Lecture notes #11

Question 1

What happens during “winter” mode (unoccupied) of an HVAC unit?

Answer 1

1. heating cycles turn off 2. fan operates only on thermostat call for heat. 3. outdoor air dampers are closed 4. air from room is 100% recirculated.

Question 2

What happens during “summer” mode (unoccupied) of an HVAC unit?

Answer 2

1. HVAC unit remains off until O/A temp reaches 65*F.
2. at 65*F, the outdoor air damper opens and purges the room with cool outdoor air.
3. the O/A and R/A dampers will modulate to 100% recirculated air when room temp. reaches 65*F and the supply air fan turns off.

Question 3

Why do we not exceed an aspect ratio of 2:1 when sizing ducts?

Answer 3

because there will be too much friction in the ducting system resulting in a lot of pressure loss.