Answered Unit 79 Review Questions.docx - Unit 79 u2022...

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Unit 79 Commercial Zoned Systems Why is outside air mixed with return air? If only outside air was used, then the load on the heating or cooling system would be excessive. How much outside air should be admitted to a space? The amount of outside air required typically depends on the number of people occupying the space and the usage of the space Can outside air ever be completely shut off from a space? Fire dampers close off the supply of outside air completely so that the fire is not fed any additional oxygen. When will a preheater turn on? The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. What is the purpose of a filter status differential pressure switch?
A device used to actuate an electric switch based on differential pressure across two points and this electric switch used to sense airflow status across the fans,

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