Welcome to Keep Your Cool - a blog tackling simple cooling optimization strategies for the busy data center operators.

For the past two weeks, we have delved into the critical topic of managing heat stress in data center environments. Last week, we discussed the Heat Stress Index (HSI) and its importance in ensuring operator safety. This week, we turn our attention to Wet Bulb Globe Temperature (WBGT) and its significance in data centers.

What is Wet Bulb Globe Temperature (WBGT)?

Wet Bulb Globe Temperature (WBGT) is a comprehensive metric used to evaluate thermal conditions and potential heat stress in the environment. It considers various factors, including ambient temperature, humidity, wind speed, and solar radiation. Developed in the 1950s following heat-related illnesses during WWII, WBGT is recommended by the National Institute for Occupational Safety and Health (NIOSH) as a reliable indicator of potential stress on the human body. In data centers, WBGT is particularly relevant for personnel working on outdoor chillers, rooftop equipment, switchgear yards, or servicing outdoor generators.

How to Determine WBGT

There are two primary methods to measure WBGT: using a WBGT thermometer or employing a mathematical formula.

WBGT Thermometer

A WBGT thermometer measures two key parameters:

• Wet Bulb Temperature: Recorded by a thermometer with its bulb wrapped in a water-soaked cloth, this measurement accounts for evaporative cooling and is influenced by both air temperature and humidity.

• Globe Temperature: Recorded by a thermometer inside a black globe, this measures the radiant heat absorbed from the environment.

Mathematical Formula

Alternatively, WBGT can be calculated using temperature and humidity data with a mathematical formula. Among the various formulas available, Purkay Labs uses the Stull Equation due to its accuracy across a wide range of humidities (5% to 99%) and temperatures (-20°C to 50°C). Utilizing our purpose-built tool, Audit-Buddy, we can determine WBGT values at multiple elevations and create an accurate heat map of the WBGT across an entire area.

WBGT Guidelines

The following table, adapted from the University of Georgia's recommendations for athletes, provides a framework for setting guidelines for outdoor work in data centers. Each data center should develop its own Standard Operating Procedures (SOPs) and Methods of Procedure (MOPs) based on these recommendations.

How We Measure WGBT

To measure WGBT in the data center, you would need to collect temperature and relative humidity data throughout your aisles. Then, we’d generate the following informational charts. Each show the three different heights of each sensor at each cabinet across the aisle.

Each Static Map allows you get a visual representation of what’s happening in the aisle environment.

Conclusion

Heat stress is a critical concern for technicians working in data centers, both indoors and outdoors. For outdoor environments, SOPs and MOPs should be guided by WBGT values to ensure worker safety. For indoor environments, particularly hot aisles, SOPs and MOPs should be based on HSI values at various elevations throughout the hot aisles. By leveraging tools like Audit-Buddy, Purkay Labs helps data centers accurately measure WBGT and implement effective heat stress management strategies.