Heat loss through walls in summer

francoisgferreira · Posts: 10

Hallo

I have att my program to this message, can you please conferm why the walls Groundfloor- Strong Room 1 gives a negative value for cooling design. The outside temp is bigger than that of the room, should this value not be positive?

Regard
Francois

Laurent_Support · Posts: 292 Location: Vincennes

Hello Francois,

You've got a negative value for your floor is adjacent to ground and ground does not have the same temperature as the outside air.

If you click on Site level and watch to the location tab > Site details > Ground temperatures, you will notice your ground is at 14°C every month (so less than 24° in the room).

You should change them to more realistic values.

Regards,

francoisgferreira · Posts: 10

You mis-understood the question, please look at the zone "Groundfloor- Strong Room 1", there my walls give the negative value...

Regard Francois

Laurent_Support · Posts: 292 Location: Vincennes

Sorry,

I have a look to the wall now Smile

The reason why walls heat flow is negative is due to the fact that outside air is always inferior to zone temperature. So heat is always going outward.

Regards,

francoisgferreira · Posts: 10

I have attached the analysis Results (excel). If I look at the roof load, it is how I expect it to react, if the outside drybulb is lower than the air-temp then the cooling load becomes smaller. If the outside drybulb is higher than the air-temp then the cooling load becomes bigger. This does not happen to the walls. Look at the highlighted colloms in the file.

Regard
Francois

Laurent_Support · Posts: 292 Location: Vincennes

Hi,

For roof you should have the same results as for walls, ie heat transfer from interior to outside (because outside temperature < internal temperature).

Now, solar radiation heat, some days, the external layer of your roof, increasing the outside air temperature next to the roof. This is why for the roof heat transfer are going from outside to the interior when sun shines a lot.

Regards,

francoisgferreira · Posts: 10

Have you looked at my result???
What you say is true but the results I get does not concure with what you just said. You are not giving me a reason way my walls are gaining energy(adding to the cooling load) at night and release energy(subtracting from the cooling load) at day for summer design. This, as you have mentioned in the previous 2 mail should not happen.

Laurent_Support · Posts: 292 Location: Vincennes

Well you may understand I'd rather use the dsb file you posted to know what is your model and settings. An result file is surely interesting but can't help me to answer you.

I apologize if I answer too quickly and I will try to give you better info with this post!
Your wall construction are heavy structure with much thermal mass. Suspecting this create a time phase offset I try a simple brick work + plaster board construction for all walls.
Results shows that heat flow is quicker inverse at morning and night. In my example, wall heat exchange are negative from 02:00 AM till 11:00 AM only.

Regards,

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