We have successfully designed, installed, commissioned, and maintained dual-duct variable-air-volume systems in a variety of low-rise and high-rise office buildings in California. The relatively low installed costs plus ease of zoning and rapid tenant fit-up have made this system the best choice for these buildings. The systems have all been of the dual-fan type with one fan for heating and one fan for cooling. Most have air economizers serving the cooling system and 100% recirculation for the heating system. The dual-duct variable-air-volume exterior zone boxes have been of the 100% shutoff type, which precludes mixing of warm and cool air. The zone controls have been mostly the pressure-dependent type without maximum volume limiters. We have experienced no complaints due to the 100% shutoff air valves, pressure-dependent controls, and 100% recirculation during heating.

Units: I-P