Estimation of Wet Bulb Globe Temperature

[Viraj_19]

Hi all,

I would like to address a query I am facing in a Project, It would be really helpful if anyone could enlighten me on the subject.

I am currently working on a project, wherein I encountered the term Wet Bulb Globe Temperature for the first time. What I have interpreted is WBGT can be calculated once the site has been executed. I am currently struggling to estimate the value of WBGT for designing the HVAC system, so as to limit the value of WBGT to require specified value as mentioned in The American Conference of Governmental Industrial Hygienists (ACGIH).

Thanks in advance.

 

[willard3]

Try here:

https://www.weather.gov/tsa/wbgt

 

[MintJulep]

WBGT is used for evaluating the potential for heat stress when working outside in the sun.

If you are designing HVAC then I guess you have an interior environment, thus WBGT is not the relevant measure.

 

[moideen]

The wet bulb will be important when design water cooled chilled water system and it is relevant where the location of the cooling tower installed is. Generally, highest WBT is considered 86F. but now example in Dubai, the WBT reaching to 89.5F. so the new enquiry for cooling tower design is set to this updated value.

 

[IRstuff]

Seems to me that exterior humidity is a consideration in the design of the HVAC, as reduces its capacity to provide cooling to the interior.

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[MintJulep]

Anyway,

WBGT is dominated by the ordinary wet-bulb temperature.

For mundane locations such as an office, library etc. the black-globe temperature will not be much different than the ordinary dry-bulb temperature.

If the location has strong sources or sinks of radiant heat then the black-globe temperature will depart from ordinary dry-bulb.

If you have access to a location with similar radiant characteristics to the space you are designing then you could measure the black-globe temperature there and use that in an estimation.

Otherwise you could do a convective+radiant energy balance calculation between a black-globe and your design environment and obtain an estimate of black-globe temperature with confidence corresponding to your assumptions of the radiant heat transfer characteristics.

Alternatively, if you have confidence in the wet-bulb temperature that you can achieve then you could do a bounding assessment to find the black-globe temperature that would cause you to exceed the WBGT limit you have, then use engineering judgment regarding the likelihood that your environment will reach that black-globe temperature.

 

[Viraj_19]

Thank you so much everyone for your Valuable information it was really helpful.

 

[Viraj_19]

MJ,
I am designing HVAC system at localized space in the area where a worker might feel Heat stress due to WBGT value greater than the limiting value. Thus controlling the WBGT either by Ventilation or Spot cooling.
Anyway, as my plant is indoor I can consider Globe temperature to be equal to Ambient Temperature.
Is my consideration correct?

Thanks in Advance

 

[MintJulep]

If the location has strong sources or sinks of radiant heat then the black-globe temperature will depart from ordinary dry-bulb.

 

[Viraj_19]

Ok that's quite clear MJ, thank you for your help.