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Development of a Humid Climate Definition
Abstract
The role of humidity in indoor air quality has
become of increasing concern in recent years. High
indoor humidities can result in microbial growth on
building surfaces, resulting in poor indoor air quality,
as well as damage to the building and its contents. In
addition to the IAQ impacts, high indoor humidity
can cause occupant discomfort.
The public review draft of ASHRAE Standard
62-1989R included requirements for installation of
dehumidification controls in buildings with
mechanical cooling located in humid climates. The
draft standard included a definition of humid climate:
where, during the warmest six consecutive months of
a typical year, the wetbulb temperature is 19°C
(67°F) or higher for 3500 hours or more, or 23°C
(73°F) or higher for 1750 hours or more. This
definition is that used in the 1993 ASHRAE
Handbook of Fundamentals to define the humid
climate region. The only areas in the continental
United States which meet these criteria are close to
the Gulf coast, all of Florida, and along the Atlantic
coast as far north as southern North Carolina
While it is clear that buildings in this humid
climate region need to be carefully designed with
regard to humidity control, it is also clear that
buildings in other areas have an equal need for
humidity control.
The work described in this paper examines a
number of potential indicators of "humid climate"
and correlates them with the prevalence of indoor
humidity problems in three building types. The
FSEC 2.3 energy simulation computer program
(Kerestecioglu et al. 1989) was used to simulate the
three building types, using weather from 10 cities in
the southeastern U.S. The FSEC software was
selected because it is capable of accurately modeling
moisture transfer within the building space and the
dehumidification performance of cooling coils at
part-load conditions, and predicting resulting
humidity levels. The buildings modeled were a retail
store (similar to a K-Mart or Wal-Mart), a large
office building, and a fast food restaurant. Existing
building models were employed for this study with
ventilation rates in accordance with ASHRAE Standard 62-1989. The HVAC systems used were
typical for these building types, without any special
humidity control measures. The selected indicators
of humidity problems are the number of hours per
year with space humidity above 60% RH and the
number of occupied hours with space humidity above
60% RH.
TMY2 weather data (NREL 1995) for 10 cities
was used for the annual building energy simulations.
TMY2 data was also used to calculate a number of
potential humid climate parameters for the same 10
cities. These included:
the number of hours and the wetbulb-degree
hours above 3 different wetbulb
temperatures,
the number of hours and grain-hours above
4 different humidity ratios, and
the sensible, latent and total Ventilation
Load Index (VLI).
The VLI is the load (latent, sensible or total)
generated by bringing one cfm of outdoor air to
space neutral conditions over the course of one year
(Hamman, et al. 1997).
The ability of each climate parameter to predict
indoor humidity problems was analyzed and
compared. Implications of using the selected
parameters to define a humid climate will be
discussed
Citation
Hedrick, R. L.; Shirey, D. B. (1998). Development of a Humid Climate Definition. Energy Systems Laboratory (http://esl.tamu.edu); Texas A&M University (http://www.tamu.edu). Available electronically from https : / /hdl .handle .net /1969 .1 /6737.