What minimum size of thermal zone can be simulated in E+?

asked 2016-05-23 00:50:21 -0500

sankar
101 ●2

updated 2016-05-23 14:21:24 -0500

Julien Marrec

29077 ●86 ●74 http://www.effibem.com/

I am using E+ for the thermal simulation of a room having double skin facade (DSF) in south direction. In order to determine the temperature of each surfaces of the DSF and more, I have considered it as a separate thermal zone. However, the size (HxLxW) of this thermal zone is only 250x180x1.3 cm. Here 1.3 cm is air cavity thickness between two facades. In the literature thermal zone of size (HxLxW), 20x170x20 cm can found where E+ has been used (example).

The question is up to what minimum zone size the E+ can simulate accurately? Is there any reference document in this regards?

The considered thermal zone has natural air flow facility.

answered 2016-05-23 12:44:39 -0500

Archmage

7185 ●3 ●11

I don't know of any references related to this interesting question. I think 1.3 cm is too small. Thinking about the formulation of the zone heat balance model, I would suggest it is the formulation of the surface convection heat transfer (between the inside faces and the zone mixed air) that would make for a lower limit. A narrow glazing gap has a quite different convection situation compared to a room. Although you can do a lot to override and select different convection correlations in EnergyPlus if you know what to do, the usual (semi-infinite) convection correlations need enough room to have some zone air sort of undistrubed by surface's boundary layer flow. Boundary layer thickness is on the order of 10cm, and you have two and need some space in the middle so I would suggest a gap of at least say 30 cm.

For a 1.3 cm gap you would want to use the window model and may be able to use the airflow window model, see WindowProperty:AirflowControl.

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Do you know if there is a way to hack the WindowProperty:AirflowControl so as to pull in air from another zone than the one that the window is attached to? I have a situation where a room is being converted into a wine storage room to be kept at 55F and I am trying to stop this window from condensing on the outside, I think if I can pull in 75F air from another zone that I can stop it, but the WindowProperty:AirflowControl only allows to pull in local zone or outdoor air, and I don't want outdoor air either.