Greenhouse and CFM

[Ray]

You're right, Dot.

Just like balancing all of the parameters of orchid culture, one must arrive at a comfortable combination for a greenhouse, too: dimensions, proportions, facing direction, covering, shade, bench layout and height, air movement, ventilation, cooling, heating, irrigation and humidification to name a few.

 

[Rick]

Generally you end up with generally hotter conditions inside the GH (because of solar input), and more moisture getting sucked out of the plants (because hot air holds less moisture than cold air)

I have part of this backwards. Hot air can hold more moisture than cooler air.

So as you heat incoming air from solar input you actually increase its capacity to absorb water from the plants (unless added from foggers or wet pad systems).

At very high turnover rates solar heat input and plant transpiration rates are less important and you're math/physics is based on the % saturation capacity of the incoming air.

 

[Rick]

You're right, Dot.

Just like balancing all of the parameters of orchid culture, one must arrive at a comfortable combination for a greenhouse, too: dimensions, proportions, facing direction, covering, shade, bench layout and height, air movement, ventilation, cooling, heating, irrigation and humidification to name a few.

I also agree, and the learning can be fun and rewarding too. But you have also built up a pretty nice collection, and I would be concerned about setting them back too much while you dial in your new system.

Despite the fact that wet pads were in use in the GH's of every good grower in TN, I started my GH with no control at all, expecting to get away with manual (daily misting and "damping down") activities.

I lost several plants, and set many more back before measuring humidity, and finding out that manual activities were pretty worthless. I added automated misting because it was cheap and easy, which was a drastic improvement, but almost floated my house off its foundation since the moisture transfer to air from large water droplets (before they hit the ground) is not efficient. Moving to a fogger system was better yet, but still left a lot of things dripping wet even when temp humidity targets were not met. My feed water is also hard and salty leaving all the plants looking like the shower doors, covered in white hard water deposits that were difficult to clean off.

The only water coming off a wet pad is in pure vapor form. Temperatures are cooled at the pad surface so not relying on the leaf transpiration to cool the air. Wet pads are not 100% efficient and can break down too, so the fogger is still integral to covering the peaks, and providing a redundancy for system breakdown.

So I guess the moral of my story is that If I had integrated a wet pad system into my GH from the start I would have shaved about 3 years off my learning curve.

 

[Rick]

After all this theoretical stuff I went and took some dimensions and measurements.

My GH is approximately 675 CF. The combined max CFM of the 2 box fans that pull air through my 8 square ft of wet pad is 6400cfm. For winter all air is internally circulated and the turnover rate would be roughly 9 turnovers per minute (roughly a 7 second turnover rate).

I increase the exchange rate by directing an increasing % of outside air through the wet pad as summer kicks in for cooling as well as humidification. But the venting and ducting is crude, so I doubt that I get a full exchange per minute with all vents and ducts wide open. Also the "push and pull strength" of box fans is not great, so the actual volume of GH air being effected without all the small internal booster fans I have placed would be low.

When the next GH is built (its in the works now). I plan on doubling the ratio of wet pad square footage to volume, and improve the ducting system.

 

[Rick]

So the question is, will I really need a 3000 cfm fan or is this overkill?

A standard Lowes / Home Depot 20" box fan is rated at over 3000 CFM. The "Weather Shield" versions cost $25.

There more expensive, durable and efficient fans than the above box fan, but if you want to feel and see the effects of 3000 cfm stand in front of a 20" box fan.

 

[gonewild]

I have a 24 inch portable fan with 4 fog nozzles mounted on it.
I can lower the temperature of our 3500 square foot warehouse by 20 degrees on a hot day (100+). That is without venting in outside air.
I would suggest that this type of setup may be as effective as wet pads in a greenhouse.
There are commercial units like this FAN but I made my own for $30 plus a used fan.

I like the wet pad method but I think with the fan/fogger combos you may get more cooling per kw of energy.

 

[Rick]

I like the wet pad method but I think with the fan/fogger combos you may get more cooling per kw of energy.

It helps that the temperature of incoming water supply is much cooler than the air temp, and foggers use a lot more water than wet pads too. You get more cooling than just the latent heat drop from pure evaporative cooling, but adding up all the sources of energy I don't think its a more efficient way to cool from a physics standpoint. However electricity is probably cheaper than water so you could come out ahead on your utility bills with a fogger.

I use an Aquafog unit (which cost a lot more than $30). It produces a much finer fog than standard low pressure mister nozzles ( about 1/2 as good as true high pressure foggers), but not as fine as you get off of one the ultrasonic foggers.

If it wasn't for the white dust factor I also probably would have been satisfied with sole use of fogging for cooling/humidification, but my water is to hard for that. I could use RO water, but that would require 2 full time systems, and lots of wasted water.

 

[Rick]

I have a 24 inch portable fan with 4 fog nozzles mounted on it.
I can lower the temperature of our 3500 square foot warehouse by 20 degrees on a hot day (100+). That is without venting in outside air.
I would suggest that this type of setup may be as effective as wet pads in a greenhouse.
There are commercial units like this FAN but I made my own for $30 plus a used fan.

I like the wet pad method but I think with the fan/fogger combos you may get more cooling per kw of energy.

Another system (in use at the Atlanta Botanical Garden GH) is the Air Washer.

Basically its a mist/fan unit that sits behind a screen to catch the water droplets and return them (with trapped dirt) to be re-misted. Chillers are added to the sump to get the big temp drops beyond what you can get from straight evaporative cooling. Atlanta is doing well with high elevation Draculas and Telepogons. The system was adapted from the textile industry (which was big in the SE).

This is more water conservative than a straight fogger, but no more efficient than any other system. I know the orchid collection manager at Atlanta, and he's never wanted to even look at the electric bill.

 

[SlipperFan]

Do you see any problem with using softened water in a fogger or evaporative cooling system?

Rick, how big is your wet pad?

Lance, I took a big gulp when I saw the price of that fan. I've seen smaller models, and have wondered how well they work.

 

[Rick]

Do you see any problem with using softened water in a fogger or evaporative cooling system?

Rick, how big is your wet pad?

Lance, I took a big gulp when I saw the price of that fan. I've seen smaller models, and have wondered how well they work.

Look back a few posts, and I put in many of the specs for my system(s).

It's 2 ft tall and 4 ft across. Typically a wet pad would be the entire width of a GH, but this was demo size for me.

Did you also see the post describing how big a 3000 cfm fan is?

 

[cnycharles]

well, softened water has had something put in to replace what you want to be excluded taken out. if you don't want what softens the water to be in your air and on your plants, .....

 

[Rick]

well, softened water has had something put in to replace what you want to be excluded taken out. if you don't want what softens the water to be in your air and on your plants, .....

Water softeners exchange sodium for calcium and magnesium. Most plants don't appreciate the extra sodium.

If you go to full ion exchange you can get essentially salt free water. If you have the money to keep up with it you can go from tap water through carbon and then into a couple of mixed bed canisters. Figure up how much water you will go through in a month and then check with your local US Filter rep to see how much it would cost to set up and run.

 

[SlipperFan]

Look back a few posts, and I put in many of the specs for my system(s).

Yes, I saw that.

It's 2 ft tall and 4 ft across. Typically a wet pad would be the entire width of a GH, but this was demo size for me.

That's what I wanted to know. Thanks!
The greenhouse where I volunteer has a wet pad like that. But I've also seen a small greenhouse with a box similar in size to yours, and the owner said she's quite pleased with it's performance. A pad across the back of my plan would not be possible, but a box such as yours, and hers, is quite possible.

Did you also see the post describing how big a 3000 cfm fan is?

Yes -- I don't think I need anything quite that big... I'm pleased to read I won't have to go that big, considering my planned awning windows, ridge vents, and now some kind of evaporative cooling (plus interior fans).

I haven't decided on the kind of water to use in the cooling system. That might have to wait until I see how much exactly I'll need.

 

[goldenrose]

Did you see the article in the recent Orchids magazine? Give you any ideas?

 

[SlipperFan]

Did you see the article in the recent Orchids magazine? Give you any ideas?

Yes, and it did. Her window configuration is similar to mine -- but I have no room for a "catwalk." Interesting article.