| 摘要 |
An improved mixing box is disclosed. The mixing box comprises an inlet end, an outlet end, a substantially closed first passage to which primary air flows from a primary air inlet and then through induction means and to and from the outlet end. The induction means are positioned intermediate the inlet and outlet ends and are operable, when primary air flows through the passage, to induce a flow of air through a first opening for mixture with primary air and delivery therewith through the outlet end. The mixing box also comprises means for controlling the rate of flow of primary air and a fan operable to induce a flow of air through a second opening and to deliver such air through the outlet end of the box. The improvement includes a closed second passage formed in the mixing box for the flow of air from the second opening to the suction side of the fan and a control operable to energize the fan when the primary air flow is below a control rate and to de-energize the fan when the primary air flow is above the control rate. Additionally, the primary air inlet can open into the closed second passage which communicates directly with the first passage and therethrough with the induction means and the outlet end of the mixing box, while the fan discharges into the first passage and therethrough into the induction means, and through the outlet end of the box.
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