With traditional air conditioning under pressure on many fronts, 2012 will be the year of phase change materials, writesTony Cull
It is time to acknowledge that phase change materials (PCM) technology offers an effective, environmentally friendly and viable alternative to air conditioning (AC) for new build and retrofitting.
The latter is particularly relevant today, when, with new building programmes under pressure, there is a refocusing of attention on refurbishment. Funding will still be an issue in 2012 and specifications are certain to come under pressure, with the emphasis on sustainability, reducing energy costs and easy, low-cost retrofitting.
Reduced carbon emissions
Against this background and in this environmentally conscious age, AC raises a number of concerns, notably the energy required to operate it and the hazardous refrigerants used. Maintenance and installation costs are also high.
Contrast that with PCM technology, which offers real opportunities to counter the energy and environmental problems caused by the growth of traditional AC. 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 required to run traditional AC systems, thus reducing both carbon emissions and other detrimental effects associated with AC.
The latest phase change materials, which have a design life of about 25 years, have high heat of fusion and provide large amounts of latent heat when changing state. The same technology can be used to provide thermal mass in lightweight buildings, achieving the same effect as buildings using traditional masonry.
Pioneering applications of active PCM systems have now extended the technology, with innovative, low-energy cooling, ventilation and heat recovery systems capable of reducing the running costs of buildings and creating fresh and healthy indoor environments. The use of a thermal energy store using PCMs, combined with intelligently controlled ventilation, is capable of actively ventilating and cooling buildings, maintaining temperatures within the comfort zone while reducing energy consumption by up to 90 per cent compared with conventional systems.
PCMs store 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.
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.
Installed in a commercial office space suffering from overheating due to high solar gains through the windows and roof, PCM has produced impressive results. Over the summer months average daily peak temperature has been reduced from above 27°C to 22°C. An estimated saving in electricity of 86 per cent was achieved during the same period, compared with a conventional air conditioning system.
PCM technology installed in school classrooms is also delivering substantial improvements in both temperatures and air quality. Typically, systems reduced the number of occupied hours when the temperature was above 25°C from 59 per cent during a spring term to 2 per cent in the summer term. In one case the number of hours when CO2 levels were above 1,500ppm was reduced from 42 per cent to just 2 per cent. School staff said the system had an 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 regulations for thermal comfort, ventilation and energy efficiency in a single, easy-to-retrofit system. And, since neither compressors nor hazardous coolants are used, such systems do not require the servicing and statutory checks required of AC systems.
Because external units are not required, PCM systems can be used where planning permission is an issue or where outside space is at a premium.
Tony Cull is managing director of Monodraught. He joined the company 20 years ago and was previously technical director for 10 years