Notes on Air Quality and Energy Savings

Tremendous savings in heating and cooling bills can result when a home is built with a good thermal barrier around the conditioned air spaces. Its important to keep in mind though that the full benefit of well insulated walls won't be realized if the rest of the structure is inefficient. Even orientation of the structure on the lot has an effect on energy savings. For example it helps to build a home with the garage facing west so that it can act as a thermal break from the western sun. Life style is another wild card when it comes to how energy efficient a structure is. If enough doors and windows are left open, it may make little difference how well insulated the walls are. Other significant factors are the number of windows and their quality, amount of shade, and attic insulation, as well as the efficiency of the HVAC equipment. Even the kind of canister lights used in the ceilings of rooms can have a significant impact on energy savings. Why? Because builder grade lights leak air out of your room into your attic. If you pay to condition your air and it leaks out of your home through leaks around windows and doors, or through your walls (especially at openings such as electrical outlets and light switches) and through openings in your ceilings then you pay to recondition that air all over again.

Its impossible for any wall system manufacturer to quote you a specific energy savings. Too much depends on factors which have nothing to do with your walls. The statement we like best in regards to energy savings and our walls is below:

"If you build your walls out of ICFs, you have effectively eliminated the walls as an energy concern. You'll get some good savings. Your total savings will then depend on how well you handle the other weak spots - roof, windows, and heating and cooling equipment. To put it another way, using ICFs does about all you can do to make the walls energy-efficient. If you are as careful with the rest of the building, you'll have an extremely economical building to heat and cool." Insulating Concrete Forms Construction - Demand, Evaluation, & Technical Practice - Copyright 2004 - ISBN 0-07-143057-1

In Austin, heat and humidity are our primary concerns. All homes, even those constructed with wood frame construction today are being built so air tight that keeping humidity down is a challenge. There are actually 3 distinct issues related to air quality and each should be dealt with separately. These issues are temperature, air cleanliness, and humidity. HVAC units are always sized for the worst case heating and cooling loads which only occur a few times during the year. What this means is that 95% of the time the unit is oversized for the actual work it needs to do as far as temperature is concerned - but what about humidity? In Austin, some of the worst times of the year for excess humidity are during months when the temperature outside is actually quiet moderate. This means that the HVAC units just don't run long enough to keep the humidity in our homes below 50%. It is at and above 50% relative humidity that bacteria and black mold begin to grow and become a problem. Back before our homes were so air tight this wasn't such an issue with humidity because the HVAC units ran a great deal and were generally pretty inefficient compared to today's standards. Today the HVAC units may not run long enough to keep humidity down so we need to stop thinking of our HVAC units as effective ways to keep humidity under control year round. We cannot fix this problem by down sizing our HVAC units to the point they run all the time either because if we did that the units would not be powerful enough to keep the home cool in the hottest months.

We recommend either the installation of a completely independent dehumidification unit which can use the air ducting system of the HVAC system, or we recommend the use of an HVAC System that has separate dehumidification equipment already built into it. Carrier and Trane are two examples of HVAC manufacturers that offers such units. There are independent dehumidification units as well, such as the one's from Aprilaire http://www.aircleaner.com/ (and others) which can be fully installed for around $1,300. These units operate not on temperature set point but on a relative humidity set point. If the humidity gets too high they come on at low energy efficient speeds, even if the temperature in the house is fine. These units are being recommended now for all wood frame construction so they are definitely a good idea for ICF construction.

Leaky structures may let in fresh air, but fresh air in Austin is neither clean or low in humidity or dust, pollution, or allergens. Rather than reverting to constructing walls that leak air or "breath" we should continue to build air tight structures but then provide for proper 1) dehumidification, 2) Manual J sized HVAC "temperature" conditioning (with minimum of 12 SEER efficiency rating), and 3) air filtration with a MERV rating of 14 or better. We recommend you add fresh air intake to your HVAC with an Energy Recovery Ventelator. The ducting and return air sizing is very important also. To effectively purify a sufficient volume of air in a home, the surface area of the filter needs to be large enough. Make sure your HVAC contractor has calculated the size of your air ducting and return vents. Improper volume of air flow is one of the main reasons HVAC systems do not operate at full service rating. All of these things must be handled properly and this is the only way to provide for a clean and energy efficient interior living environment.

In conclusion, please keep in mind that today's code standards provide minimal protection for you in regards to your health. Just because a new home is constructed and put on the market does not mean that the home will last, be free of termites or black mold, or will provide a clean, allergen free environment for your family.