Going underground

Looking at the significant number of mixed use and commercial buildings planned for London that have succumbed to the deepening recession, it would be reasonable to conclude that commercial developers would be in the depths of despair.  Indeed, some are.  However, many projects are still being designed in the capital and there’s a definite air of optimism amongst some of the more lateral-thinking developers. 

This may come as a surprise, at first glance – how could there be talk of investors and building owners making any sort of money with the City seemingly crumbling around us?  After all, a number of these development teams had been behind the now extinct projects that would have become key landmarks on the London skyline.

Nevertheless, it is no surprise to me that there remains an amount of buoyancy, as those with office portfolios are simply redirecting their attention.  Shelving (or being forced to shelve) new construction projects in favour of addressing the performance of existing stock, renovating and bringing building services up to date seems to some a less attractive investment over a new project. Yet, as a means of hugely raising rentable value within a current portfolio, it is now the way many developers are doing business.  The excesses of building new, it seems, fell by the wayside at the start of this new era when obvious waste is just not acceptable.


Refurbishment has without doubt become the sustainable option.  Not simply in environmental terms but in the basic economics of investment value.  Although cynics among us would point to the fact that it could be simply financial constraints and the collapse of the construction side of things that has shifted focus, efficiency, in every sense of the word, is now vital. 

What this means for building services engineers is that projects are under way but only where innovative and added-value solutions are integrated.  Building owners are facing a hugely competitive market with a tenant base that’s not willing to sign up to a long term lease and is able to select from a growing number of vacant premises.  Much of the available stock is high in energy use and totally reliant upon electro-mechanical cooling. The smart investors have realised that flexible and effective building services are the primary means of ensuring that one property stands out above another. 

This is particularly the case with thermal comfort solutions.  Yes, we want to ensure that we’re specifying the most energy efficient building services but air conditioning can never be considered entirely green.  However, for office space in our urban centres, temperature limits are frequently a prerequisite of any tenancy agreement and there are proven systems that suit refurbishment projects perfectly – both maximising energy efficiency through free cooling and those that are adaptable to a degree that ensures office churn can be swiftly undertaken – minimising vacancy periods.

Previously, when planning guidelines were less stringent and the banks were more ready to make enormous advances to speculative developers, there was less incentive to recycle commercial buildings.  Additionally, retrofitting building services with traditional solutions is difficult both practically and financially.  Many existing buildings do not have high enough ceilings to easily retrofit traditional VAV or fan coil air conditioning – ceiling voids of 600mm often being necessary – resulting in either major structural changes or consignment to a second class existence and investment value. 

However, an environmentally responsible solution acknowledged by architects and consultants as being ideal for refurbishment projects is underfloor air delivery.  Underfloor systems offer energy efficiency for the tenant wishing to keep costs capped and flexibility for the investor that needs to be adaptable to a changing tenant base, switching floorplans to meet demand and maximise the longevity of a property investment. Additionally, increased office productivity and thermal comfort satisfaction are reported in post-occupancy evaluation surveys.

Ideal for retrofit

Where underfloor air has advanced in recent years and become the ideal solution for retrofit is its adaptability – AET’s Flexible Space Concept for example, a CAM and HIVAR based system that has now been expanded to include an underfloor VAV system.  Depending on the nature of the installation, AET are in a position to offer a combination of air conditioning systems to suit.

With underfloor air, the floor void can easily be used as a plenum to distribute conditioned air to office space instead of installing a mass of ductwork and equipment in the ceilings.  Using a raised access floor instead of deep false ceiling void brings a net height saving per floor of approximately 450mm, since there is a minimal space requirement for ceiling voids. 

Coupling the delivery method with supply air either drawn up into the occupied space by fan assisted terminal units on the CAM system or through central plant fed, low terminal pressure passive tile units (PTUs) on the new PleinAir VAV system, allows for minimal intrusion into valuable net-lettable space, as well as giving the advantage of easy reconfiguration.

There are numerous examples of the effective use of underfloor air delivery in refurbishment projects. One is the 165,000sq ft Tricorn House building erected in the early 1970s that was moving towards demolition and replacement on investment grounds. By using an underfloor air delivery system with fan-assisted floor tiles, a shallow depth floor void allowed the floorplates to be brought up to modern day standards creating low energy, flexible and comfortable workplaces that have received plaudits from tenants and the landlord alike.

Low carbon package

AET’s new VAV underfloor system, PleinAir is a low carbon package with energy reduction and versatility its prime concerns.  For instance, the roof-mounted all air central plant can allow free cooling via the versatile PTUs, when the ambient temperature is less than 18?C – which is 84% of the year in non-coastal areas, on average.  Combined with the range of either square or round high induction floor grilles which provide up to 16 different air patterns of varying intensity, the Variable Air Volume and low terminal pressure (between 7 and 12.5 Pascals) makes PleinAir one of the most energy efficient cooling systems – up to a 14% reduction in running costs compared to a conventional fan coil system. Adding outdoor air volumes above the Building Regulations minimum can raise this reduction to over 60% – saving massive quantities of carbon emissions.

Overcoming the problem of discomfort traditionally associated with VAV solutions, PleinAir incorporates a unique AirSwitch damper using time modulation control – a new control technique for managing the way conditioned air is introduced into a space and an additional feature that stands PleinAir above previous underfloor VAV systems.  This new device eliminates instances of poor air distribution at part load conditions in fixed slot VAV terminals and the improvement in air distribution is immediately noticeable to users as well as lowering energy input by effective air-mixing to occupied zones. 

For investors, whole life costs and embodied energy have become increasingly important in construction and developers have been forced to adopt much more sustainable options by Legislative pressures.  Recycling rather than starting from scratch is a key way to keep a building’s carbon footprint low but, accompanied by the reality that offices users still demand high thermal comfort conditions, these must be provided in both the most efficient and flexible manner.  Underfloor air is the natural choice for these refurb
ishment needs.

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