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Lennox Rooftop Units with enthalpy sensors

Lennox Rooftop Units with enthalpy sensors

Lennox Rooftop Units with enthalpy sensors

(OP)
Hello,

I'm work in building commissioning. There are some roof top units with an modulating outside air damper. I would like to verify that the damper is modulating properly, however there is no test option on the controller located in the unit. Does anyone have any recommendations? Thank you.

RE: Lennox Rooftop Units with enthalpy sensors

Without a control sequence, you will not know. Find the original Engineer.

RE: Lennox Rooftop Units with enthalpy sensors

(OP)
A few of my co-works suggested that I trip the enthalpy sensor by turning a can of compressed up upside and spraying it. It should work.

RE: Lennox Rooftop Units with enthalpy sensors

Measure return air temp/humidity and outdoor air temp/humidity and calculate enthalpy from each. This time of year you'd find outdoor at higher enthalpy than return most of the time (northern hemisphere, 45° parallel or below). Ensure the OA damper is at its minimum position if OAE is higher than RAE.

Set the DAT set point high (e.g., 85°F). Cool the OAT sensor with ice (or as you mention, by spray can) and the dampers should modulate toward full outdoor air.

RE: Lennox Rooftop Units with enthalpy sensors

you should use fixed position for RTU's OA control. You cannot maintain the correct levels of OA without air flow measurement on RA/OA (too much or too little). your SF could be pulling most of the air form OA intake when modulating. AND you will have room overpressure problems.

RE: Lennox Rooftop Units with enthalpy sensors

(OP)
Thanks for the input everyone. Much appreciated.

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