Misting Systems - Part 1

If you grow plants that thrive on high humidity, or live in an area where the Summers are particularly hot and dry misting systems may be for you. When water evaporates it not only absorbs heat (good) it also leaves behind anything previously dissolved within it. The major constituents in “normal” water are the dissolved minerals such as calcium and magnesium, and metals such as iron and manganese. Other things such as chlorine, bacteria, viruses, organics are not unimportant, but for the purposes of misting we can ignore them.
In your water is (typically) hard, when it evaporates on the plants it leaves behind calcium carbonate (limestone) which can plate out on the leaves (bad). For this reason I use a mixed bed anion/cation water softener that reduces mineral hardness to practically zero. Reverse osmosis systems (becoming cheaper by the day) are also effective (no quite as good but much cheaper). You cannot use a salt-based softener since it removes calcium hardness for sodium (really bad). Other systems that can avoid water actually getting on the leaves can do without the costly softening process. Picture is of the mix-bed softeners (rented from Culligan). They must be regenerated every 1-3 months depending on usage.

Part 2
My misting system consists of the softeners, a series of timers, piping, and nozzles. Others have used a thermostat or humidistat to turn on the system. There are advantages to each method. The timers energize a 12 volt DC solenoid valve delivering the treated water to overhead ¾” pvc pipes fitted with low volume nozzles. Misting timing changes frequently throughout the year. In Summer, my timers fire the system every 4 minutes for 4 seconds. Picture is of the timers. I am a do-it-youself guy but you can buy a single timer to do what these three do.

Part 3
The pipes run the length of the greenhouse about eye level and have nozzles about every 5 ft. My nozzles are large, rated at 8 gallons/hour. Most systems use smaller nozzles rated at 1-2 gph. The large nozzles cover a wide area but at the expense of higher water use. Municipal water pressure is typically 50 psi or higher and should work with most nozzles. Other systems use continuous fogging or evaporative coolers. All can be effective and the choice depends on your growing conditions and the types of plants you grow. We grow mostly rainforest plants that thrive in very high humidity. Most of these plants grow in fairly hot areas, but many are from higher altitudes where temperatures are moderate. Misting really helps control high temperatures and supply the moisture these plants need.

A good selection of misting systems is at [HYPERLINK@www.charleysgreenhouse.com]

Hopefully others will add posts on their experience with misting/fogging/evaporative cooling systems. Picture is a single nozzle firing.

Dave.

When I first posted this I did it in three separate posts, a "classic blunder."

Here is the correct hyperlink http://www.charleysgreenhouse.com/index.cfm?page=_a1&cid1=203

This message was edited Sep 2, 2006 3:02 PM

Hi Dave,

Excellent thread!

You are right, without treatment of the water, even water from a municipal supply, you will have problems with lime build up and salt toxicities in the plants. I use an RO system. RO systems are not without problems. You have to replace the filters frequently. My water is so hard that about every 6-9 months I have to replace a membrane. The biggest problems is supply/demand. The RO units make water slowly, and that is not how you use it. I have a large deep well tank and I can probably store 15 gallons of water, but that is about it. I always worry whether there will be enough water for the mist system after watering in the mornings in July!

My system is suspended from the ceiling. I use 1/2" PVC with nozzles similar to yours every 4 feet. Mine are arranged upside down, over the aisles of the GH so that drips don't land on the plants. The main 24VAC signal comes from my climate controller (thermostat). The signal runs through a relay controlled by a misting timer, so it comes on only when it hits a certain temperature, and then it comes on according to the frequency set on the misting timer. This is analagous to what you have in the second picture, I believe, which is basically a 24 hour timer plus a frequency timer.

Dave, what humidity do you maintain in the GH? Any trouble with foliar diseases with that much humidity? My fogger is also controlled by the climate controller, but this signal runs through a humidstat which shuts it down if the humidity is over about 60%...I figure at that humidity level I'm not going to get much evaporative cooling effect anyway.

I am interested in your mixed bed water softener. How do you regenerate? Is the entire system shown in the picture? If so, it is as compact as a regular water softener, and certainly takes up less space than my tank. How much does it cost, if I may ask?

SB

Good comments/questions.
My first system was RO - it was a refurbished 300gal/day unit somehow used in kidney dialysis. It worked OK but I really needed to repump from a tank as you do (I didn't, using a air-baldder tank to maintain about 25 psi - not the way to do it).

It's difficult, I think, to try to maintain a particular humidity. I keep my Oregon Scientific temp/humidity monitor right next to my easy chair in the house and watch the readings all day. The ambient humidity varies considerably and, of course, we are looking at the relative humidity (RH). When air gets really hot it can hold a tremendous amount of water, so 40% humidity when the temperature is 95 isn't all that low. In Summer, my RH starts at 80-90% in the mornings (probably due to left over moisture). By 3:30 (peak temp due to west side tree shade) it's usually holding around 40-50% (ambient RH 30-40%)

I have no problems with foliar disease (this may be too high for other plants), but:
1 I'm growing mostly Bromeliads (rainforest plants), and
2. I have a large fan running on "high" all the time. (I've had two at times, a good idea)
I have crushed limestone on the ground (which isn't good for pot stability) but the additional surface area also helps water making it to the ground to evaporate.

The "softener" is actually a two step process. The first tank is actually a sodium exchanger (Yes - I said that was really bad [by itself]) and the second is the mixed-bed exchanger. Having the sodium exchanger (cheap to regenerate) makes the mixed bed exchanger (costly to regenerate) more efficient. I learned about ion exchange talking to my power plant people who treat hundreds of gallons of boiler quality water daily. I regenerate by calling Culligan - they are here the same day with a new set of tanks. The mixed bed tank is regenerated with Sodium hydroxide and Hydrochloric acid, not what you want to handle. Here's a link for the gorey details on ion exchange http://www.remco.com/ix.htm

If you look closely at the top of the left tank, you can see a small neon lamp which glows when the water conductivity (a good measure of the lack of dissolved minerals) is very high. When it goes out, quality is starting to deteriorate (it's "fail-safe"). The cost is high, the price you pay for very high quality and convienence. A regeneration costs $175 and I do about 4/year (I am evaporating a lot of water with those 8 gph nozzles and I need to keep the Bromeliad tanks watered). That's a lot of $$$ but this is my prime life interest!

RO has had tremendous cost reduction recently, I would guess due to peoples due concern for the quality of their drinking water. RO also has the advantage of removing bacteria, viruses, metals, and almost everything else. Do an eBay search for RO and you find pages and pages of package systems. If I had it to do over I would strongly consider RO, but it does add to complexity and the water quality (hardness removal) is not as high.
Dave.

p.s. I'd love someone to post on building do-it-yourself benches. Mine are built out of 2x2 with mostly galvanized wire mesh. My wood is failing (it did last 25 years) but I'd like to find a non-sag material for the top that doesn't cost a fortune.

Dave I went to Lowes and got the wire racks that they sell for closets. You can get them in a lot of different sizes. I think they are called ClosetMaids shelving.

I'll check it out. Thanks!

Here is my overhead mister.

Great stuff!!!
You guys way to high tech for me!!!
I just use the coiled stands with a mister ,with a fan directly behind the mister.
My well water is really hard that it leaves deposits,spots on the leaves.
I also have a 6x8 pond in the middle of the greenhouse,with a fan blowing over the top of the pond,it always keep the humidity level at 50% or more.

Linda,I use those those white wire shelves there great and inexpensive.