NCEES 2011 Practice Exam HVAC & Refrigeration Problem 506

[omar51389]

A room in a building has the following characteristics: 

   Sensible heat gain = 90,000 Btu/hr

   Latent heat gain = 40,000 Btu/hr

   Supply air to the room = 3,600 com @ 55ºF db

The room is kept at 78ºF db/ 45%rh. Outdoor air conditions are 92ºF db/ 76ºF wb. Outdoor air ventilation for the room is 700 com. The cooling coil entering-air temperature and leaving-air temperature, respectively are most nearly:

In the solution, the equation for the load is shown as QT = SH + LH + OA = 163,264 BTU/hr.

If SH= 90,000 BTU/hr and LH = 40,000 BTU/hr, then OA has to be 33,264 BTU/hr. I don't know how they calculated the OA load..... can someone help explain how they got that?

 

[Habib]

The ventilation load is calculated by:

Qven=700x(h@OSA condition-h@space condition)x60/v at space condition 

hope that helps, if not I can post my solution.

 

[Habib]

One correction, v should be at OSA condition instead of space condition. It will not make much difference though 

 

[omar51389]

Perfect. Thank you!