Sustainability is a hot topic these days. There is an incentive to go green in every corner of the marketplace, if not for the sake of combating climate change, then for the financial advantages, or simply to keep up with modern fashion trends. The building industry is no exception.
Buildings contribute approximately 40 % of global energy usage per year, which puts them among the top priorities for developing and implementing sustainable practices. To quote Laustsen (2008), “the implications of such potential reduction [in the energy use by buildings] should not be underestimated, as the scale of energy efficiency in buildings is significant enough to influence security policy, climate preservation and public health on a national and global scale.”
In the building industry, sustainability is a complex issue. It affects every aspect of the building, from design and location choice, through to building materials used and the type of light bulb fitted at a person’s desk when the building is finished.
However, when it comes to sustainability in buildings, one feature stands out; heating, ventilation and air conditioning (HVAC) systems. HVAC systems alone can account for up to 40 % of the energy use of office buildings. However, rather than discuss HVAC systems in general, I am just going to cover the ventilation codes important for sustainability.
The importance of ventilation hinges, as said in a previous blog, on the fact that ventilation is the key component of IAQ regulation. Recognition of the adverse effects of poor IAQ led to the first major inclusions of ventilation in building codes. Over time the standards for IAQ have evolved, such that in modern codes for ventilation there are a host of requirements and recommendations.
These include requirements for filtration, recirculation limits, and minimum required ventilation rates for different types of buildings and occupation densities (see Table 6-1 in ASHRAE Standard 62.1). These requirements have a critical goal: keeping occupant dissatisfaction below 20 % and minimizing potential adverse health effects of pollutants. Essentially, ventilation codes are a requisite for regulating IAQ, and it is that fact that makes ventilation codes important for sustainability in buildings. Acceptance of the need for ventilation to regulate health, safety, and comfort, led to the realization that ventilation would become a crucial factor in building design, and ultimately in the energy consumption of buildings.
That realization created a second major avenue for regulation of ventilation in building codes (other than in standards for IAQ); standards for energy efficiency. Thus, because ventilation affects codes for IAQ, it affects codes for energy efficiency, and thereby how building sustainability is managed.
In codes for energy efficiency, ventilation is dealt with on various levels. Recommendations for how ventilation should be managed to maximize energetic efficiency are based on the fact that there are three basic types of ventilation; natural (passive, such as through open windows or doors), mechanical (electronically driven), and a mixture of the two. Regarding sustainability, there is a worldwide emphasis on the use of natural ventilation where possible, as this obviously requires no energy usage.
A perusal of scientific articles on sustainability from the last decade will reveal an almost ubiquitous recommendation for a shift toward more use of natural ventilation, in addition to evidence for the potential energy savings afforded by using natural ventilation. Indeed, rating systems such as Hong Kong’s BEAM Plus (Building Environmental Assessment Method), the Building and Construction Authority’s Green Mark, and the United States Green Building Council’s LEED (Leadership in Energy and Design), all provide incentives for introducing natural ventilation where possible.
However, despite the enthusiastic recommendations, natural ventilation has numerous issues. Firstly, outdoor air may not be better quality than indoor air. In some big cities, outdoor air can have harmful concentrations of some pollutants, and therefore need to be filtered upon entry into buildings (see below).
Secondly, natural ventilation is unreliable in its consistency and source. As a result, it may not provide the necessary ventilation rates, humidity levels, or temperature to maintain comfort. Thirdly, in multi-zoned buildings, natural ventilation is difficult to manage such that all occupied zones are adequately ventilated. Lastly, and perhaps most importantly, natural ventilation is difficult to legislate. These combine to diminish the role of natural ventilation in sustainable building design (see Tables 1 and 2 in Chenari, B., Carrilho, J.D. & da Silva, M.G., 2016).
Because of the limited usefulness of natural ventilation, most modern buildings (and retrofitted buildings) have a mixed or fully mechanical ventilation system. As such, current codes for energy efficiency of ventilation systems still generally only pertain to mechanical systems, giving requirements for energy recovery, fan power, and system design, among other features relevant to mechanical systems. These codes are vital for sustainability, as they provide guidelines for different strategies to regulate mechanical ventilation which can incur massive energy savings (generally between 20 – 60 %; see Table 3 in Chenari et al., 2016).
These savings are pertinent to building developments worldwide, but Asia is of particular interest. Asia is experiencing rapid growth and development. For instance, in China, the population growth is 16 – 18 million a year, with approximately 3.5 million new apartments being built annually. The need for new, larger, and more sophisticated buildings that typifies Asia’s rapidly growing population and economies underpins its influence on sustainable building practices.
However, there are two main factors that make Asia especially important regarding the effects of ventilation codes on sustainability:
- Many Asian cities are located where it is scorching and humid in summer, or icy in winter, or both (for example, see figure 1). In these climate zones, the largest energetic component of HVAC systems is regulating the temperature within the building. Ventilation is a key element of this energetic load because the rate that air is exchanged, in addition to the energy recovery efficiency of the ventilation equipment, directly affects how much work the heating/cooling system need to do (see Equation 2 and discussion thereof in Persily & Emmerich, 2012).
Figure 1. Climatic zones in China as indicated by the Chinese Ministry of Construction. The locations of four major cities are indicated. Adapted from Laustsen, J. (2008) Energy efficiency requirements in building codes, energy efficiency policies for new buildings. International Energy Agency (IEA), 477-488.
- Asian cities have the worst air quality on the planet. In November 2016, The Guardian ran an article entitled, Clouds of filth envelope Asian cities: ‘you can’t escape,’ which provided vivid imagery of the dire situation Asia is in. The World Health Organization (WHO) has listed South East Asia as one of two regions with the highest rates of premature death caused by poor air quality in the world. The terrible state of the outdoor air quality in many cities in Asia drastically reduces, if not eliminates, the potential for utilizing natural ventilation as an energy saving mechanism. As I said above, ventilation must, first and foremost, regulate IAQ at acceptable levels. Energy savings are secondary to issues of health, safety, and comfort. This means that developments (and renovations of old buildings) in Asian cities will have to focus on means of saving energy available in mechanical systems, such as introducing demand controlled ventilation, energy recovery wheels, and advanced filtration to allow greater recirculation of air. Moreover, it means that some strategies for reducing the energy consumption of ventilation systems, such as reducing flow rates, cannot be implemented if they compromise IAQ (lowered ventilation rates will increase the concentration of contaminants exponentially; figure 2).
Figure 2. The concentration of different pollutants with different emission rates (EF = emission factor (mg/m2.hr-1)), as a function of the ventilation rate of the building.
Ventilation has a strong influence on sustainability in buildings. As Pérez-Lombard et al. (2011) put it, “ventilation service uses thermal energy for outdoor air treatment and electrical energy for filtration and distribution to conditioned spaces. Consequently, IAQ requirements are directly linked to the energy efficiency of HVAC systems. For this reason, although some countries address both subjects in different standards, it is impossible to entirely dissociate air quality from energy use”.
In general, building energy codes are incorporating standards for energy conservation in ventilation, primarily through encouraging maximum use of natural ventilation. These codes are, for the most part, voluntary, despite their high potential for energetic and monetary benefits. In Asia, ventilation codes are especially important for sustainability in buildings, because Asia has unique problems with a very wide range of climatic conditions experienced by big cities and extremely severe pollution. The means that Asia uses to minimize the energy demand of adequate ventilation will therefore strongly contrast other parts of the world, such as large areas of Europe and North America; areas with more temperate climates, and much fewer issues with outdoor air quality.