Tuesday, August 4, 2015

Passive House and Health

On my last post I touched on the mold potential. I could probably do an entire post on Mold - but I am not a doctor, nor am I a certified mold specialist. I know it's bad, you know it's bad and we'll leave it at that.

In this post I will be talking about the general health benefits that come standard with a Passive House. Some of the more common health problems that can be attributed too poor indoor air quality include:  
  • allergies
  • head aches
  • asthma
  • sleep problems
Conditions which impact your indoor air quality:
  • Mold
  • High Relative Humidity
  • Low Relative Humidity
  • House is too leaky
  • House is too tight
  • High CO / CO2 levels
  • Little Kids - I guess passive house can't fix that one (6 out of 7 isn't bad)
Current methods used to manage the "symptoms" resulting from these underlying issues:
  • Air purifiers
  • Electrostatic furnace filters
  • Dehumidifiers in the summer
  • Humidifiers in the winter
  • High powered exhaust fans
  • Open windows -  which can bring in dust pollen and other allergens from the outdoors
A passive house doesn't require use of any of those methods in order to maintain superb indoor air quality! The Passive House combines
  1.  an Airtight Envelope
  2. Thermal Bridge Free Construction 
  3. Lots of Insulation
  4. Highly insulated Windows with Proper Orientation and Installation
  5. Properly Designed, Installed and Commissioned Ventilation System 

(20C = 68F ; 0C = 32F ; 360g = 1.5 cups)
So in the winter a 1 millimeter wide gap can lead to 1.5 cups of water getting into your wall every day! Think about that the next time you turn on the humidifier!



How do the Passive House Elements work together to make the home healthier for the occupants? Let's touch on each component that can negatively impact your indoor air quality.

Mold
According to FSEC There are 4 requirements for mold growth.

 1) Spores - originate from actively growing mold; they can develop from mold growing within your home or be carried in from the outdoor air via open windows or other air penetration points, they are nearly impossible to prevent
 2) Food - in homes, primarily wood, mold likes wood, especially the moist kind
 3) Appropriate Temperatures - basically anything between 40 (mold in your refrigerator) 120 (mold in your attic) again this is difficult to impact as humans and mold tend to thrive in a similar temperature range
4) Considerable Moisture - Ah ha! We can control this one. By keeping all of the surfaces close in temperature (remember the 6 degree temperature difference we discussed in the last post?)  and with near elimination of air leaks, we can keep the dew point of the indoor air well below the surface temperature of all interior surfaces thus eliminating condensation - Remember 1.5 cups of water per day!

Where does all of that water come from? Warm air can hold more water vapor than cold air

Lets take a cold soda sitting on the counter on a summer day. The surface temperature of the can is relatively cold. It is so cold in fact that when the room temperature air hits it, condensation forms on the can.

If we can prevent the condensation we can control the moisture in the air which can directly reduce mold growth.

Relative Humidity 
The ventilation system is designed to remove air from the kitchen and bathrooms and supply fresh filtered air to the living spaces and bedrooms. The flow rates of air are so low, respiration and normal day to day living (i.e boiling water for your kids macaroni and cheese) replace the moisture that the system is removing - this maintains a comfortable, consistent Relative Humidity - keeping the air moist in the winter (no humidifier needed) and keeps the air dry in the summer (no dehumidifier needed)

Poor Indoor Air Quality / House is too tight / Sleep
As we discussed above, the ventilation system is constantly bringing in fresh filtered air from the outside and delivering it to the living spaces. The stale odorous air is being drawn out constantly, and before being exhausted outside, the heat from that air is transferred to the incoming air.  

This style of ventilation allows for indoor carbon dioxide levels to be controlled to levels similar to those outdoors (in contrast to our common building practices where indoor levels are much more concentrated than outdoor levels). Elevated carbon dioxide levels indoors can lead to complaints of drowsiness, or headaches.  
Having a constant flow of fresh filtered air in the home will also improve the quality of sleep, reduce the stuffiness of a tight house and will ensure all of the odors are being removed. Also because it is filtered air you reduce / eliminate the pollen that result from open windows.

There are actually some studies that show there are measurable health benefits for people moving from normal homes into passive homes because of the superior indoor air quality and tight construction. 

My next post will go into some more detail on the ventilation system and CO2!

1 comment:

  1. No wonder relative humidity, a factor of air quality that should not be underestimated, has gotten more and more attention the past years. considering home is the place we spend most of our time, maintaining ideal indoor humidity levels is an essential element of living consciously.

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