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Radiant fractions to surfaces

asked 2017-12-29 15:20:31 -0500

Jim Dirkes gravatar image

updated 2018-03-08 15:31:18 -0500

Dear Forum,

(Note: also posted this on the E+ Yahoo forum)

I am using the ZoneHVAC:HighTemperatureRadiant object in a model and am trying to double check the fraction of radiant energy that I'm assigning to:

  • People
  • walls
  • Floor

At the moment (and largely using values from an example file), I'm assigning 5% to people, and the remainder to the floor. Do any of you who are familiar with this object have recommendations regarding how to assign those radiant fractions?

Thanks in advance. Happy New Year, too!

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answered 2017-12-30 01:02:42 -0500

Avi gravatar image

From the Engineering reference:

Several things should be noted about the fraction of heat that is radiated directly to people. This parameter is somewhat sensitive and will have a direct impact on the thermal comfort models. This is exactly the intent of the high temperature radiant heaters; however, one must use caution when determining this fraction since overestimation of this number might lead to predictions of thermal comfort where in fact it does not exist. In addition, this fraction of radiant energy to people does not have a direct impact on any of the surface heat balances. The thermal comfort energy balance is completely separate from and has no bearing on the zone air or the surface heat balances. Thus, in order to not “lose” this amount of energy from the perspective of the zone air or the surface heat balances, the model assumes that any radiation from the high temperature radiant heater that is incident directly on people is accounted for in the thermal comfort model using Equation but is also assumed to be added to the zone air heat balance via convection from people to the surrounding air. This guarantees that the people within the space feel the direct radiative effect of the heaters and that this quantity of energy is not “lost” within the heat balance routines.

So your Floor and walls should sum up to unity and people should be low around the 5%.

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Thanks, Avi. That's helpful.

Jim Dirkes gravatar imageJim Dirkes ( 2018-01-02 16:01:09 -0500 )edit

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Asked: 2017-12-29 15:20:31 -0500

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Last updated: Dec 30 '17