Heating and Ventilating

Building services are the single most adapted elements of a building during its lifetime. Glan Blake-Thomas explains how underfloor air conditioning helps solve spatial, comfort and energy efficiency issues in renovating existing commercial buildings
Underfloor air conditioning solutions deliver greater flexibility, adaptability and re-usability when retrofitting and refurbishing commercial buildings. Not only can taking your air conditioning underground help cut the lifetime costs of commercial buildings, but it can also enable existing office space to be effectively recycled without automatically increasing first cost.

AT&T have indicated that in the 40-year life cycle of a building only 11 per cent of the cost is accounted for in its original construction, 14 per cent in its financing, 25 per cent in modifications made during its use and a vast 50 per cent in its operation. Often reducing first cost increases reconfiguration costs.

With these percentages in mind, it is worth reflecting on the imbalance currently placed on the importance of initial costs over the far greater running, modification and operational costs of a commercial building. Where is the value in passing on the cost of cheap, inefficient design to future tenants instead of bringing real value for money over the lifetime of a building? Designers in the main assume that to reduce life cost one must spend more at the construction phase. This need not be the case.

Flexible modular approach

The key to achieving these savings has been a modular, more flexible approach. We are all familiar with raised access floors and the flexibility they bring to cable management. Typically, these more efficient buildings make use of the raised access floors for cable distribution, but have also used the access floor as the main distribution route for all services, including duct free comfort air-conditioning. Such solutions achieve high standards of flexibility and air quality with modular components that can be quickly and easily re-configured should the internal environment change because of office churn.

We call it a Flexible Space System. This approach will also deliver benefits in retrofitting and upgrading existing buildings for modern office needs, particularly where height of space is limited.

It is important to remember that some 10-20 per cent of the energy used in buildings over their lifetime is in the form of embodied energy incorporated in materials and in the process of building itself. Demolition also brings with it the huge problem of an ever increasing volume of building materials, which need land fill sites and incinerators while involving major energy costs to transport the waste. So, instead of demolishing a building and starting again, it is far more environmentally considerate to recycle buildings.

And yet, older office buildings often need air conditioning to offer comfortable working conditions. Retrofitting air conditioning in this type of building can be tricky with a typical fan coil, VAV or split system air-conditioning requiring the creation of a false ceiling, often in the region of 450mm - 600mm depth.

Since many older style offices do not have sufficient headroom to allow such installation, the result can be either major, expensive structural changes or, if this is impossible, building demolition followed by new build construction.

If the floor void acts as a plenum to distribute conditioned air to the office space then this problem is solved. Using a raised access floor of 200-300mm instead of a false ceiling for air-conditioning, ventilation, cable and power distribution services brings a net height saving per floor of approximately 200-300mm, by eliminating the 450-600mm needed in the ceiling for ductwork to service the air conditioning.

Fine examples of this can be seen at Bloomberg in Finsbury Sq and Tricorn House in Birmingham.

In this approach, each floor of the building is divided into a number of zones, depending on the potential use and occupancy density of the area. Each zone is then supplied with chilled or warmed air by a conditioned air module (CAM). The underfloor void is split into supply and return air plena using easily relocatable, airtight baffles. Air travels back to the CAM for re-conditioning via return air grilles located over the return plenum.

Fan tile units recessed into the floor void as part of this system draw up supply air from the plenum into the occupied space. Since these fan tile units are not restricted by duct or pipe connections, they are easily interchangeable with floor panels in a matter of minutes. This allows for easy reconfiguration of the system to accommodate changes in office layout with minimum cost and disruption, again helping to keep whole life costs as low as possible should new tenants take over the space.

Looking down towards the floor instead of upwards towards the ceiling as the home for HVAC services demands a very obvious change in perspective. But it is a change that brings real benefits over the lifetime of a building, right from its initial cost of construction or renovation through to its modification and operation.

The Flexible Space System is already proven to deliver these benefits in high profile projects across the globe with landmark installations at the Platinum LEED Certified Parkview Green in Beijing; Kuala Lumpur's Menara Telekom building and Hong Kong's Nina Tower, among many others. A change in perspective can help us achieve equally impressive whole life cost savings in considerably more new-build and retrofit schemes across the globe to the benefit of consultants, contractors, their clients and the tenants who, ultimately, occupy the space.

The author is managing director of AET