Author Topic: cave cooling systems - CoolBot  (Read 1537 times)

Offline Morry Stu

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Re: cave cooling systems - CoolBot
« Reply #15 on: March 12, 2014, 05:44:09 PM »
It would depend on the size and type of cave to workout how much "oversize" to go. You really need to talk to a refridgeration mechanic/engineer and get the formulars to do it properly.


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Offline Morry Stu

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Re: cave cooling systems - CoolBot
« Reply #16 on: March 12, 2014, 06:45:30 PM »
OK, was just looking at the coolbot and it appears that it fools the air-cons FIN thermostat by heating it up and then uses its own sensor on the fins to detect when it is about to freeze and shut the unit down until it defrosts.

It pretty much does the same as putting the fin sensor near a warm lamp but has the added sensor that decects when the fins ice up.

My method was to change the fin sensor with a unit that you could set at the point that it started to ice up and cut the compressor but keep the fan running to draw air over thru the fins, speeding up the fin defrosting and still blowing cool air.

The coolbot just cuts the whole unit until the fins have defrosted. Its a safe plug n play unit

You dont need any tools or have to do anything to the aircon with the coolbot, whereas my method you need to change the thermostat which is something you cant do if you easly without any knowledge about electricity and airconditioners. Mine is NOT a plug n play method

Offline John@PC

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Re: cave cooling systems - CoolBot
« Reply #17 on: March 12, 2014, 07:15:57 PM »
But it's interesting that Sailor hasn't experienced icing of the coils.  Question: If target temperature is 55F and humidity is kept at 85% would you experience icing?  Stated another way, if you can keep the dew point above the coil (fin) temperature would you avoid icing?

Offline Morry Stu

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Re: cave cooling systems - CoolBot
« Reply #18 on: March 12, 2014, 08:09:31 PM »
I dont know. Would depend on a few factors like humidity, airflow, cooling fin temps, gas type & working pressure.

I have a mate who is a refridgeration mechanic so I will ask him more about it.

Give me a few days.

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Re: cave cooling systems - CoolBot
« Reply #19 on: March 12, 2014, 08:25:17 PM »
.....and, scene.  Arnaud's head just exploded.    :o

Man, to have been born with your intrinsic gifts, fellas....
- Paul


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Offline jwalker

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Re: cave cooling systems - CoolBot
« Reply #20 on: March 13, 2014, 08:02:46 AM »
But it's interesting that Sailor hasn't experienced icing of the coils.

I was wondering that too , I would imagine there is some icing of the coils , but the unit is big enough that the room cools to the desired temp and shuts off before the fins are completely iced up to the point that air flow is cut off.

When Trying to maintain high humidity , as in a cheese cave , I think one of the most important things would be to make sure your unit is big enough to avoid icing up.
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Offline Sailor Con Queso

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Re: cave cooling systems - CoolBot
« Reply #21 on: March 13, 2014, 08:51:27 AM »
But it's interesting that Sailor hasn't experienced icing of the coils.
For me, the solution is 3-fold. Use the largest AC unit that you can. This means faster cooling and saves a LOT of electricity in the long run. I use a commercial 12x12 walk-in cooler as my cave. It has a built in cooling unit, but it is 3-phase. Since I am not refrigerating, that would really be overkill. So I use a small, efficient 110v window unit instead. I think it is 10,000 BTU. Second, because I am aging in Vac bags, there is much less humidity in my cave and less risk of icing up.

Third, if you don't open the door very often, your cave will stay cool and run very little. This also means much less risk of icing.

While the Cool Bot does use a fin sensor, that is really not a solution. When the Cool Bot detects icing, it simply shuts the entire unit off and doesn't keep the fan going. If your cave is starting to get too warm, that could be a BAD time to shut off the cooling.
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Offline Mike Richards

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Re: cave cooling systems - CoolBot
« Reply #22 on: March 13, 2014, 11:13:09 AM »
My unit is significantly oversized (it's for a small room and is cooling down a closet-sized space) and because of that, I've never seen ice on the fins.  The fan on my unit runs non-stop, too, so even if it were to ice up a bit during a cooling cycle, it would thaw pretty quickly because I'm constantly pulling "warm" air past the fins.  I haven't done it yet, but I keep intending to take one of the meters from work and determine the cycling frequency--how often does the compressor kick on and how long does it stay on for.  Maybe I'll do that this weekend.

Quote
But it's interesting that Sailor hasn't experienced icing of the coils.  Question: If target temperature is 55F and humidity is kept at 85% would you experience icing?  Stated another way, if you can keep the dew point above the coil (fin) temperature would you avoid icing?


Without trying to be insulting to anyone, I'll explain how all this works just so we're all on the same page.  An accurate description of humidity approaches the subject from the concept of partial pressures--the pressure caused by the vapor form of a substance when it is in equilibrium with the liquid form at a given temperature.  That's a little confusing for most people, so instead we talk about the air as if it can "absorb" a certain amount of water.  At a given temperature we say that there is a maximum amount of water the air can "hold" and if more water gets in the air, it will start to condense out--turn into a liquid.  At higher temperatures the air can hold more water, at lower temperatures it can hold less.  We discuss a ratio of the amount of water in the air divided by the maximum amount of water the air can hold at that temperature.  We call this ratio the relative humidity (RH).  By cooling down warm, wet air, liquid water will start to condense out and by heating cool, wet air, the air will start to feel drier.

The study of all this stuff is called psychrometry.  Here's a chart that can help determine what's going on in your cave.  http://www.truetex.com/psychrometric_chart.gif  You read this chart by knowing a few pieces of information.  The dry bulb temperature, at the bottom, is the temperature you measure with a regular thermometer.  The RH lines are curved lines moving across and up the page.  On the bottom of the chart, find the temperature your cave is at, go up the chart from that temperature until you hit the relative humidity line for your cave's relative humidity.  If we use 55 F and 85% RH, we'd be down and to the left of the center of the page, a little below the word "dew".  To help keep track of things, I like to mark that point (where my cave is at).  If you now go from that point directly to the right until you reach the axis (the end of the chart) you'll be able to see how much water there is in your air relative to each pound of air (not terribly useful for us right now).  If, instead, you go directly left from the point you marked, you'll run into the curved top/left side of the chart with the words, "Wet bulb and dew point or saturation temperature" above it. On that line you'll be able to read off a temperature.  In our example, the temperature we would hit would be just under 50 F.  That is the dew point for the air in your cave.  So, if you cool your air down to that temperature, water will start to condense out.  This means if your cooling fins are below that temperature (and they almost certainly are when the compressor is running), water will begin to condense out of the air onto the fins.  This (now liquid) water on the fins will continue to cool until it reaches the temperature of the fins.  If the fins are below freezing, the water will freeze and ice will start to develop.  This ice essentially insulates the fins and makes the unit less effective.  If the fins are not below freezing, this won't happen...or, if the compressor turns off before the water freezes, it probably won't happen, either because the water will run off the fins and, depending on how long it is before the condenser kicks back on again, will evaporate back into the air.

You can also use this chart to determine how much water is being extracted from the air (and how much you need to put back in the air to keep it at the same humidity), how much energy is being removed from the air, or to determine relative humidity if you don't have a hygrometer (you need two thermometers--one that's normal and one that has a wet cloth around the bulb/sensing portion of the thermometer).

Again, to keep ice from freezing up the fins, you need to make sure the fins stay above freezing (not easy to do--you have to mess with the unit; running the fan at the highest speed possible could also help with this) or ensure the compressor turns off before too much ice has formed (easy to do with an over-sized unit or if a device specifically watches for this--like the cool bot).

Please complete problems 6.2, 4 and 7 for next time when we'll be talking about entropy.
« Last Edit: March 13, 2014, 02:33:56 PM by Mike Richards »
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Online ArnaudForestier

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Re: cave cooling systems - CoolBot
« Reply #23 on: March 13, 2014, 11:57:33 AM »
Have no idea what this means, but wanted to ask you guys.  Randolph Hodgson, of Neal's Yard; from the Babcock series, artisanal makers and affineurs:

Quote
You can set up refrigerators specifically for aging rooms, using a static coil, using low speed fans and raising the temperature of the refrigerator coil.  It's not the most effective way of cooling, but in this case it's the best, because more effective cooling also means more effective drying which is not what you're after.

What does this mean, in practice?
- Paul

Offline John@PC

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Re: cave cooling systems - CoolBot
« Reply #24 on: March 13, 2014, 12:45:01 PM »
Paul:  It sounds like he's forcing more air through the coils to keep the coils from dropping (much) below the dew point.  He's exactly right that effective cooling means colder coils and more vapor condensation at high humidities.

Mike:  A good and thorough explanation.  It sounds like you're a pretty good "psychromatrist" ::).   I think one of the more important takeaways in your explanation is that in any refrigerated enclosure, if you want to maintain high %RH and the fridge is in a relatively warm environment than every time the compressor runs there will be condensation causing the humidity to drop. Therefore the need to have some means to "add back" the water vapor with a wet towel, pan of water or humidifier.  If your enclosure is in an unheated garage (like mine is) it will be hard to maintain humidity during the hot months with the compressor runs frequently, and during winter when external temperature drops below your aging temperature the compressor will not run at all and %RH may reach saturation if the door isn't periodically opened or some type of moisture absorbent isn't deployed. 
 


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Offline NimbinValley

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Re: cave cooling systems - CoolBot
« Reply #25 on: March 17, 2014, 06:32:23 PM »
This thread has moved on from my original post but I thought I would update people on my CoolBot.  I installed it and have never thought about it since.  It just sits in the background and does its stuff.  I bought a good quality aircon unit which is oversized for the room and run it on silent mode so there is minimal airflow.  Fantastic.  Im very happy with it.

NVD

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Re: cave cooling systems - CoolBot
« Reply #26 on: March 17, 2014, 06:53:14 PM »
Nimbin, thank you for the update, and I hope I haven't hijacked your thread in some way.  Would you mind sharing the room size, and the make/model/btu's of your AC?
- Paul