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Re: [EnergyPlus_Support] Lowtemperature radiant object:

Good question, Geert. In my experience these changes bring little change. 

In principle, the surface area in m2 is the largest impact. If said area is at temperature x, then the convection heat transfer from surface to air at temperature y is limited by the temperature difference (which may also change the convection coeff.) and the exchange surface area.

How little water flow, tube length, etc. does one need before the transfer rates between water tubes and concrete become less than that between surface and room air? 

Concrete has a high conduction coeff. so the heat propogation time lag from tubes to surface is very small.

However, the heat capacity of water volume in the tubes and the thickness of the concrete may impact on how long the surface stays at temperature after zero flow. This time lag effect may be the only factor of major importance. It will effect how fast the surface gets to temperature and how long it takes to cool down.  

Mit freundlichen GrüÃ?en- Sent from my iPhone (excuse the brevity)

i. A.
Jean Marais
b.i.g. bechtold
Tel.   +49 30 6706662-23

On 19.10.2013, at 17:53, <geert.bellens@xxxxxxxxxxxxxxxxxxxxxx> wrote:


I'm using a lowtemperatureRadiant:VariableFlow to simulate a chilled ceiling. The results seem to be correct.


However, when I'm playing with the properties of the chilled ceiling, nothing happens...


Changing the tube length from 1760 meters to 176 gives no difference, even if I reduce it to 10 meters...

Changing the tube spacing (internal source) from 0.05m to 0.3 meter gives no difference

Changing the tube diameters doesn't change anything.


Euhm... is this normal? How is a lowtemperatureradiant object being calculated if changing these parameters won't change a thing in the results ?






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