Chilled ceilings and beams can protect the environment by working with it
The temperature of water drawn from boreholes in the ground or ground coiils can enable it to be used to provide cooling using chilled beams and ceilings with little, if any, mechanical cooling.
Growing numbers of services engineers are building chilled beams and ceilings into their designs in the search for more innovative and flexible low energy solutions, says Alan Green.The market for chilled beams is growing far faster than most other building-services sectors, with BSRIA expecting a 40% increase in 2007 compared with 2006. Legislation is clearly having a major impact, Part L of the Building Regulations in particular, but engineers are also seeking ever-more innovative ways of reducing the carbon footprint of buildings as clients wake up to the climate-change challenge and their goals for corporate social responsibility. This rapidly changing market background creates an unprecedented opportunity for building-services engineers to demonstrate their ingenuity. Earlier this year, for example, London South Bank University received a special award from the Carbon Trust for its development of an ingenious solution for cooling the Underground rail network. 30 Mt of groundwater are pumped out of the Tube every day to prevent flooding. The university engineers designed a method for diverting that groundwater at around 12°C through heat exchangers to provide sustainable cooling for the tunnels and platforms. ‘Low grade’ groundwater is an underused source of energy-efficient cooling for a wide range of applications. In the case of London Underground, engineers would solve three problems at a single stroke by using a bit of imagination. They tackle the serious problems caused by overheating on the network, with temperatures forecast to rise above 42°C on deep-level lines next summer, which will force temporary closures on health grounds. They also ease flooding problems caused by a rising water table. All problems are tackled for a very low energy penalty. London Underground admits it is spending thousands of pounds a year on energy just pumping this water out of the tunnels and is delighted at the prospect of avoiding that cost and diverting the water to better use. Creative
This kind of creative thinking is just what engineers are looking for to reduce energy costs in buildings. Conventional air conditioning is under increasing pressure because of the large amounts of energy it consumes cooling chilled water the to very low temperatures (5 or 6°C) required by all-air and fan-coil systems. Chilled beams, on the other hand, work extremely well with higher chilled-water temperatures of 12 to 14°C from naturally sourced groundwater. This combination can, in some cases, provide ideal comfort conditions to a commercial building with minimal use of mechanical cooling. Across London, engineers are looking at sites where boreholes can be drilled to extract groundwater for cooling and heating. The location of hundreds of 19th century wells has also been mapped to see if they can be re-opened to avoid the cost of new drilling works. Ground water is becoming big business, and its combination with chilled beams could be the ultimate sustainable building-services solution. However, chilled beams and ceilings are also coming into their own thanks to a range of other benefits that make the design engineer’s job easier. For example, the energy-efficiency ratio (EER) of a chiller rises to about seven with chilled beams because chilled water is delivered at 13 or 14°C compared with the 6 or 7°C required for fan coils. That higher EER amounts to an overall improvement in energy efficiency of around 15% over conventional air conditioning. Using groundwater as the main source of chilled water or running dry coolers in the winter enables chillers to remain idle for large parts of the year, further increasing savings. The designer will need to provide for de-humidification of the ventilation air, but this can be achieved with a small supplementary chiller. Flexibility
The absence of moving parts means chilled beams are far quieter than conventional air conditioning and also last far longer and require minimal maintenance –— so lifecycle costs are much improved. Increased cooling capacity can be delivered by using active beams, which enhance the induction of room air through the cooling coils. These can also be adapted to offer heating as well as cooling. ‘Multi-service’ beams integrate other services such as lighting, smoke detectors and BMS outstations. These are usually pre-fabricated offsite, so offering the further benefit of simplifying and speeding up the installation of building services. Architects also appreciate the greater flexibility afforded by such an unobtrusive cooling system that slots neatly into ceiling systems. Fresh air is provided without draughts, so occupants work in a healthier and more comfortable environment, and there is less chance of ending up with the classic office complaint of some people being too hot and others too cold. Overheating buildings is an increasingly troubling issue, but it must be tackled without driving up energy costs. Chilled beams and ceilings provide an elegant solution in tune with today’s environmental situation that satisfies many of the criteria for truly sustainable engineering. Alan Green is chairman of the Chilled Beam & Ceiling Association.