Q? humidity? dew point? = Swamp Cooler Y or N?

16 years ago

OK, here are the numbers for today on a graph. What I am trying to figure out is if a Swamp cooler will work here or not.

First number is temp and second is dew point for Thursday 19, 2007

2am 70/66 5/am 68/66 8/am 70/65 11/am 84/66 2pm 90/65 5/pm 91/66 8/pm 83/65 11/pm 76/66

Humidity is at the same times as above. the chart did not fit

Humidity (%)

2am/83% 5am/91% 8am/79% 11am/45% 2pm/34% 5pm/34% 8pm/45% 11pm/64%

So if you go with the humidity it will work, but if the dew point is the number it get iffy.

SO SWAMP COOLER OR NOT.

If it can not lower at least 5 or 10 degrees is it worth it?

Thanks in advance

1eyedJack and the Dawg

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Comments (20)

stressbaby
16 years ago
It should work midday, at least.

Here is a link that might be useful: wiki link
ole_dawg
Original Author
16 years ago
Baby,
Are you arriving at that conclusion using Humidity or Dew Point. That is my problem. I have read on here some people saying that humidity is not the number, it is dew point.
very confusing.
Thanks
1eyedJack and the Dawg
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stressbaby
16 years ago
Short answer is both.

Your numbers are similar to mine this time of year. IMHO, the VPD is high enough midday to gain benefit from evap cooling. Go halfway down the Wikipedia page and you'll see an example at 90F, DP 68F, and a 15F drop in temp with evap cooling.

Somewhere around here I have a version of this Excel spreadsheet that adds a line to calculate the VPD in kPa. Basically, on the spreadsheet, it is (Es - E), but in this version the units are different.

BTW, when I plug in your 2pm numbers I get a slightly different result.

Here is a link that might be useful: Calculator
ole_dawg
Original Author
16 years ago
Sbaby,
What kind of unit do you have and how large an area do you cool.
Here is a link I found that sells portable ones at, what appears to me, very reasonable prices and they pay the shipping.

http://www.air-n-water.com/evaporative-cooler.htm

The $139.00 Newair is the one I was looking at. IT says it will handle 200 sq ft. which is about double the size of my (in consturcttion) GH.
Thanks
1eyedJack and the Dawg

OH, I don't understand all the tech mumbo jumbo.
stressbaby
16 years ago
Basically it is this: you, like me, are getting enough of a rise in temp midday to allow the air to hold more water vapor. That's why the RH dips so low midday.

VPD is the Vapor Pressure Deficit...the higher it is, the more water vapor the air can potentially hold...the further the air is from saturation.

I use a fogger and overhead misters, not an evap cooler per se.
ole_dawg
Original Author
16 years ago
SB,
Thanks,
So how do I arrive at the VPD? Is there a formula or do I require some special kind of instrument? I have seen, years ago, a thermometer that the guy spun around to take a reading. Something like maybe "wet bulb" or something like that.
1eyedJack
stressbaby
16 years ago
I found the calculator with the right units (kPa) on my old computer. Email me through GW and I'll send it to you as an Excel file. I tried to send it straight to you, but I cannot add an attachment through the GW.

At 2pm your VPD is a hefty 3.17!

SB
ole_dawg
Original Author
16 years ago
SB,
3.17 - is that bad?
sending my email address
Jack and the Dawg
stressbaby
16 years ago
Ole dawg and whoever,

Generally, plants like the VPD 0.8-1.0 kPa. Disease begins at 1.5. I'm not aware of any sources that suggest the level at which evap cooling starts to make sense, but I strongly suspect that at 3.17, you are there.

Did you get the spreadsheet?

Wait! I uploaded this spreadsheet calculator to Google Spreadsheets a few months ago! I had forgotten. Here it is, published.

[My thanks and apologies to the original author (who I cannot identify now, as I cannot find the spreadsheet online anymore). I modified the original to calculate Es-E and convert it to kPa, the more commonly used units for VPD.]

Here is a link that might be useful: Dew Point and VPD calculator
stressbaby
16 years ago
Rats, the published version doesn't permit you to change the numbers. Anyone who wants the actual Excel spreadsheet can email me...with you own copy, you can enter the numbers and it will recalculate the dew point and VPD for you.
dcarch7 d c f l a s h 7 @ y a h o o . c o m
16 years ago
IMO:

1. As long as relative humidity is not 100%, you will get some cooling from evaporation.
2. If your water source is cold, say well water, you will get "sensible heat" cooling.
3. If the sun is out, the leaves will get heated up by solar energy, air movement will help cooling the leaves to air temperature, regardless of humidty.

dcarch
ole_dawg
Original Author
16 years ago
Thanks to everyone who has commented. I have decided that I will give it a try. I can buy one fairly cheap and if it works inside then I will buy one for outside. My A/C bill is eating me alive and I think that between the A/C set higher and a swamp cooler I should be able to reduce it a lot. I will be able to play with the unit both inside and outside so if it doesn't do what I want outside it will not be a total loss.

{{gwi:301136}}
1eyedJack

{{gwi:43006}}
The Dawg

Thanks again
1eyedJack and the Dawg
gardnergal
16 years ago
Hello Dawg and Jack,
Perhaps if you removed your hat and jacket the heat would be bearable...but then Jack would still be sultry.
I'm not sure what you mean about "inside" and "outside", but I have the following comments, for what it's worth.
I have a HFGH which is experiencing low humidity, which my orchids in turn are not crazy about. Among other things, I saw an evaporative cooler on Craigslist for $45 and decided it was worth the money to see if it helped. (Until now I thought the humidity was too high in my ecosystem to make one effective.)
It brings the temperatures down about 4-5 degrees F., and brings the humidity up to what I consider to be an acceptable level (from ~43%rh to 57%rh). I use it for a few hours in the early afternoon. It only draws 73 watts, but it uses about 2 gallons of water a day to work, and it needs to have fresh air for proper operation. And it only holds a few gallons, so it needs to be filled daily.
So using it in my plans to make the gh self-sufficient is not a great solution (need to be there to fill it up and open the doors daily), but it does work if monitored.
Regards to Jack,
Ann
ole_dawg
Original Author
16 years ago
Da, but it was very cold with a bitter wind blowing from the Northwest and for that reason my face is so red. I have just come off duty from my Submarine,
The Red October. Sultry? I thought only women could be Sultry. If you posted you email address in the My page area you could receive messages that the whole world could not read? It will still come thru the system and does not show your true address. Da?
Inside is inside the house, Outside is in the yet to be completed GH. I just got more supplies today so progress will be made on Friday. Tomorrow I must go to Columbia for surgery. A quickie in the Dr.Âs office, but it will require the entire day so construction will be halted until Friday.
The unit I am looking at is quite modern and holds enough water to run for about 18 hours without a refill. It also accepts ICE, but I doubt it would last long here in the heat. It only draws 85 watts and has all the whistles, bells and gongs.
I am able to keep a close eye on things as the GH will be just outside the door. I am very interested in seeing how much it would drop the Temp.
Today it hit 103 at mid day. If it lowers the temp by only 10 degrees I would be happy.
Regards to Ann
From 1eyedJack and the Dawg
gardnergal
16 years ago
sultry: 1. oppressively hot and close or moist; sweltering: "a sultry day" 2. oppressively hot; emitting great heat: "the sultry sun" 3.characterized by or associated with sweltering heat: "sultry work in the fields" 4. characterized by or arousing heated temperature or passion: "a sultry brunette".
ole_dawg
Original Author
16 years ago
Hot Dog or Dawg,
The swamp cooler arrives tomorrow. Today was 109 and it is still 101 @ 7:18pm. Too hot to do anything at all. I will give it a try and let everyone know if I wasted my money or not.
1eyedJack and the Dawg
greenhouser
16 years ago
Today it was 107 here and 120F in the GH. That's as high as that thermometer goes.
ole_dawg
Original Author
16 years ago
GH, What was your humidity? I checked mine at 7:00pm and it was still below 40% If your humidity is low enough the swamp cooler will work for you.
1eyedJack and the Dawg
orchiddude
16 years ago
Today it was 100F and the greenhouse was 85F most of the day. I think I saw 82F later this afternoon.
Yo swamp cooler should work fine. My fogger works wonders.
ole_dawg
Original Author
16 years ago
It arrived late yesterday and I hooked it up. humidity @50% It did not do much cooling. I took it outside with a humidity of 33%. Some better, but a disappointment. I called them and they said that it should be pumping out cold air and that the unit must be defective so to return it for another one. Seemed like nice people, we will see that they try to charge me for return freight.
This morning is seems to be doing better, but i am still going to return it.
1eyedJack and the Dawg

Q? humidity? dew point? = Swamp Cooler Y or N?

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