Building Efficiency and Indoor Air Quality - You Can Have Both

Abstract

Providing ventilation for acceptable indoor air quality per ASHRAE Standard 62-1989 does not require large increases in utility costs. Building efficiency does not have to be sacrificed for a healthy building. The ASHRAE 62- 1989 requirement for office ventilation is 20 cubic feet of fresh air per occupant. However, the Standard also allows various controls strategies to achieve the same result. This paper will describe the methods and application of several of these options. However. due to length restrictions, systems design criteria and comparisons will not be addressed. The simplest and most commonly used method is reducing the fresh airflow based on building occupancy, or demand control ventilation. This is currently done with carbon dioxide sensors controlling inlet dampers or fan control systems. As the people load varies causing changes in carbon dioxide level, the controls can vary the amount of ventilation air entering the building. A second method is removing the contaminants with added or special filtration. This allows more air to be recirculated but has specific limitations. Filters can remove large particulates and some chemical contaminants by changing the filter media. However, a minimum amount of fresh air, approximately 20% to 30%of the full 20cfm per person. is still required to remove the carbon dioxide and other contaminants not removed by the filters. Another group of methods is energy recovery systems including; sensible heat wheels, desiccant heat wheels, heat pipes, and run around loops. These methods can be used on some packaged equipment but is normally provided on makeup air units and central air supply systems. These built up units offer opportunities to combine heat recovery, special filtration, humidity control and demand control operations.