Resolving Cooling Challenges at the Edge

By CIOReview | Wednesday, August 10, 2016
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After the welcoming a wave of disruptive trends notably the cloud, mobility, social networking, and big data, edge computing is the next change that is pushing beyond the conventional data center to the network edges.

Edge computing decreases the amount of data that needs to be transferred, the resulting traffic and its travelling distance. It places data and control functions, high bandwidth content, and applications to be more accessible to the end user. By doing so, there would be significant reduction in cost, improved quality of services and the much desired reduction in latency.

Although edge computing is definitely the future, like all data centers, the ones at the edge also have power and cooling issues. The expulsion of the heat from by the systems in these data centers requires certain methods and cooling installations. The conventional wall mount AC systems that are generally used in enterprises do not match its cooling needs and even those that are of the  IT cooling grade are larger in size when compares to computing cabinets, constricting the physical area available for the installation of edge computing racks.

Even if enterprises try to expand or renovate their current working space to accommodate the IT grade AC systems, they will also have economizer, to think about.  The economizer reduces the need for mechanical refrigeration, which would save the energy that may be lost during cooling with ambient air  at temperatures that are considerably low.

One particular method companies can opt for, to tackle heating, is High Density Rack Cooling (HDRC).  In this method, the focus is on directly cooling the server racks within the data center space. This cooling method is of four types:

In-row server cooling: These are cooling cabinets which are of the same size as the server racks, installed between them. The space between two racks approximately matches the heat load. These coolers contain cooling coil and fan. The hot air generated by the server is drawn over the coil, cooled and sent back into the room.

Top-Hat Fan Cartridges: These cartridges are basically fan boxes, mounted on top of the server racks with an Electronically Commutated (EC) fan at the rear. The EC fan controls air flow across the server racks depending on the heat load.

Both the in-row server cooling and top-hat fan cartridges do not reduce energy consumption as they transfer heat to the air, which has to be further cooled through Computer Room Air Conditioning (CRAC) Unit, before it is discarded in a chiller. The usage of CRAC units consumes more floor space, which is again undesirable.

Passive Rear Door Cooling Coils: These are replaceable rear doors with chilled water coil mounted inside. These coils are reliant on the server fans to push the hot air across the resistance of the cooling coil. The maximum cooling capacity of these rear door cooling coils is around 20kW.  Most passive rear door coolers are limited to low and medium rack cooling.

Active Rear Door Cooling Coils: Active rear doors are comprised of a chilled water coil, EC fans, water control valve, and PLC controls. They provide the exact cooling capacity, airflow, and water flow for any changing heat load. There are three types of active rear door coolers:

• Bolt-on Active Rear Door Coolers: They consist of chilled water coil and rows of fans. They have a low coil area and limited fan capacity. Hence these coolers have a low server heat removal capacity of 8 kW and are ideal for low and medium density rack cooling.

• Active rear door coolers (Pumped Refrigerant): They consist of pumped refrigerant coils and fans. The server heat is absorbed into the refrigerant and piped out to a mechanical chiller to discard the heat. They have a heat removal capacity of around 30 kW.

• Active rear door coolers (Chilled Water): These coolers replace the rear door of the server rack with a full-sized cooling coil and multiple EC fans. They have a heat removal capacity up to 45 kW and are ideal for high density rack cooling.

Apart from HDRC, companies can also consider employing Total Liquid Cooling (TLC) or Prefabricated Modular Data Centers. In case of TLC, the server components are submerged in a dielectric fluid that absorbs heat. The method does not require any mechanical compressors or cooling infrastructure.

Prefabricated Modular Data Centers consist of purpose-built components that offer scalable data centre capacity with multiple power and cooling options. These modules can be integrated into an existing data centre footprint.  The advantage of opting for these data centers is that they have inbuilt cooling options and additional cooling peripherals are seldom required.

Edge computing is a matter of utmost importance for the American Society of Heating, Refrigeration and Air Conditioning Engineers Standard 90.1 or simply the ASHRASE standard 90.1, which is the benchmark for commercial building energy codes and a key basis for codes and standards around the world.  This standard provides the minimum requirements for energy-efficient design of most buildings, except low-rise residential buildings.

This particular standard has been adopted by all states and the law enforcements ensure the guidelines of this standard are maintained very critically. Although data centers were an exception to this for a long time, the 2010 edition of the standard removed this exemption, placing highly stringent energy efficiency requirements on computer cooling systems.

Considering the cost and importance of high-performance computing systems, their environment is a priority and should be addressed by experts familiar with the intricacies of IT environmental control. Companies considering the adaptation of edge computing should make sure that they build storage spaces which are large enough to accommodate the devices and peripherals of the required standard.