How can we improve our indoor air quality? Why a stand-alone air purifier is not the only bet?

(The excerpt is published on All Tech Asia.)

Air pollution has become a serious problem hanging over the heads of Chinese people, both literally and figuratively. In an effort to avoid the discomfort of a heavily polluted sky, many people limit outdoor activities and stay indoors, thinking that this keeps them safe.

An annual mean PM2.5 concentration of 35 µg/m3 was set by the World Health Organization as the highest mean concentrations, which are associated with about a 15%+ long-term mortality risk relative to the suggested level.

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Source: World Health Organization

China uses a more liberal standard of 75µg/m3. A study led by a statistician at Guanghua School of Management at Peking University found over the past 3 years, half of the days in Beijing were “unsafe” (PM2.5 concentration > 75µg/m3), and 20% in Shanghai. Vulnerable people suffer from visibly longer lasting respiratory sickness and chronic allergy, which leads to the absence of work or school. Air pollution has become a smokeless war haunt Chinese people. People limit outdoor activities and stay indoors for the “tranquility” they think.

On average, people spend 90% of their time indoors. People definitely deserve better indoor air quality, but indoor air is not necessarily safe. Indoor air quality in the U.S. is generally worse than outdoor air quality, according to a study by the US Environmental Protection Agency. In China, indoor air is slightly better than outdoor air, but only when outdoor air reaches hazardous levels. Most buildings in China don’t have the mechanical ventilation systems. The indoor air is cross contaminated by cooking odor, bathroom exhaust, secondhand smoke and other other pollutants.

Building design defects

The building stock in China is a mix of old and new buildings. Some reports have claimed that many homes in China will be demolished and rebuilt in 20 years. New commercial buildings are equipped with mechanical ventilation systems. However, most buildings without mechanical equipment can only rely on natural ventilation; opening windows therefore simply means bringing “fresh” smoggy air inside.

iaq-outside-vs-inside

Image illustrated by author

You might say that people keep their windows tightly closed when the AQI is extremely high. Have you ever thought about the exhaust fans in the kitchens and bathrooms? The exhaust fans expel the oily and moist air outside. Then the house is depressurized, and the unfiltered outside air is sucked into the buildings through small cracks and gaps, due to the simple physics of pressure differences.

IAQ-depressured.png

Image illustrated by author

Moisture damage is the hidden killer that people usually underestimate. Moisture damage is caused by design failure, and leads to the material deterioration of the building, as well as damage to human health. Mold usually grows inside the building enclosure materials, like in the walls.

Pollutants from building materials

Many materials used in construction can be harmful to human health. For example, Volatile Organic Compounds (VOCs) are chemicals that can evaporate under normal indoor atmospheric temperature and pressure conditions, making them a health hazard. Other notorious chemicals include formaldehyde, some fire retardants, BPA, heavy metals, and others. The exposure risk increases in the case of children, pregnant women, unborn fetuses, senior population, and sick people.

A simple and affordable solution for individuals is a stand-alone air purifier. However, there are larger scale solutions that can be pursued that are more efficient and sustainable.

Fixing the design defects

As mentioned earlier, Chinese developers are busy demolishing aging buildings and building the new ones. Sophisticated building designers can make the building better insulated and airtight, a solution which reduces energy waste, while also increasing comfort. In the winter, all the inside warmth generated by heating systems, human bodies, showers, cooking, or electrical appliances can be kept inside rather than being leaked outside.

The next step will be to improve the whole building ventilation system. In the winter, the interior temperature is warmer than the exterior. The cold outside air first passes through an air purification membrane. Then, the outdoor cold air is preheated by the heat from the passing of the inside air through the air exchanger. Two streams of air exchange their energy, but without direct contact. This system, installed in the airtight and insulated building, brings purified fresh air as well as energy savings.

iaq-ventilation

Image illustrated by author

Moisture problems can be avoided by better wall design. Simulation tools help designers add a waterproof but vapor-permeable membrane in the right position, keeping water away from the critical elements of the wall. Because it is vapor-permeable, it allows the vapor to travel through the wall. The wall can dry out and therefore won’t provide a bed for mold.

Improving building materials

Choosing safe materials is a solution that is simple to say, but hard to implement. Chemicals are added to the building materials for better performance, affordability, durability, and fire safety. As a trade-off, they become threats to human beings when they accumulate to a high level. People ask for safe materials, but they find that manufacturers don’t understand the different raw materials used, because of their weak control of the supply chain. Additionally, a lack of surveillance discourages manufacturers from watch their suppliers.

Concerns and long-term challenges

The first step is always to insulate and seal buildings. Based on common practices in the US, this major renovation takes 6 months to 1.5 years per building, depending on the existing conditions.

The design for a better indoor environmental quality requires longer and more carefully coordinated planning. Architects need to coordinate with mechanical engineers to identify a proper place to put a ventilator: it should be a place where you can have shorter ducts for incoming air. You don’t want too much cold air passing through the duct to the ventilator at your warm home in the winter, as it is not energy efficient. Likewise, I am sure you won’t like the idea of putting your intake vent next to your neighbor’s kitchen exhaust fan.

The ventilation system is less appealing for smaller residential building owners, but it makes sense for buildings that have a larger space to install the ventilation system.

The filters play a pivotal role in cleaning the outdoor air. Changing the filters on time adds to the maintenance cost, but ensures the long-term effectiveness and safety of the ventilation system. Most ventilators allow different types of filters; make sure to choose the one suitable for your application.

The holistic design approach of insulation, air tightness and a building-level ventilation system is absolutely more complex than natural ventilation. It requires more energy to produce all the materials and to deliver to the site for assembling or installation, so it is essential to understand the lifetime cost.

Today, we don’t only count for the on-site cost of the heating, cooling and ventilation for a 50- to 100-year lifespan, but also count all the energy consumption from the material extraction, production, shipment, installation to the long-term operation and maintenance. Designers should think systematically and make their own judgement as to whether this approach fits each individual building.

Residential buildings may have the chance to be upgraded in the next round of “demolish-rebuild” development, but institutional buildings are not so lucky. Most schools in China are public ones, and rarely seem to be relocated or renovated. They are the next generation of the workforce and are the future of the country, but also a group of people vulnerable to air pollution.

It remains a great challenge to perform a comprehensive renovation at schools, both in terms of the capital investment, and in terms of trying to schedule renovations around term time.

(This article was edited to a simple version and published on All China Tech for the general public)

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