Ground-to-air heat exchangers

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Does anybody have success modeling a ground-to-air heat exchanger in

The ground-to-air heat exchanger is a network of underground pipes aimed
at preheating / pre-cooling the outdoor air.

Any suggestions for modeling this system?



Demba Ndiaye

Demba Ndiaye's picture
Joined: 2011-09-30
Reputation: 200

This system is also known as earth (to) (air) heat exchanger,
air-to-soil heat exchanger, soil-to-air heat exchanger, "puits

Any advice on how to model this system will be highly appreciated.


Demba Ndiaye

Demba Ndiaye's picture
Joined: 2011-09-30
Reputation: 200

eQUEST doesn't allow you to directly model earth tubes. Depending on your
level of eQUEST skill you can make some thermodynamic approximations of how
the earth tubes will effect your annual energy use if you first perform some
external calculations to estimate the performance of the tubes based on
their proposed design (ie: how will the earth tubes impact the entering
outdoor air temperature you see at each air-handling system).

I believe that other simulation programs have the capability to directly
simulate earth tubes which I recommend you investigate.

Michael Tillou, PE, LEED

Michael Tillou's picture
Joined: 2011-10-02
Reputation: 0

What I have previously to model earth-tubes is to
manipulate the weather file that is going in eQUEST.
In my case it was pretty straight forward because the
space being served was internal so there was no heat
transfer from external walls. Hence I was able to use
this method.

1) Modeled the air temperature coming out of an earth
duct in TRNSYS. TRNSYS has ground-air HX types but
also a specific type( Type 260 developed by
Hollmuller) that can model earth ducts.

2) I then manually modified a tmy2 file for the
location and replaced the dry-bulb, RH and dew-point
with the properties of the air coming out of the tube.

3) Converted the TMY2 files to DOE-2 weather file.

Again, I had to do this because we were evaluating the
total energy savings of an earth duct for
preconditioning. Modifying weather files is definitely
not recommended if the building or space sees outside

Hope this helps.

Gerald Pde's picture
Joined: 2011-10-01
Reputation: 0


What is your approach of modeling trombe walls in eQuest.

Someone in the archives suggested defining an exterior wall assembly
with spandrel glass/air gap/mass wall.

In my model, the effects of doing so are negligible.

Suggestions, suggestions ....

Thanks for your input.


Demba Ndiaye

Demba Ndiaye's picture
Joined: 2011-09-30
Reputation: 200

I tried to model Trombe Walls for a project I was doing in Asheville, NC
in eQUEST. like you, I drew a blank. There are a couple of things you
could use:

1. SunREL - a software program developed at NREL for passive solar.
2. You could also perform hand calculations based on the LSR/SSF method
3. Our office worked with Penn State to optimize the Trombe Walls and
other aspects of the building using CFD.

Good luck

Vikram Sami, LEED AP

Vikram Sami's picture
Joined: 2011-09-30
Reputation: 0

Use a sunspace and look at the documentation in the DOE2.2 manual.

Michael Andelman's picture
Joined: 2011-09-30
Reputation: 0