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Newly install window mount evaporative cooler for summer

This is a discussion on Newly install window mount evaporative cooler for summer within the Semi Hydro / Lights / Greenhouses / Accessories forums, part of the Orchid Culture category; O.K. guys and especially those of higher intelligence than myself (Many I am sure). Though ...

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  1. #1
    orchidsal's Avatar
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    Default Newly install window mount evaporative cooler for summer

    O.K. guys and especially those of higher intelligence than myself (Many I am sure). Though I have researched it on the Internet I have not gotten a definitive answer for my question. I have three 'cool mist' humidifiers going in a 8 Ft. X 13 Ft. greenhouse (On 24/7). Heres the real question and I hope I am not being silly. Am I adding more humidity to the air in the greenhouse or just cooling the air? The reason I ask is that at 81 degrees F. the Cooler came on automatically yesterday afternoon as it should, but I noticed the humidity readings on the humidifiers etc. all dropped considerably. When it gets 100 degrees outside in this very arid, high desert area I still of course need ths large 3500 Evapoarative cooler, but not so much now. Thanks in advance for your comments! AL

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    The higher the temps, the more molecules 'vibrate' and the more space to allow for other molecules. More water can be 'dissolved' into the air at higher temps, less at lower temps. That is the simple explanation. In Ohio, we get very hot, humid summer days. When a cooler front moves in, it causes the vapor to condense and fall as rain. The air cannot hold as much vapor at the lower temps. So, if your cooler lowers temperatures, it is acting like a cold front. Evaporation lowers temperatures, too, by using energy. I hope this helps.
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    Thanks Leafmite. It sounds to me that the cooler will be just fine when I need it most. AL
    Last edited by orchidsal; March 28th, 2012 at 11:34 PM. Reason: typo error

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    Michael Saar is offline Senior Member
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    When you operate the humidifiers alone 24/7, they continue adding moisture to the atmosphere to the greenhouse (a closed system) to the point of saturation, or the maximum allowed by the infiltration of dry air into the greenhouse and the capacity of the humidifiers. (What was the relative humidity of the greenhouse air when the cooler came on?) When the cooler operates, it displaces an equal volume of greenhouse air with cooled air. The relative humidity of the cooled air depends on the humidity of the outside air and the capacity of the cooler to evaporate air. The volume of air being replaced renders the humidifiers ineffective. (Assume the volume of your greenhouse is roughly 1000 cu.ft., and your cooler supplies 3500 cu.ft./min., you replace the air in your greenhouse 3 times/minute. The humidifiers don't have a chance! Plug in whatever real numbers you have and the result will be the same.)

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    Thanks Mike! I understand exactly what your saying. I know evaporative coolers are used in nurseries in hot, dry areas such as mine. I can tell you that if its 100 degrees F. outside it is 90 to 95 degrees F. in the greenhouse. A bit hot for me and I think the orchids. I was thinking of setting the thermostat for the cooler up to say 85 degrees F. so I am stressing myself and the plants less, but keeping humidity up to 60% plus when the cooler is not running. Humidity percentage per the humidifier display's are 22% today after the cooler was on for a while. What do you think? AL

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    22% sounds entirely too low. Make sure the pump is working and the pads are getting evenly wetted. What is the rated cfm of your cooler? What make and model? Do you have a big enough exhaust air opening that you get full volume from the cooler? If the cooler is working properly, it seems you should get a higher RH than 22%. Another thing to check is the outdoor temperature and the temperature of the air as it leaves the cooler(before it has a chance to mix with GH air). More questions than answers right now.

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    Al one important fact you have to tell us is whether your humidity readings are absolute humidity (AH) or relative humidity (RH) ?? Because AH is always lower at cooler temperatures than at warmer temperatures. If these readings are indeed for RH, then I would suggest you run at least one of your evaporative cooler just inside the GH (recycling the same air) rather than driving outside air in.

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    Hi Amey; I wish I could say that a interior evaporative cooler would work, but I've tried a couple different brands with just a minor (at best) increase in humidity and hardly any cooling effect. This is why I stepped up to a large capacity window mount cooler. Believe me when I say I wish the portable units worked better! Humidity is RH by the way. Thanks for your concern! AL

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    Quote Originally Posted by Halloamey View Post
    Al one important fact you have to tell us is whether your humidity readings are absolute humidity (AH) or relative humidity (RH) ??
    Percentages are always relative.

    An evaporative cooler will increase the humidity and decrease the temperature, but if you're talking about a box type evaporative cooler (as opposed to a wet wall with a much larger surface area), the humidity increase may be quite small. With an air turnover rate of 3x per hour, virtually all your humidified air is gone in 20 seconds, and replaced by outdoor air that has been humidified and cooled by the evaporative cooler. A box type evaporative cooler may only increase the humidity by a few percent, but that is enough to significantly reduce the temperature. If your outdoor air is very dry to begin with, you may have very dry greenhouse air whenever the intake/exhaust fan kicks on. Once it shuts off, the humidity will slowly increase from evaporation within the greenhouse. You can use humidifiers, misters, foggers, etc to increase the humidity more quickly in between exhaust cycles, or you can use additional shade cloth to reduce the amount of exhausted air. I am going to try some fogging heads this summer to either complement or replace my evaporative cooler. I'm eager to see what effect it has. I will be using RO water to prevent hard water deposits.

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    O.K. you guys I did some testing and the humidity was around 60% before the evaporative cooler came on and around 50% humidity after being on at least 20 minutes. Temperatures were 81 degrees F. on the nortern exposure glass wall and 75 degrees F. on the opposite south wood wall (It's a attached lean-to greenhouse). when I set the cooler to come on. MICHAEL you were right about something being wrong. The person who I hired to put the cooler in did a nice job, but he forgot to turn on the water............................All cooler pads are wet and I set the automatic switch to where the pump comes on 4 minutes before the fan. Fifty percent ain't perfect, but I think it's a big improvement. I also kept a door to a ajoining utility room open (I usually always have it closed. Thanks to you all!, and especially Michael for being patient with me. AL

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