22 research outputs found
Sensitivity of Low Sloped Roofs Designs to Initial Water and Air Leakage
Liquid water in low sloped roofs almost
always causes problems. Roofs are
designed only to control the migration of
vapor, if at all. Small amounts of water
leakage/penetration, may cause mold
growth or catastrophic corrosion in current
roofs systems. In a recent paper by the
authors the effect of exterior surface
emissive and absorptive properties was
found to have a significant effect on the
moisture performance of a roof that had a
leak. Depending on the surface
characteristics, roof systems can be
designed to effectively manage water
penetration, but at an energy cost. In the
roofs system examined previously, air
leakage was not included.
In the present study, the authors reinvestigated
the effect of water penetration
and the influence of air leakage on the
hygrothermal performance of a few
selected roofs. The drying potential of a
groove ventilated roof is examined. The
performance concept is based on the fact
that warming up of air in the groove
increases it's ability to transport moisture
to the outside. Solar radiation raises the
temperature of air in the grooves and on
average, during a sunny summer day 0.5 L
of water can be ventilated out of the roof
per 1m width of the roof.
In this paper, one climatic condition was
investigated; a hot and humid Climate
representative of Houston, TX. The
specific questions that the paper addresses
are: What are the vapor and liquid control
dynamic involved in the moisture
migration of a roof in Houston TX? and
how does airflow influence the
performance of a roof that is initially wet ?
A state-of-the-art numerical model was
used to address these issues. Results
showed that the drying potential depends
on the ventilation rates. The roof system
with ventilation grooves dried out faster
from the initially wet stage than the roof
without the ventilation grooves. The total
increase in heat loss of the roof was found
to be between 0 - 5 % depending on the
thickness of the insulation. The ventilation
can cool down the temperature of the roof
in the middle of a hot and sunny day thus
reducing the heat load to the inside
Integrated Hygrothermal Performance of Building Envelopes and Systems in Hot and Humid Climates
In hot and humid climates the interior and exterior
environmental loads that building envelopes must
respond to are larger than many other climatic
conditions. Moisture-originated failures in low-rise
residential buildings have put a significant pressure to
change construction codes in North America.
Solutions to moisture induced problems may be
difficult when several interacting mechanisms of
moisture transport are present. A new approach to
building envelope durability assessment has been
introduced in North America; a moisture engineering
approach. This requires system information about the
wall systems as constructed along with aging
characteristics coupled with advanced modeling that
0 term allow the designer to predict the Iong-term performances of building envelope systems. This
permits the comparison and ranking of individual
building envelope systems with respect to total
hygrothermal performance.
Critical information can be obtained by investigating
the one to one relationships of a building envelope to
interior and exterior environments, however, the total
behavior of the actual whole building is not
accounted for. This paper goes one step further, by
incorporating the individual hygrothermal
performances of all walls, roof, floor and mechanical
systems. The direct and indirect coupling of the
building envelope and indoor environment with
HVAC system are included in the analysis. The full
house hygrothermal performance of an aerated
concrete wall system are examined for a hot and
humid climate. The hour by hour drying potential of
each system was then numerically analyzed using
weather conditions of Miami (hot and humid
climate). The results clearly demonstrate the limited
drying potential for the wall system in that climate.
Furthermore, the selected exterior thermal insulation
strategies and interior vapor control strategies in this
study clearly show the critical behavior of the full
house with respect to drying initial construction
moisture. The results show the importance of the
total hygrothermal behavior of the whole house to the
coupling between the various envelope parts, interior
and exterior environments and HVAC system. From
these results moisture control strategies are identified
for the whole house hygrothermal performance
The Effect of phase changes of moisture on the hygrothermal behaviour of walls subjected to hot and humid climates
Peer reviewed: YesNRC publication: Ye
Influence of waterproof coating on the hygrothermal performance of a brick facade wall system
Peer reviewed: YesNRC publication: Ye
Moisture transport in building envelopes using an approximate factorization solution method
Peer reviewed: YesNRC publication: Ye
Moisture conditions of non-ventilated, wood-based membrane roof components
Peer reviewed: NoNRC publication: Ye
The effect of waterproof coating on hygrothermal performance of a high rise wall structure
Peer reviewed: YesNRC publication: Ye
Numerical simulation of experimental freeze conditions in glass-fiber insulation
Peer reviewed: YesNRC publication: Ye
Effects of gestational age and prenatal and perinatal events on the coagulation status in premature infants
Objective: To study prospectively the effects of prematurity and perinatal events on the coagulation status of premature infants. Patients and main outcome measures: Blood samples from premature infants born before 37 gestational weeks were taken for analysis of coagulation factors II, V, VII, and X and platelet count. Results: A total of 125 premature infants, 71 boys, were studied at the median postnatal age of 40 minutes (range 12–100). The lowest median activities of coagulation factors II, V, VII, and X and the platelet count were observed, as expected, in infants (n = 21) born at 24–27 weeks gestation. Twin B (n = 14) had lower median activities of coagulation factors II, V, VII, and X than twin A. Infants with evidence of mild asphyxia (Apgar score at 5 minutes < 7 or cord pH < 7.26) had significantly (p < 0.05) lower levels of coagulation factors II, V, VII, and X and platelet counts than infants without asphyxia. Infants who were small for gestational age (SGA) had significantly (p < 0.05) lower levels of coagulation factors V and VII and platelet counts than infants of appropriate size for gestational age. Other prenatal and perinatal variables examined (sex, maternal hypertension and/or pre-eclampsia, antenatal steroid use, mode of delivery, Apgar scores) did not show any significant associations with coagulation status, which may be explained by the small number of infants studied. Conclusions: The data strongly suggest that there are distinct differences in specific coagulation tests in different patient populations, which could assist in the identification of extremely preterm, SGA, or asphyxiated preterm infants who may be susceptible to haemorrhagic problems perinatally