Increasing earth tube radius increases the supply temperature ?

asked 2020-06-09 09:16:37 -0600

Prethvi Raj
291 ●1 ●5

updated 2020-06-09 12:49:15 -0600

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hello,

We are modelling earth tube for a project and we would like to know is it possible to visualize the velocity of the air passing through the tube.

With volume flow rate and the radius of the pipe it is possible to guess the velocity But, we need to know the how the velo city is simulated to debug few errors.

Because I believe increasing the size of the tube reduces the velocity of the air for a constant supply which in turn supplies much colder/heated air then smaller radius with increased velocity.

Regards, Prethvi, Building Performance Analyst, TRAJECT 361.

C:\fakepath\Pipe radius vs Inlet Temperature.JPG

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answered 2020-06-09 10:49:23 -0600

Aaron Boranian

14155 ●83 ●24 http://bigladdersoftware.com/

First, you should add the Earth Tube Standard Density Volume Flow Rate output variable to confirm that the supply airflow is constant as you change the earth tube radius. Once you have confirmed that, you can use the following output variables for further debugging of why you see changes in supply air temperature:

Earth Tube Air Mass Flow Rate (would tell you how air temperature change is affecting air density)
Earth Tube Ground Interface Temperature
Earth Tube Outdoor Air Heat Transfer Rate

It doesn't look like there is an output variable for air velocity, so you will need to manually calculate that with volume flow rate and pipe area based on radius. This can either be post-processed after each simulation, or you can use Energy Management System (EMS) (Scripting module in DesignBuilder) to create a custom air velocity output created by EnergyPlus.