Visit the Energy Systems Laboratory Homepage.
Preconditioning Outside Air: Cooling Loads from Building Ventilation
Abstract
HVAC equipment manufacturers, specifiers and
end users interacting in the marketplace today are
only beginning to address the series of issues
promulgated by the increased outside air
requirements in ASHRAE Standard 62- 1989,
"Ventilation for Acceptable Indoor Air Quality", that
has cascaded into building codes over the early to
mid 1990's. There has been a twofold to fourfold
increase in outside air requirements for many
commercial building applications, compared to the
1981 version of the standard. To mitigate or nullify
these additional weather loads, outdoor air
preconditioning technologies are being promoted in
combination with conventional HVAC operations
downstream as a means to deliver the required fresh
air and control humidity indoors. Preconditioning is
the term applied for taking outside air to the indoor
air setpoint (dry bulb temperature and relative
humidity).
The large humidity loads from outside air can
now be readily recognized and quantified at cooling
design point conditions using the extreme humidity
ratios/dew points presented in the ASHRAE
Handbook of Fundamentals Chapter 26 "Climatic
Design Information". This paper presents an annual
index called the Ventilation Load Index (VLI),
recently developed by the Gas Research Institute
(GRI) that measures the magnitude of latent (and
sensible) loads for preconditioning outside air to
indoor space conditions over the come of an entire
year. The VLI has units of ton-hrs/scfm of outside
air. The loads are generated using new weather data
binning software called ~BinMaker, also from GRI,
that organizes the 239 city, 8760 hour by hour,
TMY2 weather data into user selected bidtables.
The VLI provides a simple methodology for accessing
the cooling load impact of increased ventilation air
volumes and a potential basis for defining a "humid"
climate location.
Citation
Kosar, D. (1998). Preconditioning Outside Air: Cooling Loads from Building Ventilation. Energy Systems Laboratory (http://esl.tamu.edu); Texas A&M University (http://www.tamu.edu). Available electronically from https : / /hdl .handle .net /1969 .1 /6736.