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[mlappin]

So got done with the largest four day festival in Indiana, first two days were beautiful, low to mid 70’s, very low humidity, 3 rd day was a little warmer, today (last day) was miserable, high 80’s and humid. Got a lot of smart *ss comments today about not needing anymore heat, just like the other festival we did in June in the same type of weather. However I did have a few that said if I can figure out how to make a stove blow cold air they’d buy it

I spent  considerable amount of time talking to a few of the festival board members and they are good with me having a live burn next year, just have to get the town fire marshall to go along and if he does then usually so does the state fire marshall. May have to rent 3 or 4 spots at $440 a pop but I think it will be worth it.

First thoughts were a stirling engine, they have models that run on hot water, however the power output is even lower than a standard stirling as the temperature differential isn’t high enough with hot water unless you can super cool the cold side (think dry ice). Have a stirling engine running off the hot water coming out of the stove running a small automotive alternator connected to marine battery to even out any variations in alternator output then a power inverter connected to the battery then have a high efficiency window AC unit plugged into the power inverter :thumb:

Another thought is thermal electric generators, have just begun to research those. Would probably still go the battery/inverter/ac route with that as well as the output of those are DC.

[BoilerHouse]

If you can get it to work, it would demonstrate what you can do with energy and should stir up some interest. 
Any hot air engines I have seen work best when they are direct fired and pump water.  The energy input is high grade and the water helps produce the temp difference.  As you have pointed out, using a hot water input you would need something with a low temp to create the delta T and get half decent efficiency.  This might appear inconsistent as you are using something cold to eventually produce something cool.  You could use ambient air, and have the engine coupled to a fan.  On a hot day it would feel like AC (LOL)
I had never heard of TEGs and had to run to Wikipedia.  Interesting that the design has been around for almost 200 years.  A huge stumbling block would be their very low efficiency - stated at around 5%.  Factor in a loss in the alternator, slight loss in the battery and a somewhat larger loss in the inverter and you would need a large TEG to power a room sized AC.
One thing you could consider is a hot water absorption refrigeration system.  Proven design, been around forever, they once sat in central cooling plants everywhere (but less so now).  They are mechanically simple but thermodynamically they are a bit complicated.  I do not know if small demonstration units exist and I have no idea how easy it would be to build a small custom unit.
I am not sure if any of this has been helpful, but if I stumble on anything that could be useful I will be sure to post it here.

[juddspaintballs]

You're not going to power an AC off of an inverter unless you go huge, and even then, a single battery won't run it.  The startup wattage required for the compressor is massive.  Even if you get the Striling to power it on for one cycle, the subsequent cycle will probably crash the system.  You'd be better off using fans for demonstration.  If you really want to use AC for demonstration, direct drive an auto AC compressor off of the Stirling.  Think about it in terms of losses: you're using mechanical rotation converted into electrical output (loss) to run through wires (loss) to store in a battery (loss) to run through wires (loss) to run through an inverter (huge loss) to run through more wires (loss) to turn an electric motor (loss) that turns a compressor (loss).  You could use the mechanical rotation of the Stirling to run a belt (loss) to turn a compressor (loss) and be done with it. 

[mlappin]

You can get high efficiency window units now that pull less than four amps when running, or less than 500 watts. volts x amps equals watts. 120x4=480. Some high end inverters approach 90% efficiency. Not sure a car compressor given thats its driven by a gas engine is near as efficient as the cute little compressor in a HE 4000 BTU window unit.

I’ve heard of hot water absorption chillers before, just thought a stirling engine would be a lot cooler as people can see it work, with a chiller or TEG’s not much to see far as the workings.


First thought was to take a wisconsin v4 and modify it, remove the camshaft, pushrods and lifters and leave the valves in to seal the cylinders, bore the spare plug holes out to allow 1” pipe to be threaded in, connect one bank to the other and make a double 2 cylinder stirling, but for starters 180 isn’t hot enough for the hot side and have too much friction with the piston rings, and babbet style rods and main bearing, most stirlings use light weight material as possible and all ball bearings. Seen a lot of em that use graphite pistons.

Two cylinder stirling.

http://www.animatedengines.com/vstirling.html


I think with only 180 for the hot side and ambient air for the cool, need to stick to a LTD (low thermal differential) stirling, some of those have ran on a 1/2 degree celsius differential.
With a low differential engine they either need to be pretty massive to ever generate enough power to run an alternator or compressor or if scaled down just use it to turn a fan. Thinking find a reproduction airplane prop and use it as a fan/flywheel.

LTD stirling:

http://www.animatedengines.com/ltdstirling.html


https://youtu.be/5EsbKbVRe38

The first two links should be animated, if they aren’t try turning off your adblocker or similar app.

[mlappin]

Reason I was thinking an AC unit, the wife has had previous cardiac issues and something similar to COPD, those hotter days play hell on her if she can be out at all. We take a window fan with us and run that off the supplied power to the space we rent, in June it wasn’t near enough but the local police left the station unlocked for her so she could sit in the AC for awhile.

I’ve also thought about getting the smallest generator head I could get, but now speed becomes imperative to maintain 60 hertz. A car alternator isn’t near as depended on a constant speed to output voltage. Have also wondered if such a thing as a DC powered AC unit would be available for like campers so we can skip the inefficiency of using an inverter.

[mlappin]

Wonder how well something like this actually works?

Only pulls about 3 amps at 12volts.


http://www.ebay.com/itm/Icenplug-Q25PLUS-12V-Portable-Air-conditioner-Camping-Vehicles-Aircrafts-Boats-/231899044110?hash=item35fe42990e:g:a50AAOSwiylW~r32

[BoilerHouse]

Thanks for posting the animations.  There is no reason the AC unit in the link provided would not work, but its such a simple design that it could be easily made.  It is basically a motorized ice box.  A wooden box with a bunch of ice, radiator, small water pump, and fan courtesy of the Stirling engine and voila,
modern AC with old world charm.

I am a big fan of Mr. Petes You Tube machining videos.  He has done several on hot air engines.  I attached one that he happened to post a couple months ago, in case you have not seen it yet.

https://www.youtube.com/watch?v=tipPFgOxMho

[mlappin]

So picked up several Stirling Engine models off Amazon, sometimes I just need to see it and play with it to wrap my head around it. Surprisingly simple once you get your hands on one.

First two are LTD (low temperature differential) Stirlings, the last is a typical Stirling engine, runs off 91% rubbing alcohol, 70% will work but is considerably less vigorous. I was amazed to see that 91% rubbing alcohol burns around 1000 degrees F or better checked with my Thermal Works pyrometer.

Interestingly enough the second one running in a bowl of ice will run a lot longer than the one running off heat, eventually the top plate (the cooling plate) picked up heat as well and it will stop after almost an hour, while the one in a bowl of ice will run until all the ice is melted and the water starts to rise towards room temp.



https://youtu.be/zbhzmOqkKaY

[mlappin]

A LTD running off the hot side of the heat exchanger at a festival we did this weekend, once outside it ran all day with 65-70 degree ambient air and some breeze from the wind.

Had one on the heat exchanger and another in ice on our table, had everyone from children to seniors stopping to ask just what they were.

https://youtu.be/j3kuqNJzqBM

[mlappin]

A flat plate stirling with a cam drive for the displacer.


https://www.youtube.com/watch?v=8QE-CmKxz40&ab_channel=sergeibroeska