High pressure (1000 psi) fog systems?

[DavidCampen]

With the exhaust fan off then the fog can get very thick. I haven't pushed it as far as possible yet but I have had it where visibility from one end of the greenhouse to the other (20ft) is highly obscured.

I could probably get it so thick that I wouldn't be able to see from one end to the other, I will have to try that. At the moment though I am still working on other aspects. I am having trouble running the motor at less than 1/3 speed so this weekend I am replacing the 1/2 hp drive and motor with a 1 hp drive and motor. I am also still working out my nozzle placement and later I plan to replace the 1000 psi nylon tubing with stainless steel tubing so I can run the pressure up to 2000 psi.

[Tindomul]

Thats cool, what sort of plants are you going to grow that they need fog? Are you going to try to grow cloud forest species??

[DavidCampen]

I am not planning to grow any plants that "need fog". The high pressure fog system is just a method for supplying humidity and cooling. On hot, dry, late summer days in Southern California, when my exhaust fan is running at 2000 cfm, I will need to be evaporating up to the pump limit of 1/2 gallon of water per minute to maintain humidity at 80%.

[Paul Mc]

Does the zoo med control only work in relation to RH and warmth, or could it be used for RH and cooling?

[catwalker808]

Fogging systems are a very effective means of cooling & humidifying a greenhouse. A number of years ago, we spent over $10,000 & I spent over 3 weeks (on & off) installing a dedicated water line, electrical lines, special water filter banks, a very good high volume, high pressure pump, distribution lines & pre-fabbed lines with installed stainless steel fogger heads (with drain valves). Also special timers for time of day intervals & on/off duration.

The system did a wonderful job of cooling a small 5000 sq foot shade house & half of an adjacent 2500 sq foot greenhouse. Ideally, if fogger jets are at least 12 feet high, the fog drifts slowly down & evaporates by the time it reaches bench level, cooling & humidifying the air on its way down. Because of the low height of that shadehouse, I could only suspend the fogger lines at 6-1/2 feet above ground level. In order to evenly disperse the fog in the 50x100 shadehouse, we put in 140 fogger heads. This is probably more than twice as many heads as would normally serve a higher structure. The other greenhouse was taller, so we only used about 30 fogger heads in the half that we fogged.
When the fogger went off, it was like being in a cloud & summer temps dropped probably 15-20 degrees. And of course, you could not see through the fog. We also needed a large number of heads, because the sides were also shade cloth with a lot of good cross ventilation.

I selected a high pressure pump with more capacity than necessary. (It’s better to under work an oversized pump than to overwork an undersized one).

I don’t anticipate that most people would be considering even this size of fog system. But there are some basic requirements regardless of size.

1. You will need to calculate the number of fogger heads that will evenly cool and/or humidify the greenhouse.
2. The pressure pump should have sufficient capacity to handle the number of heads.
3. Your water supply line should have sufficient capacity to feed the pump. Insufficient water supply will cause your pump to chatter (not from feeling cold, but from insufficient water in the pump) & this can damage the pump. A dedicated copper supply line is also a good idea. PVC lines can enable algae growth in the water supply line.
4. A good 2 phase water filtration unit is also important. Debris & impurities can damage the close tolerances within the pump. Even very tiny debris or deposits will clog the fogger jets.
5. The oil in the pump needs to be changed, depending on usage.
6. The fogger heads need to be cleaned. If filters are not effective, jets will clog frequently. Even with proper filters & good water, deposits & impurities will cause some clogging. Cleaning requires the use of very fine stainless steel wire inserted into the jets. Sometimes jets need to be removed & soaked in a mild acid to dissolve accumulated deposits.
7. Yes there is a lot of maintenance involved.

A little word of warning. I know it sounds high tech & impressive to use 2000 lbs of pressure. But for a relatively small system 2000 lbs can be very dangerous. With relatively few outlets for relieving pressure, a malfunction could send nozzles, connectors or other parts flying around like bullets. Very dangerous, especially in close proximity. Our system had a large number of nozzles & was easily capable of 1500 lbs or more; however, I only operated it at less than 600 lbs, for extra margins of safety (even though it was designed to easily handle the higher pressures). With the fine nozzles, we still had a true fog.

Rather than seeing how high pressure you can achieve, it would probably be much safer to see if you can achieve desired results with lower pressures & very good ultra-fine nozzles.

[DavidCampen]

Originally Posted by catwalker808

Rather than seeing how high pressure you can achieve, it would probably be much safer to see if you can achieve desired results with lower pressures & very good ultra-fine nozzles.

Thanks for the warning but I have expert knowledge of constructing and operating high pressure systems.

The purpose of the 2000 psi lines is not "seeing how high a pressure I can acheive" but rather so that I can control flow rate by varying pressure. I plan to use .008 inch orifice nozzles which should operate well at pressure above 250 psi. By varying the pressure from 250 psi to 1800 psi I should be able to vary the flow by a factor of about 2. I will set up a PID feedback control loop to alter pump speed (and thus pressure and flow) according to humidity.

[catwalker808]

Your posts sounded like you knew what you are doing. My warning was more for readers who might want to try an inexpensive or do it yourself system & then really pump it up, more than the components can handle.

You & your plants should be cool & comfortable this summer. Good luck.

[Ghost Hunter]

If you have a cooling unit, i.e. A small a/c or something else it can control that too.....within reason of course.


Living life one photo at a time.

[DavidCampen]

I have replaced my 1/2 hp motor with a 1 hp motor and the system now works much better. I can set the pump speed to as low as 4 hertz (1/15 of full speed) and have the system run reliably.

I replaced my nozzles that were spaced along the length of the greenhouse with an array of nozzles that are at the far end of the greenhouse from the exhaust fan. I am using 0.006 inch diameter orifice nozzles that deliver fog at about 50 ml/minute (3/4 gallon per hour) at 1000 psi.

At the moment I am using an array of 7 of these nozzles to deliver 3 to 5 gallons per hour of fog (as the nozzle pressure varies from 400 to 800 psi). This is enough to keep up with my moisture requirements on sunny spring days in Southern California but when we get into the heat of late summer I expect that I will need more. Soon I will have replaced all of the 1000 psi rated nylon tubing with stainless steel tubing and fittings rated for more than 2000 psi and then I will be able to run the system at up to 1600 psi to be able to get 7 gallons per hour out of the array of nozzles.

[OzPhal]

G'day David, how did you go with your system? I'm interested in seeing some pictures of the finished fog

Originally Posted by DavidCampen

I have replaced my 1/2 hp motor with a 1 hp motor and the system now works much better. I can set the pump speed to as low as 4 hertz (1/15 of full speed) and have the system run reliably.

I replaced my nozzles that were spaced along the length of the greenhouse with an array of nozzles that are at the far end of the greenhouse from the exhaust fan. I am using 0.006 inch diameter orifice nozzles that deliver fog at about 50 ml/minute (3/4 gallon per hour) at 1000 psi.

At the moment I am using an array of 7 of these nozzles to deliver 3 to 5 gallons per hour of fog (as the nozzle pressure varies from 400 to 800 psi). This is enough to keep up with my moisture requirements on sunny spring days in Southern California but when we get into the heat of late summer I expect that I will need more. Soon I will have replaced all of the 1000 psi rated nylon tubing with stainless steel tubing and fittings rated for more than 2000 psi and then I will be able to run the system at up to 1600 psi to be able to get 7 gallons per hour out of the array of nozzles.