Re: [TRNSYS-users] Unusually slow run time

[Fred Betz <fbetz@aeieng.com>]

Julian,

I am simulating a run-around heat recovery loop. 

What I had to do is use two coils (heating and cooling) for each side of the loop as the heating coil won't cool and the cooling coil won't heat with the change of the weather. 

I have a simple algorithm that operates a damper that diverts the cold air one way and the hot air another way depending on the ambient condition and if cooling recovery or heat recovery is desired. 

The time step is 1 hour as the controls algorithms are based on the ambient temperature and there is a significant, ~10C band between operating in heating or cooling mode.

I tried 0.1 hr as the time step and had the same result. 

What I noticed is that about 20 hours before the simulation slows down the ambient temperature starts to drop from 5C to -17C. Then the temperature levels out at -17C and the pump and fans shut off for the night. Maybe the combination of low temperature and no flow causes the equations to break down, but I find that difficult to believe. 

It runs through the 7+ days without any difficulty and the run around loop appears to be operating correctly during those times. I have also been able to run it quickly for other parts of the year. 

Fred


FRED BETZ  PhD., LEED AP 
SUSTAINABLE SYSTEMS ANALYST
 
AEI | AFFILIATED ENGINEERS, INC.  
5802 Research Park Blvd. | Madison, WI  53719

P: 608.236.1175 | F: 608.238.2614  
fbetz@aeieng.com  |  www.aeieng.com  



-----Original Message-----
From: Julian Röder [mailto:Julian.Roeder@ruhr-uni-bochum.de] 
Sent: Thursday, April 01, 2010 10:35 AM
To: Fred Betz
Cc: trnsys-users@cae.wisc.edu
Subject: Re: [TRNSYS-users] Unusually slow run time

What are you simulating in Trnsys? What happens at the time of 200 hours
in your simulation? Anything that switch of or on in this time? Have your
tested to change the simulation time step?

Julian Röder

> I have a simulation that runs the first 200 hours very quickly and then
> essentially freezes.
>
> If I allow it to continue to run it calculates the next time step in
> approximately 60 seconds to 5 minutes.
>
> Anyone have any thoughts on why the calculations of each time step are so
> inconsistent and how to remedy this?
>
> Thanks,
>
> Fred
>
> Fred Betz  PhD., LEED AP
> Sustainable Systems Analyst
>
>
>
> AEI | AFFILIATED ENGINEERS, INC.
> 5802 Research Park Blvd. | Madison, WI  53719
>
> P: 608.236.1175 | F: 608.238.2614
> fbetz@aeieng.com<mailto:fbetz@aeieng.com>  |
> www.aeieng.com<http://www.aeieng.com/>
>
>
>
>