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Preconditioning Outside Air: Cooling Loads from Building Ventilation
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.
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