Case 8

Air Balance Analysis

A multizone model of a laboratory facility of the Westinghouse Savannah River Company was developed in order to analyze current operating characteristics of the supply and exhaust ventilation system and investigate proposed modifications to the ventilation system. The facility consists of three buildings comprised of office, laboratory and corridor spaces. The ventilation system is a once-through system designed to prevent air movement from more "clean" spaces to less "clean" spaces, e.g. air should not be allowed to flow from the laboratories to the office spaces. For this project, the entire duct system was implemented in CONTAM. This was the most extensive duct system ever implemented using CONTAM to date. Fan curves were implemented in CONTAM based on manufacturer fan curve specifications.

The air balance between different zones of the facility was analyzed under various operating conditions of the ventilation system supply and exhaust fans including fume hoods to determine proper direction of airflow between zones. A base case was developed based on normal operating conditions of the current ventilation system. This case revealed that operating characteristics were in line with desired performance with respect to relative space pressurization. Other cases were developed to investigate air balance conditions when certain fans were shut off for maintenance purposes or when a process upset condition occurs in the facility during which corresponds to a minimal exhaust-only condition. Another case involved the modification of fume hoods in one of the laboratory spaces. Among the findings of this project, the simulations revealed that some of the fan-off conditions could lead to undesirable differential pressures between clean and less-clean spaces, the process upset condition requires more makeup air than currently available, and that the proposed fume hood modifications would not be supported by the current duct system.