The DBB Project

Project Description

Highslide JSThe aim of the project is to demonstrate and further develop a clean, low carbon approach to building construction and operation known as Dynamic Breathing Building (DBB). 

CALA’s Hazledean house in Balerno is the world’s first DBB.  In a departure from the conventional, the house was fitted with a DBB roof system comprising around 400 Energyflo™ cells between timber rafters that, together with an extract Mechanical Ventilation Heat Recovery (MVHR) system, should significantly reduce the carbon footprint of the house that is associated with space heating and cooling

A key feature of the DBB approach is that the building shell or façade can, if desired, retain conventional form and appearance.  T o the observer there would be nothing unusual about the look of the building when viewed both externally and internally. This is a significant departure from the status quo, as the reduction in energy use is achieved through a design solution that is integral to the building structure and not an after-market add-on. 

It is thus possible to have an energy efficient building without being required to make is look different. The sketches and plans show a house that fits in with the CALA design tradition and target market.

Cells in roofs

To incorporate the Energyflo™ cells into the construction a system had to be devised to get them into the house quickly and efficiently. As the CALA house in question was substantially designed it was decided to trial a roof-mounted DBB system rather than the walls as this required little modification to the build process. To fit the cells into the roof the depth of timber had to be increased slightly so that the cells could be fully accommodated without affecting the bracing required between rafters in the roof structure.

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The CALA Hazledean house included an MVHR unit in its original design. It was therefore necessary to collect the air flowing through the roof-mounted cells to supply the MVHR unit.  The fresh incoming ventilation air is preheated first as it passes through the Energyflo™ cells by conduction heat recovered and then further preheated as it passes through the MVHR unit by heat from the warm exhaust air from the house. Beyond the MVHR unit, the air is moved as per the standard CALA system with ducts going to and coming from various points around the house.

To provide a system for mounting the cells and collecting ventilation air the FastTray mount system was developed. The trays, which ran the length and width of the space between roof rafters, were made of pre-cut and folded twin-wall polycarbonate sheets that were both light and strong. The trays were sealed to prevent the incoming air from flowing other than through the cells to the duct take-off point on the underside of the trays that was provided for this purpose. Additionally there were end pieces which sat flush on the roof base and came together to with the opposite tray on the other side to provide a seal between the indoor and the outdoor environments

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Air supply

In order to complete the system the air had to be collected from each to the trays and supplied to the heat exchanger for the next stage in the process. In the CALA house, flexible ducting was connected between the exit point on each of the trays and a central duct that ran the length of the attic designed to allow an equal pull through each of the trays and so an even draw of air across the tray assemblies. Once the air was gathered it was moved by a jockey (booster) fan. This small fan was installed to account for the extra resistance to flow that the dynamic system could place in comparison to a simple air supply drawn directly from outside. An in-line silencer was fitted to prevent any noise from the DBB system getting through to occupants over and above the standard CALA heat exchanger ventilation system.

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The complete system

The complete system is shown in the above roof cross section diagram.  This illustrates  how air supplying the MVHR unit comes through the FastT ray cell assemblies before being ducted in to ventilate the house. The exhaust air flowing through the MVHR unit is exhausted conventionally from the house.
The relative complexity of the DBB system used in the CALA project house is compatible with the research nature of the project, where the intent was to observe performance at the level of individual trays and cells . Future commercial deployments of the roof system would be much simpler, to achieve the desired performance at a fraction of the cost.

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Sponsors The University of Aberdeen EBP Cala Carbon Trust