It is time to acknowledge that phase change material technology offers an effective, environmentally-friendly and viable alternative to air conditioning for new and existing buildings, according to Tony Cull.
It is generally acknowledged that in this environmentally-conscious age air-conditioning has a number of detrimental effects. One of the major factors is the power required to operate it. Typically, ac requires kilowatts of power to run. Refrigerants used are extremely hazardous to the environment. Older types deplete the ozone layer and contribute to global warming. And even newer HFCs have over 1,000 times the global warming potential of CO₂.

Contrast that with phase change material (pcm) technology, which offers real opportunities to counter the energy and environmental problems caused by the burgeoning growth of traditional air conditioning (ac) in both new and existing buildings. The application of pcm is capable of providing powered fresh air ventilation with the added capability of storing and discharging large amounts of latent thermal energy. All this is achieved using a fraction of the power (approximately 40W) required to run traditional ac systems, reducing carbon emissions and the detrimental effects usually associated with ac.

The latest phase change materials, which have a design life of around 25 years, have high heat of fusion and provide large amounts of latent heat when changing state (or phase). The same technology can also be used to provide thermal mass in lightweight buildings, achieving the same effect as a building constructed using traditional masonry techniques.

Monodraught has pioneered the application of active pcm systems and has now extended its use of the technology with the introduction of the ceiling-mounted Cool-phase system. This cooling, ventilation and heat recovery system reduces the running costs of buildings and creates a fresh and healthy indoor environment.

The use of a thermal energy store using pcm, combined with intelligently controlled ventilation, can actively ventilate and cool buildings - maintaining temperatures within the comfort zone, while reducing energy consumption by up to 90 per cent compared to conventional cooling systems.

The latent heat property of pcm stores large amounts of thermal energy, which is then charged and discharged by passing air over a heat exchanger. During summer nights cool outside air is passed through the heat exchanger, recharging the thermal energy store. As internal temperatures rise, air is passed through the heat exchanger to provide cooling. The total cooling provided is a combination of the thermal energy stored within the unit, the effects of free cooling and night time ventilation.

System works all year round

In winter, the principle works in reverse, trapping waste heat and using it to warm cool fresh air entering the building. The system works all year round to ensure a fresh and healthy environment, monitoring temperatures and CO₂ levels to automatically determine how much ventilation or cooling is required.

The tried and tested system was installed in 2009 for property company Workspace, in a commercial office space that suffered from overheating caused by high solar gains through the windows and roof. The temperatures in the offices, and an identical 'control' space, have been monitored since then, with impressive results.

Over the warmest six months of 2009 the average daily peak temperature was reduced from over 27 to 22 deg C, and an estimated saving in electricity of 86 per cent was achieved during the same period when compared to a conventional air conditioning system.

Commenting on the significant achievement, a spokesman for Workspace says: 'We anticipate that this new application of pcm technology will offer a step change in our energy and annual maintenance costs, which we will be able to pass on to our cost conscious tenants.'

More recently a system has been installed in a central London school and is already delivering substantial improvements in both temperatures and air quality. The system reduced the number of occupied hours where the temperature was above 25 deg C, from 56 per cent during the previous spring term to 0 per cent in the last summer term. During the same period the number of hours where CO₂ levels were above 1500ppm was reduced from 42 to 0 per cent.

School staff also reported that the system had a significant impact on the children's learning, improving both concentration and behaviour.

This combination of energy savings, cost savings and environmental benefits enables systems using pcm technology to meet the requirements of building regulation for thermal comfort, ventilation and energy efficiency in a single easy to retrofit system.

And since no compressors or hazardous coolants are used, such systems do not require the servicing and statutory checks required of air conditioning systems, further reducing running costs.

PCM derived cooling systems also have additional significant advantages over conventional cooling systems.

As external units are not required, systems can be used where planning permission is an issue or outside space is at a premium; systems such as our own are also modular and scalable, enabling them to be easily installed in small spaces or expanded for larger areas or densely populated environments; and they can be installed as stand-alone systems or alongside existing hvac solutions to improve their performance and reduce a building's energy usage.

• Tony Cull is managing director of Monodraught