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A heated exchange

technical & practice An office refurbishment in Ipswich satisfies the requirements for air tightness together with background ventilation

Dynamic insulation (DI) is sometimes called 'pore ventilation' and has been used in timber-clad and timberframed buildings in Scandinavian countries since the 1960s. It is the principle by which air is pulled or pushed through the insulated structure of a building, due to air pressure differentials on either side. Usually, a fan mounted at high level creates the pressure difference within the interior, to draw air in.

Effectively using the building itself as a thermal store, the air entering through the insulation layer 'captures' heat, which is attempting to leave the space. Heat exchange takes place, thereby improving the effective U-value of the insulation and tending to bring the heatout/heat-in dichotomy to a 'steady state' condition. In theory, the Uvalue achieved through DI would tend to zero. Not all walls of a particular building may be appropriate, for various reasons. For example, the insulation material must be porous, as the incoming air is passed through it, and picks up heat stored in the structure. But the more that the surface area of a building is designed to satisfy the dynamic insulation specification, the more costand heat-efficient it will be. Similarly, multi-faceted buildings - offices with atria, which expose more surface area to external air, for example - also benefit more from the principles and efficiencies of dynamic insulation.

To ensure that drafts are eliminated, air-sealing the building, especially around windows and doors, is essential. In the light of the requirements of Building Regulations Approved Document Part L, dynamic insulation usefully resolves the paradox between air-sealing and controlled ventilation.

Recovery systems The energy saved by not having to heat the internal space as much as would otherwise be necessary if no heat exchange took place, must exceed the energy of the fans, in order to make DI a viable proposition in terms of capital investment.

Air flow of approximately 0.5-5m/hour is sufficient to accommodate heat recovery. So very low power is needed to facilitate the system's operation, as both fan speed and energy consumption are low.

The fan exhausts the drawn air, and is fitted with a heat exchanger to recover the heat from the newly warmed incoming air.

Pro-flux dynamic insulation is the label applied to the process of air movement, as described above;

flowing in the same direction as the heat flow. Contra-flux dynamic insulation concerns air moving in the opposite direction to the heat flow.

Negative pressure, (drawing air into the building - the usual application process for DI), benefits from the insulation acting as a filter on the incoming air, thus providing a cleaner source of delivered fresh air than opening a window.

For a responsive and efficient system, the air supply - reliant on mechanically induced air pressure differences - should be linked to a building management system (for monitoring and control), to ensure that the fan is responsive and adaptable to changing external pressures and temperatures.

Making the upgrade The Environment Agency's (EA) existing buildings in Ipswich, Suffolk, date from the early- to mid-'70s and are in a poor state of repair. The contract works have been broken down into three distinct phases:

Phase 1 - convert the store building into offices. This scheme is effectively new build work, as the structure was the only non-office building and in a very poor state of repair. It is to be totally gutted and its external structures will be stripped down to the basics and reclad.

Phase 2 - refurbishment of the existing main office building. This building is a steel-framed structure, encased in concrete, with a brick/block wall at ground level and asbestos-coated profiled steel sheet ('Galbestos') on the blockwork inner leaf, (similar to the stores building), with a pitched roof over an original built-up felt, flat roof.

Phase 3 - refurbishment of the secondary concrete framed, brick/ block cavity-walled office building, to provide better facilities and general improvements.

The brief was to upgrade the buildings cost-effectively, but in a way that can be applied to other EA building stock of a similar nature.

The work, which includes a full space-planning exercise, and an audit of accessibility compliance, is intended to take more than two years, and will be carried out while the buildings are in occupation. By providing an open-plan environment (in lieu of cellular desk arrangements) airflows are impproved. By utilising the store building as office space, the architect has provided respite for the staff from their temporary accommodation in demountable units and badly insulated blocks.

Chris Exley, project architect with The Charter Partnership, says that both he and the rest of the design team 'wanted to make the structure, fabric and services work together'. It was a desire for holistic thinking that led to a retention of the good points (like the blockwork thermal mass inner leaf ), and which has potentially resulted in a strategic way of assessing design issues. The architect is looking to formalise this approach to design.

Monitoring the dynamics The low-level cavity wall to the stores will be retained and filled with insulation. Above this height, the Galbestos will be removed, and the new structure will comprise 125mm softwood studs with a 12.5mm plasterboard inner lining. The studs will be infilled with cellulose insulation, with a 9mm panel-vent outer board, overlaid with 50 x 38mm treated vertical battens, clad with 150 x 25mm untreated cedar board and StoRender feature panels.

Exley says he 'didn't want to reinvent the wheel', and consulted Gaia Architects, which has worked on several projects with dynamic insulation. Gaia Architects has the empirical data on the air-flow rates required and consequent energy savings, and The Charter Partnership has adapted the specifications (which provided the best results elsewhere) to suit the conditions.

The building will be monitored as a matter of course, so that empirical energy data can be compared with previous energy expenditure.

CREDITS

CLIENT The Environment Agency ARCHITECT QUANTITY SURVEYOR Downey & Warren STRUCTURAL & CIVIL ENGINEER Richard Jackson Partnership DYNAMIC INSULATION CONSULTANT Gaia Architects CONSTRUCTION COSTS Approximately £2 million START ON SITE September 2002 CONTRACT COMPLETION 2003 AREA 2,500m The Charter Partnership, Ipswich ENERGY & SERVICES CONSULTANT The Energy Practice

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