IAQ Analysis and Contaminant Transport

IAQ Design Analysis

Typically, IAQ is dealt with during design by requiring minimum ventilation rates on a space or whole building level. The prescriptive approach contained in ASHRAE Standard 62.1-2019 and 62.2-2019 provide minimum ventilation requirements in cfm (L/s) per person and/or cfm/ft² (L/s*m²). The IAQ Procedure in Standard 62.1 is a performance-based procedure that addresses designing to maintain acceptable levels of known contaminants. CONTAM can be useful in implementing this approach to designing for acceptable IAQ both from the point of view of ventilation system and building material impacts. Other features of IAQ design that can be addressed include the consideration of outdoor air contaminant levels, the potential use of contaminant filtration to treat outdoor and re-circulated air, consideration of intermittent or variable occupancy, and distribution of ventilation air to multiple spaces.

CONTAM can be useful in implementing prescriptive design methods by analyzing the impact of prescribed ventilation rates on resultant contaminant levels various indoor and outdoor contaminant sources. CONTAM can also be used to address prescriptive methods that allow for for intermittent or variable occupancy within a building. Ventilation rates can be adjusted by changing supply and outdoor air intake rates (i.e., varying damper positions or cycling the ventilation system fans on and off) to the intermittently occupied spaces. The variation in ventilation could be carried out in such a way as to maintain contaminant concentrations within acceptable levels at all times. The method by which the ventilation rate is varied depends upon the type of contaminant source that is being controlled, i.e., occupant related or not. The method involves lead or lag times of providing ventilation air depending on the type of source of the contaminant that is being controlled. CONTAM can be used to model the source and develop contaminant profiles. From this information, ventilation control strategies can be implemented in the CONTAM building model in the form of scheduled fan on/off times and system airflow rates. Simulations can be performed and results reviewed to determine if the ventilation strategy would maintain contaminant levels according to design requirements.

Performance-based methods of designing for IAQ can also be addressed using CONTAM. For example, the Indoor Air Quality Procedure presented in ASHRAE Standard 62.1-2019 consists of identifying known contaminants of concern, specifying acceptable levels of these contaminants, and providing ventilation that prevents the acceptable levels from being exceeded. CONTAM can be useful in analyzing contaminant levels based on contaminant source strengths, design ventilation rates, and air filtration and cleaning system characteristics that might be implemented in the ventilation system design. While CONTAM could be useful in verifying ventilation system design, it could also provide a means of documenting the design.

Building Material Impacts - CONTAM can be used to analyze the IAQ impacts of building material emissions. Although designers might implement "low-emitting" materials in a design, it is often difficult to quantify the effects of using such materials. CONTAM enables the analysis of different materials within a building design on a quantitative basis.

Contaminant Source Isolation

Contaminant source isolation refers to the prevention of contaminant transport from one zone having a know source into another. Some examples of contaminant source isolation issues include parking garages, toilets, and radon entry from the soil. These situations involve establishing airflow or pressure differentials between different zones of a building to control contaminant migration. The ability to use CONTAM to define complicated multizone systems enables the analysis of contaminant transport not only between zones that are immediately adjacent to each other, but also the less obvious transport paths related to elevator and stair shafts, service chases, and duct leakage.

One example of a CONTAM source isolation problem is the analysis of radon entry into and transport within a building. CONTAM provides a pressure-driven source model that can be used to effectively simulate the transport of radon from the soil into the building through cracks in a building foundation. Because the source is pressure dependent, the relationship between the pressure differences associated with different ventilation scenarios, stack and wind induced flows and radon transport into the building can be analyzed. Further, CONTAM could then be used to investigate the implementation of various radon mitigation strategies including fan pressurization and depressurization techniques.

IAQ Investigations

CONTAM can be useful in investigating IAQ problems as they occur in existing buildings. Using CONTAM one can establish a building geometry and system features and use CONTAM to gain insight into why a building is behaving the way it does. For example, if a room in a building is experiencing elevated contaminant levels from a known source, CONTAM could be used to investigate potential transport paths and methods to mitigate the transport of the contaminant to occupied zones. CONTAM analysis can be particularly useful when coupled with the measurement of relevant parameters such as system airflow rates, differential pressure, contaminant concentrations, wind and indoor and outdoor temperatures. CONTAM has been used as a tool to investigate building operating conditions that lead to radon entry from the soil and to size a fan system to alleviate the problem.

Exposure Analysis

Exposure analysis refers to the determination of the amount (dose) of a contaminant to which a building occupant would be subjected within a building. This analysis requires knowledge of contaminant concentration time histories, occupancy patterns within a building and occupant ingestion rates. CONTAM provides the ability to calculate contaminant time histories using transient simulation techniques and to define occupant inhalation rates and occupancy patterns within a building. Together this information can be used to provide average and peak exposure levels as well as average and peak dosages of contaminants of concern.