Earth-air heat exchangers and solar chimneys for HVAC

[tsgrue]

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Do any of y'all have experience with analysis, design, and performance of earth-air heat exchangers (EAHEs) and/or solar chimneys for small-to-medium structure HVAC applications? I have read multiple studies on these systems with installations from India (Delhi area), Switzerland, United States (mid-west), and other locations. In each case, the performance was good to very good. I am interested in such a system for two small earth-sheltered/bermed 6 room bath houses at recreation facilities. All the siting characteristics appear very good. Can someone give me feedback on their experiences with such systems?

Thanks!

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tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation

http://hhwq.blogspot.com

 

[stanlsimon]

I am only aware of one U.S. installation somewhat similar to what you describe, at a residential building that was built to modern German standards. The facility is owned by Concordia Language Camp in Minnesota. They should have some data on how well the earth tubes performed, because that was a year ago.

 

[stanlsimon]

tsrue,

A web site which describes the initial building project is

http://minnesota.publicradio.org/display/web/2006/07/27/greenhouse/

Give me some time and I will try to find a contact. I too am interested in these systems. The diagram you pasted in would probably have to be modified for my climate zone.(8000 heating degree days and lots of wind)

One modification to consider is to use a turning scoop to aim into the wind. Another scoop could aim out of the wind to act as an exhaust. The solar chimney looks like it was designed for a mild winter climate.

The heat transfer thru the tubes looks like a college heat transfer problem, you would need to make some assumptions for convective heat transfer coeficient, wind velocity, reynolds number, ground temperature, r value of pipe, etc. but these steady state calculations only give you rough ideas. The standard approach for these weather related energy calculations is to divide the year into bins of outside temperature ranges. Each bin is given a number of hours. If using wind driven ventilation you would need to to apply a different average wind velocity to each temperature bin. If using the solar chimney, you could assume a book value Sol-Air temperature for the stack and then find your bouyancy driven stack velocity. If the sun doesn't shine for a whole day you would need a fan driven backup.

How about some optimization, let the tubes reverse operation periodically, so that they recharge the ground temperature? This will call for some more mathematics. Also some dampers to redirect the air flow, so that your restroom air doesn't get pushed into the rest of the building.

hope this helps a little.

S.L. Simon
slsimon@tds.net

 

[stanlsimon]

Here is the Architect's TElephone # & email.

612-210-8230

stanner@intep-10.com

 

[gepman]

Interesting concept. Can one of you two give the following?

1) A good link to a general description of this type of system.
2) Briefly explain the advantages of this system over a ground source (water) heat pump?

 

[GMcD]

The Earth Rangers Centre in Ontario, Canada also used earth tubes for the fresh air intake system. See this link, and Google "Earth Rangers" by Enermodal Engineering.

http://www.cement.ca/cement.nsf/48e...a0050f778/$FILE/ER Brochure March 31 2004.pdf

The earth tubes are not meant to replace water type geo-exchange systems, but are intended to be used for the fresh air intake path to pre-heat ventilation air in winter, and pre-cool the air in summer, using the ground coupling.

Gepman- I just Googled keywords: earth tube design air intake, and got pages and pages of hits to general descriptions right through to design material.