HVAC Systems

Question 1

Describe the data center rooftop units used on campus? Please include the following in your discussion:

Answer 1

System Description and Type – MAU and RTU (RTU’s are HVAC units dedicated to PBB areas, contain compressor, expansion valve, evaporator, and condenser unit)

Compressor and Refrigerant Type – Hermetically sealed, digital scroll compressor, R410A

Location and Suites utilized – 2 MAU per suite, 11 RTUs in PBB

Operating Set Points – Dew point set point 53 degrees

Maintenance Scope of Work

                       Quarterly 

MAU

                     Semi-Annual 

Exhaust Fan

CRAC

                          Annual 

FPT

RTU

Filter

Refrigerant Check

Coil Cleaning

Electrical Connection Check

Question 2

What actions do I take in the event of a controller failure leading to a loss of BMS Control to make-up air units?

Answer 2

Use EOP

Check local screen on MAU

Monitor suite

Question 3

How many make-up air units must run in one data hall?

Answer 3

None, depends on the environments. One preferably, second on standby

Question 4

Describe the 3 critical set points we are currently using in the MAU

Answer 4

Dew Point (53), Cooling (70), and Heating (50)

Question 5

Describe the actions required should an engineer receive a datacenter MAU alarm on the BMS. What environmental BMS values should be monitored to determine satisfactory MAU operation?

Answer 5

Investigate space from thermal conditions | check roof for MAU operation. BMS should be monitored for Heat Setpoint, Cool Setpoint, and Dew Point.

Question 6

How do you reset an alarm on a PBB RTU?

Answer 6

Go to HMI, Check alarm, clear via screen

Make sure the supply fan is on before walking away

Question 7

Describe the 4 phases of the basic refrigeration cycle

Answer 7

Compression: Low pressure gas is pulled into a compressor where it is compressed into a high pressure, high temperature gas.

Condensation: Gas enters condenser where exhaust fans transfer heat outside. Refrigerant is cooled in the process, turning it back into a liquid state.

Expansion: This high pressure liquid is pushed through an expansion valve which regulates the flow of refrigerant moving through the evaporator. Liquid refrigerant is turned into a gas due to the expansion process.

Evaporation: Cold liquid refrigerant is pushed through evaporator coils. Hot air is blown across coils removing heat from space. Heat is transferred to liquid refrigerant turning it into a gas.

Question 8

Explain in detail how to take a CRAC unit offline?

Answer 8

Let command center know, click lock icon, enter 2210, go to settings, down to turn unit off, switch on to off.

Question 9

Shutting down a CRAC unit is a relatively simple process. What is the worst case scenario when shutting down an iCOM CRAC unit?

Answer 9

Shutting down a whole group. Make sure “Unit” is selected.

An alternate one doesn’t come on/No redundancy

Question 10

Define the rule of thumb for how many KW theoretically equate to 1 Refrigerant Ton

Answer 10

3.5KW; 1 ton – 12,000 BTU

Question 11

Describe Cascading iCOM control

Answer 11

All CRACs working as 1 fan design UF static pressure. CRACs working in parallel to maintain pressure. It will ramp on/off CRACs depending on underfloor static pressure. Varies supply fans on CRACs to control the underfloor static pressure. Setpoint is 0.06 inch of water column.

Question 12

How do you identify the location of a suspected water leak underfloor and how is it reset?

Answer 12

Go to CRAC, lift floor tile, look for leak, dry the leak, dry the cable, reset on LT460 box