Posts Tagged ‘ventilation’

Indoor Air Quality

Thursday, October 29th, 2009

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Indoor Air Quality

Indoor Air Quality (IAQ) is more than mitigation of unsavory odors. In times of cheap energy when most homes were not air conditioned, natural ventilation diluted pollutants. Modern energy-efficient homes minimize infiltration and exfiltration through airtight construction and consequently accumulate all manner of unsavory and undesirable things in the indoor environment. Keep in mind, simple controlled ventilation will mitigate poor IAQ, but with an energy penalty. Let’s consider common indoor pollutants.

  • Radio Active Contamination – Radon (Radon-222) , an odorless, inert, naturally occurringradioactive gas is a ‘daughter’ of radium-226. Though not considered by authorities to be a particular threat to health, it can cause bronchial irritation and some authorities say it poses a risk of lung cancer. Despite its half-life of 3.82 days, one must remember that its material source continues to produce it forever. Learn from the EPA how to inexpensively test your home for the presence of Radon: A Citizen’s Guide to Radon.
  • Particulate Contamination – Dust, including pollen, animal dander, dust mite droppings, are commonly occurring pollutants that contribute to odors, respiratory problems and asthma.
  • Moisture Contamination – High relative humidity promotes stale odors and the growth of fungi, mold and bacteria. Acceptable relative humidity lies between thirty and sixty percent; ideally fifty percent.
  • Gaseous Contamination – Carbon Dioxide (CO2) is not a pollutant, per se, but undesirable when concentration exceeds 800 ppm (parts per million), Methane (CH4), Propane (C3H8), Hydrogen Sulfide (H2S): all but the last are undetectable to olfactory senses. CH4 and C3H8 come from gas stoves. H2S is a product of well water, sewer gas and flatulence.
  • Volatile Organic Compound Contamination – common household solvents, hobby supplies, dry-erase markers and others.

Learn more about indoor air pollution from the Environmental Protection Agency (the EPA).

IAQ Dilution Methods

Demand-Control Ventilation (DCV)

Carbon-dioxide (CO2) sensors continuously measure concentration (in ppm). The control systemCo2-Sensors enables outdoor air ventilation when indoor concentration exceeds 800 ppm. Why 800 ppm? ASHARE (the American Society of Heating Refrigeration and Air-conditioning Engineers) recommends limits of 1,000 ppm for schools and 800 for office buildings. Adults exhale CO2 concentration around 35,000 ppm. Over several years, we have determined that the optimum balance between indoor air quality and energy efficiency balances well with 800 ppm.

A suitable exhaust fan and motor-operated dampers form a simple ventilation subsystem. DependingY8150_ResidentialVentilationSystem on return-air duct pressure dynamics, the exhaust fan may be unnecessary. Naturally, induction of untempered outdoor air has an energy penalty. The Honeywell Y8150 Fresh Air Ventilation System is an inexpensive solution when used with a reliable and accurate carbon-dioxide sensor.

Energy-Recovery Fresh Air Ventilation (ERU)

Specialized heat-recover ventilation equipment dilutes all the aforementioned undesirable components without energy penalty. It transfers heat and moisture between fresh and exhaust airER150_HeatRecoveryVentilatorUnit streams. Used in conjunction with a reliable and accurate carbon-dioxide sensor, it provides optimum IAQ at the lowest cost. Perhaps the best product on the market is the Honeywell ER150B and ER200B Energy Recovery Fresh Air Ventilation Systems.

Intelligent IAQ Management

Intelligence is the key to best practices for management of indoor air quality. Rockwall Controls designs and installs intelligent residential control systems that coordinate all mechanical air conditioning equipment with the actual use of the home for optimum IAQ and energy efficiency.