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Greenhouse questions

Discussion in 'Growing Areas' started by mrbreeze, Jun 9, 2012.

  1. mrbreeze

    mrbreeze Anglican Supporting Member

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    I'm finally getting close to having a greenhouse built. I've got various questions that I would really appreciate any input on from people that have real-world experience. Many of them have to do with my deep fears that the Oklahoma weather will be a disaster if i don't plan for major cooling. I'll probably get a passive gas heater (southern burner). The gh will be 8' x 16', cedar, with a tall peak. Any input or advice on the following would be greatly appreciated:

    1. Motorized vs. passive intake vents: I’ve always thought that with a high peak and a decent exhaust fan I could get away with passive ones. I’m probably going to have limited electrical outlets although I could conceivable change that. Related to that….
    2. Number of electrical outlets: my site already has one coming out of the ground. My understanding is that you can add multiple boxes on one circuit but I’m a bit worried that one circuit won’t be enough. I anticipate an exhaust fan and a couple of oscillating fans and a pump or two for a wetwall and a misting system. Since the pumps would be intermittent, I wouldn’t think that electrical load would be too great. But then I’ll probably want/need lights.
    3. Single vs. double door: originally I planned on two doors like a French door but for cost savings and since the overall size isn’t that great, I’m wondering if one door might be enough.
    4. Solar roof vents: I’m assuming the ones with wax or oil in the cylinders are fairly standard and would plan to have at least two or maybe four to work with the intake vents to exhaust hot air from the top. Any thoughts on that?
    5. Slab only vs. slab with gravel: I believe the contractors are planning on pouring a slab largely because the minimum concrete load is 3 cubic yards and they’ll have to pour footings. So they say they might as well use the extra for a slab. I assume that could get pretty slippery so I’m thinking pavers or gravel on top if needed. Also for humidity I wonder if the slab getting wetted down would be as good as gravel?
    6. Exhaust fan vs. passive air flow via root vents and intake vents: with a high peak I wonder if I could get away with not using an exhaust fan? Since it routinely gets over 100 degrees here in summer, it worries me overall. But it does seem like the convection might be enough by itself.
    7. Twin-wall panels vs. triple wall: I could save a lot of money by going with twin wall but I wonder if I would just be trading the cost of extra heating/cooling. Also I could kind of mix and match, i.e. put triple wall on the top and west and north, where extra insulation would be a benefit, but that would complicate things a lot. Related to that…
    8. Panel attachment with screws or with H/U-channel fittings: the contractor wants to use the fittings but that will add a major cost factor and will get really complicated trying to determine the length and quantity of each type of fitting. I have a book on building greenhouses and it says to just screw the panels to the frame. I would think doing that with maybe some adhesive along the edges or weather stripping would be a lot cheaper, maybe stronger, and easier, and might actually look better.
    9. Wet wall vs. aquafogger or other type of cooling: I definitely like the idea of the wet wall but it adds a lot of complications, including I would probably have to build it myself (the contractor has never built a gh and has no clue about a wet wall). I do think some kind of cooling will be an absolute must. I’ve read some forum posts where people really seem to like aquafoggers.

    Again, thanks to anyone that takes the time to respond. I know everyone is busy and these are a lot of questions. But this is the time for me to figure a lot of things out and avoid major problems in the future.
     
  2. msaar

    msaar Member

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    1. See below
    2. Although I once operated an 8’x12’ greenhouse on a drop cord from the house, I would advise 2 circuits if it’s not prohibitively expensive
    3. Single door. Your greenhouse will only be 8’ wide; what would you want to move in or out which wouldn’t fit through a 36” wide door?
    4. Since you will likely have some sort of cooling system, these would probably only serve as an emergency vent.
    5. If you will have sufficient concrete, a concrete floor would be an advantage from a hygiene standpoint. Traction would not be an issue if you have a broomed finish applied. (This is the finish normally used on sidewalks) It would provide less humidification than a floor that is open to the ground. By all means install a concrete walk if you know your bench layout. I have concrete walks with weed block fabric and crushed stone under the benches. I have weeds and ferns that still grow in the stone. If you have a totally concrete floor, you need to consider where water goes when you water.
    6. You will not be able to provide sufficient ventilation passively in an OK summer. You should count on providing a minimum of 1 complete air change per minute. Calculate the volume of your greenhouse and you will have the required cfm.
    7. I think double wall would be adequate. The bigger winter heat loss concern is the infiltration of cold air. The additional $ would be better spent on a thicker panel, sealing cracks, weatherstripping, etc.
    8. I would use some type of cap bar system, and bed the panels in sealant. Screwing panels directly to wood framing is problematic where two panels butt together, where you only have half the wood to screw into. Since you say you will be using cedar, I assume appearance is important (I would recommend treated pine otherwise). The cap bars would be much neater looking. The intermediate fastening can be screwed directly. You will need to seal the upper ends of the panels with metallic tape, and the cap bars will cover the shiny tape.
    9. Because of the amount of air you will be moving, you will definitely need some type of evaporative cooling system. Have you considered using a “swamp” cooler? With a wet pad system you will have to have louvers (preferably motorized) the size of your pads. A swamp cooler allows you to introduce cool air low and exhaust high. Gravity vents (non powered) are feasible for exhaust where you wouldn’t use them to introduce outside air(they are susceptible to wind blowing them open.

    I don’t know what you mean by a high peak-how many feet?
    I've only answered the questions you asked; if you have more, feel free.
     
  3. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    Now that is great news! Here are some thoughts I have (in no particular order).

    I use the solar vent openers. They work during power outages and are very straight forward. I have one up vent up high and a swamp cooler down low. If you have a wet wall, you will need an exhaust fan.

    When I built my larger greenhouse (21 x 21) I put in way too many vents since what I was replacing had very little venting and was a low roof. I started with 4 vents up top at 13 feet (each one 18" x 48") and 2 vents down low that were the same size on the opposite. It pulled through so much air, so fast everything was dry before the next day. I closed up both vents down low and kept only one up high. Even when the swamp cooler isn't blowing in air, some is pulled through the opening. My greenhouse is the opposite of tight construction, so there is air coming in through gaps and under the door. If you put in too many vents, you can close them up, but it isn't so easy to add one. I should add that my vents are vertically positioned so having them be larger works well. If it was lifting the weight of the vent, having them so large might not work.

    I would agree that more than one circuit is best. I have 6 outlets in the big greenhouse because I let the electrician talk me out of as many as I wanted. I frequently regret having listened. I just never seem to have one where I want to put that extra fan. Think about where you might want fans (up high, down low) so you get enough outlets. I have more fans on the floor than up high and now have one on the floor that is angled up to get more mixing of air between the top and bottom. I did have overhead lights put in this one and it is well worth the effort and expense.

    I have dirt floors with deep gravel. Unless you have under bench misters or a fogger, a concrete floor makes a greenhouse hard to maintain humidity. Gravel has a lot more surface area than a flat floor so will give you more cooling effect.

    Single door. I have had doors on the north side of the gh that open inward and have grown mounted plants on them. I chose a door that opens outward on subsequent construction.

    I used aluminum fittings to hold the panels in place. I've been told that screwing them in place is not a good thing to do, but don't remember exactly what the reasons were. A friend used plastic fittings and said they were very difficult to use. Also, when you use fittings, you have to account for the space they take up. I had a nail pounder (not a finished carpenter) build my big house and we put the studs on 4 ft on center. That meant I had to trim every piece of polycarbonate to account for the fact that the panels themselves were 4 ft because the fittings took up another 3/4" or so.

    I used pressure treated wood that I painted with a stain/preservative so that it is dark brown. I absolutely recommend it over the redwood we have available here. Judging from the experience of friends, it isn't going to rot in my life time and the carpenter bees won't touch it.
     
  4. mrbreeze

    mrbreeze Anglican Supporting Member

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    Thanks guys. I showed the contractor one from a catalog that is from cedar. I think that's the main reason he is suggesting it. I had thought pressure treated lumber but from what I gather the cedar should last plenty long enough. I'll probably move before it rots either way. Plus it would look nice.

    I think I'm convinced about using the fittings rather than screws. I have a book that says to just use screws but more than a few people have suggested against it. The bar fittings are damn expensive though! Not to mention the complexities of figuring out how many and what length to get. I always hated math...

    And I'm now thinking a swamp cooler may be a smarter way to go vs. a wet wall. Probably more up front cost but should be a lot easier in the long run. One complication to the whole thing is I won't have a water source plumbed in. There is no reasonable way to do it since the closest water is on the other side of the yard and on the other side of a concrete patio, etc. So i'm going to have a hose bib installed and just hook up a hose. I haven't done any research yet into swamp coolers so any advice on those would be highly valued.

    And I think i'm convinced about the value of extra circuits/outlets. I was hoping to save some $ on that but in the end, it would likely be worth the extra expense.

    Still not sure what to do regarding solar roof vents. If I go with a decent exhaust fan it will probably be overkill to also have roof vents at the peak. I'm too lame at math to figure out how tall it will be. The walls will be 8' and the roof supports will also be 8' and the width will be 8'. Gotta be over 12' and maybe 14'? Pythagoras probably knows. ;)

    It'll have a drain on one end. I plan to re-use as much stuff as I can from my indoor setups. I have a ton of 4' light fixtures and two misting systems plus a lot of wire grates I can use for hanging things. From what I gather, under bench misting is the way to go for humidity. I guess watering will have to be done by hand.
     
  5. KellyW

    KellyW Orchid wonk Staff Member Supporting Member

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    Good luck with your greenhouse. You are doing good research. My only comments are:
    Regardless of the wood used (even pressure treated lumber) treat the ends with wood preservative since they will be wet most of the time. Especially the lower ends of the studs that contact the sill plate. Even rot-resistant wood should be treated there.
    Also, if you are in eastern OK the humidity will reduce the effectiveness of any type of evaporative cooling. Check with other local greenhouse growers to find out if evaporative coolers are sufficient. It works great for me but my summer rh is between 10 and 30%. Your rh is probably more like 50-80%.
    Have fun.
     
  6. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    Kelly makes a good point on the humidity outside. If you can visit other growers in your area with greenhouses you can learn a lot.
     
  7. Kitty

    Kitty AKA\Debby

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    AMEN to that, visit as many as you can!
     
  8. mrbreeze

    mrbreeze Anglican Supporting Member

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    Yea, it would be nice to do that but realistically, I don't have the time for it or any good way to find out who/where they are. The construction is due to start well before I would be able to get back into our local society. Also I tried before to get some advice from them and couldn't even get them to send out a mass email. :(

    I'm in central Oklahoma where the humidity is a LOT lower than in the eastern regions. So I think a swamp cooler might be a good idea. However I did some checking last night and one of the right size would probably be around a thousand bucks or more. The money isn't such an issue, but I can't help wondering if I could create a pretty awesome wet wall for that kind of dough? Seems like the much larger area of cooler air coming in would be a big advantage as compared to the relatively concentrated ducted air coming from a swamp cooler.

    What about a window unit AC? I realize the whole point of an AC is to remove humidity from the air but since it would be pulling the humidity out of the *outside* air and pushing it into the gh, I wonder if it would be a good option since theoretically the air inside would still maintain decent humidity. thoughts? tyvm
     
  9. msaar

    msaar Member

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    How did you decide on the right size for a swamp cooler? Your greenhouse will have a volume of about 1500 cubic feet. A swamp cooler which provides a nominal 2800 cfm is available for about $400-$500. A pump for a wet pad system will cost $75-$100, an exhaust fan $150 or so, plus piping, guttering, powered shutters, etc. The volume of air from a swamp cooler or wet pad system will need to be about the same- 1500 cfm minimum. A/C is fine for the two or three feet in front of the unit. (The purpose of A/C is to cool air; dehumidification is a welcome byproduct of a properly designed A/C.)
     
  10. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    You do NOT want an air conditioner. Where did you look for pricing on the swamp cooler? You don't buy them from a greenhouse supply, they'll charge way too much. Try a home improvement center. You want a window mount (or a roof mount that can be converted). Also, places that have equipment for mobile homes is another good place to check. Do you have Sear's there?
     
  11. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    A swamp cooler can blow under a bench or down an aisle so you don't lose valuable growing area. One of the things I dislike about a wet wall is that it is hanging space lost. Assuming that you put it on a north wall so it doesn't have the sun beating down on it, that is prime space as anything hanging on a north wall blooms to the south where you can see the blooms. Another point here, don't put your mounted plants on wire attached to your south wall.
     
  12. mrbreeze

    mrbreeze Anglican Supporting Member

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    I do have a Sears! I googled swamp coolers and spent some time on Grainger's website. Apparently they have a store just a few miles from me. But yea, I was thinking I should definitely check out Lowes/Home Depot.

    Msaar, I'm going to need an exhaust fan and shutters regardless just for general ventilation so I wasn't figuring them into the overall cost of 'cooling'. I figure they'll do double duty on that plus a swamp cooler or wet wall. Greenhouse megastore has some pre-made wet wall infrastructure. I haven't really dug into them too much yet though. Here's a link: http://www.greenhousemegastore.com/...t-system-4-inch-x-12-inch/evaporative-cooling

    Marni, it will be oriented so that the long wall faces west. The long east wall will be pretty meaningless since the neighbors fence will be just a few feet away. The north and south walls will be the 8' ends. I'm imagining either a swamp cooler or wet wall being on the East wall or North wall. I envision most of the mounts and coolish/intermediate plants being on the north end. The house will sit under 60' oaks and my yard is surrounded by them on all sides plus three in the middle. So I'll have no shortage of shade. I think it should be fine for Angs, not so much Catts and Vandas. Good thing I don't grow them!
     
  13. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I have a Grainger's account and their swamp coolers are usually 25% higher than other local sources.

    I know that you are planning to use shelving you already have, but have you done a scale layout for the benches? At some point you may want to put in regular gh benches. With an 8 ft wide gh the standard layout (most bench space per square foot of gh) is 3 ft wide benches against either wall and a 2 foot aisle.

    Why would you need an exhaust fan unless you put in a wet wall?
     
  14. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I've just noticed we no longer have that emoticon for beating a dead horse.;)
     
  15. KellyW

    KellyW Orchid wonk Staff Member Supporting Member

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    My greenhouse is 8x16 as well. I have an evaporative cooler on one end and my door on the other end. My door is a storm door (from Home Depot) with a glass panel that will lower to create a screened opening. I manually open and close the storm door panel as needed, which means it is down all summer. My cooler came from Ace Hardware and I paid (if memory serves me well) $329 last fall when I had to replace it. My original one lasted 11 years. My cooler is connected to a thermostat so at least that portion is automated. I am not necessarily advocating it, but you can grow great plants and have a really nice greenhouse that is low tech and not spend a lot of money. I am admittedly jealous of all the great set-ups that I see and hear about but you can get by with much less.
    * Kelly steps down off soap box*
    Post pics of your progress, please. I would like to see how it turns out.
     
  16. mrbreeze

    mrbreeze Anglican Supporting Member

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    Have not done any kind of layout for benches. I have a fair number of potted plants but by far the majority are mounted. I figure I'll just wing it on the benches probably using concrete blocks and plastic coated metal closet shelves.

    I'll need the exhaust fan to get the hot air out! It gets bloody freaking hot here as you know. And when it isn't hot, it's still hot! Today is unseasonably cool at 88 degrees. With such a small house, I can't imagine things surviving long without almost constant evacuation of the hot air. And if I have to be gone for a few days or if the swamp cooler goes kaput, an exhaust fan would be my only hope. Do you see a scenario where I would *not* need one? I'm all ears...

    And i'm giving up on the wet wall idea officially. If I can just figure out the damn panels I'll really be making progress. I can find 10mm twin wall panels but haven't found (so far) the fittings (in aluminum) for that size. I'm tempted to try (again) to convince the contractor that some wood strips could be used to essentially clamp the panels to the house. I really don't want to use 6mm panels and I would really like to use three wall or even five wall but the cost and the fittings are problematic.
     
  17. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I've built 4 greenhouses and never had an exhaust fan. I've never been to your part of the world, so can't say anything with certainty. When it is hot here, it is dry. So if I am using an exhaust fan without a wet wall, I am pulling in hot dry air. Not exactly what I am hoping for.

    You can do several things to get hot air out. A passive system would be a vent down low on one end of the gh and another up high. The hot air rises, goes out through the upper vent and pulls in air from the other side that is the same temperature and humidity as outside. Mine upper vents are on parrafin solar arms and that works fine until things really start to heat up. That is when my swamp cooler comes on.

    You can have an exhaust fan on a thermostat that turns on when the temperature reaches a certain set point. If it is pulling through a wet wall with its pumps going it will be cooled and humidified as it goes through. If pumps aren't going (or no wet wall) same air as outside.

    You can have a swamp cooler that pulls air through wet pads and then blows that into the greenhouse. It is down low and the air pressure forces the air out of the roof vent (which opened earlier as things were just beginning to warm up). If you have an exhaust fan and a swamp cooler, you have two fans doing the same thing.

    The swamp cooler is just a squirrel cage fan in a box with 3 wet walls. When the fan is going, the water pump is also on. It is no more apt to go out than an exhaust fan. If you have a power outage a motorize vent won't be working, nor will the exhaust fan (and the shutters outside will be closed). With a solar vent, you're still in trouble, but it can pull in air through the not functioning swamp cooler.

    Perhaps others have different experience and can add to the conversation.
     
  18. msaar

    msaar Member

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    What Marni said.
     
  19. mrbreeze

    mrbreeze Anglican Supporting Member

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    Yea, everything you said makes sense. My impression is that the main reason would be just the degree of heat I'll be dealing with coupled with the small size of the gh. For instance, last year we had temps over 100 for something like 90 days including some days over 112. And overnight temps won't go below 80 for a month or two in the summer. (that's probably indicative of why there are no orchid nurseries in Oklahoma!). Maybe Robin will see this and chime in. He deals with temps that are nearly as bad as here and has two exhaust fans. Of course he *does* have a wet wall. So in the end, it is all very confusing. Where is that head banging on a wall emoticon when you need it!!??

    I think i'll end up going for a swamp cooler, two passive roof vents, two wall intake vents and an exhaust fan. I'll use misters to wet the floor which will be gravel over concrete or a combination of bare concrete and some gravel where the misters will be. Hopefully the evaporation from the floor plus the cooler will be enough. I guess in a pinch I could get two swamp coolers. Just today I found a local distributor for polygal panels which should be a big plus. Thanks to all for your help.
     
  20. John Klinger

    John Klinger Active Member Supporting Member

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    For flooring material, if you can get it, look real close at red volcanic cinder. It holds water , which really helps with the humidity.