Misting Automation Question
 

I am looking to add automation to a misting setup in my new greenhouse. I am going to stick with the hose-threaded low pressure system, but don't want to operate it manually.

I was thinking that I could use a lawn sprinkler solenoid valve to feed it and then just tie it into my existing sprinkler system/controller (which has unused "zones"). All I really need is for it to spray a few times during the hottest hours of the day. Most of the simple threaded battery-powered timers won't confine their cycles to a specific time of day, and I don't want misting at night!

Has anyone tied their greenhouse system to an existing sprinkler system? Is there some reason why this wouldn't work?

The first drawback I can see is that if I hit "rain delay" for my lawn, my greenhouse also won't get sprayed, but it shouldn't be super-hot on rainy days . . .

I use a deer feeder timer and a 12 volt pump ...the deer feeder timer can be set for 6 individual times and from 1 to 30 seconds on each activation .....

My lines are simple pvc with drip irragation misting nozzels from a local garden center.I use a drill bit just a bit smaller tham the threads on the nozzels and just screw them into the pvc pipe ...worked great for me over the chids outside last summer
....you could hook the timer to a 12 volt relay to operate any valve and use your choice of valves then

And the timer was very cheap online

It really depends how fine you want the mist to be. If you're happy with fairly large droplet sizes, most "mister" irrigation fittings should be fine so long as your water pressure isn't terrible, and you should be able to find a fairly standard battery powered on/off timer that would automate it for you. Another solenoid/valve on your existing system would also work.

If however you want really fine misting, you'll probably need a pressurized pump. I suspect the larger mistking units would do quite well in a greenhouse - assuming you have power out there. I'd run it with rainwater or RO water, rather than municipal (tap) or well/borehole water.

Alternatively, there are nice ultrasonic or spinning disk humidifiers that come in various greenhouse suitable sizes, many with integrated humidistats.

High Vs. Low Pressure
 

Yeah, I'm fine with the droplet size; no need to go to a pressurized pump. I do have exceptionally high water pressure at my house, so that probably helps!

Once I bought one of those free-standing hose connected misters for my patio, but someone had stolen the 2 brass mist nozzles from the thing at HomeDepot before I bought it. Unbeknownst to me, this left two small holes, and when I turned the water on full-blast, I was surprised. It shot one stream over my house and into the front driveway, and another one clear across the alley and over the house on the other side! Now that's water pressure!

What I really want is a reliable way to open and close a valve that is bit more sophisticated than just "spray for 10 minutes, once an hour."

A humidistat and solenoid would do that; if the humidistat and solenoid are different voltages or ac vs dc, then you can always use a relay to switch the solenoid. This has the bonus of turning the mister on when it needs to be on, rather than your best guess at likely times/durations (i.e. sunny morning vs overcast afternoon, sudden hot/cold dry/humid spells). You can also wire a thermostat in parallel if you want that to also control the solenoid. I recently built something like that that controls a fan on my balcony.
You also get timer relays that stay on for a certain period of time and then switch off.

It's better to get a solenoid that requires power to open rather than to close (I think most of them are built that way for obvious reasons).

As Discus pointed out.... Humidistat and NC 110v solenoid valve is your best option. If you find that it turns on alot then you may want to get a fogger so you don't rot your plants.

My system allows for a setting from 1 second to 30 seconds of time misting and up to 8 times daily ...and I have found that outside in the open 15 seconds once every 2 hours is more than enough watering and humidity even in a open air setting ....I use a 12 volt diaphram pump made for rv use just like mist king sells I just bought mine at the local hardware store ...

If its not too late. I went to one of the big box stores and got one of those hose end timers and hooked it up to one of the low pressure systems. Works like a champ.

I'm still using this and have added a 2nd tower but reduced the number of fogg-its to 6 on each tower... http://www.orchidboard.com/community...ng-system.html

If your issue is more about humidity & cooling, rather than watering your plants, you might want to consider a misting system that has two branches, each with a simple & separate shut off ball valve. The connected branches are controlled by a single solenoid valve that can also be turned on manually.

One branch goes overhead & can be used to gently water your plants. This would normally be shut. The other branch goes on the ground under the bench. Both branches can have fogger or mister heads (very inexpensive screw ons for pvc irrigation lines).

For regular use, just leave the top branch valve closed, so that only the under bench misters are open. When the solenoid valve opens, the under bench misters go on. There are advantages to under bench misters. They wet the ground & help humidify the GH, without wetting the plants. Therefore, the misters can be turned on repeatedly, without rotting your plants.

The misting immediately cools the GH. The evaporation from the wet ground also continues to cool the GH for an extended period of time. The immediate cooling can be 15-20 degrees F. The extended cooling lessens as the water evaporates from the ground. But by then, the misters go on again before it gets too hot. Once an hour for a minute or less, during the hottest times of the day, should do it. From my experience.

Repeated misting & drying from the top, during hot weather, can leave lots of ugly mineral deposits on your leaves (depending on your water quality). From my experience

Repeated top misting can also salt out & rust the metal components of your GH. Again from my experience.

There are inexpensive garden timers that control both time & duration, for turning on your solenoid.