Roof's Heat Gain

rahmiandarini · Posts: 43

Dear Sir,

I am now simulating a simple building in a tropical climate of which its solar angle is always high. I want to prove that applying roof insulation will reduce cooling energy demand.
However, when I checked heat gain trough the roof, it receives less than 0.5 heat of solar radiation. Therefore, when I applied roof insulation, then the reduction of cooling nergy demand is not significant.
Could you explain that problem?
I attached the graph of the simulation result.

Thanks,
Rahmi

Laurent_Support · Posts: 275 Location: Vincennes

Hello Rahmi,

I presume your roof space is set onto a building block.
Roof internal temperature is quite high (often 2°C above outside temperature). So you should see important energy flow from roof space to your story through internal floor.

I don't see any Floor (int) curve on your graph.
Could you confirm me that high delta temperature between roof and story generate heat flow?

If true, insulating the roof floor will bring you nice cooling energy savings.

Let me know more precisions if you don't get expected results.

Regards,

rahmiandarini · Posts: 43

Dear Sir,

In fact, my problem is that I found the 'roof heat gain' is very small (less than 10%)compare to the solar radiation.
Even I use the simple building of Case 600 ASHRAE, and using steel (0.0135 thickness) as roof material.
I attach the graph.

rahmiandarini · Posts: 43

This is the graph based on case 600 ASHRAE, with the roof material of steel, 0.0135 m thicknes.

Laurent_Support · Posts: 275 Location: Vincennes

Hello,

I understand you interrogation. Roof heat flow is a deltaT and solar radiation effect (but also wind and may be rain could have an impact).

Another difference could be the m2 you choose to normalize your kWh (all surfaces or occupied only). Also you could have a look to radiant and operative temperature in the zone to see metal roofing radiant consequences to the comfort.
At least you could try to calculate by hand the heat flow at an hour to validate the data you see.

Regards,

rahmiandarini · Posts: 43

Dear Sir,

Thanks for your suggestion.
I have calculated the heat balance, and the 'roofs' resulted by DesignBuilder apparently is only the conduction in the roof material.
I have to add convection, shortwave and longwave radiation which is resulted by energy plus, and I have a reasonable result.

Thanks,
Rahmi

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