Air Conditioning Equipment and Systems

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.

Determine the Room Power Distribution Strategy. The two (2) main decisions in developing a room power distribution strategy are: (1) Where to place the power distribution units (PDUs)?, (2) Whether to run power cables overhead or under the floor?

Determine the Cabinet Power Distribution Strategy. In deciding how power will be distributed through the cabinet, use of dual power supplies, and cabling approach, it is important to understand the impact of power distribution on cooling, particularly as it is related to air flow within the cabinet.

Determine the Room & Cabinet Data Cabling Distribution Impact. Typically, there are three (3) choices in delivering network connectivity to an RLU. They are: (1) Home run every data port from a network core switch, (2) Provide matching port-density patch panels at both the RLU and the core switch with pre-cabled cross-connections between them, such that server connections can be made with only patch cables at both ends, (3) Provide an edge switch at every rack, row, or pod depending on bandwidth requirements. This approach is referred to as zone switching.

Establish a Cooling Zone Strategy. Recall that effective computer room cooling is as much about removing heat as it is about adding cold. Generally speaking, the three (3) equipment cooling methods along with their typical cooling potential can be determined from the following table: