A Review of Home Airtightness and
Ventilation Approaches for Florida
Building Commission Research
FBC Mechanical Technical
Advisory Committee Meeting
June 25, 2014
A Research Institute of the University of Central Florida
Tasks
Task 1: Conduct a literature review, examination of
experimental data, and calculations of energy impacts
of using or not using various types of ventilation
systems.
Task 2: Develop alternative approaches to achieving
acceptable levels of ventilation while avoiding the risks
associated with super-tight home enclosures and
potential mechanical system failures.
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Literature Review
Over 40 articles, research reports, presentations and
code documents were reviewed.
Information sources included:
• American Council for an Energy-Efficient Economy (ACEEE)
• American Society of Heating, Refrigerating and Air-Conditioning
Engineers (ASHRAE)
• Building Science Corporation (BSC)
• Florida Solar Energy Center (FSEC)
• International Code Council (ICC)
• Lawrence Berkeley National Laboratory (LBNL)
• US Environmental Protection Agency (EPA)
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Literature Review
Wide consensus that both controlling infiltration and
providing mechanical ventilation is necessary for
homes, but determining appropriate levels for each is
much more involved.
• Considerations must include:
– Energy use
– Indoor humidity impacts
– Combustion safety
– Ventilation system performance
– Maintenance
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Cooling Season Infiltration
• Loose House
• Tight House
– Higher moisture load
from outside than tight
house
– Heat (sensible) load over
entire cooling season
similar to tight due to
small indoor / outdoor
temperature diff.
AC runs
and
removes
moisture
A/C
– Small relative humidity
improvement in the
house
– Very small energy
savings
High dew
point
outside
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Heating Season Infiltration
• Loose House
• Tight House
– More dry air from
outside than tight house
– When heating, wind
speeds and temperature
difference larger than
when cooling so there is
more heating load
created than for tight
house.
Heater runs,
moisture not
removed
A/C
– Higher relative humidity
due to interior moisture
generation-- possible
condensation if single
pane glass or metal frames
– About 15% heating savings
Low dew
point
outside
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Air Tightening
• Air tightening allows control over where and
how much outside air enters a house
• Measured 2009 Florida Code home average
ACH50 = 5.6 (31 home sample)
• 2014 Code requirement is <= 5 ACH50
• Air tightening shown to provide limited summer
energy savings and more significant percentage
savings in winter
• Mechanical ventilation energy use may exceed
air tightening savings
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Arguments for Build it Tight
• Control infiltration sources and rates
• Reduce peak winter drafts and loads
• Can use continuous mechanical ventilation to
deliver required air year round
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Arguments Against Extremely Tight
• Unbalanced airflow (such as exhaust fans,
unbalanced return air or duct leakage) can
depressurize the interior space leading to
combustion appliance spillage, back-drafting and
flame roll-out
• Lack of fresh air when mechanical ventilation
system fails
• Can create winter moisture issues
• In Florida, small savings from tight to extremely
tight
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
How Much Outside Air?
• Health related research almost non existent
• Agreement that there are indoor pollutants
• Quantity of outside air required has been
more of a consensus than a science
• 2012 IMC / 2014 FMC: continuous ventilation
at 0.35 ach but not less than 15 cfm/person
• 2012 IRC / 2014 FRC: continuous ventilation
rate provided by Table M1507.3.3(1)
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
How Much Outside Air?
• Movement toward health-based whole house
ventilation; LBNL researching and working to
incorporate a health metric into the 2016
version of ASHRAE 62.2
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Ventilation Performance and Failure
• Limited whole house ventilation performance
and failure research results available
• Significant number of systems not complying
with Code requirements
• Component failure
• Installation issues
• Homeowner understanding and maintenance
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Recommendations
“Reasonably tight” with neutral or slightly
positive mechanical ventilation
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Specific recommendations include:
• Do not require further air tightening beyond the 2012 IECC
level of 5 ACH50
– Savings too small
– Potentially significant health and safety risks from mechanical
ventilation failure or unbalanced airflow if house gets too tight
• Focus on sealing pathways between indoors and attic,
garage and crawlspace
• Move toward health-based ventilation standards- will
require collaborative research
• Educate public about pollutant sources and controlling
them in homes (Green home programs attempt this)
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Specific recommendations include:
• Ventilation system design
– Flexible airflow rate: provides flexibility if/as
recommendations change and allows seasonal
adjustments
– High efficiency fans: allows oversized fans to run
at low speeds (for runtime vent); also may soon
be possible to specify 0.2 or 0.3 Watts/cfm instead
of 2014 FEC specification of ~0.35 Watts/cfm
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Specific recommendations include:
• Ventilation system design (cont.)
– Positive pressure or balanced: provides air source
control and reduces risk of exhaust dominated
systems driving moist air through envelopes
leading to mold and mildew at low permeability
locations
– Moisture removal: have means to remove
moisture introduced by the ventilation air (DBPR
Indoor RH research)
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Specific recommendations include:
• Ventilation system design (cont.)
– Proper intake locations: 2014 FEC requirement not
allowing ventilation air to come from attics,
crawlspaces, attached garages or outdoor areas
close to pools or spas should be added to IECC
– Also do not allow sources near insecticide spray
locations, car exhaust, AC condensers or dryer
exhausts
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Specific recommendations include:
• Balanced ventilation systems as one option
– Supply and exhaust ducts
– Allows balanced or positive house pressure
– Requires first cost and energy use of two fans
– Enthalpy (energy) recovery ventilation (ERV)
option reduces heat and moisture gains from
ventilation air, although not effective at times in
swing seasons; also maintenance issues
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Specific recommendations include:
• Supply only ventilation systems as another
option
– Energy use and first cost of one fan
– Can be combined with dedicated outdoor air
systems (DOAS), standard air conditioners and/or
dehumidifiers to remove moisture
– Runtime option + appropriate controls can be
effective during peak cooling and heating seasons;
can raise humidity during swing seasons
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida
Specific recommendations include:
• Consider mandating some type of alarm
system for when a whole-house ventilation
system failure is detected (limited field studies
raise concerns about longevity, homeowner
operation and maintenance of these systems)
• Initiate Florida whole-house ventilation
system effectiveness and failure study.
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FLORIDA SOLAR ENERGY CENTER — A Research Institute of the University of Central Florida