# Vertical Wind Tunnels using green technology

I wish to create a state-of-the-art vertical wind tunnel for indoor skydiving. By state-of-the-art I mean using green technology to create the power necessary to push air, and I would like to reclaim as much energy I can from the movement of air, drive shafts, and anything else I have not thought of but you may have knowledge of. Most tunnels require about 1000 hp to move enough air in a 3 metre wide tunnel. I want a 6 metre wide tunnel and that would require much more energy, and if I can exhibit how this can be done using minimal energy production through innovation and ingenuity then it would be a good example for others, and will of course reduce operating costs. Thank you.

berkeman
Mentor
I wish to create a state-of-the-art vertical wind tunnel for indoor skydiving. By state-of-the-art I mean using green technology to create the power necessary to push air, and I would like to reclaim as much energy I can from the movement of air, drive shafts, and anything else I have not thought of but you may have knowledge of. Most tunnels require about 1000 hp to move enough air in a 3 metre wide tunnel. I want a 6 metre wide tunnel and that would require much more energy, and if I can exhibit how this can be done using minimal energy production through innovation and ingenuity then it would be a good example for others, and will of course reduce operating costs. Thank you.

Welcome to the PF.

Please tell us your thoughts on how you will accomplish this. Please include calculations for where you will be able to conserve energy.

Thank you for taking the time to inquire about my post. I could detail my thoughts, certainly, but at this point I am not clear as to my direction but for the true starting point of such a project: energy, and how to make best use of the newest technology of which I don't think I am fully up to date on. I plan to read the suggested threads below before so as to potentially update my knowledge on the subject.
I do know the conventional wisdom would state there's no free lunch concerning created energy and thereafter attempting to increase it. I'm thinking outside the box and though my lunch will not be free it will be substantially discounted.

Baluncore
Consider a solar updraft tower as part of the solution. https://en.wikipedia.org/wiki/Solar_updraft_tower

Build your free-fall chamber near the base of the tower where you can gently pinch the section to increase the air velocity. It will only operate when the sun is out, but it might be used to generate an energy credit when not being used for free-fall.

A wider skirt or taller chimney will gather more solar power. Area and height limitations will dictate the percentage of the required power may be generated by the tower. Even if additional power is required for a fan, the use of any updraft tower should improve the environmental bottom line.

russ_watters
Mentor
No offense, but an idea like that would be worth millions of dollars; Don't you think people who do know the physics/engineering have been working on such things, given that there would be a lot of money in it? And you want us to invent it for you here? Do you really think that is realistic?

Gold Member
I honesty don't think it would be worth millions. Vertical wind tunnels for this purpose are a very niche market. In trying to transfer the hypothetical concepts to a more conventional configuration, the high additional cost of such a system would price most users that could benefit out of the market (i.e. universities) and wouldn't be worth the additional cost to most of the rest (i.e. government) who can afford the power draw of a more conventional design.

Still, even if it was a lucrative idea, I totally agree it would be silly to expect a bunch of us to basically invent it for someone else for them to benefit.

Baluncore
Still, even if it was a lucrative idea, I totally agree it would be silly to expect a bunch of us to basically invent it for someone else for them to benefit.
I'm happy to throw in ideas because the OP will have to do all the work of selecting and integrating the collection of suggestions received. The idea is only 2% of the invention. Making the prototype is another 2%. I hope our suggestions make possible a successful business that employs many and earns it's investors a good financial return.

I am often presented with challenging problems. I solve them using ideas I get from all over the place, including from OP's questions and member's replies here on PF. This is a two way exchange of ideas. It is a community.

Gold Member
I'm happy to throw in ideas because the OP will have to do all the work of selecting and integrating the collection of suggestions received. The idea is only 2% of the invention. Making the prototype is another 2%. I hope our suggestions make possible a successful business that employs many and earns it's investors a good financial return.

I am often presented with challenging problems. I solve them using ideas I get from all over the place, including from OP's questions and member's replies here on PF. This is a two way exchange of ideas. It is a community.

I get it, and usually I'd agree. I happily throw out idea when it's an idea that is already well-thought-out and they are generally looking for help with a piece of it. This, though, feels like someone fishing for the answer to the entire project. Maybe I'm wrong, but that's just how it read to me.

russ_watters
Ah, how interesting. The two gentlemen agree that knowledge should not be freely disseminated... a side note, would there ever be a situation where you would think knowledge should not have a pricetag?
Now, on the topic before us, please, this is not quite rocket science. Vertical wind tunnels (VWT) are straightforward. Calculations indicate 925 bhp would generate enough air velocity for a 3 metre diameter flying chamber. One can, roughly speaking, take four V8 enginesrive sha that can develop 250 bhp, add a fan or propellor blade to each, run them at the correct and constant rpms necessary to combine their airflow through a vertical tunnel to achieve the desired velocity. Attach a generator to each drive shaft and reclaim some juice. Have your engines run biodiesels. Now that's about it for the conventional thinkers. No big deal. I have a few other ideas for green energy feeding machinery to move blades that push air. And the gentleman's comment about varying the diameter of the tube I understand and appreciate.
The intellectual challenge is straightforward. Air is flowing in a closed loop system. The movement of air requires a push by power. The very fact that circulating air through the chamber is at a high velocity means at any point in the circulation chamber one may remove energy from the wind. But the 'no free lunch' principle means that what was removed is replaced by the powered machinery - call it an engine. But can one outthink conventional wisdom and have a system in which the use of the engine that results in moving air is arranged and augmented so lunch, if not free, is severely discounted -- and without using fossil fuels.
One may decide on optimal engines and optimal blades to create the desired velocity. But a solution that harnesses the wind's power without the need to recreate that original wind velocity through the use of the engine is something that you cannot come up with whether you get money or not - it would violate a principle of physics. But there must be a way through technology and efficiency, through the manipulation of the tunnel diameter as suggested) and the use of outside green energy sources to augment the principle energy production that the end result would be an example of what can be done -- when there's a will there's a

Baluncore
Attach a generator to each drive shaft and reclaim some juice.
No. That would be very inefficient. It smells of an attempt at perpetual motion.

russ_watters
How did you arrive at that conclusion of inefficiency?With a stationary conventional internal combustion engine, the driveshaft would spin to revolve the blades for air velocity, a belt attached -- in a similar fashion as one's automobile's fan belt -- and that belt turning a generator.... It would seem a waste NOT to do that, sir.

russ_watters
Mentor
Ah, how interesting. The two gentlemen agree that knowledge should not be freely disseminated...
That bears no relationship to what we said. It isn't just knowledge you are asking for, it is an invention. Inventions have value. You want to make money off of something we invent for you! Will you send us a check for a fair piece of our contribution? We'll happily provide knowledge for free, though:
Calculations indicate 925 bhp would generate enough air velocity for a 3 metre diameter flying chamber. One can, roughly speaking, take four V8 enginesrive sha that can develop 250 bhp, add a fan or propellor blade to each, run them at the correct and constant rpms necessary to combine their airflow through a vertical tunnel to achieve the desired velocity. Attach a generator to each drive shaft and reclaim some juice.
That would violate conservation of energy if it provided a benefit. Every HP of generator added would necessitate adding a HP to the engines to maintain the energy balance.

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Baluncore
It would seem a waste NOT to do that, sir.
Then you do not understand efficiency. Each time energy is converted there is loss.
The motors are run to turn the blades. Why take some of that energy away from where it is needed ?

russ_watters
Mentor
I honesty don't think it would be worth millions.
The OP is trying to save 200 hp. At 1200 hours per year and 12cents per kWh, that's $215,000/year per installation. [Late edit] Beyond that, depending on the specifics, it could have implications in other industries, such as mine; HVAC. Saving fan poser is a significant fraction of what I do for a living. That also means that a lot of people have put a lot of thought into this already, so easy answers will be tough to come by. Last edited: billy_joule I believe the forum is a platform for the exchange of ideas and knowledge. I do not ask anyone to make calculations, or make any inventions. I merely ask for the dissemination of wisdom and perhaps all parties learn something of interest. As for efficiency, I agree in a system solely designed for moving air generating electricity off a drive shaft will entail energy. But perhaps I was not clear as there would be the entire facility containing the tunnel that would require power. Please make no calculations that may or may not prove that energy would be better used off a commercial grid! The ideas and rapport, sir, and/or sirs, is greatly appreciated, thank you kindly. Nidum Science Advisor Gold Member First generation vertical wind tunnels just used aircraft propellers . More recent ones have shown some advances in fan technology but not really very much . Use of gas turbine ducted fan technology could possibly give significant improvements in running efficiency but it would come at very high cost . Actually, regarding saving HP, which you've equated into money, my actual intent is to NOT use fossil fuels and showcase alternative solutions. My rough calculations show with conventional internal combustion engines, the size of the tunnel I envision may require up to 2000 HP to move the air at the velocity I desire. If I had diesel engines, and used bio-diesel, it would cost a bit more than the current price at the local station. Of course any business must concern themselves with the bottom line, but this project is about alternatives, the future, and how best to go about thinking 'outside the box' to achieve such a goal. Nidum Science Advisor Gold Member More like 4000 HP . It doesn't matter how the air moving system is driven - you still need a high power air moving system and nothing will change that fact . All that input power has to come from somewhere . I'll have to look into gas turbine fan technology. I have been considering aircraft engines. I recall KLM flew using alcohol for fuel, but my research is incomplete in this area. RollsRoyce has some interesting engines developed but I haven't all the details to accurately describe herein what they've managed to do. russ_watters Mentor Then you do not understand efficiency. Each time energy is converted there is loss. The motors are run to turn the blades. Why take some of that energy away from where it is needed ? It is more than just an efficiency issue, it is the useful energy itself that is the problem. I'm not sure the OP got that from my previous post, so I'll try again, with an example: If you are spinning a fan that requires 1000hp, you use a 1000hp motor or engine. Then you decide you want to "recover" 500hp of that, so you attach a 500hp generator to the system. But oops, now you need an input of 1500hp instead of 1000 and you therefore haven't gained anything. The way I understood the hypothetical scenario was an internal combustion engine with a pulley and belt hookup on the drive shaft to turn a generator would produce electrical energy that could feed the infrastructure of the facility, such as lighting, and although that would could be measured in HP, the decider would be once converted to kWh and see if it may be ginancially worthwhile boneh3ad Science Advisor Gold Member Yes but do you have any reason to believe that this would provide an advantage? When you hook up a generator to your shaft, if the shaft is losing 500 hp to the generator, then the generator is still only able to use maybe 300 hp of that. There's an efficiency issue in that transfer just like there is when you pour more chemical energy in the form of diesel fuel into the first engine and get less hp out of it than what you pour in. So, the more links you add in this chain, the greater the number of places where you are losing energy due to the second law of thermodynamics. I honestly can't see how hooking a generator up to the shaft to power lights and computers and such would be more efficient than just running them off of normal building power or just slapping some solar panels on the roof and using those to power the lights. Most wind tunnels are currently run with electric motors that run off of the building's existing power architecture anyway. In essence, then, you are trying to build a system here that can provide power to your wind tunnel in a manner that is more efficient (or at least less carbon-intensive) than just using the electricity produced at a power plant somewhere. As of right now, you aren't likely to realize savings in money or carbon by using an on-site diesel generator rather than mains electricity. If your goal is to simply find a greener replacement for running the whole facility off of mains electricity, you are probably better off just installing solar/wind in your building to provide as much power as is feasible, or exploring something like a solid-oxide fuel cell such as the Bloom Energy Servers that Google uses to power some of its data centers. Those are only cost effective in some parts of the country, though. Mech_Engineer Science Advisor Gold Member I wish to create a state-of-the-art vertical wind tunnel for indoor skydiving. By state-of-the-art I mean using green technology to create the power necessary to push air, and I would like to reclaim as much energy I can from the movement of air... The way you "reclaim" this energy will be to have a closed-loop recirculating wind tunnel system, this would be a seriously big construction project considering you want to build one with a 6m diameter (this would officially be the biggest in the world, the largest right now is 5.2m). You should take a look at existing companies that make these kind of facilities, take for example Aerodium which markets a 5m recirculating wind tunnel. They say their recirculating tunnels start at 1.5 million euro, probably for the 3m model; I have to think the 5m unit is at least 3-4 times as much... It would take a team of engineers with specialized knowledge in aerodynamics to design a wind tunnel like you're proposing (not to mention quite a pile of money). Mech_Engineer Science Advisor Gold Member Take a look at the below source also, they estimate the construction of a 12-16 ft (3.6 - 4.8 m) recirculating wind tunnel facility will run between$7 million - $10 million USD. If you're wanting to build the biggest in the world, figure even more than that. http://www.indoorskydivingsource.com/articles/build-an-indoor-skydiving-facility/ IndoorSkyDivingSource.com said: Costs, Construction & Ownership For a portable machine, expect to invest at least$500,000 USD for the tunnel equipment itself. You might be able to find used portable machines for less, but be very careful when purchasing used. On top of these base costs you will need to factor shipping, construction, land and operation costs into your business plan.

Recirculating tunnels are much more complicated and most companies offer a range of services all the way from equipment only to turn-key operations. To open a project to the public, most modern recirculating tunnel projects (12 - 16 ft diameter, permanent installations) require an investment of $7-10 million dollars. The cost of the machine is included in this number. For reference on the lowest end you can find some manufacturers offering recirculating tunnel components only starting at$1,700,000 USD.

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russ_watters
Mentor
The way I understood the hypothetical scenario was an internal combustion engine with a pulley and belt hookup on the drive shaft to turn a generator would produce electrical energy that could feed the infrastructure of the facility, such as lighting, and although that would could be measured in HP, the decider would be once converted to kWh and see if it may be ginancially worthwhile

1 hp is 0.746kW (at 100% efficiency).