In minimum outdoor air mode, if the coil path air damper
is fully closed and the relief air damper
is fully open, but one or more zones is not receiving adequate outdoor air, then the SAT temperature controller will be overridden to lower the supply air temperature, thus closing the bypass damper and increasing outdoor air entering through the coil air path.
A damper control system for preventing reverse airflow through the exhaust air damper
of variable-air-volume air-handling units.
recirculation air damper
leakage (10% of full flow)
This fluctuation is not observed in the simulation because the movement of the air damper
was not taken into consideration in the computation.
The slight downward trend is the result of additional economizing, and hence lower pressure drop across the outside air damper
, as well as reduced air leakage from the ducts, at low flow conditions.
Variables examined for system level validation included cooling and heating coil valve positions, room air temperature, outdoor air damper
position and hot water flow rate.
Because the outdoor air dampers
modulate to maintain supply air temperature, they are often at minimum, and the supply air temperature setpoint will often reset above the 55[degrees]F (13[degrees]C) minimum setpoint.
Fully opening the outdoor air damper
rather than tracking the other dampers reduces pressure drop and fan energy, and it ensures there is no backflow through the relief damper for systems using Airflow Tracking control (see Reference 3 for more details).
When the chillers stop on cold days, I open the outside air dampers
to 100% and open the precool deck to 60%.
In addition, the fan must create a low enough pressure at its inlet (B) to overcome pressure losses associated with drawing the return air out of the zone and through the return air path (which might include a return grille, ceiling plenum, and some ductwork), and then to draw the air through the return air damper
, filter, and coils inside the terminal unit.
For the fresh air damper
leakage, three cases are studied.
The outside air inlet at the roof was equipped with a minimum outside air damper
that was operable for demand-controlled ventilation and an economizer damper that was operable by standard airside economizer controls.