Roof inside surface temperature


I am studying the inside surface temperature of a roof cover for an open-air space. I want to measure this temperature’s impact on the overall radiant temperature for comfort. The roof cover is proposed as a simple metal sheet roof, but I want to see if adding insulation improves the thermal comfort. I have tried two different methods to calculate this:

  1. The HB UTCI component
  2. The inside surface temperature and mean radiant temperatures
    However, I was surprised when the inside surface temperature and the UTCI results were worse when adding the insulation which is quite contradictory.
    I would be grateful if someone could point out my mistake or tell me how to do this better. (142.1 KB)


Hey @Julioamodia89 ,

If you are modeling this open air space as a honeybee Room, then you need to boost up the infiltration to something really high that will make the air temperature in the room comparable to the air temperature of the outdoors (eg. 100 ACH of infiltration). If you do this, you should typically see that the insulation has an overall cooling effect instead on the indoor temperatures instead of a warming effect.

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Hi @chris,

Thank you for your tip. However, I am a bit confused about the logic behind it. First I tried having operable windows with 100% openable area and always on, showing that the inside surface temperatures were higher when insulation was included. But when I remove the windows and add the infiltration, as you mentioned, the inside surface temperature changes to more reasonable results.
In both cases, the interior air temperature is the same as the outdoors for all the hours of the year. However, the surface temperature results are completely different. Is there any explanation for this? Is the solar radiation from the windows trapped by the insulation preventing the heat from dissipating to the exterior?

Hey @Julioamodia89 ,

If you model your room with windows, then all of the E+ solar and radiant heat calculations are going to run by treating the room as an enclosed greenhouse, even though you have specified that the windows are 100% operable and so you’re getting a lot of air flow through them.

So the MRT of your zone is just going to be very high with all of that sun coming through the windows, it gets absorbed by the floor (heating it up), and then that heat gets re-radiated from the floor to the ceiling and all of the windows (which are typically opaque in the far infrared part of the spectrum), thereby heating up the interior window surface temperature. In a case like that, you might what a ceiling with less insulation so that the heat re-radiated from the floor can conduct through the roof and escape.

If you don’t like the infilrataion suggestion, another way to get your “reasonable results” is to model your Room with large operable windows but just make sure that the windows are well-shaded. In a case like that, you should find that the ceiling insulation is helpful.

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Thank you @chris, that makes all sense.

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