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Thread: Pricing Greenhouses

  1. #9
    Tony Paroubek's Avatar
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    At least your temperatures are pretty moderate ;> That helps!

    Yes it is possible to have heating and venting that is too excessive. The plants don't really like to have rapid changes in temperature.. or be blasted by alot of direct heat or cold. Gas heaters also have to get to operating temperature first so if it it way oversized it will have more waste in preheating the heater then shutting down quickly afterwards.

    There are various ways of doing it and lots of decisions based on how far away the structure is, how good your alarm system is, or your ability to get there whenever there is a problem, or budget etc etc etc...

    IGC has a great Faq area where you can find lots of other calculators and advice on various greenhouse systems http://www.igcusa.com/faq.html

    so, lets start with your venting/cooling. Your local humidity is fairly high already so swampcoolers will be only marginally effective and with air temperatures not too bad you are probably better off just going with simple exhaust fans with a fogging system for humidity control. To calculate how much air you need to move you need to calculate the volume inside the greenhouse in cubic feet. You then need to size your exhaust fan to remove that volume every few minutes. I use two exhaust fans of the same size and set one to come on about 5degrees sooner than the other. My fans are sized so that only one usually runs except on the hottest days. So one fan can totally exchange the air every few minutes while both combined will do it twice as fast. Too fast though and you get yourself a nice windtunnel that will suck your plants dry in no time!

    So during the Summer here as the greenhouse warms up. (note that my underbench fogging is set for temperature control not humidity)
    intake vents open
    Fogging goes on
    first exhaust fan goes on
    second exhaust fan goes on

    Heating is pretty straight forward. You could go with two smaller units that will basically run in conjunction or you could go with one main heater and a smaller one for backup emergency. I don't think I would go with two full sized.. heaters can get pricey and they take up alot of space too.

    If you size your heaters so that you can reach your desired high temperature on the coldest night that you might ever reach then you have built into your system plenty of extra margin and for most nights there will be more than enough reserve heating capacity. The heaters will also not run for excessively long periods or be so oversized as to waste alot of fuel as mentioned above. With a smaller structure I would me more inclined to go with a larger main unit and a small backup vs two that will run in conjunction to give you the capacity you need.

    Some other thoughts that kinda go along with heating systems, and greenhouses in general..
    Greenhouse air circulation to help distribute/mix greenhouse air so you don't have all the hot air sitting at one end.
    You may want seperate day and night temperature settings for your heating/cooling systems. Particularly if you plan to have more than one temperature zone.
    Use equipment designed for greenhouses. Items from the hardware store for household use won't last.
    Wet greenhouses and electrical equipment = potentially dangerous, make sure everything is ground faulted! I use all ground fault breakers. Simply grounded isn't enough.

    Hopefully I haven't scared you too horribly. It really isn't that bad if you plan it all out. But you can see how much planning it can take to put together a properly balanced greenhouse so that changing the size later can drastically alter your growing conditions/equipment needs.

    Final thoughts. Inflated poly (greenhouse grade) is cheapest but the insulation is not as good. Rigid double or triple wall Polycarbonate looks great has better insulation but is noticeably more expensive. Forget glass. You would need a solid concrete foundation to support the weight, and the insulation factor is worse than the inflated poly.

    Final final thoughts. Once it's up and running it will take some time to figure out what will grow best and where inside the greenhouse. Placement of heater, vents, air circulation fans etc will all affect various areas of the greenhouse. You will find some areas are naturally warmer and others cool, or some have brighter light than others and so on.

    Any questions just holler!
    Is that a Nepenthes in your pocket or you just happy to see me?

  2. #10
    Let's positive thinking! seedjar's Avatar
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    Not scared at all. This is all great information; thanks! How often does rigid polycarb need to be replaced? I was very disappointed with the durability of the flexible stuff. I was thinking glass would be nice because it lasts - heat loss was a concern, though. I'll definitely keep that and the weight in mind. This weekend I'll have a better idea of what I might be working with - I'm sure I'll have more questions by then.
    ~Joe

    PS - I saw a greenhouse heater that could run at different wattages with different resulting BTU outputs. I assume that at lower wattages, it would heat more slowly and to a lower operating temperature. Do you think that would be a decent control for temperature concerns? It also had a separate fan control, built-in thermostat and three-way switch (off, on, thermostat.) Seemed like a good deal for my purposes, and I haven't found many electrics yet that compared in terms of $s/BTU.
    o//~ Livin' like a bug ain't easy / My old clothes don't seem to fit me /
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  3. #11
    Tony Paroubek's Avatar
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    The rigid polycarbonate about 15 years, the 4year greenhouse poly you can stretch to 5 or 6 without problem usually. Amount of shade cloth and how many months out of the year will affect the durability of the plastic. The more full sun directly on the greenhouse covering the shorter the lifespan. The times I listed though are with full sun all day every day. They are quite durable to the UV.

    Inflated poly also has it's own set of challenges though with keeping it inflated hehe
    Is that a Nepenthes in your pocket or you just happy to see me?

  4. #12
    Let's positive thinking! seedjar's Avatar
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    I see... that's much better than I thought. What about your own setup? Did you buy a greenhouse kit or construct your own? I've seen a lot of people say it's much cheaper to build one from scratch, but I'm kind of thinking that a steel frame would be better than wood, and I'm no metalworker.
    ~Joe
    o//~ Livin' like a bug ain't easy / My old clothes don't seem to fit me /
    I got little tiny bug feet / I don't really know what bugs eat /
    Don't want no one steppin' on me / Now I'm sympathizin' with fleas /
    Livin' like a bug ain't easy / Livin' like a bug ain't easy... o//~

  5. #13
    Tony Paroubek's Avatar
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    My first greenhouse is just one of those cheap steel hoop houses with the inflated 2 layer poly covering. I bought that one from a friend many years ago. The new greenhouses are steel gutter connected type. Much bigger with alot more headroom and tall straight sides.

    I have seen some very nice homemade structures so if you are handy with carpentry you could probably put something together. They are not too complicated. Anchoring and structural support against the wind would be your main concern based on your weather. That and support for any hanging equipment. Pressure treated lumber will certainly last plenty long. I have seen some kits and setups made out of pvc pipe... Not a good material in my opinion.
    Is that a Nepenthes in your pocket or you just happy to see me?

  6. #14
    Tony Paroubek's Avatar
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    Oh and no I have not built my greenhouses totally.. they are kits. Like a giant erector set! But I have put together plenty of benches and endwalls and such from lumber
    Is that a Nepenthes in your pocket or you just happy to see me?

  7. #15
    Let's positive thinking! seedjar's Avatar
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    How do you think one of those steel kits would stand up to the wind I described? This property is up on a hill so I'm a tiny bit concerned. There is an old 1890's-era garage that's still standing on the same area, though, so it seems manageable.
    I am good with carpentry, but I've never done framing before - just building furniture. Depending on what kind of help from friends I'm able to get, building my own may be an option, but there are only so many favors I can call in so I've got my eye on kits for now.
    ~Joe
    o//~ Livin' like a bug ain't easy / My old clothes don't seem to fit me /
    I got little tiny bug feet / I don't really know what bugs eat /
    Don't want no one steppin' on me / Now I'm sympathizin' with fleas /
    Livin' like a bug ain't easy / Livin' like a bug ain't easy... o//~

  8. #16
    Tony Paroubek's Avatar
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    I don't think it would be a problem as long as the structure is properly anchored.
    Is that a Nepenthes in your pocket or you just happy to see me?

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