Monitoring Physical Threats in the Data Center

Overview

UPSs, CRACs and code-required fire systems monitor themselves. The distributed threat categories that need design are listed in Table 1: air quality to IT (temperature, humidity), liquid leaks, human presence and activity, airborne hazards to personnel, and supplemental smoke or fire. The paper gives a basic and an optional sensor set with placement rules.

The basic set is three temperature sensors (top, middle, bottom) on the front door of each IT rack, one humidity sensor per cold aisle at the front of a rack mid-row, rope leak sensors around each CRAC, around cooling distribution units and under raised floors, and spot sensors for drip pans and low spots. High-traffic rooms warrant rack door switches on every rack; low-traffic rooms need only a room door switch. VRLA batteries do not release hydrogen in normal operation, so no room hydrogen sensors are needed; wet-cell rooms have special code requirements.

Sensor data is aggregated on the IP network by distributed aggregators rather than wiring every sensor to a central point; aggregators distributed by physical area, each with alerting, avoid a single central point of failure and reduce network drops. Suggested default thresholds: air temperature high 25 °C (77 °F), low 20 °C (68 °F); humidity high 55% RH, low 40% RH (ASHRAE TC9.9 class 1). A temperature change of 5.6 °C (10 °F) in 5 minutes likely indicates a CRAC failure. The thresholds reflect the 2004 ASHRAE envelope, and the record's design note asks that they be updated to the current recommended envelope. The paper also suggests that design tools could place sensors automatically from simple preferences such as how much traffic the room gets.

Key points

1. Distributed threat categories: air quality, liquid leaks, human activity, airborne hazards, supplemental smoke/fire.
2. Three temperature sensors (top, middle, bottom) on each rack front door.
3. One humidity sensor per cold aisle, at the front of a rack mid-row.
4. Rope leak sensors around every CRAC, cooling distribution unit and under raised floors.
5. No room hydrogen sensors for VRLA batteries; wet-cell rooms have special code requirements.
6. Default thresholds: temperature 20-25 °C, humidity 40-55% RH.
7. 5.6 °C change in 5 minutes likely means CRAC failure.
8. High-traffic rooms: door switch on every rack; low-traffic: room door only.

Using it in design

• Auto-place 3 inlet temperature sensors per rack front, 1 humidity sensor per cold aisle, and leak rope around every CRAC/CDU and raised-floor water path.
• Add rack door switches when the room access profile is high traffic, and generate a BOM with one aggregator per zone.
• Warn on wet-cell batteries in the white space without hydrogen detection and a separate battery room.
• Keep alarm thresholds editable, update them to the current ASHRAE recommended envelope, and add a 5.6 °C-in-5-minutes rate-of-change alarm.

Who should read it

Engineers and operations teams designing data-centre monitoring and sensor layouts.

Related standards

• ASHRAE TC9.9 Thermal Guidelines
• IEEE 1635/ASHRAE 21

Publication details

Authors

Christian Cowan; Chris Gaskins

Publisher

Schneider Electric

Year

2011

Document number

WP 102

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation