Why do our cars have better air quality than our homes?
As noted in an earlier post, Elon Musk has a penchant for silly names. He claims his cars’ ventilation system has a Bioweapon Defense Mode. They described it in a press release:
Inspired by the air filtration systems used in hospitals, clean rooms, and the space industry, we developed a HEPA filtration system capable of stripping the outside air of pollen, bacteria, and pollution before they enter the cabin and systematically scrubbing the air inside the cabin to eliminate any trace of these particles. The end result is a filtration system hundreds of times more efficient than standard automotive filters, capable of providing the driver and her passengers with the best possible cabin air quality no matter what is happening in the environment around them.
© Tesla Motors
The system was capable of reducing interior air pollution, from Beijing levels to undetectable. This is not a gimmick, as Will Oremus of Slate noted:
As Tesla points out, the World Health Organization calls air pollution “the world’s largest single environmental health risk,” contributing to more than 3 million deaths each year. Recent studies have put that number even higher. Either way, it’s more than twice the global death rate from auto accidents.
Yet in our houses and apartments, we do almost nothing about this. In many homes there is at best a bathroom exhaust fan and a paper filter on the furnace. According to the US Consumer Product Safety Commission,
If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Unless they are built with special mechanical means of ventilation, homes that are designed and constructed to minimize the amount of outdoor air that can "leak" into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky."
We have been saying this for years on TreeHugger: You cannot think about energy efficiency without thinking about air quality. The more you tighten up your house, the more stuff is going to stay in it.
THE CPSC notes that apartments have many of the same indoor air problems; In fact, they are probably worse, given that they often lack any form of cross-ventilation, they often get their makeup air filtering in under doors to the corridor, stack effects can create all kinds of strange air flow patterns.
Consumer product safety commision/Public Domain
So what can people do? There are three main strategies, the first and best probably being source control- keep this stuff out of your home in the first place. This series has been particularly interested in biological contaminants:
Biological contaminants include bacteria, molds, mildew, viruses, animal dander and cat saliva, house dust mites, cockroaches, and pollen. There are many sources of these pollutants. Pollens originate from plants; viruses are transmitted by people and animals; bacteria are carried by people, animals, and soil and plant debris; and household pets are sources of saliva and animal dander. The protein in urine from rats and mice is a potent allergen. When it dries, it can become airborne. Contaminated central air handling systems can become breeding grounds for mold, mildew, and other sources of biological contaminants and can then distribute these contaminants through the home.
The best way to deal with these are to have a proper ventilation and exhaust system, keep the humidity down and..
Keep the house clean. House dust mites, pollens, animal dander, and other allergy-causing agents can be reduced, although not eliminated, through regular cleaning.
People who are allergic to these pollutants should use allergen-proof mattress encasements, wash bedding in hot (130 degrees farenheit) water, and avoid room furnishings that accumulate dust, especially if they cannot be washed in hot water. Allergic individuals should also leave the house while it is being vacuumed because vacuuming can actually increase airborne levels of mite allergens and other biological contaminants. Using central vacuum systems that are vented to the outdoors or vacuums with high efficiency filters may also be of help.
Other strategies include ventilation improvements- the CPSC writes:
Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Opening windows and doors, operating window or attic fans, when the weather permits, or running a window air conditioner with the vent control open increases the outdoor ventilation rate. Local bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located and also increase the outdoor air ventilation rate.
But outside air can be lousy, and when you run a kitchen and bathroom fan, the makeup air has to come from somewhere. That’s usually uncontrolled leakage through the walls, under and around doors and windows, and could be bringing in dust and worse.
The only way to really deal with it is to have a tightly sealed home and a controlled ventilation system, using a heat or energy recovery ventilation system. Some of these now have HEPA filters that will give you your own Bioweapon Defense Mode.
I know that I often slip into Passivhaus or Passive House shill mode, but here again, they get it right. Elrond Burell writes in a wonderful parody of Musk's press release, inserting Passivhaus for Tesla:
Health and safety are important to Passivhaus. Just as a Passivhaus protects the occupants from thermal discomfort, draughts, condensation and mould, it also protects them against the statistically more relevant hazard of air pollution. Inspired by the air filtration systems used in hospitals, clean rooms, and the space industry, Passivhaus ventilation technology has developed a filtration system capable of stripping the outside air of pollen, bacteria, and pollution before they enter the house and systematically scrubbing the air inside the house to eliminate any trace of these particles. The end result is a filtration system hundreds of times more efficient than standard ventilation systems, capable of providing the homeowner and occupants with the best possible indoor air quality no matter what is happening in the environment around them.
It should be noted that passive house HRVs are a notch below HEPA because it takes a lot of energy to push the air through a HEPA filter, and energy consumption on Passive House is severely constrained.
I am also going to slip back into modernist minimalist mode, because it is so much easier to really keep clean. On WebMD they recommend regular vacuuming with a HEPA filter equipped machine, and “Don't forget walls, carpet edges, and upholstered furniture, where dust accumulates. For best results, vacuum two or more times each week and wash out your filter regularly.” And when you are done with the vacuum, Mop it up. Mopping picks up the dust that vacuuming leaves behind.
90 years ago, Neutra, Le Corbusier and Bijvoet promoted sunlight and fresh air; Mies van der Rohe promoted light tubular furniture that was easy to move around so that you could clean. Today, most of us have to make the air fresh ourselves with filters, but there is still a lot to learn about designing for disease from the early modernists. And there is a lot to learn from Elon Musk, who apparently really understands air quality.
Next: Materials matter.