INDOOR AIR QUALITY (IAQ)

Good IAQ is an essential component of having a healthy home. What good is
a residence if, although it consumes very little energy, it does not provide a
place where the body and soul can relax, refresh and renew?

Achieving excellent IAQ at Sage Farm involves both source control and
provisions for generous amounts of ventilation when needed.

SOURCE CONTROL: Source control involved the initial identification of potential sources, followed by decisions to eliminate potential sources and rely on exhaust ventilation where the source could not be eliminated. Each potential source, the following information can be provided:

Combustion-related sources: For primary heating, the old oil-burning furnace was eliminated and replaced by an off-peak Electric Thermal Storage (ETS) unit. When this was eliminated, IAQ was improved because there was no longer an oil storage tank in the basement contributing a low level of VOCs to the air my family was breathing. Other advantages include a weaning from a fossil fuel based heating system to the possibility of purchasing green power – electricity generated from sustainable sources. Also, without an air-breathing combustion unit in the basement I could improve the air sealing here because my need for combustion air was eliminated. The final icing of the cake is that the ETS unit has some standby losses to the basement, so this now tighter basement is now warmer in the winter. My propane space heaters both have sealed combustion units so that combustion air is drawn in via a pipe around the exhaust vent.

Propane for cooking: The products of combustion and cooking odors are captured and removed from the house with an exhaust system that is directly above the cooking surface. As long as this system is turned on when cooking is occurring, these products of combustion are captured and discharged directly outdoors.

Emissions from wall oven: Even though we cook with propane, we bake with electricity. Since our wall oven has a self-cleaning function, an exhaust grille is located directly above this exhaust location to capture and remove any air contaminants generated during the cleaning cycle.

Copier emissions: My copier has a dedicated exhaust fan and duct system to capture and remove the numerous air contaminants generated from the copier.

Mold control: The key to preventing mold growth is by preventing elevated levels of moisture from occurring in the house. While moisture control is achieved by the heat pump water heated discussed below (See Integrated Design), keeping mold from growing is also added by the absence of wall-to-wall carpeting.

VENTILATION: For the exhaust fans used for source control to work effectively, there needs to be a pathway provided so that replacement air can easily find its way into the house. Otherwise, the exhaust fan works hard and depressurizing the house and drawing air where it can, but unfortunately not effectively. You can't have it both ways, despite what your builder may say.  If you have tight house without a pathway provided, your exhaust fans will not work effectively; they will consume electricity but not move a lot of air.  Contrast that the inlet pathway working in concert with the exhaust fans.   At Sage Farm, the ductwork of the forced hot air heating system was extended to include a connection to the outside via a 6" round duct. This way, whenever the house needs replacement air for an exhaust fan, air is drawn unimpeded from the outdoors, mixed and tempered by the air in the ducts and then drawn to the exhaust fan. In addition, when the recirculation fan of the off-peak electric heating system is on and heat is added to the house, this outdoor air is heated as well.

INTEGRATED DESIGN: One important system at Sage Farm that contributes to both energy efficiency and good IAQ is the heat pump water heater. Not only does this unit heat the domestic hot water using one-half the electricity as compared with direct electrical resistance heating, it provides both moisture management and demand-controlled ventilation. The moisture management occurs automatically as part of the unit’s operation. After warm moist air begins to accumulate in the house, due to showering, dishwashing or clothes washing, the water heater goes on recharge and exhausts this warm humid air from the house to extract both sensible and latent heat from it as the next batch of water is heated. Since the use of hot water roughly reflects the activity level in the home, and there is a definite mechanical ventilation component associated with this water heating, the end result is that the amount of ventilation provided is roughly proportional to the level of human activity in the home. That is, if no one has been home for a while, there has not been recent hot water use, so the water heater and its associated mechanical ventilation will not occur. When people do come home and use enough hot water to have this heater go to recharge, then the ventilation will occur as well.


For information on these aspects of the indoor environment, or other questions about whether a healthy and productive indoor environment is being achieved, please email
David W. Bearg
, PE, CIH or telephone at 978-369-5680.