compressed air to heat question

Hello All,
Let me start by saying I'm not a refrigerator person. I am trying to use compressed air to heat my shop that doesn't have electricity. I recently purchased a 10 hp compressed air windmill. I have two 1,100 gallon propane tanks to store the compressed air. My windmill puts out 30 cfm @ 175 psi. I've been using the stored air for pneumatic tools and air motors in the shop. I'm in the process of adding a third storage tank. Since I have an abundance of stored air I want to use the overage to heat my shop. Is it possible or would I be better off using one of my air motors to drive a generator and use an electric heater? I've been using propane for heat. Can someone point me in the right direction? Thank you for your help.

Hi Steve.
As a "fridgie" of many years. I have read your pleasant post with interest.
I can honestly admit however, I do not have a clue what you are asking for?

I will read with interest any clues you can give.

Grizzly

The most direct way would be to use the discharge from the compressor to heat water, and circulate the heated water through a floor slab or fan coil.
It also gives you ability to store the heat as warm/hot water for later use.
Unfortunately, it will move you further away from adiabatic storage which will have an effect on the efficiency at point of use.

Do you live an area of high wind availability?
What are you ambient temperatures like?

An automotive A/C compressor driven by an air motor in a heat pump configuration would be a more efficient way to heat than a generator and direct electric heat setup, provided you have a heat source which will allow for operation at a reasonable level of efficiency.

If your air is stored, it is also likely to cool down, if this is expanded, it will actually cool "Joule Thompson effect"
So even if you us it for rotation, the exhaust air, must be vented external to the heated area.
As Flyin says use to heat water from the discharge from the compressor, then perhaps use a air drive motor (used air vented to outside), to drive a refrig comp, depending upon the heat water storage temp, you could use this as the heat source and the cond. to boost the a separate water stream to a more useful heated temp

I am aware of a site that uses a lot of compressed air for their production process. The have recently installed several plate heat exchangers, one for each compressoer. The secondary side of the heat exchangers are now being connected to normal central heating radiators to heat the factory and offices. Thermal specialists have calculated that they have about 80kwatts of rejected heat from the 8 air compressors that at present is being wasted.
A secondary by product is that by using the heat rejected via the heat exchangers, they will also save on the running costs on the air cooler/driers.
Dependant on the amount of compressed air that you use, you may be able to harvest the waste heat via a plate heat exchanger.
The use of low grade heat via an underfloor heating circuit would make the most efficient use of the waste heat as you would not need to obtain such a high flow temperature. It may be best to put in a fairly large buffer tank to store the central heating water for the times when the compressors are not running.

Steve O,

My opinion:

1) Use heat rejected (using the oil coolers and/or discharge air temperature) to heating

2) Use a heat pump if 1) is not sufficient to your needs

I'd start by working out how much energy you need to heat your shed, then work out how much energy the wind is providing, then take away the energy you are already using to run the air compressor and see if you have enough 'spare energy' to heat your shed.

Easiest thing might be a generator and some infra red heat lamps to warm you up rather than the whole shed.

.

If you are considering connecting an air drive motor / rotor thingy-ma-bob
directly to an electrical generator or other such device as long as you have
enough air and can regulate it correctly it will work.

If you are considering connecting it to a refrigeration compressor you could
use it to power a heat pump and again that would work.

Both those options are inefficient but both are possible and because you start
with a free energy source (the wind) it is entirely do-able.

Regards

Rob

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Quote:

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Originally Posted by Rob White

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If you are considering connecting an air drive motor / rotor thingy-ma-bob
directly to an electrical generator or other such device as long as you have
enough air and can regulate it correctly it will work.

If you are considering connecting it to a refrigeration compressor you could
use it to power a heat pump and again that would work.

Both those options are inefficient but both are possible and because you start
with a free energy source (the wind) it is entirely do-able.

Regards

Rob

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Electric heating coils or infra red lamps would be worst than the heat pump.

Thank you all for taking the time to respond. I have an unlimited air supply from my windmill. I'm trying to figure out the best way to use my excess air to heat the shop. The ambient temperature is in the 40's. My two 1,100 gallon propane tanks are in the low 30's. I have consistent winds at 10mph which keeps both tanks at 175psi. I'm not sure of the most efficient way to use the excess air to create heat.
Thanks again,
Steve O

My air compressor is 60' up at the top of the tower. The two 1,100 gallon tanks are outside and colder then it is in the shop. Since I have a spare air motor I was thinking about using it to power a generator since I have no electricity in the shop. I am in the process of getting a third used propane tank.

Regards,
Steve

Some unproven anecdotal numbers for you based on nothing more than experience and stuff I've read on the net.

You need about 4-6hp of compressor to generate 3/4-1hp using air. Now, if you have unlimited air for free then it becomes a different prospect. You are going to get significant heating from the compression, so if you can insulate the discharge line from the compressor you stand a good chance of recovering significant heat from there. I'd be using an air motor of some kind to be running an open compressor (like a car AC unit) to run a heat pump of some kind. Recover what you can from the discharge heat and get the rest from the ambient.
The concept of a compressor at the top of the tower becomes significantly more efficient proposition!

Quote:

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Originally Posted by Steve O

My air compressor is 60' up at the top of the tower. The two 1,100 gallon tanks are outside and colder then it is in the shop. Since I have a spare air motor I was thinking about using it to power a generator since I have no electricity in the shop. I am in the process of getting a third used propane tank.

Regards,
Steve

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If you have enough air and if you can rotate the generator at the
correct speed you will be able to generate power, just do it outside
the workshop because as you vent the air it will have a significant
cooling effect and you don't want that in the workshop.

Rob

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Air compressors are notoriously inefficient. 90% of their work done is rejected as heat so as was stated above you need to capture the heat from the air as it leaves the compressor. After its entered the tank you're too late and as air is released the tank will cool rapidly. Go to sites for Kaeser, Ingersol Rand and Atlas copco to see how they are capturing the waste heat and try to replicate the principal of what they're doing for your own purpose

Quote:

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Originally Posted by Bigfreeze

Air compressors are notoriously inefficient. 90% of their work done is rejected as heat so as was stated above you need to capture the heat from the air as it leaves the compressor. After its entered the tank you're too late and as air is released the tank will cool rapidly. Go to sites for Kaeser, Ingersol Rand and Atlas copco to see how they are capturing the waste heat and try to replicate the principal of what they're doing for your own purpose

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I ended up buying a vortex tube and should have it later this week. Ill take some pics and let everybody know how well it works. From what I have been reading the vortex tube is noisy on the cold air end will need to be vented to outside the shop in the winter. I can then rotate the tube in the summer and use it to cool the shop. Thanks to everybody that took the time to post back.

Regards,
Steve O

Received the Vortex tube today, much smaller then I thought it was going to be.Attachment 9987

Quote:

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Originally Posted by Steve O

I ended up buying a vortex tube and should have it later this week. Ill take some pics and let everybody know how well it works. From what I have been reading the vortex tube is noisy on the cold air end will need to be vented to outside the shop in the winter. I can then rotate the tube in the summer and use it to cool the shop. Thanks to everybody that took the time to post back.

Regards,
Steve O

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