This article was published in Oct 2014, Building Review Journal Vol 29 No. 5.
INDOOR AIR QUALITY AND VENTILATION
Air is a basic human need of course, but the quality of that air is vital. Just as we instinctively feel that ‘sea air’ or ‘country air’ is cleaner and fresher than the air in our cities, so the air quality in our places of work varies, and can have a significant impact on health and resulting productivity.
Office occupants can be exposed to a range of airborne pollutants that typically include chemicals, micro-organisms and particles originating from sources both within and outside the building. Ozone, offgassed volatile organic compounds (VOCs), allergens and asthmagens make for a veritable cocktail of potential pollutants that may come from building materials, carpets, finishes, cleaning products, office equipment and traffic; while the carbon dioxide exhaled by office workers themselves can be detrimental when left to amass in high concentrations.
The various health implications associated with poor indoor air quality – from respiratory problems to infections to irritants – have been the subject of research for a long time and are well established. But as we better understand the impacts, so our understanding changes on what is considered acceptable or desirable. Design strategies that ensure good air quality are a pre-requisite for a healthy and productive working environment. Although both are important, there is distinction between ensuring a supply of fresh air through ventilation, and stopping pollutants at source by minimising the ‘offgassing’ of materials, both of which are discussed below.
HIGHLIGHTS: KEY RESEARCH
Seminal research in 2003 identified 15 studies linking improved ventilation with up to 11% gains in productivity, as a result of increased outside air rates, dedicated delivery of fresh air to the workstation, and reduced levels of pollutants.
A meta-analysis in 2006 of 24 studies– including 6 office studies – found that poor air quality (and elevated temperatures) consistently lowered performance by up to 10%, on measures such as typing speed and units output. This analysis appeared to demonstrate that the optimum ventilation rate is between 20 and 30 litres/second (l/s), with benefits tailing off from 30 up to 50l/s. This is significantly higher than minimum standards required, which are typically between 8-10l/s (although these vary considerably by country).
Similarly, in a 2011 lab test which mimicked an office, a range of office-related tasks were carried out with the presence of airborne VOCs. Increasing ventilation from 5l/s to 20l/s improved performance by up to 8%.
Reduced absences may also be a key indicator of the benefits of good indoor air quality for businesses. Short term sick leave was found to be 35% lower in offices ventilated by an outdoor air supply rate of 24 l/s compared to buildings with rates of 12 l/s in a 2000 study. The same study estimated the value of increased ventilation to be $400 per employee per year.
CO2 levels are one way to measure air quality, and can occur as a result of poor ventilation. High CO2 levels have been found to impact tiredness or decision-making in a number of studies. One recent lab-based study using simulated decision-making tasks showed CO2 having a significant detrimental impact (11%-23% worse) at 1000 parts per million (ppm) compared to 600ppm, despite 1000ppm being widely considered acceptable.
The greater the height available above the occupants’ breathing zone, the greater the space available for ‘stratification’, i.e. temperature gradient, which is beneficial for both natural ventilation and low level air supply/displacement ventilation. This also impacts cooling strategies, and users’ perception of space through the ‘look and feel’.
Volatile organic compounds (VOCs) are chemicals commonly used to produce building materials, furnishings, fittings, adhesives and sealants. The familiar smells of a freshly painted room or newly installed carpet are all from VOCs and your instinct to open a window is correct. While some VOCs and other toxins do not have a noticeable odour, these smells are generally telltale signs that less than healthy chemicals are in your midst. It can take months or years for the compounds to completely ‘off-gas’ and these chemicals can persist long after their smell fades.
There are long established links between building materials and human health, from the formaldehyde found in particle board to the asthmagens found in some kinds of paint, flooring and interior finishes. Fortunately, products such as low and no-VOC paint and green certified furnishings and other fit-out components are available in many markets. Environmental Product Declarations are an important element of transparency. The well-considered selection of healthy finishes and furnishings goes hand-in-hand with adequate ventilation rates to ensure good indoor air quality and should be implemented as part of any sustainable fit-out and ongoing purchasing program.
DESIGN STRATEGIES: GOING FOR GREEN
Increasing fresh air
Outdoor air renews oxygen for breathing and dilutes pollutants. Increasing ventilation rates to the sorts of levels suggested in some of the key research above provides a real challenge for designers, if it is not to lead to significantly increased energy usage. The decision whether to naturally ventilate, provide air conditioning, or a mixed-mode system is a complex one, and relates closely to thermal comfort.
Air conditioning and ventilation systems can provide fresh air rates above those required by the prevailing local standard. This is recognised by dedicated credits for increasing fresh air rates in many green building rating tools. However, this must be balanced with strategies for mitigating any associated increase in energy demand to ensure a balanced approach.
There are many experts who argue that in appropriate climates, a mixed-mode system allows for optimal outcomes for both occupants and energy use. A comprehensive analysis by Carnegie Mellon concluded that natural ventilation or mixed-mode conditioning could achieve 0.8 – 1.3% savings on health costs, 3 – 18% productivity gains, and 47 – 79% in HVAC energy savings, for an average ROI of at least 120%.
As global temperatures climb and urbanisation continues apace in rapidly developing countries, one of the absolutely key challenges for designers of green, healthy buildings is how to ventilate and cool offices in warm climates without a massive increase in energy use. It points to a clear need for further innovation in design and ever more efficient systems that minimise energy use.
Limiting pollutant sources
Rather than simply diluting pollutants, it may be more effective and energy efficient to reduce pollutants at source. Strategies to minimise the sources of pollutants include dedicated exhaust ventilation to print rooms, photocopiers and laser printers (that emit ozone) and the specification of low and zero emission carpets, finishes and adhesives. (See ‘cross-cutting’ box for more information.)
There is also good evidence to support the indoor air quality benefit of certain indoor plants, which scrub specific pollutants from the air, when located in the breathing zone of office workers. However, in a well ventilated building, the benefits of plants are mostly limited to their psychological and aesthetic values.
Whether it is perceived to be too high or too low, temperature – or more accurately, thermal comfort – is a hot topic in the workplace. The thermal environment is comprised of air temperature, surrounding surface temperatures, air speed and humidity. A person’s perception of thermal comfort depends on their metabolic rate, clothing, and personal preference.
Within a certain temperature range – e.g. between 16 and 24 degree Celsius – there are not the same direct risks to health that poor air quality brings. In fact, studies have shown that humans are remarkably adaptable to temperature in a way that they are not, for example, to air quality.
However, that does not mean that thermal comfort is not important for occupants – far from it. Although measuring the productivity impact of thermal parameters is problematic, most studies suggest that moderately high temperatures are less tolerated than low, and there is a very large body of work that demonstrates the perception of thermal comfort has a significant impact on workplace satisfaction.
User control over thermal comfort is a key factor. Where occupants are able to adapt to their thermal environment by adjusting clothing, varying air speed across their bodies or adjusting blinds, then wider variations in temperature can be tolerated.
HIGHLIGHTS: KEY RESEARCH
An analysis in 2006 of 24 studies on the relationship between temperature and performance indicated a 10% reduction in performance at both 30C and 15C compared with a baseline between 21C and 23C18, leaving little doubt as to the impact thermal comfort has on office occupants. A more recent study in a controlled setting indicated a reduction in performance of 4% at cooler temperatures, and a reduction of 6% at warmer ones.
A 2007 study analysed the capital cost, energy cost and indoor air quality benefit through health and productivity improvements of six heating, ventilation, and air conditioning (HVAC) strategies for the Australian climate and market. It concluded that displacement ventilation, with circulation of 100% fresh air, was the optimal choice for maximising indoor air quality and thermal comfort, while minimising energy costs. It was estimated this option added AUS$248/m2/year in value for tenants.
Put simply, if an office worker has more control over their environment, they tend to be more satisfied as a result. One study found that individual control over temperature (in a 4°C range) led to an increase of about 3% in logical thinking performance and 7% in typing performance. Another suggests up to 3% gains in overall productivity as a result of personal control of workspace temperature.
This does not only apply to temperature. A 2006 study tested effectiveness of adjustable deskmounted personalized air supply devices on perceived air quality. Greater satisfaction with air quality was reported with desk-mounted devices despite ventilation rates being the same. Similarly, providing individuals with personal control over light levels with dimmers in offices can lead to improvements in satisfaction and mood. Subsequent research added comfort, improved motivation, and greater ease of task performance to this list of benefits.
DESIGN STRATEGIES: GOING FOR GREEN
Thermal comfort is essential for a happy and productive office occupier and can be enhanced by providing control and adaptability to occupants and by addressing the thermal environment beyond just air temperature. Of course, heating and cooling strategies have major implications for energy use.
An ‘adaptive’ model allows temperatures to drift down in winter and up in summer, resulting in lower energy consumption and longer periods when natural ventilation can be employed for cooling in mixed mode ventilated buildings. But for the benefits of adaptive comfort to be realised, users must have direct control of their environment. This is readily achieved in a cellular office where individuals have ownership of an operable window but problematic in open-plan environments. Some user control may be provided in air-conditioned environments through user adjustable floor ventilation or task air systems that provide individual ventilation through the desk.
One of the most rapidly developing areas of research and innovation is in wireless sensor technology, which enables sophisticated monitoring and logging of temperature, humidity and lighting. Going even further, digital technology is likely to become embedded more and more in building structures; equipment; and even our clothing and person through wearable technology. This is bringing high-tech personalisation of the indoor environment much nearer.
Perhaps one of the simplest innovations is not in technology, but in working practice, through encouraging office workers to dress comfortably and casually. In Japan, the government has run the CoolBiz campaign every summer, explicitly aimed at reducing electricity consumption used for cooling in offices. Workers are encouraged to wear light, breathable clothes, and to ditch the stuffy suit jackets and ties. Facilities managers are encouraged to allow office temperatures to rise as high as 28 degrees, (a temperature which needs higher air velocities to be acceptable).
Control of thermal environment
Most office buildings specify requirements for the control of the air temperature only. Thermal comfort can be improved and energy consumption lowered, by providing attention in the design to the active control of radiant temperatures too. Like traditional heating radiators, chilled ceilings are one solution that provides heat exchange through both radiative and convective processes. This has the benefit of providing better thermal comfort and a more efficient way of generating and transporting cooling. This means that in summer slightly higher air temperatures can be tolerated when radiant temperature is lower, and vice versa in winter. For naturally ventilated buildings, night purge ventilation can pre-cool exposed thermal mass. This provides radiant cooling benefit to the occupant for the following day, further enhancing comfort perception at times of warmer air temperatures.
End note: This article is an extract of the Health, Wellbeing and Productivity in Offices report by the World Green Building Council which was sponsored by Jll, Lend Lease and Skanska. For more information on the report, please visit: www.worldgbc.org/health-and-productivity.