ApacheSim Error

[quitoBIM]

Hi,
when i run the simulation, it shows the window with the information about SunCast. I pressed yes and then it starts. The problem starts after a few seconds calculating. It shows me a window with this message in it:
Error: Surface temperature instability in room 04172957. Possible remedies: add thermal capacity to construction SGFLR ; reduce time step; set control radiant fraction to 0; check gain and ventilation levels; reduce MacroFlo opening areas.

My question is; what should i do about this that won't affect my results? I don't understand which room it is, because there's no room 04172957 on my list. By thermal capacity it means changing the U-value or something like that? I tried reducing the time step, but it didn't work. I don't know where to change the radiant fraction or check the gain and ventilation levels.
I don't understand what this Error means... I my other parts of the model I didn't have this error.

Hoping someone can help me

Enrique

[vajindarladdad]

Hi Enrique,

The instability problems are most commonly caused by:

1. MacroFlo openings that are too large (eg 50% openable area).
2. Very large gains turned on suddenly.
3. Setting the Control Temperature Radiant Fraction (Apache View -> Settings -> Building) to a value greater than 0. We recommend using the default setting (control based on air temperature).
4. Extremely lightweight structures – e.g. large areas of walls or roof made entirely of glass. These can give rise to a ‘surface instability’. Adding a small amount of thermal mass to the construction by increasing the density of a layer usually overcomes the problem.

Resolution:
Please reduce the time step to 6 (or less if required) minutes and give a try to run the simulation.

[PCully]

one last thing Enrique, the message tells you the Room ID not name or number. When you select a room in ModelIT the Room ID is displayed at the bottom of the workspace, you can also see it when you query a room in any thermal view (it's on the General tab of Room Data).

A quick way to get a list of all rooms is via the ModelIt Check Report (Settings menu >> Model... >> Tick Zones then click the Check button) - this will give you a list of all rooms that shows;

- Room Number(the index in the rooms list where the room appears)
- Room ID (the internal ID for the room, this never changes and is often given in error messages from VE)
- Room Name (The name of the room as you named it and also what is displayed on the room browser list)

Phil

[ZapBran]

Might want to do a little digging into why there's an instability - Apache is a simulation engine and simulations can become unstable (not just thermal ones) when they are struggling... why are they struggling? Mainly because we are putting something under stress... thermally it'll be heat transfer swinging up or air blowing through.

Sounds like you have a something on the ground floor (or an upper exposed floor) going amis.
do:
• "Find=04172957" in modelit
• place that room into a new grouping scheme group by itself so you don't need to search for it again.
• check out the adjacencies (all expected external are external and internal are internal).
• move to apache and check out your casual gains (no massive loads hitting it if it's a riser etc).
• move into macroflow and see if there are windows or doors suddenly flying open at the same time you are telling the boiler to heat the space to 30°C on Rabbie Burns night.

Or just lower the time-step 'cause sometimes that's all you can do.

Zap.

[quitoBIM]

I tried modifying those parameters, but nothing happened, it still gives me that error. I modified the internal gains and ventilation levels, and checked the adjacencies. I also reduced the time step, but still nothing happened. I'm not using MacroFlo.