[bldg-sim] RE : earthpipes

[Pierre.Hollmuller at cuepe.unige.ch]

> From: John Davit 
> To: bldg-sim at gard.com
>
> Hi All,
> I am currently trying to model a gym which would draw in air through 
> earthpipes that could be used for either passive heating or passive 
> cooling depending on space temperatures and ground temperatures. The gym 
> would probably need mechanical ventilation to draw out air through the 
> pipes. The critical quesiton would be, what is the air temperature coming 
> out of the pipes and how much cfm is needed to offset sensible+latent 
> people heat gain and lights in the gym.
> Is there a way of simulating earth coupled pipes in eQUEST. If not, 
> what are the other whole building analysis tools that can simulate earth 
> coupled pipes.
> Thanks

Dear John Davit,
Dear All,

We (at Geneva University, Switzerland) have been working quite a bit on
earthpipes. If you read french, you may be interested in my PhD (which can be
downloaded on www.solarenergy-thermal.ch/ecran12.htm => Recherche :
"Hollmuller"). Otherwise some preliminary results can be found in "Cooling and
preheating with buried pipe systems : monitoring, simulation and economic
aspects", P. Hollmuller, B. Lachal, Energy and Buildings, 33/5, 2001, pp.
509-518 and/or I can send you a ppt-presentation of main results.

Main results are :
1) If you want to completly dampen day/night temperature oscillation (which
might be sufficient for cooling in Mid-European climates), you need around 20
cm earth around each tube. Exchange surface (m2) should be around 1/10 of
airflow (m3/h). If tubes are beneath ambient, theyhould be burried around 60-80
cm deep.
2) If you want to completly dampen summer/winter oscillation (which is needed
for preheating in Mid-European winter), you need around 3 m earth around each
tube. Exchange surface (m2) should be around 1/5 of airflow (m3/h). If tubes
are (at least) 3 m deep, but in a plane and close to each other (instead of 6 m
apart from each other), exchange surface (m2) should be around 1/1 of airflow
(m3/h).
3) If tubes are close underneath building (< 3m) and latter is being maintained
over a whole season at a different temperature than ambient (like in
Mid-European winter), than the earthpipes will take (major) part of its energy
directly from the building, and not from the soil. This may give rise to a net
energy loss instead of an energy gain!
4) If earthpipes for preheating (winter) are being used in series with a
heatrecovery system on waste air, than (an important) part of the energy gain
by the pipes is being "stolen" from the heatrecovery system, which will produce
less (net gain by the pipes < input-output difference).

We have developped a numerical simulation module for earthpipes which takes
into
account sensible and latent heat-exchange between air and tube as well as full
3-dimensional heat diffusion in soil. The model has benn validated both against
several in-situ monitored systems as well as against a fully developped
analytical solution. Developped as a FORTRAN subroutine, it is fully compatible
with TRNSYS (and edited by TRANSOLAR as a complementary module to the standard
package). If links to a FORTRAN subroutine or to a DLL can be made, other
simulation environments might try to use the routine.

Cheers
Pierre Hollmuller
Centre universitaire d'etude des problemes de l'energie
Universite de Geneve - Switzerland
email : pierre.hollmuller at cuepe.unige.ch




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