With their high efficiency and ability to harness free cooling, chilled beams and ceilings are likely to set the new sustainable efficiency standard, predicts David Leatherbarrow.
Almost every commercial and institutional building in London has been air conditioned since the 1960s. This has not simply been due to fashion or increased luxury; in fact, it has become a necessity due to the intensive use of buildings with high occupancy rates and heat generated from office equipment and lighting.

Add to this the trend in architectural design for fully glazed buildings which allow more solar radiated heat to penetrate the building, and it is easy to see how most modern buildings in cities no longer require any heating at all, except during exceptional winters or when resuming work after a winter break.

Times are changing

However, times are changing and this is having as significant impact on the design of our hvac systems. Air conditioning was not an issue when energy was relatively cheap and the environmental and economic impact was not yet part of the agenda. Although the professional team did their best to reduce the building's energy footprint, everything was judged on an investment payback and most improvements were discounted. Saving energy did not save enough money to justify the capital investment.

For air conditioning to work, heat needs to be removed either by circulating cool air or water through terminal devices which control its distribution within the building. This heated air or water is then returned to a heat exchange system which rejects the heat to atmosphere and re-cools the circulating air or water. Of course, all this activity takes energy to circulate cool air and control the system using multiple fans, pumps and refrigeration compressors.

Energy is no longer cheap and the environment can't sustain the impact of this level of energy usage. This has changed everyone's attitude and energy awareness was heightened, even before Part L of the building regulations legislated energy standards that would enforce change.

With the introduction of environmental assessment methods such as BREEAM and LEED, and new legislative standards such as the Carbon Reduction Commitment, the demand for 'green' buildings is having a major impact on the products specified, dramatically changing the way that commercial offices are designed and constructed.

Two systems dominated

So what can be done about energy requirements for air conditioning to meet modern demands?

Two systems dominated the institutional office market for 40 years - variable air volume (VAV) and fan coil units (FCU), but for the last 15 years there has been a third alternative in the form of chilled ceilings and chilled beams.

Considering air conditioning at the design and construction stage is essential to help reduce requirements. With this in mind, we are left with a few choices: natural ventilation if the cooling is very low and the building design allows its use; chilled ceilings for medium cooling demands, and chilled beams for higher cooling capacities.
But why should these latter two systems be a preferred choice? Both require less input energy per kW of cooling achieved than previous systems, which certainly answers sustainability demands.

They use water as the heat transfer medium and the circulating water is at a temperature above the dew point of the space so the system requires less energy to cool the water.

Operational savings occur because chilled beams use higher chilled water temperatures than traditional cooling systems. This has the advantage that it allows the chillers to operate more efficiently and to take advantage of free cooling for much of the year. The raised water temperatures also enable renewable solutions such as ground water cooling to be considered.

Chilled beams and ceilings offer a more effective air supply because of their ability to recirculate air within a space. Experience has determined the quantity per person required in order to maintain good air quality to meet occupancy requirements. As a result, fewer air changes are needed so ductwork and air handling units can be smaller. This reduces construction costs while also enabling exhaust fans and chillers to be downsized or run at a lower speed. This, in turn, reduces emissions and cost in use.

Integrated service modules (ISMs), which incorporate building services such as lighting and CCTV, have at their heart chilled beam technology. This newer technology addresses whole life costs as it offers a 25-year lifespan. On top of this, the solutions can be controlled via individual building zones and can therefore help meet efficiency targets.

SAS International's own pre-fabricated ISMs are produced off-site in a dedicated manufacturing environment for delivery to site as finished units. Our in-house team designs, manufactures and installs the units, providing client certainty and a solution which is cost effective.

Lower maintenance costs

Maintenance costs too tend to be lower when using chilled beams because they contain few moving parts; there are no internal fans, no filters to clean, or actuators to repair in the occupied space, which helps ensure a trouble-free operation over their life expectancy.

As with any air conditioning solutions there is a chance that an element may need replacement and, with chilled beams and ceilings, as well as ISMs, the unit would need changing in its entirety. However, with fewer moving parts to malfunction this is a rare situation to encounter.

Studies on first cost have shown that these systems are no more expensive to purchase and install than the previous industry standard systems. They are inherently cheaper to operate, so the question has to be why are these types of systems not being installed in the majority of today's new buildings and being aggressively retrofitted.

Clients, developers and letting agents are familiar with the cost of historic systems and are comfortable with their benefits and disadvantages. However, Part L of the buildings regulations will mean change is inevitable.

I predict that chilled beams and ceilings will set the new sustainable efficiency standard.

• David Leatherbarrow is director of SAS International