Cigar Forums banner
1 - 7 of 7 Posts

·
Registered
Joined
·
365 Posts
Discussion Starter · #1 ·
With the warm weather I've been turning on my vinodor to keep temperatures around 65F. An unfortunate side effect of running the cooling hardware is that RH falls pretty hard every time the compressor starts up. This issue is particularly bad with compressor refrigeration because refrigerant evaporates into the evaporator panel at a very low temperature. So cold that condensation becomes visible close to the injection point on the cooling panel in about 30s and ice even begins to build up in about 2min. As cold temperatures propagate over the evaporator panel condensation rapidly pulls moisture out of the cabinet and RH levels can plunge down to 40% in 5min. This is pretty hard on cigars and can cause mold issues when the condensation collects leaving areas that are permanently wet. I note that many users of thermoelectric vinodors are also observing condensation issues so I hope this post might provide some information leading to helping fellow BOTLs with thermoelectric storage. I would have preferred to have used a thermoelectric vinodor, but large ones just don't seem to be available in Canada. We've got lots of little 8 bottle units, but no 28 bottle units. I do like how big my 35 bottle vinodor is though. Lots of capacity if I can tackle the condensation issue.

TL/DR: I bolted a 1/2" thick hunk of aluminum into my vinodor and buried a temperature sensor in it so an external temp control device can maintain my cabinet conditions without condensation. See pics!

I had first attempted to fix this issue with an external temperature control device which would monitor temperature of the evaporator panel directly, instead of the cabinet temperature, so I could cut power to the compressor before very high levels of condensation would occur. This helped hugely, but I still always had a little bit of condensation collecting. RH levels were a nice consistent 65% varying by a percent from day to day, and temperature was holding nicely at 65F, but the wetness always made me worry about mold. I made some temperature measurements about my evaporator panel to see how cold the cold spots on the panel were and found that significant areas of the evaporator panel was still getting well below dew point for the temp and RH conditions I wanted to maintain in the cabinet. Even the addition of fans didn't solve this issue so I decided to do something more significant to tackle the problem.

A little background on the field of psychrometrics: SKIP THIS IF YOU HAVE A LIFE. Otherwise light up a smoke and read on. It's a long one...

The field of psychrometrics deals with the behavior of evaporated water in air at varying temperature conditions. It is a field which is particularly pertinent to the HVAC (Heating Ventilation and Air Conditioning) industry which often seeks to provide temperature and humidity conditions that are comfortable to live and work in. Wikipedia has some nice info on the field:

Psychrometrics - Wikipedia, the free encyclopedia

Basically if you want to maintain an air environment of a given humidity (say 65% @ 65F which was my target) in a room of higher ambient temperature, you need to extract heat with a cold surface which does not get so cold as to also condense moisture from your cabinet atmosphere.

http://upload.wikimedia.org/wikipedia/commons/9/9d/PsychrometricChart.SeaLevel.SI.svg

That diagram describes the behavior of an air and evaporated water mix at sea level air pressure.

For us to achieve cooling without condensation we need to prevent our cooling surfaces from getting below the dew point temperature in the cabinet conditions we want to maintain.



The green lines I added indicate the conditions I wanted to maintain (65% @ 65F) and the dew point at which condensation would occur (100% @ 53F). Basically you start with the conditions you want to maintain (point 1) then traverse to the left (cooling the air at constant grams of water per kg of air) until you hit the 100% RH line which is the point at which condensation begins. Incidentally a cigar stored at 65% RH and 65F will be at a RH a little bit below 60% when it warms up to 70F which in my mind is just right for smoking!

What does it all mean?!

Assuming you want to keep your stogies at my proposed conditions, you need to keep your cooling surfaces from getting below 53F. This is a bit of a bugger because 53F is not much of a temperature differential to extract heat in comparison to a desired temperature of 65F. In order to get effective heat extraction at such a small temperature differential, you need to get some turbo convection going by either putting in a leaf blower or massively increasing the effective area for convection.

You also need a large exposed area that is as close to 53F as you can get which is why I bolted in such a thick panel of aluminum. Thick panels are very thermally conductive which means that the temperature across the entire panel is going to be pretty consistent. I ran some very nerdy numbers to arrive at that necessary thickness which I am not going to get into because my cigar is going to go out.

So, two CPU fans, one right at the expansion point of my vinodor evaporator panel where I expect the panel is going to get coldest, and one near the bottom circulating air vertically to stir air at closer to the bottom of the vinodor.

Construction piccies:



Cut to the chase: My big aluminum panel 13" wide x 12" long bolted against the evaporator panel of my vinodor. Two fans too. I'm missing a few screws at this point, but I get that a lot it seems. On the left side of the picture is a thermocouple stuffed into a hole drilled into the side of the plate.



Ghetto temperature controller: I really wish I had gotten the nice project box offered by the manufacturer who made this temp control device. I didn't find it while shopping their site. Next time I get some stuff to control some sous vide gear I'll pick up their project box and finish my build. For now I live dangerously. 110VAC isn't all that bad...

Universal 1/32 DIN PID Temperature Controller Universal 1/32 DIN PID Temperature Controller [SYL-1512A] - $36.95 : auberins.com, Temperature control solutions for home and industry

You also need a thermocouple:

K Type Thermocouple for BBQ Smoker Oven. [TC-K6H] - $9.55 : auberins.com, Temperature control solutions for home and industry



Tracing the coolant paths: I taped up a sheet of paper and rubbed a crayon across the paper so I could plan my bolt hole pattern in the aluminum plate. The evaporator panel appears to be made with a hydroforming process which starts with a pair of soft aluminum plates which have been forged together leaving a labyrinth of passages to be "inflated" by hydraulic pressure. I saw bolt holes drilled through the corners so I surmised that I could drill between passages. It seems to have worked. Coolant didn't come blasting out into my face when I drilled the plate. First hole was pretty exciting though.



Aluminum plate bolt hole pattern: I taped the path trace I crayoned onto my plate of aluminum to bang in some centermarks for drilling. Aim for spots which are well between coolant paths for bolt holes. I unscrewed the cooling panel in my fridge and found a coolant conduit sitting behind the plate. Good thing I didn't drill away because it lay behind two of my planned bolt holes. My plate is held on by M3 bolts and nuts behind the plate. Before mounting the plate I spooted on a bit of thermal junction paste (CPU stuff) onto the coolant paths to improve heat conduction between the cooling panel and the plate.

Final Notes:

I note that after 36hrs of operation that I get NO signs of condensation in my cooler. I'm also maintaining a rock solid temperature and RH. I did note an odor from the thermal junction compound when I first applied it. I decided to run a hair dryer blowing into my fridge for awhile to warm the paste and outgas any volatiles. After 12hrs of rest overnight with the door closed I note no odor from the paste. After the paste outgassed I put on the plate. I poked around with a thermometer after a compressor cycle and found that I have a few degrees of temperature differential between the evaporator restriction where the cooling panel is coldest and the very bottom of the plate. That's ok as the coldest point on the plate is still about 60F which is above dew point.
 

·
Wildman
Joined
·
556 Posts
Nice work.

I used lots of fans (120mm ~50 cfm) on a "Off" delay timer with fan run time set to ~6 minutes on. Compressor runs about 1 minute per cooling cycle as the fans provide increased coupling between the plate and the air inside the box as well as stir up the cooled air over the temperature probes. Evaporator plate fans start with compressor run. Thus far, 0 condensation. My Igloo freon rig looks very similar in design to what you have pictured.





Temperature probes for remote temperature controller and digital hygrometer are mounted on the side of the cooler near the front.



Based upon the suggestion of a friend, I also added 10 x Ice Substitute packs inside the cooler to help maintain temperature by dampening swings. Three on each side and four at the top. They claim these cool packs are denser than plain ice/water. They probably contain salt water.

 

·
Registered
Joined
·
365 Posts
Discussion Starter · #5 ·
KaChong are you still around? I'm trying to do what you have done.. need some info.. please help. What's the thermocoupler attach to? Can you give me a run through?? Thanks!
Sorry, I'm not on all that often anymore.

I drilled a hole into the side of my aluminum plate on the left side:

A little dab of thermal junction compound and I can directly measure panel temperature with the thermocouple. Instead of controlling the air temperature in my humidor, I set my thermostat to control the plate temperature so as to assure that it does not plunge below 14C. Condensation will start at 12C so I like to have some headspace in case there is some overswing on the cooling coil. Ideally I would have a second thermostat monitoring air temp that I would put in series with my plate temp thermostat. I let my house get cold in the winter and it'll hit 15C during the day. A secondary thermostat would be useful in preventing the cooling compressor from turning on at air temps above 17C since no additional cooling is req'd. Basically I only want cooling when two conditions are met: air temp exceeds 18C, cooling plate temp exceeds 14C. Right now my compressor will turn on at 16C even if the air temp is at 17C. Not really a huge deal, but I should get around to fixing it someday.

I hope this helps!
 

·
Registered
Joined
·
365 Posts
Discussion Starter · #7 ·
The addition of a high capacity heat sink would be quite effective on thermoelectric units, especially since they can be modulated with PID control. That little controller sold by Auber Instruments can be configured for PID control which would provide more stable control than can be achieved in hysteresis mode. Unfortunately I can't get TE coolers that large easily in Canada. I'd rather use one because compressor devices can't be turned on and off at the frequency required for PID control.

You could probably get away with a thinner plate with TE coolers because PID control can duty cycle control the thermopile and hold it at a temperature instead of what a compressor does which is either blasting coolant that gets down to -30C when the compressor is running, or room temp when it's not.
 
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top