Guide to Home Ventilation & IAQ
The purpose of ventilation is to provide fresh (or at least outdoor) air for comfort and to ensure healthy indoor air quality by diluting contaminants. Historically people have ventilated buildings to provide source control for both combustion products and objectionable odors (Sherman, 2004).
Currently, a wide range of ventilation technologies is available to provide ventilation in dwellings including both mechanical systems and sustainable technologies. Most of the existing housing stock in the U.S. uses infiltration combined with window opening to provide ventilation, sometimes resulting in over-ventilation with subsequent energy loss; sometimes resulting in under-ventilation and poor indoor air quality. Based on the work of Sherman and Dickerhoff (1998), Sherman and Matson (2002) have shown that recent residential construction has created tighter, energy-saving building envelopes that create a potential for under-ventilation. Infiltration rates in these new homes average 3 to 4 times less than rates in existing stock. As a result, new homes often need provided ventilation systems to meet current ventilation standards. McWilliams and Sherman (2005) have reviewed such standards and related factors.
According to ASHRAE standard 62.2-2004, published by the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE, 2004), single, detached residential buildings are required to meet a whole house ventilation rate based on the number of bedrooms in the house, the number of occupants, plus an infiltration credit (3 cfm per 100 sq. ft plus 7.5 cfm per additional occupant which includes a 2 cfm per 100 sq. ft allowance for infiltration). There are a variety of ways to meet this standard either through mechanical systems or via natural forces.According to Home Energy Magazine May/June 2000, a “good ventilation system" should:
- Provide a controlled amount of unpolluted outdoor air for both comfort and dilution
- Have at least a 15 year life
- Be acceptable to operate by occupants (low noise, low cost)
- Not detract from the safety and durability of the house.”
Mechanical technologies must include:
- Continuous exhaust systems
- Intermittent exhaust systems
- Exhaust with make-up air inlets
- Intermittent or continuous local exhaust with make-up air from inlet in return
- Continuous supply
- Intermittent supply with inlet in return side of HVAC System
- Combined exhaust and supply (Balanced)
Sustainable technologies, which are those whose motive forces are principally temperature difference and wind, must include:
- Infiltration with operable windows
- Passive Stack Ventilation
- Solar Chimney
- Hybrid Systems
There are a wide variety of systems currently on the market that can be used to meet ASHRAE Standard 62.2. While these systems generally fall into the categories of supply, exhaust or balanced, the specifics of each system are driven by concerns that extend beyond those in the standard.
Some of these systems go beyond the current standard by providing additional features (such as air distribution or pressurization control). The market will decide the immediate value of such features, but ASHRAE may wish to consider relevant modifications to the standard in the future.
ASHRAE may also wish to consider expanding the standard to allow sustainable technologies—that is, passive or hybrid technologies that principally rely on natural driving forces rather than fans to transport the air. Such systems have been used for millennia and are currently used in Europe to satisfy ventilation requirements. R&D is necessary to develop such systems for the US, but they have great potential for green buildings.