Comprehensive Whole-House Ventilation Strategy
Most of us are familiar with the air quality index system that predicts outdoor
air quality ranging from good to hazardous. The system warns those with respiratory
problems to avoid outdoor exertion on bad days.
However, the Environmental
Protection Agency indicates that indoor air pollutants in office buildings, public
areas and homes may be two to five times, and sometimes as much as 100 times,
higher than outdoor levels. This is a special concern since most people spend
90 percent of their time indoors.
Poor indoor ventilation at home can
have an adverse impact on occupant health and comfort, especially for those that
have greater sensitivity, such as children, the elderly and those with respiratory
problems such as asthma. Inadequate ventilation can also increase the chance of
moisture problems if humidity is not expelled from within, or if humid air from
outside is drawn in without adequate conditioning.
are required to include ventilation systems capable of continuous operation, which
is unique in the homebuilding industry. Most homes built on-site rely primarily
on natural ventilation via leakage through the building envelope.
order to develop improved ventilation strategies for manufactured homes, MHRA
has undertaken a course of research that will formulate a baseline for evaluating
whole house ventilation and make common-sense recommendations based on solid scientific
Needle in a Haystack
The impact of airflow on building performance has traditionally been one of the
most difficult phenomenons to quantify and predict.
is affected hour to hour by a myriad of complex and dynamic factors both inside
and outside the home. Amongst others, these factors include wind speed, temperature,
humidity levels, and homeowner activities such as bathing, cooking, and the opening
and closing of doors and windows. With all of these variables, the complexity
of conducting conclusive research is challenging.
It is clear that meaningful
solutions do not lie in a piecemeal approach. Instead, the engineering of a whole-house
ventilation system will best spur significant and cost-effective improvements.
As a first step, the MHRA Whole House Ventilation Steering Committee conducted
a review of existing research to investigate existing whole-house ventilation
requirements and design strategies. This review helped the committee to describe
optimal design characteristics and to develop a testing protocol for further research.
Additionally, the findings of MHRA's concurrent research on manufactured
homes in hot and humid climates and on attic ventilation reinforced the need for
development of a comprehensive whole-house ventilation strategy. As a result,
these three research projects have been brought together under a single umbrella.
New Technology, New Techniques
past, infiltration, or the leakage of air in and out of the house through unintended
gaps, has provided a large portion of the ventilation. However, with the advent
of energy-efficient building technologies and materials, homes now have a tighter
envelop that limits natural ventilation. Additionally, research has shown that
under certain conditions, a home can experience air pressures that increase filtration
of hot and moist air into a home's wall, attic and roof cavities.
order to maintain acceptable air quality, modern ventilation systems must be designed
to supply fresh air and exhaust stale air, either by natural or mechanical means.
Additionally, other activities and materials that add to indoor air pollution
or excessive water vapor must also be considered in determining an acceptable
whole-house ventilation solution. For example, even normal activities such as
cooking, bathing, breathing and maintaining house plants can introduce excessive
levels of water vapor into the home.
Future research will seek to establish whole-house ventilation
strategies, home designs, and construction and operational parameters that result
in homes that reliably maintain internally balanced air pressures, a healthy air
quality and that include a mechanism to dehumidify and condition fresh air.
Out of this research, design recommendations will be made for several ventilation
systems that meet the performance targets established by the Department of Housing
and Urban Development (HUD). The research on the performance of manufactured home
ventilation systems will enable manufacturers to make better informed decisions
on design and give consumers more satisfaction with their home.