How about covering the air intake in tomato vines? Grow them in hydroponic autopots and they will probably relish the extra minerals. And you get yummy (yucky) tomatoes.

Nathan, I'm thinkin' I'm not gonna take the tomato vine idea too seriously....besides, "air intake"? huh?

Why not? Tomatoes are very effective at evaporating water. And they are cheap, don't need an expensive and fragile water purification system and produce a viable crop. If you don't like tomatoes (I don't) maybe watermelons or squash.

Air intake = bit where air comes into your greenhouse. A north side wall could be replaced with a set of louvres and a mesh to support the vines.

I think we have a bit of practical and geographic disconnect going on here.

I can now see the intention behind your vine suggestion but a few practical things won't fit the concept.

1- the existing intake shutters face out on what will very soon become a paved walkway

2- the northside side (as well as the other three sides) are cement block kneewall up about a meter

Besides, I'm still not buying the idea that any amount of tomato vines will give me control over the humidity 24/7. Even IF it were possible; I'm growing tomatoes big enough (ie. with lush enough foliage to provide free moisture) in March? I'm at 38 degrees N here!

Well it's your choice. Personally given a choice between a $50 solution (grow plants over intake with a fan) and a $500 solution (RO and evap cooling), I'd spend some serious time thinking about the cheap option. But if you are dead set on a mechanical process maybe foggers are a better idea, being less affected by minerals. Some people claim that the mineral dust affects the plants, but I'm dubious (as it probably washes off anyway). A waterfall, or a large rainwater tank might also work.

You don't need to have the intake on the northwall, it's just convenient. The vines could grow equally on the east or west walls. (or the south, but then you'd be blocking the sun) The vines should be grown on the inside of the greenhouse, not the outside, if that's what you're thinking?

I'm at 38 degrees S, coincidently :) (well 37.75 according to WP) We can grow tomatos all year round in an unheated greenhouse.

Well, if you're not taking Nathan's advice, you're exactly right about the RO and the fogger, the setup and whatnot.

D.

dmarin, how shall I say this? Nathan seems to be offering advice with genuinely helpful intent but, no, I'm not taking his advice. Too too many don't-works in it for me....so then,

do you use a RO and fogger ? or RO and misting ? what size gh? any idea how many gallons of RO water your system uses on the hottest summer day?

Steve

Well clavero you dropped a small hint in your first post that should answer all your questions!

You say you are going to fill a tank with RO water and use a pump to send it to a misting system?

Collect rainwater and send it to the tank, build a very simple solar distilation system and let that fill your tank.

Do what we talked about on other threads, fill trashcans (tanks) with well water and bubble air through them for a day or two before transfering the water to your mister tank.

The fact that you are going to use a booster pump for the misting system gives you so many options. Most people just connect a mister to their water supply.

I'm genuinely interested in the idea. I think it should work, indeed Nick agrees (coincidently they've been talking about these ideas over at alt.solar.thermal):

... wrote:
>... Basically you dig a deep 'foundation' and in the middle of the
>greenhouse build a plenum from the bottom of the pit to the top of
>the greenhouse. At the bottom of the plenum you would cut several
>4" holes and attach 4" black sewer pipe with holes in it to go all
>directions. Then fill the foundation with some sort of thermal mass
>material... prolly rocks or gravel. Then a blower is attached to
>the top of the plenum to blow air down in to the rocks. I would
>presume that if a slab foundation were to be poured there would be
>some sort of vents around the edge to allow the warm air to escape
>back in to the greenhouse. The blower would blow the hot air from
>the day down to heat the rocks and then at night the rocks would
>warm the cooler air.

I think this could work well for a house in a dry climate, but it might
become a mold factory in a greenhouse. Green leafy plants in the sun
can evaporate lots of water, about 1 pound per day per square foot of
floorspace. This (1000 Btu/ft^2) is about the same as the amount of sun
that falls on a south wall in Phila in January, so a greenhouse might
decide to use ALL of the sun that falls on it for evaporation, with no
sensible heat gain...

The usual way people prevent greenhouses from becoming swamps is to turn on
ventilation fans to blow lots of water vapor (and solar heat) out of the
greenhouse during the day. Then they turn on propane heaters at night.
An energy-conserving greenhouse without lots of daytime venting still
has to deal with humidity buildup. From heat transfer and energy storage
points of view, humidity might be good, with condensation indoors.

We might even reuse the distilled water. PA has an approved "Sundrive"
alternative wastewater treatment system using an large greenhouse with
plants (eg reeds) on top of a waterproof liner, but the greenhouse has
to be almost as big as the house it's treating wastewater for, since
the water leaves the greenhouse in vapor form. A condensing or multiple
effect distillation greenhouse might be good for water reuse in the
Southwest, where water is scarce and sun is plentiful...

I'm going to think about this as an idea for my greenhouse, which probably has higher temps than yours.

I wonder if a reverse osmosis system is really what you want to use? They are principally designed for low volume processing of drinking water. If you are worrying about clogging of misting heads, wouldn't you really want a good quality high volume in-line sediment filter and a conventional water softener. Then you don't need holding tanks, extra pumps, and extra plumbing because you are working at the full water line pressure. You can probably save some money too.

chris, I get the idea of collecting rainwater and the simple solar distillation but can you fill me in on the "bubbling air through well water" idea...is this going to reduce dissolved solids?

cottagefarmer, part of the gh will hold orchids and I've been repeatedly warned off conventional water softeners due to added salts content. I assumed a basic sediment filter would be part of the RO inlet; it was DS build up in fogger heads (mister heads), glazing and plant surfaces that is the concern.

nathan, I'm not dissing the tomato idea in general...its just that it is not pratical for my situation. The gh is small, the floor paved brick and the kneewall prevents planting low in the gh anyway.

You could run the softened water to the misting system and use non-softened water to water the plants.

I think the idea of bubbling air is to expose the water to lots of CO2, which precipatates out Ca and Mg.

I'm with cottagefarmer though, hard water alone won't block misters. It might leave a residue on the plants (which might be washed off when you water).

On the other hand, evap cooling doesn't use much water, so a rainwater tank sounds like a good option, or town water. If you have a small greenhouse, why is using bore water important?

We alsoways have to be careful about terminology here. In my mind we have misters and foggers. A mister will run directly of mains water pressure (500kPa) and use say 10L / hour of water producing droplets that are visible to the eye.

A fogger, on the other hand, produces sub micron drops, runs on a pressure of say 2MPa and uses almost no water. Foggers generally are only available from specialists or in complete units and require stainless steel or similar piping and fittings.

Which are you thinking of?

For orchids, you absolutely MUST use either RO or collected rainwater. Now, for an RO unit that puts out something less than 100GPD, I'd just fill some garbage cans for a resevoir.

For clarification, did you really mean foggers as in ultrasonic misters to raise the humidity, or do you mean for drip irrigation?

I really think for either purpose, you'll be fine with a 100 or more GPD RO unit(about $150 or less), plumbed into a large tank/garbage can with a float shutoff. Unless you've got a huge greenhouse, I think you should be fine.

D.

For those of us who use misters for cooling, there really isn't an issue of what the water contains in terms of ions, since the idea is to get the water to evaporate (and thus cool) before it gets to the plants, the ions going back to their non-hydrous form. Obviously, you want to filter out all of the particulate matter, which can be done with as little as a sediment filter, because that is what clogs up the works. The same holds true for foggers. Neither of these methods requires water processed through a reverse osmosis system. BTW, the subject of orchids only came up after my post about using a water softener. Perhaps, if one is asking for advice from the community, one should provide details of the entire problem in the original post.

Let me start with an apology...cottagefarmer, sorry I failed to mention the orchids in the original post. Not an intentional oversight, just a head full of too many details.

Its often difficult to merge information from various sources and not only do I not always rememeber to ask all of the specifics of a question but often the answers to an initial query run so tangental to the original question, that its hard to stay focused.

I also try to be senstitive to the length of a post, so I apparently fall short in the details in the process.

Please all, accept my apologies and, if you still have patience, let me try and restate my situation:

The gh is small (about 120 sq ft), wood frame, uses a 34" high kneewall of cement block,covered with 10mm twinwall. Floor is mortared used common brick that slopes to a central drain.

pics via the URL below

It currently has a 16" exhuast fan on thermo, two 16" shutters in the east wall, two 8" circulation fans running low speed 24/7 and (for starters) uses a 1500 watt milkhouse heater to keep night temps around 55-60.

The plan (we all have to have a plan huh?) is mixed use in the Intermediate Greenhouse temp range, which I understand to be min 60 at night max mid 80s with a humidity range somewhere between 50- 75%. We'd like to maintain a small collection of orchids (of various types to the intermediate temps range) yet also start spring flower and veggie seeds, perhaps root a few cuttings etc.

The gh has only been in operation for less than a month...mostly empty. So far the temps hold OK but the humidity hovers at mid 40s at best during the day.

I do not plan a drip system for the gh. Plants will be watered and fertilized individually, or by "group". I do understand that misting and fogging are two of the ways to control and maintain a rise in humidity and that the two systems (fog vs mist) emit a different size water droplet and, of the two, I have read that the small fog droplet size is better for the plants than the (relatively) larger mist droplet size.

(I thought I was trying to get input about which of the two systems people were using but, perhaps I failed in that communication as well)

Of the two, at least for a start, I am currently (as of 10pmPST last night) looking at the Rainmaker Misting system from Ecologic that uses a high pressure pump and nozzles that produce 50-100 micron size water droplets (about $240). I understand that this is a misting system and that "fog" droplets would be smaller (less than 50 micron)but the cost differential between the two systems (at least from these folks) is big (roughly $240 vs $980). I'm not trying do this gh on the cheap but I'm not made of $ either.

I do hear, even within the current answers to my orignal post, a difference of opinion about whether RO is "necessary" for such a system for use on orchids..at the moment my leaning is toward the RO system BUT it might be prudent for me to try the misting system without the RO and watch carefully what happens.

It seems to me that cooling (in contrast to only maintaining humidity) is a plus to the deal. Since the gh needs additional humidity and, since that humidity in the form of injected mist would also help cool the gh, I can't see how the two don't work hand in glove, at least to a point.

Thanks for your patience.

Steve

Here is a link that might be useful: gh pics

Awesome pics of the GH Steve. Afraid I'll be of little assistance with your dillema but I did want to say thanks for the various stages of construction in the pics.

My only experience with RO's is installation for drinking water and a lack of line pressure suitable for water and ice in a fridge. I think you'll definately need a secondary bladder with some kind of float shut-off to cut the feed line from the RO and a pump system for the mister/fogger. The holding tank on the RO will only refill what is used so a shut off on the feed to the secondary bladder will prevent over production and save you money on replacement membranes (filters). Without a secondary bladder you won't achieve adequate water pressure, even for a ice maker.

clavero: If humidity is the problem, rather than cooling, you just need more plants or less air leakage.

For cooling, another good solution is to just irrigate the floor. just run a soaker hose around the floor connected to a humistat near floor level.

cottagefarmer, if you were evaporating in a separate chamber and just moving the water vapour, then yes the salts wouldn't be a problem, but if you are evaporating salty water in a cloud over the plants, where do the minerals go? p.s. thanks for the lighting info, it was very helpful!

The RO system works great and the foggers are wonderful. I would recommend both. You might also check on using a demineralizer. The demineralizer will do the same thing the RO unit does. My studies show that I can get less than 2 PPM of DS on either the RO or demineralizer. The demineralizer will give you more water in less time, without the waste water. I use the waste water for other plants from the RO. Really not waste.

orchidude...sorry for the time lapse here. I'm also in the final stages of an interior house remodel and time just seems to vanish.

When I google demineralizer, I get what appears to be ion exchange systems, right? I want to be sure I understand your suggestion before I evaluate the two.

Thanks

Steve

Has anyone used an ultrasonic fogger for GH humidification and cooling? These devices apparently do not require a high pressure pump and will siphon water from a reservoir. Depending on your water quality, treatment with reverse osmosis/deionization may be necessary.
Check this site: http://www.nutramist.com/humid.html
http://futuregardens.com also sells the basic components you need to construct your own device.

lite: they look cool, but I found the replacement discs expensive. You also need a lot to get a useful amount of fog.