[EnergyPlus_Support] Multiple earth tubes serving a thermal zone

["marziasedino" <marziasedino@xxxxxxxx>]

Hi,

I am trying to model an Earth Tube ventilation system where multiple 
earth tubes serve unique thermal zones, in a building with multiple 
thermal zones.

As E+ only allows me to define one earth tube per zone, I modeled an 
individual equivalent earth tube for each unique zone, where:
- length is fixed based on site constraints
- air velocity is fixed at an optimal speed (approximated) for 
optimal heat transfer (two iterations, at 2 & 4 m/s respectively)
- airflow (m3/s) is dictated by fresh air requirements for the 
thermal zone and split 
- radius is then dictated by the overall required airflow value for 
each zone after having defined an optimum velocity for the air within 
the tube

But I am not getting good results: the temperature of the air 
entering the zone after passing through the tube is almost equal to 
the outdoor drybulb temperature.

Also, by playing with parameters I found out that the only way to 
achieve a modest reduction in output temperature from the earthtube 
would be by keeping its velocity very low, almost steady. But this 
will not be accurately representing the real proposed system 
operation and conditions.

Given that varying the radius of the earth tube supplying each zone 
to allow for maximum fresh air intake has not proven successful in 
realising equivalent performance of multiple smaller ET's, I guess 
the solution would be to provide a limited amount of air through the 
ET (under ideal parameters including radius!) and the remaining 
through a conventional system.  I might then scale any benefit in 
energy reduction from the use of this single tube by which ever 
multiple of additional ET's I may choose to supply the unique thermal 
zone with?

Do you have any better suggestions?

thanks a lot!

Marzia






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