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Camilo, I am not familiar with the table that is mentioned. The documentation notes that values for Kair0 are typically between 7 and 11 kJ/h.K.m2 and Kair1 are between 14 and 18 (kJ/h.m2)/K/(m/s). What I have typically done is to use some basic heat transfer equations to calculate the Nusselt number for a few different flow rates through the ducts as a function of the Reynolds and Prandtl numbers. From the Nusselt number, you can then get the inside convection coefficient and fit the values to arrive at Kair0 and Kair1. I think my method over predicts the inside convection coefficient but I haven't found a better way to do it One critical thing about earth tubes is to keep the flow turbulent. Without knowing what kind of input changes you made in your simulation between the cases that do and do not show total energy differences across the earth duct it is hard to guess what might be happening. Best, David On 6/24/2012 01:38, Camilo Arias wrote:
-- *************************** 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 |