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COMIS: An Interzonal Air-Flow Model

To provide good indoor air quality and to correctly size a building's space-conditioning equipment, the designer must understand air-flow patterns. A knowledge of interzonal flows is required to determine the impact of infiltration and natural and mechanical ventilation on indoor air quality. Mathematical models can determine infiltration values for all air-leakage and weather combinations.

Interzonal air-flow models calculate air-flow-related energy losses and the flow distributions in buildings. These models fall into two categories: single and multizone. Single-zone models assume that a building can be described by a single well-mixed zone. They are usually used for modeling single-story, single-family houses with no internal partitions (all inside doors are open). For detailed research uses, however, most buildings should be characterized as multizone structures even when no internal partitions are present. Researchers have developed models that simulate the interzonal flows of buildings with more than one well-mixed zone.

Office building with arrows indicating airflow input and output

COMIS's Structure

Conjunction of Multizone Infiltration Specialists (COMIS) is a recent development in interzonal air-flow modeling, with a modular structure that helps it stimulate buildings more effectively than earlier multizone air-flow models. It can be used as a stand-alone model with input and output features, or as an air-flow module for thermal building simulation programs. It can also serve as a module library for other models.

The COMIS program was designed during a 12-month workshop at Berkeley Lab in 1988 and 1989. In 1990, the Executive Committee of the International Energy Agency's Energy Conservation in Buildings and Community Systems program created a group of experts from nine nations to continue this work. In early 1998, this group released COMIS 3.0 and a user interface designed for UNIX- and Windows-based systems, IISiBaT. More than 200 copies of the program are in use in at least 15 countries.

Modules in COMIS include air-flow equations for large vertical openings, single-sided ventilation, and different opening situations for various window constructions.

Key Components

COMIS models the air flow and contaminant distributions in buildings. The program can simulate several key components influencing air flow: cracks, ducts, duct fittings, fans, flow controllers, large vertical openings (windows and doors), kitchen hoods, passive stacks, and "user-defined components." COMIS allows the user to define schedules describing changes in the indoor temperature distribution, fan operation, pollutant concentration in each of the modeled zones, pollutant sources and sinks, opening of windows and doors, and weather data. The "flexible time step" implemented in COMIS enables users to model events independent of the frequency with which the weather data are provided.

The COMIS air-flow calculation is based on the assumption that indoor air flows reach steady-state at each time step. The contaminant transport is based on a dynamic model and has its own time step, based on the time constant of the most critical zone. The two models are coupled. Results for air flows and contaminant levels are reported in terms of tables by COMIS and in graphical form by some of the user interfaces.

The Environmental Energy Technologies Division is conducting several ongoing COMIS-related projects. Researchers are integrating COMIS into EnergyPlus, the next generation of thermal building simulation models under development by EETD and the University of Illinois. An aerosol deposition model for rooms and ducts is also in development, as are a room model (MIAQ4) at the University of California, Berkeley. We are planning a new module dealing with air flow through staircases and Concordia University is developing a zonal model that will also be integrated into COMIS.

COMIS and IISiBaT are available for downloading.

— Helmut Feustel

For more information, contact:

  • Brian Smith
  • (510) 486-4677; fax (510) 486-6658

 

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