The air we breathe
- 1. Building Services FEATURE Air we breathe taken for granted by Patrick Durrant T he president of the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE), William Bahnfleth, sees a critical shift in thinking from a goal of indoor environments that are acceptable to occupants, to a fundamental obligation to provide indoor environments that are truly healthy and productive, while conserving resources. Compliance with building ratings schemes generally means that the air breathed by the majority of building occupants is of an acceptable standard, however this less than optimum air quality has a significant effect on performance and long-term health. Outdoor air is the only source of ventilation supply air but this fresh air is generally contaminated with motor vehicle emissions, including diesel particulates from trucks and buses. Building filtration systems are generally designed to remove the larger particulates but not the gases, and so our lungs become the final filter. Dr Ronald Wood, director of Innovative Plant Technology, stresses that the non negotiable goal for sustainable buildings must be to provide healthy, pollution free air to building occupants. The drive for energy efficiency without sufficient regard for building occupants can have significant adverse economic consequences for both building owner and tenant. Although it looks like a green wall, active botanical air filtration is a high efficiency system with no leaks, no bypass and no filter changes. Its closed loop system is self-regulating, self-repairing, with no toxic residues and operates 24/7 in the dark as well as the light. Contaminated air is drawn through the planted wall, transferred from the gas phase to the plant root biofilm and metabolised by the associated micro-organisms before returning as clean, uncontaminated air back to the breathing zone. It has excess capacity to supply clean, unpolluted air equivalent to 80% of the required outdoor air supply for an office space, resulting in reduced energy costs from lower ventilation rates, reduced maintenance and replacement of fans and filters. According to Wood, direct source control with air filtering is the only method to capture contaminants at or near the source. Australian Standard 1668 1.2.2012 The use of ventilation and air conditioning in buildings Part 2 Appendix D allows cleaning recirculated air to provide equivalent dilution effect, ie equivalent outdoor air, but this still delivers less than optimum indoor air quality. The three critical components of indoor air quality (IAQ) management are generally source control, dilution and air cleaning. Source control Low volatile organic compound (VOC) construction materials are important, however there are no regulations of chemical emissions from commonly used building materials. Some industry associations have developed environmental certification schemes but their legal standing is in doubt. Dilution Wood says the conventional approach to diluting the toxicity of the air by increasing ventilation rates is only treating the symptoms, not the cause; substantially increasing capital, operation and maintenance costs. In addition, this approach results in little appreciable improvement in breathable air quality, as some indoor chemical reactions occur faster than the ventilation rate. Air cleaning Most building filtration systems dont remove gaseous pollutants or ultrafine particles. Upgrading existing heating, ventilation and air conditioning (HVAC) systems to high efficiency particulate air (HEPA) filtration usually requires a complete refit of the air handling system due to potential leakage from mismatch of filter frames and increased energy consumption from the higher pressure drop (>250Pa). Complementing the HVAC filter system, active botanical air filtration reduces unwanted gaseous pollutant and particle recirculation. This results in typical system pressure drops of less than 75Pa with the reduction in high ventilation rates leading to a potential 20% energy saving. Biofiltration of the air circulating within the building envelope provides unpolluted, clean, cool air, reducing the need for 20-30% outside air to be conditioned. This provides savings on energy costs and contributes to thermal comfort by an average decrease in temperature of 0.5属C an effective way of achieving ASHRAEs goal of a healthy indoor environment while saving resources. A living green wall in Umow Lais Melbourne office Photo: Ronald Wood Engineers Australia | December 2013 57