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Re: heat transfer with water-bearing stratum of the soil



Dear Adriana,

With "interacting" do you mean ground water movement? In any case, ground water effects are not easy to incorporate. We try to take into account two effects: natural ground water flow (advection) and thermally induced convection. Both may affect operation of a ground loop system especially in cooling operation. We use a numerical model (HST3D) developed by the USGS to estimate effects of ground water on the system. The disadvantage is that it is not possible to model the heatpump - heatexchanger - borehole with this model, only a heat flux can be specified and the temperature response to different ground water regimes can be compared.

This model can not be used with TRNSYS however! For relatively simple (small) systems the effect of ground water flow can be incorporated by changing the soil thermal conductivity. Using HST3D and a line source approach you can estimate the '"apparent" conductivity from the temperature response to a specified heat flux (given the real conductivity of the ground and ground water flow). This conductivity can than be used in the TRNSYS ground heat exchanger model. that should give you a good idea about the order of magnitude of the effect.

I have some results of experimental measurements we carried out, so if you are interested please send me your email address and I can send you the PDF's.

Best wishes,

Henk Witte


Dear trnsys users,

I'm working on ground coling.
Does anybody know if there is a type for modelling ground heat exchangers interacting with the
water-bearing stratum of the soil? Such interaction is not taken into account in the Duct Storage Model
type.


Thank you


Adriana

----------
Adriana Angelotti
PhD student
eErg end-use Efficiency Research Group
Politecnico di Milano, Dipartimento di Energetica
Piazza Leonardo da Vinci 32
20133 Milano
Italy
ph +39.02.2399.3859
fax +39.02.2399.3940


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