Is Your Data Center in the Right Class to Support Real-time Learning? (Part 2)

Would you like to save 1/3 of the cost of your data center ventilation system, and up to 40 percent of the cost to run your data center’s chiller? Let’s discuss cooling and underfloor tips for your school’s data center.

In my last post, I listed 5 questions to answer in building or improving your district data center to provide the reliability you need for real-time learning. The questions came out of my attendance at a Data Center Design class sponsored by BICSI. The 5 questions were:

  1. How reliable is your electrical system, from the utility all the way to the racks?
  2. Have you designed your cooling to maximize reliability and efficiency?
  3. What is going on under the floor?
  4. Have you designed and tested your security?
  5. What about wide-area-network redundancy?

I covered the Question 1 - Electrical System in detail last time. In this post, I want to discuss Question 2 – Cooling and Question 3 – Under Floor Issues.

Cooling

The data center is usually defined as the school or district’s main location for storing computer data. It is also a large consumer of mechanical cooling. As the number of servers in district data centers have grown, we in IT have looked to our facilities departments to add more cooling. However, we have not always examined how effectively cooling is delivered.

The key to maximizing cooling efficiency is to design a clear path for cooling to reach the equipment. For most data centers the cooling is provided by air distribution systems, so the path is defined by airflow. Cool air should enter your data center, be drawn through racks to cool equipment, then exit the data center space as hot air to be exhausted or returned to be re-cooled. The more unhindered the path, the more efficient the cooling system.

According to Ian Seaton of Chatsworth Products, designing data center airflow with proper separation between cold intake air and hot exhaust air can save up to 1/3 of your data center ventilation and 40 percent of your chiller cost (as presented at BICSI Fall 2014 Conference, Anaheim, California). Mr. Seaton holds a patent for airflow performance algorithms.

Here are some tips to design a clearly separate airflow path:

  • Know your equipment airflow requirements. Identify where your switches and servers take in cool air and exhaust hot air. That way, you can introduce cool air to their fan intake units, and plan a clear path for exhausting hot air. Ideally, each rack should have all its equipment with the same fan layout – all front to back or all back to front. If equipment exhausts out the side of the unit, you will need to plan for a “chimney” between racks for the air to rise away from the equipment.
  • Use cover plates in racks to close up openings and direct air flow through the equipment. Creating a clear path for the air to flow only through the equipment fans maximizes cooling.
  • Plan rack cabling to avoid interference with air flow. Once you know where cool air comes into the rack equipment and where hot air exhausts, you can arrange cable management to avoid interfering with the airflow. According to research sited in Mr. Seaton’s presentation, cable interferences can reduce fan throughput by as much as 50 percent.
  • Provide sufficient ceiling height to allow hot air to rise above the racks and leave the space. A minimum ceiling height of 10 feet is recommended.
  • The best layout of racks in an air distribution system is to have one aisle with both sides requesting intake air (cold aisle) and the next aisle with both sides exhausting hot air (hot aisle). One option is to actually enclose the cold aisle above the rack. This creates a tent around the cold aisle, and further forces intake air through the equipment to exit the cold aisle. See illustration 1 of a cold aisle containment unit for racks.

 

 

Most of our school data centers use traditional forced air cooling. However, there are also some new methods of cooling. Rack-oriented liquid cooling introduces cooled water loops into the equipment racks. This method is good for high density rack configurations, like racks full of blade servers. Even if rack-oriented liquid cooling is not used yet, data center designers may want to take advantage of this option in the future. Introducing under-floor water piping allows this option to be added at a later date.

Under Floor Issues

Air flow is not only important above the floor, but under the floor as well. Returning to air flow systems, here are tips for under-floor air distribution:

  • Since the under-floor space is also an air distribution plenum, cabling in this space should either be in conduit, be listed for data processing, or should be plenum rated (the most common option).
  • Arrange under-floor cabling and electrical distribution to work in the direction of airflow, and thus minimize obstructions to airflow.
  • Maintain air seal at cable openings in the floor. By cutting down on other openings, this will allow the maximum amount of air to reach the cold aisle. Ian Seaton claimed that properly sealing up openings in a floor system can increase the underfloor plenum’s efficiency by 90 percent.

In addition to airflow under the floor, proper design of under-floor systems should include a water drainage outlet, water detection and smoke detection systems. Under-floor spaces should be on a regular maintenance and inspection schedule, to remove debris and keep them free from obstruction.

If you are inspired to re-design your data center cooling system, remember that the temperature at the room thermostat is not what is important. Measure temperature at the inlet side of the rack, and compare it to the outlet temperature at the exhaust side. The inlet temperature is at the point where the system is about to supply cooling to the equipment.

I would like to know if you already have stories of cost savings from revising cooling design. Please comment on this blog post if you have a story to tell. Inspire us all to more efficient cooling.


Craig Williams is the director of information services for Illinois School District U-46 in Elgin, Illinois. He and his team are overhauling the district’s infrastructure and seeding technology into classrooms, to ensure the all of the district’s culturally-diverse students have the opportunity to expand their learning and achievement. His previous work with schools, first as a building architect, then as a technology design consultant, provides him with a broad perspective on planning for improved student learning. Williams currently serves on the Board with the Illinois CoSN chapter - Education Technology Council of Illinois. 

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