Conservation Organization Need's Expert Advice on Bat Cave

[TNCave]

Intro:
Hello everyone, I am certainly not a refrigeration engineer or expert. I am a cave and bat conservationist working for The Nature Conservancy. I joined the forum for the express purpose of gaining useful information and contacts relative to a big project I am working on. I hope this is OK and that I've not violated any forum ethics.

Help Needed:
My name is Cory Holliday and I'm the program director for The Nature Conservancy's Cave and Karst Program. Currently, we are designing an artificial cave to attract hibernating bats. The cave will be built in TN and needs to function as a passive cold air trap. Just like a natural bat hibernation cave, we will not be using any artificial or enhanced cooling, we will be relying on cave design and the laws of physics.

I have a preliminary design and would be happy to receive comments from members of the board, and I would love to consult with an expert if one could be recommended. The draft design can be seen at: http://s107.photobucket.com/albums/m286/TNCave/Cave%20Stuff/Artificial%20Cave/

I'm assuming this is a pretty complex question with many factors including local climate and weather, desired temps, local topography, etc. Very basically, it'll be in TN, at the bottom of a hill with berms channeling cold air into the main entrance, and we're hoping to sustain temps around 5-7C for the coldest parts of the winter.

Any help, tips, comments, etc. would be appreciated. Feel free to email me directly at cholliday@tnc.org

Thanks,

Cory

[chillerman2006]

Welcome to RE Cory

Natural Cooling...Hmmmmm

Something different to learn

Interesting project Mate and am hoping some of the more technical Guru's here will add their useful input

Definately come to the right place

R's chillerman

[frank]

Hi Cory

If the project is intended for above ground then, with the tall 'chimneys' or Atriums, your design could benefit from natural ventilation using the Stack Effect. The drawback of this is that any internal cooling cannot go below the ambient temperature.

If the design is intended for below ground construction, then I fear you may need some form of forced mechanical ventilation to achieve any sort of temperature control.

If I read your post correctly, a type of 'cave' construction will only benefit from the low ambient conditions near the entrance, because, without the wind blowing in the right direction, the internal areas will be warmed by the surrounding earth, keeping it above your desired 5-7C

[al]

Hi Cory

Welcome to the forum, it would be great for all of us if we could watch this progress to a solution, as CM says a chance to see something new!

al

[TRASH101]

Hello Cory,

An artificial cave? Why not build it underground and use what a true cave uses to form its habitat?

I take it that ventilation is to be avoided to the greater part or will the the bats roost with air movement greater than any natural thermal convection currents?

What is the sub soil temperatures in the locality? Is it feasible to cool the artificial cave lining?

So many many questions to ask and be answered for any interested party ;)

[mad fridgie]

This is a narrow band to control naturally, especially if the natural ambient swings by large amounts. No idea what TN is. best guess Tennessee? But no idea of the local conditions.
So you have two issues, controlling the natural airflow (wind, density change,temp) Do you have a required fresh air make up (nothing to do with temp), the other is calculating the gain or losses from the structure and then calculating the thermal mass of the structure to compensate for the losses and gains, to keep within the you desired internal temp range. You could look at using a phase change material (PCM) with a melting point of 6C. Placed evenly through out the structure. This would help with temp stability
Are you only looking at winter conditions only.

[TNCave]

Hello Everyone,

Thanks for the great feedback and questions. I can tell already, that we may need to consult with a pro in a more formal format. If there is anyone TN based that you all could recommend, it would be appreciated.

This artificial cave will be below ground and completely covered with at least 3' of soil. It will also be toward the bottom of a slope and the main entrance will have berms directing downflowing cold air into the artifical cave. The chimney entrance is well above the main entrance and will have a large dampner similar to a woodstove.

The construction will consist of a rebar shell, a closed cell foam layer, then covered on both sides with spray on concrete (Shockcrete). It will be in northern Tennessee where avg. ambient is around 12C, and winter temps swing from -13C to 10C. Natural hibernation caves in the area have rock temps somewhat stable in the 5-7C range during the coldest parts of the winter, although air temps do fluctuate quite a bit. The natural caves that serve as bat hibernation sites in TN are cold air traps. They are usually at the bottom of a slope and have entrances at multiple elevations.

We are trying to do this without the use of artificial climate manipulations like forced ventilation or chiller lines. This is designed as a long term project and reliance on "the grid" or mechanization is too risky for hibernating bats.

Please keep the questions and hopefully answers coming.

Thanks,

Cory

[simon@parker]

i remember the romans used to produce ice by trickling water down a rock pile usind natural wind/breeze to create a refrigeration effect am wondering if you could not go back to the very very basic principles of refrigeration to produce yr temp range with only a very small amount of technology to control it ? just an idea am sure one of the fridge jedi will be able to expand on it or say it not feasable a very interesting idea i hope you keep link updated :)
you can us whole cave as a massive dessert cooler the evaporation of water will cool cave will take a genius to work out but it can be done might require a little R an D but it is possible

[josei]

This artificial cave will be below ground and completely covered with at least 3' of soil. It will also be toward the bottom of a slope and the main entrance will have berms directing downflowing cold air into the artifical cave. The chimney entrance is well above the main entrance and will have a large dampner similar to a woodstove.<br>
<br>
The construction will consist of a rebar shell, a closed cell foam layer, then covered on both sides with spray on concrete (Shockcrete). It will be in northern Tennessee where avg. ambient is around 12C, and winter temps swing from -13C to 10C. Natural hibernation caves in the area have rock temps somewhat stable in the 5-7C range during the coldest parts of the winter, although air temps do fluctuate quite a bit. The natural caves that serve as bat hibernation sites in TN are cold air traps. They are usually at the bottom of a slope and have entrances at multiple elevations.<br>
<br>
We are trying to do this without the use of artificial climate manipulations like forced ventilation or chiller lines. This is designed as a long term project and reliance on "the grid" or mechanization is too risky for hibernating bats. <br>
<br>
Cory

Hello Cory:
Some tips for the successful completion of the study of "air and humidity of a bat cave":
1-I never heard of experts in this type of study. This is not a refrigeration nor air conditioning case.

2-Sould be done a study ( I think, by some school of mechanical engineering), taking into account the actual conditions of cave at the site where will be installed.
3-Another possibility is to make simulation, modeling with software.

4-In any case, study should determine the internal environmental conditions as temperature, humidity, air velocity, and number of bats, and also air external conditions such as: direction and velocity of the air, the dry bulb temperature, wet bulb or relative humidity.
Josei bsme