PDX DCEO Qualification Card

What is a purge and how do the affected air handlers and exhaust fans respond to a purge request?

A purge is a 100% utilization of both air handlers and associated exhaust fans, designed to quickly cool a room in an emergent situation. Manually and by the purge panel when pressure is ± .75 and or temp is above 95° (data hall) 105° (electrical room)

What is an Area Controller (AC)?

Area controllers are used to modulate the equipment in each individual area to maintain the local temperatures within a specified range.

What is the normal operating temperature and humidity Inside the IGLOO's

Humidity: 20%-60% Temp: 61-77 F

What position do each of these dampers default to when the air handler is off: Bypass Air Dampers

Depends on the settings in your building. Could be open or closed.

What position do each of these dampers default to when the air handler is off: Outside Air Dampers

100% Closed

What position do each of these dampers default to when the air handler is off: Return Air Dampers

100% Open

What position do each of these dampers default to when the air handler is off: Supply Air Dampers

100% Closed

Where are the mechanical loads powered from?

Mechanical load are powered from the House/Mechanical Service Distribution Board (HSDB/MSDB) and are powered by catcher when main power is lost.

Where does the BMS system sense outside air pressure?

At the Air Handling Unit inlet

Discuss Delta vs Wye connections.

Delta: 3 lines of equal voltage in a triangle configuration.
V*line* = V*phase*
I*line* = I*phase* x sqrt(3)
I*line* lags I*phase* by 30 degrees

Wye: 3 lines of equal voltage in a 'Y' configuration with a fourth, neutral line connected at the point where the 3 main lines merge.
V*line* = V*phase* x *sqrt*(3)
I*line* = I*phase*
V*line* leads V*phase* by 30 degrees

Discuss Wet Bulb vs Dry Bulb

Dry Bulb is the air temperature. Wet Bulb is the air temperature at 100% humidity. They are used to determine relative humidity.

How does a generator produce electricity?

Uses mechanical energy of rotor to induce movement of electrons in stator windings, producing alternating current.

A current is applied to the armature via commutators and brushes. A mechanical prime mover rotates the armature within the stator. The combination of magnetic fields produced by the armature current and the movement created by the prime mover creates the requirements for current to be generated on the field windings.

How does a transformer work?

A transformer produces step changes in voltages between a primary and secondary winding.

Each side of the transformer consists of electrical windings wrapped around an iron core. The magnetic field of the primary winding induces a voltage on the secondary winding and produces current. The current produced on the secondary winding is proportional to the difference in number of coils/turns from primary to secondary.

How does a variable frequency drive work?

A VFD converts incoming AC power to DC power via a rectifier. The DC power is then inverted back to AC power via IGBTs at a desired voltage and frequency that correlates to desired changes in speed of a motor. This allows precise controlling of motorized equipment.

What are the pump/fan affinity laws?

Pump laws describe the changes in flow rate, pump head, and power that result from a change in either the diameter of the pump impeller or impeller speed.

Where:
Q=Volumetric Flow Rate
dp=Head/Pressure
P=Power
n=impeller speed
d=impeller diameter

Q1/Q2=(n1/n2)(d1/d2)
dp1/dp2=(n1/n2)^2(d1/d2)^2(2)
P1/P2=(n1/n2)^3(d1/d2)^3(3)

What is Apparent Power (S)? What're the units?

Combination of Real and Reactive power. Measured in Volt-Amps.

What is Capacitance (C)? What're the units?

Property of component to oppose voltage change. Measured in Farad.

What is Current (I)? What're the units?

Flow of charge past a point, measured in Amps.

What is Inductance (L)? What're the units?

Property of component to oppose current change. Measured in Henry.

What is Kirchhoff’s Current Law?

Kirchhoff's current law states that the current entering any node/junction is equal to the current leaving that node/junction.

In Series: Current is constant. (Itotal=I1=I2...)

In Parallel: Current is additive. (Itotal= I1+I2...)