A demand-controlled ventilation system composed of a louvered panel heater and a pair of electrically-operated damper chambers with separate air inlets and outlets, is shown in Figure 9.6. The upper damper chamber is provided with adjustable louvers to reduce the face velocity, and the system is load-balanced at the louvered panel heater. A more detailed description of this system will be given in another paper.
The pressure drop along the path of least resistance must always be taken into account when designing a draft tube system. The path of least resistance can be the corner of a room, entry to and exit from a room, a window with screens, a door frame, or a bathroom exhaust duct.
The power generated by a fire rated nonbypass alarm is finite. As the alarm is triggered, the blower motor is turned on to pull air through the sash. In some cases, the sash may be closed too late, enabling fire to grow unchecked before the fire alarm is sounded.
The design goals of a fire rated nonbypass system are to have a low efficiency and a high face velocity during sash opening and to limit the face velocity to a low percentage of the free-venting face velocity (fvs) to prevent fire propagation through the nonbypass hood.
Design exceeds the performance goal when the blower efficiency is less than the design limit with the same closed sash, because the increase in blower efficiency in the open condition cannot be recovered during sash operation. The operation of the system to maximize blower efficiencies is discussed in Section 9.2.4. d2c66b5586