The variable volume HVAC system has become the standard in office buildings because of its lower first cost and its low operating cost. A number of concerns about the VAV system, including indoor air quality, maintainability, and comfort, have resulted in some designers’ consideration of other HVAC design alternatives. The double duct HVAC systems that were popular in the late 1940’s and the 1950’s might be a reasonable alternative to the VAV system. Probably the major criticism of the double duct system was its poor energy efficiency which was due to the mixing of heated and cooled air streams. The question addressed in this paper is whether or not a double duct system could be designed which would be as efficient as a VAV system. The strategy was to use air handling units with multiple cooling coils and heating coils. In this way each exposure would have a separate heating and cooling coil, and the interior spaces would also be conditioned using a separate cooling coil. The annual energy use simulations conclude that a double duct system designed in this manner can be as energy efficient as a standard VAV system with one cooling coil.

Units: I-P