Friday, July 27, 2012

ASHRAE 62.2 & the BPI

The world is filled with acronyms and the 'green' world has, I claim, the most. The Building Performance Institute (BPI) which certifies most of the energy auditors working on existing homes is adopting the American Society of Heating Refrigeration and Air conditioning Engineers (ASHRAE) newest standard for ventilation.  The introduction below is from a manufacturer of blower doors - equipment used to test the leakiness of a building's envelope.

To put it simply: a tight house saves energy and properly managed outside air improves indoor air quality. Combine the two and prosper financially and in health and comfort matters.

A Look at ASHRAE 62.2-2010

Over the last year or so, many of you have had to learn about the new ASHRAE ventilation standard. For BPI followers, the new 62.2-2010 will replace the old 62-89 standard on January 1 of 2013. Many DOE low-income weatherization programs are currently using 62.2. And for those of you working in new homes built to the 2012 IECC – it is happening now.

In the coming months, there will be new emphasis on 62.2, so let’s take a look at the basics. Even though you can get a lot of condensed versions, and even apps that do the calculations for you, it is always best to have and understand the actual standard.

So what is this new 62.2 standard? 
It is a mechanical ventilation standard used to determine the amount of constant or intermittent ventilation to install if your evaluation shows you need it.  Ventilation can be exhaust only, supply only, or balanced. It can be constant or intermittent, and in existing houses you can get a credit for a leaky building that can replace part, or all, of the requirement.

62.2 also requires items like a weather-stripped garage door, a vented dryer, compensation for combustion air, quiet fans, and either measuring fan output or using a prescriptive table for maximum fan exhaust duct lengths.  Check the standard for a more complete list.

The standard has a default table for determining ventilation, but using the calculation will usually end up with a smaller fan, so it may be worth the time and effort to do the math.

The past standards have been based on either the volume of the building or the number of occupants. This new standard is based on both floor area and number of occupants.

The first thing to do is determine floor area. 
The standard uses “occupiable area” that it defines as any space within the pressure boundary: so if you have included the basement as part of the envelope, include that area.

Next, determine number of occupants.

The standard uses the old standby of bedrooms +1.

The ventilation formula is: 
One percent of floor area plus 7.5 times the number of occupants equals the CFM of full time ventilation. Or mathematically,
(Area X 0.01) + (Bedrooms+1 X 7.5) = CFM ventilation.

So as an example - a 2200 ft2 house with a 1100 ft2 occupiable basement and 3 bedrooms would end up like this:

(3300 X 0.01) + (4 X 7.5) = (33) + (30) = 63 CFM of full time ventilation

The standard also has a table for determining intermittent fan use, and it ends up to be more run time than just a ratio would come up with.

So, no magic - everything can be done from tables or the calculation. And remember - tightening a house then re-ventilating it, are both part of the same strategy.