# Presentation: 035513

## Data Center Controls

**Data Center Controls**

- Mark Hydeman, P.E., FASHRAE Taylor Engineering, LLCmhydeman@taylor-engineering.com

## Control Issues

- Temperature Control
- Humidity Control
- Airflow Control
- Feedback and Diagnostics
- IT Integration
- Others

## Temperature Control

- Design Conditions
- Maintain inlet conditions at servers between 68°F and 77°F
- 59°F to 90°F allowable
- At 77°F most server two speed fans go into high speed
- Solutions
- Feedback from racks
- Hardwired or wireless EMCS sensors
- Network data exchange with server on-board sensors
- Reset supply temperatures upward to keep most demanding rack satisfied
- Can have local temperature zones with distributed CRAC/H units

## Rack temperatures with UF supply

- Reset SAT to keep rack EATs within design range
- Keep SAT above minimum for design

## Humidity Control

- Avoid if at all possible
- High humidity is usually limited by cooling coil dew-point temperature
- Low humidity limit is not well supported (see previous slides)
- If you decide to humidify, do all of the following:
- Use high quality dew-point sensors located in the data center floor (Visalia see NBCIP report: _http://www.buildingcontrols.org/publications.html_)
- Use adiabatic (not steam) humidifiers
- Direct Evaporative Media
- Infrared
- Ultrasonic
- Best to provide on MUA unit.
- Control all humidifiers together if distributed.

## Real Survey of CRACs

## Airflow Controls (UF)

- All supply fans controlled to same speed
- Set speed to maintain differential pressure setpoint under floor (can use multiple sensors)
- Reset differential pressure setpoint by highest rack temperature (slow acting loop)

## Reset of floor pressure to satisfy racks

- Tate Perforated Floor Tile Performance vs. Underfloor Pressure

- Potential reset range

## Control Sensors (UF)

*© 2004, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from ASHRAE Thermal Guidelines for Data Processing Environments. This material may not be copied nor distributed in either paper or digital form without ASHRAE’s permission.*

- Cold Aisle

- Hot Aisle

**P**

- Locate one (or more) pressure sensors
- in a box(es) under the floor.  Locate
- holes in box to avoid drafts on sensor tip

**T**

- Locate one (or more) temperature sensors towards the top of the racks

## Airflow Controls (OH)

- All headered supply fans controlled to same speed
- Set speed to maintain pressure in supply header
- Control dampers to maintain racks at temperature
- Reset pressure setpoint to keep most open damper at or near fully open

## Data center layout

*© 2004, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from ASHRAE Thermal Guidelines for Data Processing Environments. This material may not be copied nor distributed in either paper or digital form without ASHRAE’s permission.*

- Overhead Supply

- Cold Aisle

- Hot Aisle

**P**

- Pressure sensor in supply duct main

**T**

- Locate one (or more) temperature sensors towards the top of the racks

- Reset pressure to keep one damper near fully open

## Feedback and Diagnostics

- Normal Indices
- SAT (or RAT)
- CHWS
- Equipment Status
- Space Temp
- Space RH (or return RH)

- Improved Indices
- Rack Cooling Index (see next slide)
- Plant kW/ton
- LBNL’s Data Center Metric Phvac/Pservers
- Most open valve status (and location)
- Most open damper status (and location)

## Rack Cooling Indices

*Herrlin, M. K. 2005. Rack Cooling Effectiveness in Data Centers and Telecom Central Offices: The Rack Cooling Index (RCI). ASHRAE Transactions, Volume 111, Part 2, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA.*

## IT Integration

- Control system server
- Who provides it
- Where is it located
- Data exchange on server temperatures or fan speeds (SNTP)
- Gateways
- CRAC/H unit controls
- VSDs
- Electrical Panels

## Other Issues

- Power down restart sequences
- Control system redundancy (e.g. chillers)
- Distributed controllers (one per chiller)
- Redundant controllers (with heartbeat and transfer switches)
- See Engineered Systems September 2007 Article “Mission Critical Building Automation.”
- Testing coordination (see Cx section)
- Remote access/security

## Best Practice Controls

- Use high quality sensors
- Reset temp and pressure by demand at racks
- Avoid humidity controls if possible, if necessary provide it on MUA unit
- With VS fans control all in parallel to same speed
- Used advanced whole system metrics to track system performance
- Commission the controls thoroughly (see Cx section)

## Take Aways

- Environmental conditions recommended by ASHRAE can save over traditional practices
- Humidity ranges  can be broad—or no humidity control in CA
- Airflow should be controlled to meet server required flow
- Variable speed fans should be used
- Commission the controls thoroughly