In the 1970 when energy conservation was just becoming a major issue, new homes were built tighter and tighter. This kept the heat in, but it also kept poor air from escaping, leading to the commonly referred to sick building/home syndrome. Cooking odors, product off gassing, and even our breath had no place to go. Water vapor from showers, cooking, laundry and even our breathing had no place to go except into the walls, and thus molds started to grown further making these tight homes unhealthy and even uninhabitable. ( See Discussion on Mold)
The mechanical equipment in any house is probably as exciting as watching paint dry, but it is essential for your health that you get it right to avoid problems down the road.
Regulations have been adopted to require outdoor fresh air to be vented into the house ... which seems to defeat the purpose of tight walls and extra insulation. Best practices call for bringing in enough outdoor air to totally replace the indoor air every 3.5 hours. So, every 3.5 hours all that warm/moist or cool air goes outside to cool or heat nature!!! Some builders will put the air intake in the garage believing that garage temperatures are not as extreme as the outside... of course, there are those wonderful auto emissions if you start your car in the garage.
Air to air heat exchangers are a must if you wish to conserve the energy you've spend so much not to waste. A heat exchanger can capture as much as 70% of the energy by passing indoor air through grid that contains outdoor air; consequently transferring the internal energy in the air to the incoming outdoor air. If your indoor air is 68o and its 32o outdoors the heat exchanger can raise the temperature of the fresh air to around 45o running the fresh air through a furnace can help, but it still takes energy to heat cold outdoor air to your comfort zone.
In addition, we wanted fresh air delivered to every room for healthy air, particularly all of the bedrooms. After all, most of us spend a minimum of 1/3rd of our lives in our bedrooms. One of the more innovative things we did was dump air into the room and have the return through an in-wall vent. With 8 rooms, we only have 2 return vents, which reduces the amount of duct work needed. Because the envelope is very tight, we don;t need to have the fresh air near a window to maximize convection air circulation, which further limits the length of duct work required. Less ducts equals less cost in time and materials.
We located the air handling system in a central location in the house, over the pantry, to minimize the length of ducts needed and to make certain that the pressures are easier to balance within the system.
An air recirculation system filters the interior air. There is another filter on the incoming air to the heat exchanger to hopefully keep out mold spores. The net effect is that our air will be constantly filtered, enhancing the quality of our indoor air. So while we are heating with radiant heat in the floor, there is air movement throughout our structure. We don't have air conditioning installed, but this air handling system allows for the addition of cooling at a later date.
Two other features of our air system are that we have a humidistat which can increase the amount of outdoor air that is brought in if there is a wide disparity in humidity levels between indoor and outdoors. This feature hopefully keeps humidity and thus water out of our walls. We also have an over ride switch for the air to air heat exchanger that can bring in cooler outdoor air directly into the house if it is cool outside and hot inside. Frankly, opening the windows works just as well, and this latter feature is a bit over the top, but we have it as an option.
In our home there are 4 additional vents fans to exhaust air and the three of them are on timers ... one in each of the two bathrooms, one in the garage, one in the room we will use as an office to vent out off-gassed electrical equipment. Of course, there is a hood for the cooker.
We are using only electricity, so if you are using natural gas for heating, cooking or a fireplace, you will also have to have a system to bring fresh air into the combustion chamber and venting air outside to prevent carbon monoxide from entering the home. CO2 is not a problem in an all electric house.
Often, new homes have a "New Home Smell". This new home smell is generally from formaldehyde in carpets, furniture, counter tops, paint, and insulation. Electrical equipment will off-gas PBDEs, a flame retardants that has become ubiquitous in our environment ... and that's not a good thing. Finally, paints, solvents, adhesives, and cleaning products present their own health issues.
Bringing in outdoor air helps, but the best approach is to avoid these health risks up front. There are an increasing number of suppliers who market low and no VOC (Volatile Organic Compounds) products. You can explore manufacturers with environmentally friendly products at GreenGuard and GreenSeal websites (Links for the Green Products)
One final point on ducts, make certain they are sealed tightly and well insulated! This is a critical energy issue if you use a furnace and forced air heating system. According to the Rocky Mountain Institute, as much as 25-30% of the heating cost is wasted because of leaking ducts. Duct work gets your energy investment to where you want it rather than wastes it into the attic or walls. It only makes sense to make certain your subcontractor spends the extra time to seal your ducts tightly before they are covered with drywall and insulation.
One really final point, during construction, ,make certain that there is a barrier between the garage and the home. This will keep auto exhaust fumes from entering the home through walls and through the attic. In other words, the attic and space over the garage needs to be separated by a wall. It was in the BuiltGreen Checklist and it made sense, so we did it.
We welcome your comments on this site.
You can email Christine Garst at firstname.lastname@example.org
Sunday December 17, 2006 05:34 PM -0800
All Rights Reserved