[TRNSYS-users] Control of on active layer

[Cramer Silkworth]

Arnaud,

I was thinking that by "pre-heat" you meant this was the air input to an 
air handler, then the output of the air handler (to the zone) is 
constant and stability is not an issue. But if this air goes directly to 
the zone, then yes, Jeff's recommendation of type 2 is better. Any kind 
of control where you want to both *read* and *influence* zone 
temperature needs a real controller with deadbands of some kind for 
stability. 

-Cramer


-----Original Message-----
From: Jeff Thornton [mailto:thornton at tess-inc.com] 
Sent: Monday, July 13, 2009 11:24 AM
To: Cramer Silkworth; a.thome-08 at student.lboro.ac.uk; 
trnsys-users at engr.wisc.edu
Subject: Re: [TRNSYS-users] Control of on active layer

<I would like to pre-heat the inflow of the ventilation during the 
heating period to see the impact that this would have on the heating 
bill.

To do so I would like find a controller to model:
if Tzone>20°C then Tinflow=Toutside_amb
if Tzozne<20°C then Tinflow=35°C

Do you know wich controller should I use?>

<All you need is an equation:

Tinflow = gt(Tzone,20) * Toutside_amb + not(gt(Tzone,20)) * 35

the GT and LT functions return either 0 or 1, so this contruction gives 
you, in effect, an in-else statement.>

While that seems like the ideal solution, using a simple equation to 
watch the zone temperature and control the heating temperature will 
likely result in a non-convergence situation.  During one timesteps, the 
zone will likely rise above 20 C when the heating temperature is 35 and 
fall below 20 C when the heating temperature is ambient - causing an 
unstable solution.  I would suggest you use either the thermostat model 
or the Type
2 controller - they're made to handle situations like this.

Jeff



Jeff Thornton
President - TESS, LLC

22 North Carroll Street - Suite 370
Madison WI 53703 USA

Phone: 608-274-2577
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