Building Today's Green Home: Practical, Cost-Effective and Eco-Responsible Homebuilding (Popular Woodworking) by Smith Art

Author:Smith, Art [Smith, Art]
Language: eng
Format: epub
Tags: ebook, book
Publisher: F+W Media, Inc.
Published: 2009-07-31T21:00:00+00:00

Let’s make a comparison of this introduced 4" leak compared to an average home and an to an even older breathing home like we used to build (and probably most of you live in). Estimates used to show the size of typical air leaks will help the reader visualize the effective diameter of all the infiltration points (air leaks) in houses of different levels of construction quality. Let’s estimate the leak-equivalent-diameter of a well-built, tight, home may be close to the size of a basketball. An average constructed house’s diameter is closer to a large trash can. And even worse, an older, poorly sealed home may have the diameter equivalent of 4' to 6'! Thus, our poor little 4"-diameter fresh-air-intake “leak” seems to pale compared to these monster holes. Figure 6.18 shows one of those leaky little devils.

When you consider the effect of air pressure on the entire home, things are worse without this fresh air intake. Here’s analogy used by a SouthFace instructor at a recent Georgia Energy Code seminar that helped his audience get the point. He assumed that the HVAC system has about a 1,000cfm (cubic feet per minute) air flow rate. Our little fresh-air leak, controlled damper, is allowing 50cfm to be injected into the house. Since the HVAC air handler creates a negative pressure (outside air wants to come into the house) when running, existing air leaks throughout the structure would naturally allow air (pressure) to come into the home. This air could come from any source near the leak. A leaky garage wall (carbon monoxide, oils, gas scent, etc.) or a hot attic (or cold in the winter) or a plumbing stack may vent fumes. This 50cfm has to come from somewhere. With the fresh air controlled, the effective negative pressure of the house is reduced to the extent that any remaining unknown leaks in the home are minimized.

I don’t know of any residential designers, architects or builders who can specify exactly where the leaks in the house are located. I can’t. I’m not smart enough to do this. However, I can design a tight, well-sealed structure with the smallest leaks that can be built and then install this controlled leak (a fresh air damper pipe) where I want it.

The average size home in America is about 2,000 sq. ft. and a more expensive solution for fresh air intake is likely needed. The fresh air damper will have a small energy loss penalty (a few dollars a month in energy costs). This controlled leak is a relatively small price to pay to give us fresh air. However, as the house size increases, to gain fresh air, this energy loss penalty increases. The crossover point is in the range of 1600 sq. ft. and will require ERVs and HRVs. For simplicity, we will use the Southern-climate-specified ERV (Energy Recovery Ventilator) vs. the Northern-climate-version HRV (Heat Recovery Ventilator). They are similar, but the ERV system is optimized for cooling and dehumidifying. The HRV is designed for supplying heat-load needs.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.