Finding air temperature

[tkc]

Hi, I like to check what is the difference between opaque and invisible surface for a room. Does it only affect the shading or will it also affect the solar radiation acting on the surface?

I did a few simulation by setting different players to invisible and run it in ApacheSIM but the result generated shows no effect on the air temperature even though the surface setting has been changed.

From my understanding, opaque does not permit any radiation from transmitting through the surface and hence there ought to be a difference in the air temperature. Anyone is able to advice me on this issue?

Else, how could I create a "space" to treat is as a boundary layer to identify the air temperature in this range?

In addition, what does air temperature in apachesim means? If I drew a room, does air temperature means the average temperature inside this room? Or does it refer to the surface temperature (ceiling or floor ?)

[Terence]

The option available via "Set Surfaces" in Suncast is just a visibility setting. It is designed to allow you to see the solar penetration into a room for example, but it has no effect on the apache simulation results when linked with Suncast.

The Room Variable "Air Temperature" is explained in the Vista user guide.



You can view the user guides by selecting Help and then User guides in the software or by visting the following page: http://www.iesve.com/support/userguides.

[tkc]

Thanks terence for the clarification, I find some other doubts which I hope you or any other kind users are able to advice me on:

1) Are there any option in apachesim to find the surface temperature of the ceiling or even roof?
2) How should I create an "internal" room with the use of setting 100% transparent window? I cant find the right material in construction to do it

[Complex Potential]

1) Yes there are:

Before you run the simulation go into the ApacheSim (Dynamic Simulation) dialogue box and click on "Output Options". Then select all of the room in your model in the list at the bottom (holding shift works well here) and ensure the "Surface Temperatures" tick box is checked under detailed output for selected rooms.

Once the model has run, go into the vista results and go to the ceiling in question by using the "Move down one level" icon until you are at surface level and you should see surface temperature as variable. You can use this to give you any internal surface temperature. including walls, ground, windows etc. However, you cannot interrogate external surfaces.

2) You can simply add a hole instead of a window as long is it is within an internal surface. External holes though are not permitted. If you want to simulate an external hole then manually edit a glazing construction to have only a single layer of glass with a transmittance of 1 and outside and inside reflectances of 0. This should create BS EN 410 g value of 100%. You can then assign a macroflo opening of 100%/always on to finish the illusion. It's not perfect but it's pretty close.

CP

[tkc]

thanks CP.

I did as when you told me and manage to get the result. For the glazing setting, I used a default input of Clear element (full solar load transmitted) which I happen to see inside the list. It is purely air for this setup with the values u mentioned. is it similar to the custom setup u made?

[tkc]

Hi CP,

I got another issue and like to check with u.

I drew few layers above a house and set them all with 100% opening and holes at their surfaces to denote air boundary.

However, I am required to actually investigate the surface temp between ceiling and roof too. Initially I drew only 1 layer of solid surface as the roof and go under the surface temperature to find their respective temperature. However, the temperature do not exactly reflect the roof and ceiling temperature which I am intending to find.

Any other ways to go about solving this? Or should I draw an additional layers (2 layers above the house), the btm layer being the ceiling and the upper layer being the roof surface.. Additional layers above this 2 layers are then air boundary with 100% opening and holes. Any suggestion?

[Complex Potential]

Hiya

If you have the ceiling void as a separate "Room" in the model then you should be able to check the surface temperatures of the underside of the ceiling, the "floor" of the ceiling void and the underside of the roof. It sounds like you have done this but the temperatures are not what you want for some reason. Can you be more specific about how the temperatures do not reflect those you are intending to find?

[tkc]

My New Model:
| |
| AIR |
|___________________|
| ROOF |
|___________________|
| CEILING |
|___________________|
| |
| |
| HOUSE |
| |
|___________________|

My OLD model:


| |
| AIR |
|___________________|
| ROOF |
|___________________|
| |
| |
| HOUSE |
| |
|__________________ |


That is actually both the new and old model of what I did. The "AIR" layer are full opening glass window + holes in between each layer.

For the new model: I changed the default absorptivity of the ROOF and the CEILING to 0.2 for each layer, with the concrete being the outside layer followed by plaster. (Roof and ceiling both have 200mm height).

I then simulate my result using apachesim (Singapore weather file), and I did obtain the ROOF surface (being the 1st opaque layer) having the highest temperature BUT the timing for the PEAK temperature (based on air temperature) of the roof layer is between 7.30-8.30pm which may not sound logical? The CEILING layer peaks at 1.30pm (which may sound logical) as it is in the afternoon. This is purely based on air temperature which I used to assume the temperature of ROOF and Ceiling and not making use of the surface temperature at all. Am I right?

For the old model: I changed the default absorptivity of the ROOF to 0.2, with the concrete being the outside layer followed by plaster. (Roof have 200mm height).

I then simulate my result using apachesim (Singapore weather file), and likewise I obtain the ROOF surface having the highest air temperature than the air layers and even house layer. BUT the timing for this PEAK temperature (based on air temperature) of the roof layer is between 6.30-8.30pm also. I then went into the surface temperature setting to check on the ceiling temperature(based on model) of the ROOF layer which I assumed to be the roof of the building and the floor temperature (based on model) which I assumed to be the ceiling of the building.

The roof has a higher surface temperature than the ceiling which is right. However, as they peak towards the evening around 6.30-7.30pm and there ought to be a thermal lag effect where the ceiling should peak at a slightly later time than the roof but for my result they peak at almost the same timing instead. Hence do you have any idea if it is logical for the surface temperature of the roof to actually peak at 6.30-7.30pm instead of mid-noon? And also like to check if by just drawing a single layer to denote the "ceiling" as building roof and "floor" as ceiling of the building is correct? Otherwise if what I did using my NEW model is correct?

THanks a lot for your help!

[Complex Potential]

The constructions you have applied to these "layers" will be vital to the way in which the surface temperatures lag behind each other. I would check those first to make sure they make logical sense. Obviously a thin metal construction is going to have almost zero lag while a thick stone construction will have hours.

Also, the "air" layer needs to be open to the air so please make sure you are seeing macroflo vent gains within the results in this space. The air temperature in the air layer should be almost the same as the external condition.

Try also to be clear with regard to "surface temperatures" and "air temperatures" because your post is confusing. You talk about the air temperature of the roof surface for example which doesn't make much sense. Air temperature can only be applicable to a thermally defined volume whereas an internal surface within that volume can be a completely different temperature.

[tkc]

Hi CP,

The layers I set for my internal walls are concrete + plaster only. This construction is applicable to all internal walls of my model include the roof and ceiling surface. A total thickness of 200mm height as what I drawn.

For the air temperature wise, my 1st objective is to find the air temperature distribution about 5m away from the roof surface, hence I drew different layers at 0.5m interval to obtain the air temperature.

My 2nd objective is to find the difference in Surface temperature of the roof and ceiling of a cool roof which is coated with cool paint which increases the reflectivity of the surface.

In my model, when I run apachesim, they do show me the air temperature in the roof and ceiling layer too, that is not the main concern for me as I am primarily looking at the surface temperature which I may have lead to some confusion for this point.

Hence, can I seek your advice on which of my model (old or new) is more applicable to achieve the result for my studies? It is particularly the finding of the roof and ceiling temperature which I am having problem with. Should I draw 2 layers with the top being the roof surface and the bottom being the ceiling surface (like my new model) or just 1 layer (old model) will do?

In doing so, how can I know which is the exact ceiling and roof temperature of a building in real life? I was told by my supervisor that by drawing 2 layers, the floor of the "ROOF" layer which I draw will reflect the roof temp and the floor of the "Ceiling" layer will reflect the ceiing temperature. Any truth to that? he himself is not very sure of this too.