Dynamic Insulation
Dynamic insulation (DI) offers a clean, energy efficient method of delivering fresh filtered air to the interior of a building or air handling unit through an air-permeable, dynamically insulated envelope or façade.
SS95 600mm square variant of the Energyflo™ cell
The integration of fabric element into the Heating, Ventilation & Air Conditioning (HVAC) system of a building offers significant benefits. Since a proportion of the exterior skin of the building is used as the ventilation source, the flow velocity through the intervening DI media required to deliver the number of fresh air changes per hour, or litres per second, is ultra low. Under such conditions, efficient heat transfer and filtration of the incoming air takes place as a function of air change rate - the dynamic effect that forms the basis for a new and readily accessible distributed ventilation system.
Expression for dynamic U-value
It can be shown that the component U-value of a dynamic breathing envelope layer is given by:
A weighted average approach may be used to calculate the overall U-value of a wall section, roof or for the whole building, to accommodate parallel heat flow paths through static elements such as structural members, doors, windows, etc. In practice, the overall U-value is dominated by the dynamic layer, as shown in the figure below for wall construction comprising 30mm timber rain screen cladding, 20mm air gap, 135mm Energyflo™ cell, 20mm air gap and 10mm plasterboard.
Dynamic U-value versus airflow velocity
The drop in U-value is due to heat normally lost to the environment being used to preheat (or pre-cool) the incoming air, and the higher the ventilation rate the more heat (or coolth) is recovered. Clearly, as the dynamic U-value tends to zero ventilation heat loss becomes the dominant factor governing power (and energy) consumption. In the context of a DBB, what this means is that a break-even point can be found at which energy efficiency is a maximum and beyond which more energy is lost with exhaust air than recovered through the dynamic envelope.
