How do you know if your data center cooling system is operating at its peak performance? Understanding key performance indicators arms data center managers with the power to assess, track and manage cooling system efficiency. Consider these steps to develop useful metrics for analyzing cooling system performance and create a baseline for optimizing operations.

Understanding your cooling specifications

Before any measurement or analysis can be performed, you must understand the cooling system specifications of your computer room. Without this baseline, no comparison exists when reading and analyzing environmental measurements.

Typically, cooling specifications are provided using the gross square footage of the computer room. This measurement, traditionally in watts per square foot, incorporates all of the floor space including the space not utilized by racks or other equipment.

Determine your wattage by cabinet

  • Calculate the physical square footage that a cabinet consumes and multiply this by your cooling specification. For example, if your rack takes up 25 square feet (which includes space in front and behind the rack), and the cooling capacity of the room is 100 watts per square foot, then your cooling density per rack will be 2.5kW.

Understanding your IT load

Change is constant in the IT profession. Chances are the IT equipment that was used to create specifications for your data center no longer exists. During the life cycle of your data center, the IT equipment will change many times. Understanding the heat load generated by IT equipment is essential to cooling system performance.

Calculate heat load

  • Review the manufacturer’s installation documentation for each server and add up the amount of BTUs per rack. (This is the easiest method for determining your expected heat load).
  • You can also estimate your heat load by using metered PDUs in your racks. To do this, take your amperage reading on your PDU and multiply this value by the voltage to obtain your watts per cabinet. Add up the wattage totals of your cabinets and this value can be used as an estimate of your heat load generated by your IT equipment. This information can also be used to help you balance the heat load across racks.

Create a Baseline using Environmental Tests

Once the engineering specifications are understood and the heat load has been calculated for the IT equipment, you can create a baseline for environmental variables in your room. Creating a baseline involves actively monitoring strategically placed temperature, humidity and air flow probes in the computer room over a given period of time. Not only will this provide a current snapshot of how your cooling system is operating, but it can also alert you potential issues before they become problems or incidents.

Measuring tools do not have to be expensive to be effective. For example, utilizing the RSMINI by Geist Manufacturing, you can monitor up to 16 temperature, humidity and air flow probes for under $1000. Pair this with an open source monitoring software package, such as Cacti or MRTG, and you can also trend against your computer room specifications and alert when points are out of range.

Measure the temperature and humidity of your computer room

  • Place humidity and temperature probes in the cold aisles
  • Place the probes in the middle of the aisle between the rows of racks
  • Place probes, or utilize probes on your air handler units, to measure the temperature and humidity of the return air

These measurements will provide a good cooling profile of the computer room and allow you to compare the measured results to the computer room specifications. They can also indicate problems in the computer room before they impact operations.

Understanding your cooling specifications, applied IT load and environmental variables will allow you to create a baseline that will yield a properly operating and efficient cooling system. What KPIs are working for you?

One comment

  1. Virtualization and evolution of IT power systems causes many data centers to be very dynamic and diverse in power distribution and heat generation. Traditional WSF analysis can result in significant over design or hot spot vulnerability as power densities migrate through the data center.

    As a result, specification of WSF may be of little value. Rack density, total KW of heat removal capacity and the ability of the cooling system to respond to density extremes and variations are the key design criteria. While reporting the resulting value of WSF may be of interest to historians, it provides limited value to most IT managers seeking to deploy IT devices in the most efficient and effective manner.

    Proposed designs should indicate the total KW of heat removal available and maximum rack power density that can be supported at any location in the IT space (or a map of density capacities if cooling capacity varies significantly by location). Maximum efficiency and effectiveness of the cooling design requires monitoring of temperature and humidity at server inlet points, and a cooling system that can dynamically adjust capacity in response to data center operational requirements that may vary by season or time of day.

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