[BLDG-SIM] earth-air exchanger (earth channels)

Denis Bourgeois denis.bourgeois at arc.ulaval.ca
Fri Nov 21 12:27:36 PST 2003


Bonjour Hugues,

I'm unaware of any single program that automatically sets this up. A very discrete finite-... 3D conduction model would be desirable, but depending on your specific needs, ESP-r would be a very good candidate as an annual assessment tool. I've used ESP-r for underground air culvert assessment in the past and a couple of graduate students have used ESP-r for similar studies (Y. Jeong, a grad student at Concordia, and another student in Norway (a PhD student I believe) have both used ESP-r for assessing the Media School in Norway, which has an underground air culvert).

In Jeong's case, the culvert is modeled as one zone, but it is fairly straightfoward in ESP-r to subdivide this in, let's say, 10 zones (e.g., a 40m culvert could be made up of ten 4m segments) - that's what I do. This will give you a more detailed assessment, e.g., of culvert surface temperatures along the airflow path (useful for condensation assessment or to see just how effective the first segments of the culvert are in relation to the last ones). ESP-r also allows you to set up an airflow network, but 'scheduled' airflows might be OK for your needs.

The main challenge is setting up the surface boundary conditions. Without setting up a 3D conduction model in ESP-r (available, but not for the faint-hearted), you'll have to specify boundary conditions for each surface. If the culvert is deep enough, you can just feed it monthly ground profiles for ~¾ of the surfaces, with harmonics calculated with standard models (see Maitos and Argiriou) - the same models used for ground-coupled heat pump simulation. If it's deep enough, the daily variations will be minor (~ ±1°C during the course of a month). The remaining ~¼ of the surfaces will more likely feel the effect of the nearby ground surface, so ambient air might be more suitable as a surface boundary condition. If the culvert is very close to the ground surface, then it's a bit more tricky - maybe ~½ of the surfaces need ambient air as a boundary condition. You can of course 'tweak' the model to see just how sensible it is to variable changes.

Another point is setting up the right surface element 'constructions' so on one hand it remains numerically stable, and on the other the constructions remain 'thick' enough so that using monthly profiles remains valid (at least conceptually). 

Transsolar have modeled culverts for other energy consultants in the past - maybe they've set up some basic modeling approach in TRNSYS (?). Simpler empirical approaches are available: Argiriou and Maitos give an overview of existing models found in the literature.

Good luck,

----

Some references:
Jeong, Y., and Haghighat, F. (2002) "Modeling of a hybrid ventilated building, Grong School" Proceedings of the 4th International Forum on Hybrid Ventilation: An Integrated Solution for Ventilation, Health and Energy, Montreal pp.198-207.

Maitos, A. (1999) "Cooling with underground air ducts" MSc Thesis. University of Strathclyde: Glasgow. 68p.

Argiriou, A.A. (1996) "Ground cooling" in Passive Cooling of Buildings. M.J. Santamouris and D.N. Asimakopoulos, eds., James & James: London. pp.360-403.

Kumar, R., Ramesh, S., and Kaushik, S.C. (2003) "Performance evaluation and energy conservation potential of earth-air-tunnel system coupled with non-air-conditioned building" Building and Environment 38 pp.807-813.

Lay, R.M. (2003) "Earth Rangers Wildlife Centre - case study of concrete use for energy efficiency" Proceedings of the 8th Environmental and Sustainable Engineering Specialty Conference of the Canadian Society for Civil Engineering, Moncton.

Sawhney, R.L., Buddhi, D., and Thanu, N.M. (1999) "An experimental study of summer performance of a recirculation type underground airpipe air conditioning system" Building and Environment 34(2) pp.189-196.

----

Denis Bourgeois
PhD student/doctorant
École d'architecture, Université Laval
denis.bourgeois at arc.ulaval.ca

----
  ----- Original Message ----- 
  From: Hugues Boivin 
  To: BLDG-SIM at gard.com 
  Sent: Friday, November 21, 2003 1:11 PM
  Subject: [BLDG-SIM] earth-air exchanger (earth channels)


  Does anyone knows a simulation tool to evaluate energy savings by earth-to-air exchanger (earth channels) ?

  Thank you.



  Hugues Boivin
  Mechanical Engineer
  Laval University
  GRAP (Groupe de recherche en ambiance physique)

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