of the building and, consequently, in the need for ventilation. In addition, the recent NBN D50-001 standard on building ventilation itself is more demanding in terms of fresh air supply and exhaust air flows. The recovery of heat (sensitive and/or latent) from the stale air leaving the building to the incoming fresh air makes it possible to meet ventilation requirements without affecting energy consumption. This heat recovery is done through heat exchangers whose generic problem is to cross 2 fluids (fresh air and stale air) without mixing, while maximizing the exchange surface between these 2 fluids. The various dual-flow systems on the market today are all characterised by the need for cladding, which makes them expensive and difficult to reconcile with renovation needs.