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

[henkwitte <henk.witte@xxxxxxxxxxxxxxx>]

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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