Add Thermal Monitoring to Reduce Data Center Energy Consumption
Today's Challenge: Reduce Power Consumption in Data CentersThe EPA estimates that data centers accounted for 1.5% (61 billion kWh) of total U.S. electricity consumption in 2006.¹ Astonishingly, IT equipment was responsible for only half of this electricity consumption; power and cooling infrastructure accounted for the other half. Yet to date, most efforts to reduce the power consumption of data centers have addressed only the first half of the problem: the energy efficiency of the chips and components in IT equipment.
To effectively minimize overall data center energy consumption, it is imperative that the energy consumed by the cooling infrastructure be reduced as well. By implementing an intelligent cooling infrastructure, organizations will be able to accommodate higher power densities without building additional data centers. Additionally, they will reduce their electricity bill while minimizing their carbon footprint.
Conventional Cooling Infrastructures Waste Substantial EnergyThe ambient temperature in a data center or other thermally controlled environment is not constant throughout the space. Temperature varies significantly across both the vertical and horizontal planes depending on proximity to active or inactive equipment, as well as airflow. Moreover, the cooling zones of computer room air conditioners (CRACs) frequently overlap, resulting in cooling redundancy. Simply stated, data centers waste substantial power by cooling areas that are already cool, because they lack intelligent thermal-monitoring capabilities.
The ability to identify specific areas where ambient temperature needs to be reduced is the key to reducing data center power consumption. However desirable this goal, it has not been simple to implement. The complexity of wiring and interfacing multiple temperature sensors is compounded by the difficulty of managing a vast array of temperature-measurement nodes. Consequently, multipoint temperature monitoring is particularly problematic.
Efficient Multipoint Temperature MeasurementMultiple temperature-measurement nodes, combined with appropriate temperature data processing, enable an optimized environmental temperature-control system that saves power and reduces cost. To implement such a system without adding any complex wiring overhead, designers can draw on various technologies—for example, a network of wireless sensors based on Zigbee® or other wireless standards, or a hardwired approach using a simple serial interface such as Maxim's
Wireless solutions would be easy to install, since few new wires would be needed (just a tap into the local power supply to power the module). However, today's per-module cost for each sensor could be $10 (U.S.) or more, thus adding thousands to tens of thousands of dollars to the data center overhead. Alternately, a hardwired system using a simple
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Figure 1. Energy management in a server farm can be improved by adding a network of
Location-Aware Temperature SensorsMonitoring many temperatures in a data center is challenging. How will the measurement of a given sensor be associated with its physical location? Any solution that requires manual configuration is time-consuming, expensive, and prone to error. Chain-mode operation, a new feature offered on some
Figure 2. The DS28EA00 employs the chain-mode function in a typical
The chain-mode function, therefore, gives the host controller a computer-controlled and fully automated method to determine the sequential ordering of the unique ID for each device in a multidrop temperature-sensor configuration. This sequential ID information directly correlates to the physical construction of the multidrop temperature array and, therefore, the physical location of each sensor in the enclosure.³ This correlation between the DS28EA00's 64-bit ID and physical location in the enclosure enables the application to use its environmental control algorithm to measure temperature in a storage tower at different heights and/or location.
Using Parasitic PowerPowering an array of temperature sensors can add complexity and cost to a distributed temperature-sensing application. Fortunately,
At the IC level, individual
Accurate and Dependable MeasurementsA fundamental requirement for an accurate environmental temperature-control system is precise temperature measurement. For environments like a data center, temperature-measurement accuracy typically needs to be ±1°C or better. Exceeding this basic performance requirement,
The DS28EA00 also includes thermostatic-type functions with user-programmable temperature-measurement alarms which can be polled electronically. Additionally, the device's general-purpose I/O pins can be used to turn on and off visual or audible indicators, such as LEDs or buzzers, for notification of out-of-range temperature conditions (Figure 3).
Figure 3. Able to run from either parasitically derived power or from an external supply, the DS28EA00 combines a temperature sensor, GPIO, alarm capabilities, and the
In a typical server farm, each rack of multiple servers might incorporate several temperature sensors. These sensors, along with sensors from other racks in the farm, would send their temperature readings back to the host system that monitors the server farm. That host system would then control overall system cooling. Meanwhile, using its internal alarm capabilities, each
Multipoint Temperature Monitoring Reduces Cooling Energy by 30%One such system implementation by a leading manufacturer of large-scale server systems leverages the DS28EA00. In an initial implementation, the company reported a 30% reduction in cooling energy in their data center. They are now saving over two million kWh/year, which equates to a reduction of over 1300 tons/year of CO2 in the atmosphere.
SummaryCooling infrastructure accounts for half of the electricity used by data centers. Consequently, intelligent thermal monitoring is critical for effectively minimizing data center power consumption.
- "Report to Congress on Server and Data Center Energy Efficiency, Public Law 109-431," U.S. Environmental Protection Agency ENERGY STAR Program (August 2, 2007).
- For a basic overview of
1-Wireconcepts, see Maxim application note 1796, "Overview of 1-WireTechnology and Its Use," and a Flash® presentation.
- For further information on chain mode, see Maxim application note 4037, "Regain Location Information by Leveraging the
1-Wire® Chain Function—A Simple Signaling and Protocol Method Determines Device Physical Location."