Data Center Cooling Best Practices

Author:Peter Sacco

Abstract

Maintaining a suitable environment for information technologies is arguably the number one problem facing data center and computer room managers today. Dramatic and unpredictable critical load growth has levied a heavy burden on the cooling infrastructure of these facilities making intelligent, efficient design crucial to maintaining an always available data center. The purpose of this white paper is to establish a best practices guideline for cooling systems design for data centers, computer rooms, and other mission critical technical spaces.

Cooling Systems Design Goals

To establish an effective cooling solution for any new or upgraded data center or computer room, it is essential to establish a set of design goals. Experience suggests these goals can be categorized as follows:

Adaptability
1. Plan for increasing critical load power densities
2. Utilize standard, modular cooling system components to speed changes
3. Allow for increasing cooling capacity without load impact
4. Provide for cooling distribution improvements without load impact
Availability
1. Minimize the possibility for human error by using modular components
2. Provide as much cooling system redundancy as budget will allow
3. Eliminate air mixing by providing supply (cold air) and return (hot air) separation to maximize cooling efficiency
4. Eliminate bypass air flow to maximize effective cooling capacity
5. Minimize the possibility of fluid leaks within the computer room area as well as deploy a detection system
6. Minimize vertical temperature gradients at the inlet of critical equipment
7. Control humidity to avoid static electricity build up and mold growth
Maintainability
1. Deploy the simplest effective solution to minimize the technical expertise needed to assess, operate, and service the system
2. Utilize standard, modular cooling system components to improve serviceability
3. Assure system can be serviced under a single service contract
Manageability
1. Provide accurate and concise cooling performance data in the format of the overall management platform
2. Provide local and remote system monitoring access capabilities
Cost
1. Optimize capital investment by matching the cooling requirements with the installed redundant capacity and plan for scalability
2. Simplify the ease of deployment to reduce unrecoverable labor costs
3. Utilize standard, modular, cooling system components to lower service contract costs
4. Provide redundant cooling capacity and air distribution in the smallest feasible footprint

Determine the Critical Load and Heat Load

Determining the critical heat load starts with the identification of the equipment to be deployed within the space. However, this is only part of the entire heat load of the environment. Additionally, the lighting, people, and heat conducted from the surrounding spaces will also contribute to the overall heat load. As a very general rule-of-thumb, consider no less than 1-ton (12,000 BTU/Hr / 3,516 watts) per 400 square-feet of IT equipment floor space.

The equipment heat load can be obtained by identifying the current requirements for each piece of equipment and multiplying it by the operating voltage (for all single phase equipment). The number derived is the maximum draw or nameplate rating of the equipment. In reality, the equipment will only draw between 40% and 60% of its nameplate rating in a steady-state operating condition. For this reason, solely utilizing the nameplate rating will yield an over inflated load requirement. Designing the cooling system to these parameters will be cost prohibitive. An effort is underway for manufacturers to provide typical load rating of all pieces of equipment to simplify power and cooling design.

Often, the equipment that will occupy a space has not been determined prior to the commencement of cooling systems design. In this case, the experience of the designer is vital. PTS maintains an expert knowledge of the typical load profile for various application and equipment deployments. For this reason, as well as consideration of future growth factors it may be easier to define the load in terms of an anticipated standard for a given area. The old standard used to be a watts-per-square foot definition. However, that method has proven to be too vague to be effective.

Establish Power Requirements on a per RLU Basis

Power density is best defined in terms of rack or cabinet foot print area since all manufacturers produce cabinets of generally the same size. This area can be described as a rack location unit (RLU), to borrow Rob Snevely's, of Sun Microsystems, description.

The standard RLU width is usually based on a twenty-four (24) inch standard. The depth can vary between thirty-five (35) and forty-two (42) inches. Additionally, the height can vary between 42U and 47U of rack space, which equates to a height of approximately seventy-nine (79) and eighty-nine (89) inches, respectively.

A definite trend is that RLU power densities have increased every year.

Related Courses

Data Center Infrastructure Management