When the unit is in economizer mode, the relief air damper
is fully open and the coil path return damper is fully closed, such that all of the air traversing the cooling coil is outdoor air.
[H.sub.2]O) Q = airflow through each path, [m.sup.3]/s (cfm) R = relief air damper
control signal for BPP and BPA damper controls S = path resistance factor [omega] = relative fan speed based on design speed [theta] = damper blade position (1 for fully open and 0 for fully closed) Subscripts d = design EF = exhaust air fan ex = exhaust air (path) inf = envelope infiltration (path) MA = mixed air plenum (node) oa = outdoor air (path) OAD = outdoor air damper
ra = return air (path) RCD = recirculating air damper
RE = relief or return air plenum (node) rec = recirculating air (path) rel = relief air (path) RF = return air fan RLD = relief air damper
RM = room air or space (node) sa = supply air (path) SF = supply air fan TB = terminal box REFERENCES
* recirculation air damper
stuck open, stuck closed, stuck 50% open
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.
When the chillers stop on cold days, I open the outside air dampers
to 100% and open the precool deck to 60%.
At a minimum, these units include a fan, a two-pipe chilled/ hot coil and an outside/return air damper
. Air dampers
provide minimum ventilation and are capable of delivering 100% outside air in economizer mode.
It was found that when the sensor noise standard deviation is 0.1[degrees]C, the maximum CUSUM score is comparable with the value when fresh air damper
leakage is 0.005 and 0.01.
is always the difference between the supply airflow and the return airflow through path PL-1 to PL-2, and, therefore, the [outdoor air] damper size and type have no effect on the amount of outdoor air." 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).
Stuck Exhaust Air Damper
. Figure 4 shows the detection results for this fault.
Note: Variable Air Volume (VAV) systems with fixed outdoor air damper
positions must comply with this requirement at minimum system primary airflow"
During the summer season, when the cooling coil is in use, the outdoor air damper
is either maintained at a minimum position when outdoor air conditions do not satisfy the economizer control conditions; or the outdoor air damper
is maintained at 100% open position when outdoor air conditions satisfy the economizer control conditions.
Most VAV economizer systems modulate the outdoor air and return air dampers
simultaneously, the same as constant volume systems.