Intelligent Controls: a Simple Way to Optimize Your Data Center Thermal Management System

John Peter Valiulis is Vice President of North America Marketing, Thermal Management, for Emerson Network Power.

Organizations are currently adopting a number of new thermal management strategies and technologies to remove heat from the data center while achieving capital and operational savings. One of the most effective strategies is optimizing existing thermal management systems with intelligent controls that span both the unit and system levels to enable greater availability, efficiency and decision-making.

A typical misconception is that all controls require significant customization to either the cooling units and components or building management systems. This is not necessarily the case. Some thermal management controls that are integrated into certain air handling units designed for data centers require little if any customization. In many cases, they simply need to be “turned on” and utilized to realize benefits.

A common issue many data centers have is that thermal management systems have typically been designed with peak IT heat loads in mind. However, most data centers rarely operate at peak load. As a result, the output of the thermal management system does not match the varying levels of the IT load, providing too much or too cold airflow than is required for most areas of the data center; at times even not providing enough airflow to sufficiently protect the IT equipment.

Intelligent controls enable data centers to more easily reach and maintain the optimal balance point of matched cooling capacity and IT load. They accomplish this by monitoring the data center environment through wired or wireless sensors and controlling the operation of thermal management systems. Data center managers are able to dynamically adjust airflow patterns by controlling the speed of variable speed fans or drives within the thermal management units to allow cooling unit capacities to adapt quickly to changing room conditions.

Spanning Unit and System Levels

The most effective way to create an integrated cooling environment with intelligent controls is to use a technology that spans both the unit and system levels, and even integrates at the data center infrastructure management (DCIM) level for capacity and utilization monitoring. This type of system is most ideal for allowing managers to protect, harmonize and optimize thermal systems more intuitively.

Typically, before intelligent controls were available, data centers would often attempt to create an integrated cooling environment by pairing traditional unit controls with building management systems (BMS), with the BMS acting in the supervisory role. Unfortunately, this does not provide an effective, efficient option. Since the unit controls and the BMS are two very different systems, it requires expensive programming and customization to tie them together into one system. Even once they are connected and sharing information, much of the information goes unutilized and is not robust enough for data center managers to develop effective strategies for cooling.

Utilizing intelligent control capabilities with data center thermal management systems to gain a unified cooling environment can yield up to 50 percent higher cooling energy savings, depending on data center specifications and existing equipment. Intelligent controls integrated into the next generation of thermal management solutions (new economizers, air handling units and free cooling chillers) have been shown to help data center managers achieve annual mechanical PUE under 1.2.

Unit-Level Control

At the cooling unit level, the primary focus is on protection. Intelligent controls enhance data center protection by providing local access to unit-level functions and operational data, and auto-tune key operating parameters, such as fan speed, compressor utilization and economization. If oscillations outside the set points are detected, the control algorithms adjust operations accordingly.

For example, automatic cascade and lead/lag routines automatically activate and deactivate cooling units based on room load to matching cooling needs. Also, if out-of-tolerance conditions are detected, such as the refrigerant pressure approaching unsafe thresholds, the intelligent controls would lower fan speed and compressor capacity to avoid a unit shutdown and ensure continued operation.

While protection is the primary function, intelligent controls also provide efficiency gains at the unit level. For instance, when used with air handling units that employ economization, such as an indirect evaporative free-cooling unit, intelligent controls optimize its components for the changing data center loads; data center temperature and humidity conditions; ambient conditions outside the data center; and chiller plant operation (in the case of chilled water systems).

With an indirect evaporative free-cooling air handling unit, which uses a heat exchanger and features two air streams, the hot data center return air (primary stream) is taken through the heat exchanger where it is cooled by outside scavenger air (secondary stream) that has been cooled or preconditioned by evaporating water sprayed onto the heat exchanger. A blower then circulates the cooled primary air stream throughout the data center, while the secondary air stream is exhausted outdoors.

Intelligent controls at the unit level operate the scavenger fan air stream differently, depending on the unit’s current mode of operation, to control the supply air to the user-adjustable set point. During cold ambient conditions, when the unit is operated in dry mode, the unit controller adjusts cooling capacity by modulating the scavenger fan to the desired leaving air set point. The scavenger fan increases speed to increase cooling capacity or slows to reduce capacity.

When outdoor temperatures rise and the unit is unable to achieve the desired set point efficiently by only using the heat exchanger in dry mode, the intelligent controls activate the unit pumps and water is sprayed over the heat exchanger. This increases the capacity of the heat exchanger by bringing the outdoor air down near the wet bulb condition.

System-Level Control

At the thermal management system level, intelligent controls primarily manage efficiency, providing insight for action. They enable machine-to-machine communication between multiple units to prevent them from working at cross-purposes and allow the system as a whole to more easily reach and maintain the optimal balance point of matched cooling capacity and IT load. This level of teamwork is accomplished through wired or wireless sensors and advanced algorithms that automatically adjust air flow, temperature and economizer operations based on IT loads and outdoor conditions to optimize efficiency and protection.

This type of machine-to-machine communication can be used in small and large rooms. In small rooms with balanced heat loads, the designated “master” thermal management unit determines which operation the system is to perform (cooling, heating, humidifying or dehumidifying) and how much of the operation each individual unit is to perform (none, partial or full capacity). In large rooms with unbalanced heat loads, the master unit averages all network temperature and humidity sensor readings and determines the operation the system is to perform. Each individual unit determines how much of the operation to perform based on its local sensor readings.

In certain cases, four units with variable capacity fans in teamwork mode can operate approximately 56 percent more efficiently than four fixed speed units operating autonomously. At extremely low loads, the controls can place some units in standby mode for further savings.

There are a number of fundamental steps data center managers can take to ensure their thermal management systems are intelligent and self-optimizing, enabling them to achieve the highest of levels of efficiency and availability. One of the easiest steps data center managers can take is to implement intelligent controls – for the simple reason that, in many cases, it is as easy as “turning on” the controls found within many of today’s thermal management units.

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