|
Dynamic insulation is a form of insulation where cool outside air flowing through the thermal insulation in the envelope of a building will pick up heat from the insulation fibres. Buildings can be designed to exploit this to reduce the transmission heat loss (U-value) and to provide pre-warmed, draft free air to interior spaces. This is known as dynamic insulation since the U-value is no longer constant for a given wall or roof construction but varies with the speed of the air flowing through the insulation (climate adaptive building shell). Dynamic insulation is different from breathing walls. The positive aspects of dynamic insulation need to be weighed against the more conventional approach to building design which is to create an airtight envelope and provide appropriate ventilation using either natural ventilation or mechanical ventilation with heat recovery. The air-tight approach to building envelope design, unlike dynamic insulation, results in a building envelope that provides a consistent performance in terms of heat loss and risk of interstitial condensation that is independent of wind speed and direction. Under certain wind conditions a dynamically insulated building can have a higher heat transmission loss than an air-tight building with the same thickness of insulation. == Introduction == The primary function of the walls and roof of a building is to be wind and watertight. Depending on the function of the building there will be also a requirement to maintain the inside within a suitable temperature range in a way that minimises both the use of energy and the associated carbon dioxide emissions. Dynamic insulation is normally implemented in timber frame walls and in ceilings. It turns on its head the long accepted wisdom of building designers and building services engineers to ( “build tight and ventilate right” ).〔 It requires air permeable walls and/or roof/ceiling so that when the building is depressurised air can flow from outside to inside through the insulation in the wall or roof or ceiling (Figs 1 and 2). The following explanation of dynamic insulation will, for simplicity, be set in the context of temperate or cold climates where the main energy use is for heating rather than cooling the building. In hot climates it may have application in increasing the heat loss from the building. As air flows inwards through the insulation it picks up, via the insulation fibres, the heat that is being conducted to the outside. Dynamic insulation is thus able to achieve the dual function of reducing the heat loss through the walls and/or roof whilst at the same time supplying pre-warmed air to the indoor spaces. Dynamic insulation would appear, therefore, to overcome the major disadvantage of airtight envelopes which is that the quality of the indoor air will deteriorate unless there is natural or mechanical ventilation. However, dynamic insulation also requires mechanical ventilation with heat recovery (MVHR) in order to recover the heat in the exhaust air. For the air to be continually drawn through the walls and/or roof/ceiling, a fan is needed to hold the building at a pressure of 5 to 10 Pascals below the ambient pressure. The air that is being continuously drawn through the wall or roof needs to be continuously vented to outside. This represents a heat loss which must be recovered. An air-to-air heat exchanger (Fig 2) is the simplest way to do this. Annotation for Air Tight Timber Frame Construction Annotation for Air Permeable Wall Construction 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dynamic insulation」の詳細全文を読む スポンサード リンク
|