The power consumed, and heat generated, by the equipment housed in a single server rack enclosure can vary dramatically. Modern servers may demand as much as 20 kW of cooling per rack, approximately 10 times the average rack power in existing data centers. With most data centers designed to cool an average of 2 kW per rack, innovative strategies must be used to guarantee proper high density cooling.
The simple answer to this problem would be to provision a data center so that it is capable of providing 20 kW of redundant power and high density cooling to every enclosure. Unfortunately, this is not easily achieved, nor economically practical in most cases. However, there are a variety of solutions that allow high density computing equipment to be effectively deployed in conventional environments.
PTS encourages our customers to focus on the purchase of IT equipment based on functionality provided per Watt and ignore the physical size of the IT equipment. While designing entire data centers for high density remains impractical, data centers can support the limited installation of such equipment by using supplemental high density cooling systems, using rules to allow the borrowing of neighboring underutilized capacity, and by spreading the load among multiple enclosures.
Making the wrong choices when specifying a data center for high density cooling operations can needlessly increase the lifetime cost of the physical infrastructure exponentially. High density servers present a significant cooling challenge, but the experts at PTS can easily design efficient, cost-effective cooling strategies that match your needs.
PTS approaches data center cooling designs using our proven project process approach:
Design goals are established across the following categories:
Once appropriate design goals are established there are a number of additional steps recommended for data center cooling best practices.
- 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.
- 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. A definite Rack Location Unit (RLU) trend is that average RLU power densities are increasing every year. The reality is that a computer room usually deploys a mix of varying RLU power densities throughout its overall area. The trick is to provide predictable cooling for these varying RLU densities by using the average RLU density as a basis of the design while at the same time providing adequate room cooling for the peak RLU and non-RLU loads.
- Determine the CFM Requirements for each RLU. Effective cooling is accomplished by providing both the proper temperature and an adequate quantity of air to the load. As temperature goes, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) standard is to deliver air between the temperatures of 68 °F and 75 °F to the inlet of the IT infrastructure. Although electronics performs better at colder temperatures it is not wise to deliver lower air temperatures due to the threat of reaching the condensate point on equipment surfaces. Regarding air volume, a load component requires 160 cubic feet per minute (CFM) per 1 kW of electrical load. Therefore, a 5,000-watt 1U server cabinet requires 800 CFM.
- Perform Computational Fluid Dynamic (CFD) Modeling. CFD modeling can be performed for the under floor air area as well as the area above the floor. CFD modeling the airflow in a computer room provides information to make informed decisions about where to place CRAC equipment, IT-equipment, perforated tiles, high density RLUs, etc. Much of the software available today also allows mapping of both under floor and overhead airflow obstructions to more accurately represent the environment.
It is also critical to consider high-density cooling and zone cooling requirements.
- Determine the Cooling Methodology. Upon determining what cooling zone will be required, the decision of what types of air conditioners will be needed, must be made. There are four (4) air conditioner types: (1) air cooled, (2) glycol cooled, (3) condenser water cooled, (4) chilled water.In addition, it is also important to determine how heat will be rejected within the system and what type of cooling redundancy is required and available for a particular methodology.
- Determine the Cooling Delivery Methodology. Different architectural attributes affect cooling performance in different ways. For instance, designs should consider the location of the computer room within the facility (I.e. onside versus inside rooms), height of the raised floor, height of suspended ceiling, etc.
- Determine the Floor Plan. The ‘hot aisle / cold aisle’ approach is the accepted layout standard for RLUs for good reason. It works. It was developed by, Dr. Robert Sullivan, while working for IBM and it should be adapted for both new and retrofit projects. After determining the hot/cold aisles it is critical to place the CRAC units for peak performance. This may include room, row, or rack based cooling approaches. Each works well depending upon the IT infrastructure, power densities, CFM requirements, and other attributes previously discussed.
- Establish Cooling Performance Monitoring. It is vital to develop and deploy an environmental monitoring system capable of monitoring each room, row, and cabinet cooling zone. A given is that once effective cooling performance is established for a particular load profile, it will change rapidly. It is important to compile trending data for all environmental parameters for the site such that moves, adds, and changes can be executed quickly.
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