[TRNSYS-users] create two airnodes in one zone

[David BRADLEY]

Zhe,
   TRNBuild has two concepts that are important here. An "airnode" is an 
area of the building that can be represented by a single air 
temperature. A "radiation zone" is volume within the building in which 
all of the walls can "see" each other. How you decide to break up the 
building into airnodes and radiation zones depends on what is crossing 
the boundaries between them. For example if you have an atrium with a 
glass roof or a glass wall there is going to be vertical stratification 
(i.e. multiple airnodes) and it is the solar radiation that is going to 
cross the airnode boundaries so you'll combine those airnodes into a 
single radiation zone. Virtual surfaces are used as boundaries between 
the airnodes because radiation can cross a virtual surface.

   In your case, I think you have a greenhouse attached to the side of a 
building so that there will certainly be a temperature difference 
between the greenhouse and the rest of the building but there probably 
won't be very much radiation crossing the boundary between the two. In 
this case there isn't any need to define a virtual surface because there 
isn't much radiation passing. You can define there to be a "wall" 
between the two airnodes when you are drawing the building in SketchUp. 
Then when you go to TRNBuild, you can set that wall's properties so that 
it has a very low thermal resistance (high u value). In this way the 
wall will allow you to define convection between the two airnodes and 
there will be little resistance to conduction heat transfer.

best,
  David



On 07/20/2015 19:17, Zhe Kong wrote:
> Hi everyone:
> I just star learning Trnsys and come up with a basic inquiry. Does 
> anyone know how to create two airnodes within one zone in sketchup 
> before exporting into Trnsys? We want to build a one-floor greenhouse 
> mostly enclosed by glazing. The sloped roofs are also in glazing. We 
> want to do the calculation concerning solar radiation and heat flow 
> without HVAC system.
>
> Currently we built two zones (the plant one and the air one) with the 
> mutual surface set as virtual surface; however, even the two virtual 
> surfaces disappeared when being exported into Trnsys, the two zones 
> seemed to have no air flow connection. The results show that the plant 
> zone has small range of temperature change, while the air zone has a 
> much larger range. We realized we should build the sketchup model with 
> two airnodes and one zone, but we didn't figure out how to do it. 
> Another question is, in that case, is there anyway we can set 
> different inputs according to the two airnodes?
>
> Thank you in advance.
> -- 
> /Zhe Kong/
> /PhD Student/
> /University of Wisconsin - Milwaukee /
> /School of Architecture and Urban Planning /
> /2131 E. Hartford Ave, Milwaukee, WI 53211 /
> /Office 327/
>
>
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-- 
***************************
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 at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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