Fred,TRNSYS does not allow for a variable timestep. The advantage of a variable timestep is of course that when not much is going on in a building or in the system the simulation could speed up by taking a bigger timestep and potentially get done faster. We had considered adding such a capability at one point but decided that since Trnsys allows (forces?) users to define their own controllers a lot of the time, it would be very difficult to create an algorithm in the kernel that would decide on an appropriate timestep and not create havoc in the controllers. The integrator issue isn't too hard - as long as you know what the current timestep is, its not too hard to handle internally. The issue is more about agreement between the algorithm that sets the timestep and the components that control the equipment.
Best, David On 1/26/2011 00:04, Fred Betz wrote:
I'm at a conference this week and someone mentioned using a variable time step in simulations (not TRNSYS) and I was wondering if this was possible in TRNSYS. I know you can make the time step a variable in the deck. I could see using this if you want to carefully control startup and shutdown of a device, but while the device is running or not running, you could have a larger time step. This would speed up the overall run time. It would probably play havoc on the printegrator. Just wanted to start a discussion about this topic to see if it's been done successfully and when. Fred FRED BETZ PhD., LEED AP SUSTAINABLE SYSTEMS ANALYSTAEI | AFFILIATED ENGINEERS, INC. 5802 Research Park Blvd. | Madison, WI 53719P: 608.236.1175 | F: 608.238.2614 fbetz@aeieng.com | www.aeieng.com_______________________________________________ TRNSYS-users mailing list TRNSYS-users@cae.wisc.edu https://mailman.cae.wisc.edu/listinfo/trnsys-users
-- *************************** David BRADLEY Principal Thermal Energy Systems Specialists, LLC 22 North Carroll Street - suite 370 Madison, WI 53703 USA P:+1.608.274.2577 F:+1.608.278.1475 d.bradley@tess-inc.com http://www.tess-inc.com http://www.trnsys.com