The first ventilation codes were focused on health. By the late 1800’s, outbreaks of respiratory and contagious diseases in overcrowded city buildings led to the definition of proper ventilation as 30cfm per person. Not much changed until 1989, when the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) set a residential ventilation rate of 15cfm per person or 0.35 ACH. Today that rate is 7.5 cfm per person with an additional 2013 mandate for 3 cfm per 100 square feet, replacing the 1 cfm per 100 square called for in ASHRAE 62.2-2010. Even as ventilation standards grow more stringent, home performance requirements are accelerating. Tight houses are good because they save energy.
However, with sealed envelopes replacing drafty homes from the past, building professionals and code officials are having to rethink mechanical systems. The need for mechanical ventilation, allowing a home to breathe in fresh air and exhale any pollutants in a controlled and monitored way, while still preserving energy efficiency, is at the forefront of building science discussions today. Forward-thinking builders are embracing mechanical ventilation systems to stay ahead of future regulation and to satisfy customer demand for the best indoor air quality. The standard most commonly referenced for home ventilation is ASRHAE Standard 62.2, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. Developed by ASHRAE, 62.2 is the national ventilation standard of design for all homes, including up to three-story multifamily buildings. 62.2 allows exhaust-only ventilation, supply-only ventilation, or balanced ventilation. In other words, an exhaust fan or supply fan can be used, or these flows can be balanced with both a supply fan and an exhaust fan, with a combination unit such as an energy recovery ventilator (ERV). ASHRAE 62.2-2013 fan sizing is based on total square footage of the home and the number of bedrooms. The formula is: (0.03 x total square footage of the home) + (number of bedrooms+1) X 7.5 cfm). ASHRAE 62.2 provides the following table for sizing (input Ashraf 4.1a Table from E:\Articles) ASHRAE 62.2 also sets the continuous ventilation rate and provides guidance on how to increase the flow to allow for intermittent operation. Because 62.2 is the standard for ventilation in residential construction, it is used as a benchmark for many codes, certifications, and voluntary high performance building programs to define what acceptable Indoor Air Quality (IAQ) is in a home.
To verify whether a system is in compliance, the builder or rater may measure airflow in the home via a flow hood, flow grid, or other airflow measuring device. Fan operation should also be verified, with particular attention paid to exhaust airflow rates in bathrooms and kitchens. If a code requires ASHRAE 62.2 compliance, and a home fails to meet this ventilation standard, a builder is faced with expensive alterations to mechanical systems, fan capacities, and duct sizing. The International Energy Conservation Code (IECC) and the 2012 International Residential Code (IRC) set the bar for home construction. Both the 2012 IRC and IMC (International Mechanical Code) require mechanical ventilation when the air infiltration rate of the dwelling unit is < 5 ACH when tested with a blower door. Under IRC building air leakage mandates (N122.214.171.124), the air leakage rate must not exceed 5 ACH in zones 1 and 2 and 3 ACH in Zones 3 through 8. IRC Section M1507.3 governs whole-house mechanical ventilation system design. Several qualifying design options exist: • Air is exhausted when the home or dwelling unit is occupied to meet the ventilation requirements, and outside air is drawn in by negative pressure through window vents or through-the-wall vents. • Air is exhausted when the home or dwelling unit is occupied to meet the ventilation requirements, and fresh makeup air is provided to replace exhausted air via ventilation ductwork that is independent or connected to the HVAC return duct. • Outside ventilation air is supplied with a dedicated fan and relief vents allow air to escape from the home or dwelling unit when the supply air pressurizes the home. • A combination of supply and exhaust fans operate, often in conjunction with a heat recovery unit, to both supply the required ventilation air through ductwork and exhaust stale air. IRC Table M1507.3.3 provides ventilation rates based on floor area and number of bedrooms. For further code notes on 2012 IECC, visit the following link. The 2015 IMC will state that the air infiltration rate of a dwelling unit is 5 air changes per hour or less where the 2012 edition stated less than 5 air changes.
In addition, the 2015 code now references two standards for the blower door testing, ASTM E 779 and ASTM E 1827. As building codes require ever tighter, more energy efficient homes, design strategies must adapt in order to keep indoor air quality high. An ever more discerning consumer base is also driving the market as it recognizes the importance of a healthy environment in a home. People are now aware of the dangers of “indoor air pollution” and want fresher air, and radon-, VOC-, formaldehyde-, and mold-free homes for their families. In recognition of this demand, popular voluntary performance programs such as LEED® for Homes, ENERGY STAR® Homes program, and the Zero Energy Ready Home, use IECC and ASHRAE as the foundation to create a healthy, high performance home. The EPA offers the Indoor AirPLUS as a supplement to the ENERGY STAR Homes program, and Indoor AirPLUS will be required for Zero Energy Ready homes. Indoor AirPLUS, in addition to mandating ventilation that meets ASHRAE 62.2 criteria, also focuses on moisture control, pest management, protection from combustion gases, reduction of pollutants in building materials, and radon control. Under this protocol, the home's HVAC system must provide whole-house and spot ventilation, air filtration, and minimization of any condensation. Building tight and ventilating right remains the recipe, both for a healthy home and a successful homebuilder.
- U.S. Dept.of Energy, Energy, Effciency & Renewable Energy's "Guide to Home Ventilation" (PDF). www1.eere.energy.gov/buildings/openhouse/pdfs/ventilation_factsheet16.pdf
- ENERGY STAR® ventilation fan specifcation. www.energystar.gov/index.cfm?c=vent_fans.pr_vent_fans
- American Society of Heating, Refrigeration and Air-Conditioning Engineering, ASHRAE at www.ashrae.org. ASHRAE Standards and Guidelines atwww.ashrae.org/technology/page/548
- Energy & Environmental Building Alliance, or EEBA at www.eeba.org .EEBA Ventilation Guide publication www.eeba.org/bookstore/prod-Ventilation_Guide-10.aspx For a detailed analysis of ventilation system options for new homes, see the Lawrence Berkeley National Laboratory report Recommended Ventilation Strategies for Energy-Efficient Production Homes. Copies of ASHRAE Standard 62 are available from ASHRAE.