The Art and Science of Good Ventilation
How Do We Control the Air Contamination?
There are literally thousands of air pollutants and potential air pollutants. Human occupants produce some of these contaminants, including CO2, moisture, particulates, and odors. Building materials and other indoor items such as furniture also produce a variety of chemical and particulate pollutants.
In general, the contaminants that concern us are either particles or gases. The list of particulate contaminants includes:
- Mold Spores
- Pollen
- Pet Dander
- Dust
- Smoke
- Grease Particles
Good quality filters may control particulate contaminants. The most effective filtration tools, however, simultaneously circulate and filter indoor air while bringing in air from outdoors.
Among the gaseous contaminants are:
- Excess Moisture (humidity)
- VOCs (Volatile Organic Compounds - thousands of them)
- Formaldehyde
- Carbon Monoxide
- Carbon Dioxide
- Odors
Gaseous contaminants may be controlled through continually operated exhaust fans or heat recovery ventilators (HRV) and energy recovery ventilators (ERV), both of which bring in fresh air from the outside, dilute contaminants and exhaust them.
High quality exhaust fans can be used for continuous use. A very important aspect of fans designed for continuous use is that they are quieter and more energy efficient than fans designed for intermittent use. Also, it is generally accepted that continuous ventilation with a single exhaust fan does not provide proper ventilation distribution throughout the home.
Affordable exhaust fan systems now exist that integrate multiple quiet and energy efficient fans installed throughout the home. These fans can be located in bathrooms, laundry rooms and workshops. The individual fans communicate with each other using high performance home automation protocols over the power lines of the home. The intermittent usage of the individual fans is deducted from the total average ventilation required. These systems than automatically operate fans distributed throughout the home to meet the ASHRAE standard.
The Measurements |
Ventilation brings with it a few units of measure that may need explanation. The explanations and definitions in this section are used throughout this paper. 1. Cubic feet per minute (CFM) is the common measure of airflow. It reflects the number of cubic feet of air flowing in one minute. The Standard International (SI) system uses liters per second (l/s). One CFM is about one-half l/s. 2. Static pressure, usually measured in inches of water, is a measure of duct resistance. When used as part of a fan rating, it is the duct resistance anticipated when rating the airflow of the fan; if the actual duct system in an installation provides more resistance, the fan will produce less (CFM of) airflow. The SI system uses Pascals (Pa); 0.1 inches of water is about 25 Pascals. 3. Sones are a common unit of measurement that translates decibel readings into numbers that correspond to the way people sense loudness. The average quiet refrigerator operates at one Sone. Two Sones sounds twice as loud as one Sone.
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