Operative Temperature

[huijin9055]

According to ASHRAE standard 55, human thermal comfort is defined by a range of operative temperatures, which is a combination of air temperature and mean radiant temperature. Only under certain circumstances, it is acceptable to assume operative temperature is equal to air temperature. For example, when there is no radiant heating or cooling systems. I notice Simulation CFD does not report operative temperature in the result, not sure if it is calculated in the solver. We're hoping that operative temperature will be available in a future release.

[ryan.arnaudin]

Thanks for the feedback. Is operative temperature needed as a viewable result quantity, or do you just need to know that it is being used by the solver?

This help topic may shed some light on the solver approach: http://help.autodesk.com/view/SCDSE/2015/ENU/?guid=GUID-836981AF-2E89-4F5D-B420-9859B070AC65

[huijin9055]

We're hoping operative tempeature is a viewable result quantity. I think adding this calculation to the solve is not a big deal of effort since the air temperature and mean radiant temperature are already there. ASHRAE standard 55-2010 says in most practical cases, the operative temperature can be calculated with sufficient approximation as the mean value of air temperature and mean radiant temperature. Equation is given if higher precision is preferred.

[apolo_vanderberg]

Operative Temperature is a plotable result quantity when you enable Thermal Comfort within the Result Quantities dialog.

[huijin9055]

Yes, I've found operative temperature as a plotable result quantity after thermal comfort is turned on. Thanks.

However, operative temperature is not documented and discussed in the thermal comfort section of learning guide in online help, instead, mean radiant temperature is well defined, which seems a little bit confusing for the user to understand what thermal comfort actually depends upon.

[huijin9055]

Had a discussion with technical support. We realize that Sim CFD uses detail equation requiring the convective and radiative heat transfer coefficient, which only work on a surface body to calculate the mean radiant temperature and operative temperature. However, in ASHRAE standard 55 and ASHRAE thermal comfort tool, some approximations have to be used in order to get the MRT and operative temperature throughout the room spaces of a building. More info can be found in the book titled 'Thermal Comfort' by P. O. Fanger. Hope it will be an enhancement in the future version of Sim CFD.