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Greenhouse questions

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

  1. msaar

    msaar Member

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    Location:
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    Unless you just want to spend money duplicating systems, don't buy an exhoust fan and a swamp cooler. Get over the word "exhaust". Your goal is to remove hot air from the greenhouse and replace it with cooler air. You can do that in either of two ways: create negative pressure in the greenhouse causing cool air to enter through an outside opening, or create positive pressure by forcing cool air into the greenhouse, displacing the hot air and causing it to leave through an outside opening. Either way works. (Except for the nonstop wind, my weather is much the same as yours.)
     
  2. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    It sounds as if you are coming to some final decisions. But you may have to make some choices. If you have roof vents and exhaust fans, the fans are going to be sucking in air through the roof vents and that is not what you want. So usually it is a swamp cooler and roof vents OR exhaust fan and wet wall. Of course you put them all in as you mention and then turn off/disable what doesn't work for you. There are always things that need to be adjusted once you are up and running. I can assure you, though, it will be worth all of the hassel.

    My swamp coolers are the largest I could get that are set up to blow in through the wall. You just have to be careful to not listen to the salesman because they just don't understand this is not a room, it is a greenhouse and you need to move the air much more often. I always get the standard hardware store line "No, lady, you don't need the big one or the good one or the professional one..." That's when I ask for another sales person.

    When I built my bigger greenhouse (21 x 21 x 13' at the peak) I used the old one I had (5600 cmf) thinking that I would probably have to get a second one that would be on a separate thermostat to come on if it couldn't keep up. We don't often go over 100F, but we do and this one keeps the greenhouse in the low 80's.
     
  3. Magnus A

    Magnus A Ph.D.

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    I do not have a greenhouse but I have a though on your latest suggestion.

    You need to think of the operation of your combination of equipment. Do a material balance on the air movement!You know the swamp cooler capacity to push in air and that volume will always get out through the vents. The exhaust fan will only divert the airflow from the passive vent until it´s capacity gets larger than the swamp cooler and starts to suck in dry hot air through the passive vents.

    As I see it you have either a swamp cooler that push in air and cool it and hot air leave the greenhouse through the vents, OR you have exhaust fans that suck out air and cooled air enters through a wet wall and thereby cool it. A combination of the two only mess the operation up and you may end up with equipment that is costing money.

    I would go for a swamp cooler with passive vents at the roof and the base of the greenhouse. At a power failure the hot air in the greenhouse raise and leave through the roof and enter through the base vent. If powerfailure are common in your area I would think of inveting in a power reserve of some sort...
     
  4. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    No one has mentioned shading here and I thought I would bring it up. I am a big fan of aluminet shade cloth since it spreads the light and reflects heat. But for your climate I think it is going to be very important that you suspend the shade cloth rather than having lay on top of the panels. It will increase its effectiveness greatly.

    How are things coming along?
     
  5. mrbreeze

    mrbreeze Anglican Supporting Member

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    Not so good. I went to Lowes over the weekend and an old man laughed at me when I asked about swamp coolers. He claimed that our humidity is too high and that they don't sell them. I did find *one* at Home Depot that was not a window unit and was $500. Sears has quite a few on their website. I may be stuck with Grainger and they may not even #$%^&* work in this climate. I'm starting to think that the great goddess doesn't want me to have a gh.

    But...just to polish that turd....our usual summers are quite a bit hotter and drier than this one. So I kinda think that old man was full of it. My gf's parents house has a swamp cooler and while their house is totally uncomfortable, it does seem like it might be good for growing orchids! So in the end, I'll probably keep going with the plan. Need to make a new drawing with some design changes since the last one. And I need to hear from the contractor. :rolleyes:
     
  6. msaar

    msaar Member

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    Within the limited context of human habitation, the guy at Lowe's was correct. People aren't comfortable at 85 f with 60% RH. Orchids are.
     
  7. Magnus A

    Magnus A Ph.D.

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    Considered the comment you got at Lowes you need to basic research before you invest in a swamp cooler! You need to find out if it work at all ! and it is not good with guess work!
    What is your actually relative humidity outside in the summer when you need cooling? Get a humidity meter, nothing fancy but a simple one and measure the temperature and humidity. Then it should be possibly to find out the relative humidity at different temperatures with the same amount off water in the air.
    This make it possibly to predict if a swampcooler or wet wall can be used!
     
  8. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    MrB, you got the "Mister, you don't need that" routine. They frequently start mine with "Honey". It is a variation of the "you don't need the good one" I mentioned above. I don't know if that is part of the training course or they just like to sound like they know more than you do. Even though it might end up being more than you want to spend, it is going to be much less than the Malala plants you lost due to poor growing conditions.

    Sometimes the roof mount ones explain in the directions how to convert it to a window mount.

    Check here for your location: http://weatherspark.com/ It will have all the info you need about relative humidity.
     
  9. mrbreeze

    mrbreeze Anglican Supporting Member

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    I knew the guy was, shall we say...less than a reliable source. Our famous weatherman is fond of telling us at various times of year that our humidity is lower than desert conditions. As I type this he reveals that it is 45% at the moment with a 65 dewpoint. And as i've said before, this spring/summer is unusually moist and cool. I'm pretty confident in saying that for most 'normal' summers we are substantially below 40%. Anyway it's all moot because I know I have to cool it somehow and a swamp cooler seems like the only viable option.

    Side note: I just checked Marni's weather site and was pretty surprised at our 'average' numbers on everything. I guess when you factor in the usual 30 mph winds and roughly 40% humidity it just 'seems' more dry. And I'll add that over the years I've kept various orchids outside on the patio from about April to nearly November. They frequently experience temps above 100 with low-ish humidity, insane drying winds, and terrible water from the hose. And yet for the most part, they do ok. It really is a testement to how sturdy orchids are, in general.