DIY refrigerator air dryer

[rcpaulsen]

I have an idea for a DIY compressed air dryer that I've never seen before.

The least expensive refrigerated air dryer I've seen is $550 at Harbor Freight, so decided to make my own ambient air dryer using a small air-cooled aftercooler to cool what's going into the tank plus a copper pipe grid on the wall to further cool what comes out. I have an aftercooler and electric radiator fan lying around, so I planned to mount the aftercooler to the wall with its own fan instead of mounting it on the belt guard opposite the air vane compressor pulley. Why preheat the air that is being blown on the compressor head?

I recently noticed that used mini-refrigerators can be picked up for practically nothing at yard sales. Is there any reason I couldn't mount my aftercooler in one of these and forego the fan and pipe grid on the wall?

 

[GeoBruin]

I have an idea for a DIY compressed air dryer that I've never seen before.

The least expensive refrigerated air dryer I've seen is $550 at Harbor Freight, so decided to make my own ambient air dryer using a small air-cooled aftercooler to cool what's going into the tank plus a copper pipe grid on the wall to further cool what comes out. I have an aftercooler and electric radiator fan lying around, so I planned to mount the aftercooler to the wall with its own fan instead of mounting it on the belt guard opposite the air vane compressor pulley. Why preheat the air that is being blown on the compressor head?

I recently noticed that used mini-refrigerators can be picked up for practically nothing at yard sales. Is there any reason I couldn't mount my aftercooler in one of these and forego the fan and pipe grid on the wall?

I'm sure it would work to some extent however my gut feeling is that the rate of heat exchange happening with the after cooler would be much higher than the refrigerators ability to exhaust the hot air. There also may be issues with condensation in the fridge causing icing.

I have an after cooler mounted to my compressor and the air coming out of it is almost ambient temperature. There would be almost no benefit to me of putting a copper pipe grid after the cooler, however, if you could mount a pipe coil inside the refrigerator, and run the precooled air from the aftercooler through cold copper pipes, you would certainly condense out some additional water. That said, this is all going to be pretty inefficient compared to a factory solution where the heat transfer volumes have been calculated and balanced, but it will certainly work.

Try one or the other and let us know how it goes!

 

[Firebrick43]

I'm sure it would work to some extent however my gut feeling is that the rate of heat exchange happening with the after cooler would be much higher than the refrigerators ability to exhaust the hot air. There also may be issues with condensation in the fridge causing icing.

I have an after cooler mounted to my compressor and the air coming out of it is almost ambient temperature. There would be almost no benefit to me of putting a copper pipe grid after the cooler, however, if you could mount a pipe coil inside the refrigerator, and run the precooled air from the aftercooler through cold copper pipes, you would certainly condense out some additional water. That said, this is all going to be pretty inefficient compared to a factory solution where the heat transfer volumes have been calculated and balanced, but it will certainly work.

Try one or the other and let us know how it goes!

There is a benefit to cooling the air down to 40 degrees or so. The lower the temp the less moisture the air can hold. At 80 degrees air can hold 285 percent more moisture than air at 40 degrees.

That being said, one should always run the aftercooler first and reduce the heat load/moisture going into a refrigerated air dryer for the best performance

 

[GeoBruin]

There is a benefit to cooling the air down to 40 degrees or so. The lower the temp the less moisture the air can hold. At 80 degrees air can hold 285 percent more moisture than air at 40 degrees.

That being said, one should always run the aftercooler first and reduce the heat load/moisture going into a refrigerated air dryer for the best performance

I agree with everything you said. What I said is that in my shop, my aftercooler brings the air temperature to ambient so no additional cooling would be achieved by piping the air through a copper manifold surrounded by ambient temperature air. If I could cool the copper manifold (for example, by putting it in a refrigerator) it would of course help.

I also agree that the air should be precooled before going into a refrigerated unit, which is why I recommended the OP use the aftercooler first, then pipe the air through a refrigerator.

 

[u3b3rg33k]

for reference:
This is the one I have at work (it was much cheaper when bought):

FergusonHome Well Pumps

Shop our selection of Well Pumps at Ferguson Home. Large selection of Well Pumps from top manufacturers

www.aircompressorsdirect.com

note the arrows on top are confusing, I hooked it up backwards after careful examination, and it didn't drain properly.

it is a "high temp" model, since one of our compressors has no aftercooler. it has auto-drain (a must!). I use it on a 25hp compressor, and it's fine for our average peak (about 10hp). extreme excursions can result in some water blow through. the whole sizing thing seems messy, if you do bursty work you're more likely to blow water through it, unless you have a dry receiver post dryer.

in front of it I have both a water separator and an oil coalescer. HIGHLY RECOMMENDED unless you like cleaning out dryers. we never shut it off, because people forget to turn it on if we do. uses 300W or so. I also don't use the cycling feature, I just let it cycle the condenser fan. the higher dewpoint doesn't work for us.

 

[engineer2]

A refrigerated air dryer has two heat exchangers: air-to-air and refrigerant-to-air.

The air-to-air heat exchanger takes the hot air in from the compressor and also warms up the chilled air from the refrigerant-to-air heat exchanger. This does two things. It pre-cools the air from the compressor going to the refrigerant-to-air heat exchanger and it warms the air back up for your air system. This improves efficiency and prevents ice-cold air in your system.

The refrigerant-to-air heat exchanger has air on one side and cold refrigerant on the other. This is where the air is cooled to 35 degrees or so to condense out moisture. It has a water drain to collect and get rid of condensed water. The result is 35 degree dew point air.

An after cooler will get you room temperature dew point. OK for when ambient humidity is below the mid 30s or general purpose use where a little water in the line is not an issue.

 

[u3b3rg33k]

A refrigerated air dryer has two heat exchangers: air-to-air and refrigerant-to-air.

The air-to-air heat exchanger takes the hot air in from the compressor and also warms up the chilled air from the refrigerant-to-air heat exchanger. This does two things. It pre-cools the air from the compressor going to the refrigerant-to-air heat exchanger and it warms the air back up for your air system. This improves efficiency and prevents ice-cold air in your system.

The refrigerant-to-air heat exchanger has air on one side and cold refrigerant on the other. This is where the air is cooled to 35 degrees or so to condense out moisture. It has a water drain to collect and get rid of condensed water. The result is 35 degree dew point air.

An after cooler will get you room temperature dew point. OK for when ambient humidity is below the mid 30s or general purpose use where a little water in the line is not an issue.

it actually does 3 things. #3: increases capacity (HP/CFM) of the dryer by "passing" the thermal load through the air-air HX, instead of pumping it all out via the refrigeration system (for the same size refrigeration circuit, that is).

 

[cvairwerks]

Used to be the “big thing” on drying air, was to coil 40-50 feet of 1/2” or larger copper line in a plastic trash can. Put the trash can in a old refrigerator and the fill the can with water. Pipe the air thru the fridge wall and thru the copper and back out to your system. You would turn the fridge down about as low as it would go without freezing. Worked pretty well.

 

[RTM]

I don't know that the cheap little "dorm fridges" will have enough cooling capacity to do what you need, or that they would hold up long at a high run rate. Just a swag based on the Atlas Copco above, and cvairwerks idea.