Plenum Air Conditioning for Refurbishment and Retrofit Projects — AET Flexible Space
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Plenum Air Conditioning for Refurbishment and Retrofit Projects

A major design challenge for refurbishment case studies is how to incorporate high specification heating and cooling into buildings designed long before air conditioning of commercial buildings became a reality.  In the UK we have a large amount of older building stock requiring modernisation. 

Often developers will strip these buildings back the core, add modern construction materials and facades to improve aesthetics, but will still be left with the original floorplate and structure.  These structures can present a number of challenges with respect to height and available space to integrate essential building services required in order to cater to ever growing demands of tenants of modern workspace today.  In this article we look at these challenges in more detail in line with the application of Under Floor Air Conditioning to these buildings as a solution to provide heating and cooling for said buildings.


At this point it is fitting to give a general description of how plenum air conditioning works.  In brief; fully conditioned air is fed into the underfloor plenum by zonal downflow units (CAM).  The supply air is then introduced into the space via floor recessed fan terminal units (Fantile).   Spent return air can be returned to the CAM for reconditioning either at floor level or at high level depending on the configuration of the CAM.  The equipment is modular and flexible allowing easy adaptation and future change.  This also makes it an ideal choice for speculative CAT B fit out work; as the primary units can be installed during construction phase and it is quick and easy to install additional floor terminals according to tenant requirements.

Height Saving with UfAC

Making use of the plenum beneath a raised access floor as the ventilation duct is an obvious space saver.  To give an example; the floor void is usually in the region of 150 – 200mm, and a ceiling based air conditioning system typically requires a void of 600-700mm; bringing the total services space requirement to 750-900mm.  By adopting an underfloor system with floor level supply and floor level return, ceiling ductwork and lateral pipework can virtually be eliminated.  A floor void of only 250-300mm is required to accommodate the cabling and fan terminals, equating to increased headroom of 200-400mm in this example.  Where the slab to slab height is severely restricted, a slimline fan terminal unit which only requires 180mm floor void space can be used.  It is therefore easy to see the suitability of such systems with respect to refurbishing older building stock.

Tricorn House, Birmingham

Tricorn House, Birmingham

AET Flexible Space; a leading authority on underfloor systems have worked on a number of refurbishment casestudies over the past 25 years and pride themselves on the bespoke level of product and specification advice given to developers and designers working with older buildings.  Tricorn House in Birmingham is one example of a long running phased refurbishment where AET supplied underfloor equipment to one of twelve floors back in the early 2004 and are currently delivering equipment for the final floor to be completed this year.  The iconic building with its unusual floor plate shape has been fully refurbished over a twelve year period by Commercial Estates Group and AET Flexible Space equipment was originally specified as an option that would bring cooling to the inner areas of each deep space floor area, whilst maximising headroom with a restrictive 2.8m slab to underside slab height.  Over the years the system has proved to be adaptable and flexible for the multi-tenanted building easily accommodating increasing cooling load requirements through higher density and occupant demand.  Another key feature was the addition of fresh air units which introduce fresh untreated air at floor level to the CAM downflow units significantly reducing plant space riser and maintenance requirements.

20 Cannon Street, London

Cannon Street

In London, AET have worked closely with developer Allied London on two further buildings which have undergone extensive refurbishments; 20 Cannon Street, near St Paul’s Cathedral and 28 Savile Row in prestigious Mayfair.  Cannon Street was the first project to use AET’s slimline Fantile incorporating EC fan technology.  The 1960’s building had very limited structural height space and retrofitting a fan coil, VAV or split system would have required a ceiling void of up to 450mm; an option that was not viable.  Under floor air conditioning was specified and as a result, the recommended floor to ceiling height of 2.5m was achievable; whilst also creating modern high class office space.  The building had been empty since 2008, but was fully pre-let to a corporate client as a headquarters building just at the stage of completion testament to the Grade A space created.

28 Savile Row, London

Savile Row

At 28 Savile Row, an 18th Century building originally part of the Burlington Estate; Allied London embarked on another extensive refurbishment comprising a full internal strip out to the core, demolition of structural partition walls, removal of redundant mechanical and electrical services and plant as well as complete removal and replacement of the façade.  AET Flexible Space equipment was installed on each of the six floors comprising one zone per floor.  Slimline EC fan terminals were also specified to fit into the shallow 180mm floor void.  An additional space and energy saving feature of this refurbishment was installing Daikin 2-pipe heat pumps on external platforms adjacent to each floor removing the need for a central plant.  The heat pumps were fully integrated and controlled with the air conditioning system.

The casestudies cited above are just a few examples of how underfloor systems can adapt to buildings of all shapes, sizes, age and stage of construction.  Plenum air conditioning is not considered mainstream such as ceiling based systems and as a result is frequently overlooked by designers and engineers as an unknown quantity.  AET Flexible Space systems are proven to have the capability to fit all buildings, adapt to changing use of space and combine this with modularity and ease of maintenance, it can a future proof solution for challenging casestudies with a long operating life.

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