URGENT, PLS HELP

[tkc]

I run my simulation of a building to find the air temperature above a roof surface. The air layer which I build are based on 100% windows at the sides and a 100% window on the roof which act as a skylight. Construction used are based on 100% transmission.

From Vista, it shows me that at around 2.30pm my air temperature at 0.5m above the roof surface should be 34 degree. But when I used Mircoflo the max temperature is only 30.84 degree and the colour intensity does not reflect what Vista actually shows.

I export the boundary condition from vista pro with the following settings: surface temperature, air temperature, mircoflo external vent. Date using the peak day and 2.30pm with a duration of 60mins. I did not include opening flow in Mircoflo as it is meant to be open ventilation

Clearly the mircflo and vista does not reflect similar result. I am trying to find the surface temperature and also the air temperature in my building. But there isn't any clear explanation in the guide on how can I go about setting any boundary condition or which icon to click to get surface or eve air temperature.

I have tried plenty of times and failed plenty of times but just could not get what I wanted. As I am using a student version, I am refused help from the contact department of IES. Was told to visit youtube but found NOTHING on mircoflo explanation.

Urgently need this advice to clear this issue on Mircoflo if anyone could help, it is greatly appreciated.

In short, I am finding the air temperature and surface temperature of my building which vista and mircoflo are not showing the same things. Building is naturally ventilation. Please advice on the setting. thanks

[harshadj]

Vista only gives the result for the entire room. I cannot understand how you have calculated temperature at certain distance from a wall. Perhaps if you attach an image of your model as seen in Model Viewer things will be more clearer to me.

Another point, when you choose to export boundary conditions, you cannot select any particular variables to export. The values of surface temperature, air temperature, convective internal gains, macroflo opening effective sizes and macroflo opening flows are exported into the file. When importing the boundary conditions you have option to import either only the 'boundary' conditions i.e. surface temperature or gains and opening flow in addition to the boundary conditions.

If you have a naturally ventilated room and you do not import the opening flows, you will have distinctly different results than Vista.

[tkc]

This is the model I am using. Basically I edited based on the tutorial mode. The bottom is the office and I draw an additional 100mm ROOF layer above the office. Following which, I drew additional rooms of 0.5m, 1m, 1.5m and 5m height from the top of the ROOF layer. These additional rooms (0.5-5m) I added in 100% opening windows at the external wall and holes in between each layers to make them as an air space. Construction for my external windows and roof light are shown below. Pls advice if they are accurate.

Roof light:
Windows:



The exporting of boundary conditions from macro flow settings is what i followed by the tutorial model guide. I am trying to use micoflo to simulation the surface temperature and air temperature of my model. I am not sure which setting to check etc. Please advice me.

My model is to be naturally ventilated. No installation of air-con etc. In vista, the result produced are that the air temperature in the air layers can be more than 40 degree, but using this setting, i only reach a max range of 32 degree.

If i did not import opening flow, how will it affect my model? My model is to be naturally ventilated, so should i import opening flow for this? Please advice on how should i proceed with the setting in mircoflo to obtain a accurate simulation

[tkc]

any assistance?

another question is under mircoflo setting for .. what does the air velocity and initial temperature refers to? it is the external air velocity and external surrounding temperature?

http://fixpicture.org/medias/1390829595 ... titled.gif

[harshadj]

TKC,

I am not entirely sure if the method you are using is right for this kind of analysis. If you add zones above the top floor. The roof ceases to be a roof and becomes an internal floor. This would result in different physics. Similarly adding zones above the building will result in solar gains/ solar incidence on the roof being different from the actual value in absence of the zones. For calculating the external surface temperature you can back calculate from the internal surface temperature. Any building physics book will get you the formula to do so.

On another note, MicroFlo cannot do energy based external simulations. Only the internal simulations include effect of the heat transfer.

[tkc]

hi harshadj,

just like to check even if I make the skylight as a 100% window opening, ies wont be able to treat it like an air boundary? From my simulation, I obtained an reverse effect as what I am expecting. The air temperature close to the sky light has higher temperature and decreases down the layers until the office layer. In fact, the air temperature should have been highest nearest to the roof of the office building and decrease as it goes further away as they are treated as air layers.

My prediction is that they did not treat the sky light I set as air layer which result in higher air temperature nearer to the top of the surface.

In addition, can I enquire what are the meaning of the air velocity and initial temperature in the setting of mircoflo as what I mentioned above.

How can I go about to obtain the similar results like what I obtained in vista calculations assuming I removed all air boundarys layers which I set?