PDX DCEO Qualification Card

Discuss the expected response for the following alarms: Sump high level

Check sump water level. Check water high level switch wiring and functionality. Verify proper operation of floats. Verify fill valve is fully closed. A power cycle is required to recover from this condition.

Discuss the expected response for the following alarms: Sump low level not met

Check sump water level. Check water low level switch wiring and functionality. Verify proper operation of floats. Verify fill valve is fully open. A power cycle is required to recover from this condition.

Discuss the expected response for the following alarms: Supply fan failure

Before turning unit OFF, check status of motor protection overloads; if one is OPEN, try reenergizing the motor by turning ON the motor protection switch. If the motor overload triggers again, there is likely damage to the motor, or motor wiring. Turn OFF CRAH unit power using the main power disconnect switch from the control panel. Check affected motor and wiring, and overload. Recycling power to the CRAH unit is necessary in order to recover from this alarm condition.

Discuss the expected response for the following alarms: VFD failure

Intervention is required to investigate and take actions as necessary. Check VFD status, wiring, and parameters configuration. Replace equipment if necessary. A power cycle is required to recover from this condition.

Discuss the primary concerns during peak summer temperatures of a sump pump failure

Sump pump failure will lead to evaporative media dryout- resulting in unwanted lower humidity and higher temperatures.

Discuss the purpose of the UV system and how it works in the air handler

UltraViolet Light (UV Light) is used to disinfect the water system of germs, viruses, mold, bacteria, and fungi. This is accomplished by exposing the water to UV Light waves.

Explain a refrigeration cycle.

A warm, low pressure refrigerant gas enters a compressor. This pressurizes the warm gas which then enters a condenser. In the condenser, heat is transferred out of the gas causing it to condense in to a pressurized liquid. This high pressure and relatively cool liquid then passes through an expansion valve. The pressure drop causes some of the liquid to flash to gas with the result being a low pressure, relatively cool liquid/vapor mix. This mix then enters an evaporator where it absorbs heat energy and completely boils, becoming a warm, low pressure refigerant gas.

Explain how the air handler responds to a clogged/dirty filter

Unit fans will speed up while producing little/no air flow.

Explain how the system reacts to changes in each of the previously listed D/P

When compared to command setpoint, if Room (or Supply Duct) to Outside Air d/p is too high then exhaust fans will speed up. If too low, then exhaust fans will slow down. Differential pressures exceeding  +-0.75 inches water trigger a Purge. Filter differential pressure will eventually create a dirty filter alarm (setpoint varies by site).

Explain how the temperature detectors are used to maintain a SAT setpoint?

The area controller selects the 2 warmest cold aisle sensors and calculates the average which influences the SAT setpoint for the area.

Explain how to isolate a single fan motor that has failed from a running air handler

Place unit HOA to OFF. Open unit Main Disconnect. Identify and open associated fan motor breaker. Close unit Main Disconnect. Place unit HOA to run. 

Explain how to use a psychrometric chart

A Psychrometric chart consists of the following:
X-axis: Dry Bulb temp
Y-axis: Humidity ratio, Dew point temp, vapor pressure
Upper limit: Saturation curve temperature
Diagonal axis: Enthalpy

The chart is read by taking any two known parameters, and identifying the point of intersection.

Explain how you change out the canister for the igloo humidifiers

Stop unit and allow it to cool to ambient temperature.Disconnect cylinder hose clamp and plugs. Release cylinder strap, tilt cylinder forward, and remove cylinder and associated O-Ring.

Explain the sump level float switches and their use

Low water level: when reached, fill solenoid opens to fill tank. Pump will de-energize to prevent overheating.

Operational level: Pump energizes for evaporative cooling.

High level: When reached, drain solenoid opens to drain excess water. Fill solenoid de-energizes.

Explain what the following D/P readings are used for: Cold/Hot aisle

Hot and cold aisle readings are inputs sent to the area controller, which are then sent to the MCC. The MCC will  evaluate the PID output passed on from the area controller and then send a common pressure PID output to the area controller that will drive all exhaust fans to operate in a similar manner, increasing or decreasing speed as the MCC commands to meet setpoint. Initial hot aisle ser point should be +0.01" W.C. relative to the OA

Explain what the following D/P readings are used for: Filter

Filter DP readings are utilized to tell us when filters are dirty and need to be replaced or cleaned.

How does humidity affect evaporative cooling?

Evaporative media is designed to work with hot or warm air. That air passes through the media where the water is present to create evaporation. If there’s already a lot of moisture in the air (humidity), there’s not going to be as much evaporation. This may also lead to more moisture in the system, which can lead to drips as well as rust if the unit isn’t serviced properly.

Identify the location of purge panels in the building

Located on the front wall of each ERM/POD.

List which differential pressures (D/P) are monitored by BMS operations

Room to Outside Air, Supply Duct to Outside Air, Air Handler filter, and mist eliminator. 

What are the expected positions for the following dampers in direct cooling mode: Bypass Air Dampers

Modulating