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DeltaT between surface temperature and Room temperature is very high in energy plus

asked 2018-02-21 07:17:46 -0500

Siva's avatar

updated 2018-02-21 08:29:18 -0500

I am doing One Floor Radiant Cooling. since I am not getting the desired temperature, I have removed all the sources of heat generation and just kept envelope (I cannot remove that,although). I have considered a temperature as low as 5 degC and could attain the desired temperature. few things are noticed

1) The delta T between the Floor surface temperature and air temperature is around 12k. why so huge delta T? there is a delta T between source and surface which is because of thermal resistance of the intermediate layers which is understandable. but the MRT is comparable to Air temperature. does this mean, the cooling is not happening?

please see the attached image. how to pull this huge delta T

please see the attched IDF file

image description

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If you want to remove the external heat gains/losses through the envelope you can switch all surfaces with exterior or ground boundary condition to adiabatic, and then remove window or change to a construction that is virtually opaque. If you have not already, you can get rid of infiltration.

David Goldwasser's avatar David Goldwasser  ( 2018-02-21 16:30:02 -0500 )edit

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answered 2018-02-21 15:32:45 -0500

First, double-check that you are plotting output variables correctly: Is Zn001:FLR001 really the floor surface for WEST ZONE?

If so, then mean radiant temperature (MRT) can be calculated in different ways. It seems that the output variable in your image is from a Zone object's calculations for MRT. This approach uses a surface area × emissivity weighted average of the zone inside surface temperatures. Another option would be to set Mean Radiant Temperature Calculation Type and Surface Name/Angle Factor List Name input fields in the People object for WEST ZONE in order to account for specific placement of occupants within the zone. Then, you want to add the Zone Thermal Comfort Mean Radiant Temperature output variable to the IDF and run a new simulation to generate that new MRT output variable.

Some things that might be causing this large temperature difference between radiant floor inside face temperature and zone air temperature:

  • Other wall, window, and ceiling surfaces in the WEST ZONE are much hotter than the radiant floor surface
  • Other wall, window, and ceiling surfaces in the WEST ZONE have much more surface area than the radiant floor surface
  • The thermal absorptance of the inside material layer of the radiant floor surface is too low, reducing it's radiant heat transfer potential
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Asked: 2018-02-21 07:17:46 -0500

Seen: 304 times

Last updated: Feb 21 '18