building a greenhouse

Discussion in 'Gardening and Agriculture' started by telegramsam, Oct 13, 2008.

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  1. telegramsam

    telegramsam Member

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    If I get some sheets of clear plastic is this good enough for a greenhouse or do I need actual green sheets of plastic? Also can the greenhouse help keep the plants warm in the texas winter to where I can grow past the end of the season or would I eventually have to bring them in?
     
  2. notorious

    notorious Member

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    you may put a pot of boiling water in there before it gets completely freezing cold if it starts freezing over outside
     

  3. JeepHammer

    JeepHammer Well-Known Member

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    Exactly.

    There is something called 'Thermal Mass'.
    A concrete or brick wall or tank of water, anything with high density that absorbs heat readily in the daytime, and releases it at night.

    In the early days of man up until the early 20th century, rocks were often laid in the fire box of fireplaces or outdoor fires and heated up,
    Then were taken in and placed under skirted or what we call a 'Dust Ruffle' on the beds.

    Beds were usually nothing more than wooden frames with slats across them, or ropes to suspend the user, there weren't very many mattresses, and the ones that were out there were much thinner than we use today...

    The rocks heated up throughout the day by the sun, or by cooking or working fires would release their heat most of the night,
    The insulated skirt on the sides of the bed would keep the heat released from being dissipated by drafts, and it would migrate up and help keep the user warm for several hours.
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    Early homes used 'Passive Solar' by building porches in the east, south and west sides of the home.
    In the summer, the sun goes much higher in the sky, so the porces shaded the front of the home, making it cooler.

    However,
    The porch roof length was sized to allow fall, winter and spring sun strike the front of the home, helping to warm it earlier in the morning, and later in the evening.

    Southern homes traditionally had long porches on the south, and often slightly shorter on the west, and shorter yet on the east side to take the chill out of the home in the morning...

    Northern homes in cold weather climates had much shorter porches, to allow more sun on the home more of the year, since the climate is colder, you would want to scavenge as much solar heat as you could.

    Older homes in cold climates will often have NO porch roof on the East side, and a much shorter porch roof on the south and west.

    You will also find in desert areas where homes are subject to extreme heat in the daytime, and down to freezing temperatures at night, they build from Stone, brick, block, Adobe (mud brick) ect with very thick walls facing East, west, south.

    The idea of the extra thick, extra dense material was to buffer the temprature swings through out the day.

    Thick, dense walls were thermal mass at work.
    As the sun shone on them in the day time, they felt cool inside.
    As the outside temprature dropped like crazy outside at night, the warm wall gave up it's heat to the occupants all night!

    You will see this to a lesser extent in cold climate homes with brick or stone on two sides, south and west... (and some times the entire house).

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    'Thermal Mass' that isn't being powered in any way is called 'Passive Thermal', meaning you don't have to act on it an any way (except for maybe a coat of flat black or flat dark brown paint).

    If you just allow them to heat up in the sun in the day time, and discharge that heat at night, then make your 'Thermal Mass' face the sun, and paint it flat black if you can.
    (some people don't want such a dark color in their work space, so dark, flat red brick color is a viable choice too)
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    If you intend on growing in the winter,

    Consider making 'Solar Heater' collectors and piping hot water to your Thermal Mass heater to help it warm up in the day time.

    Since in a green house you can't allow the daytime temprature to get too high or it will effect the plants,
    You may need to vent the excess heat that builds up in the building/room that would normally help raise the temprature in the 'Thermal Mass' of your choice...

    Enter some 'Solar Thermal Heaters',
    And they are nothing more than boxes with tubing running inside of them,
    And they are painted black inside, so they get warm when the sun is out.

    The Tubing contains 'Water'
    (It's actually an 'Anti-Freeze' mixture if you live where it gets below freezing)
    Is circulated through your plant beds in the day time, and heats up the soil which will spend all night shedding the heat to the room.

    If you have plants that are root temprature sensitive,
    Run the tubing through a 'Thermal Mass',
    That concrete or brick wall or water tank we discussed.

    If you add a small solar panel PV panel (PV=Photo Voltaic, it makes electricity and small ones are very inexpensive) And small pump wired together,

    The system is self sustaining...
    Sun comes up, warms up the water in the tubes outside.
    The sun also makes electric current in the solar PV panel that turns the pump 'On'.

    The warm water is circulated through out your green house, and heats up the 'Thermal Mass' where coils of tubing are embedded in the thermal mass.

    The colder thermal mass absorbs the heat from the coils indoors, the liquid inside is cooled as it gives up it's heat to the thermal mass,

    Then the cooled liquid is returned to the outside heaters for re-heating by the solar powered pump...

    When the sun goes down, the pump shuts off, but that's good since you box collectors aren't getting warm anymore anyway...

    Once the pump shuts off, the heat in your indoor thermal mass can't expell it's eat out to the outdoor boxes, and it sheds 100% of it's stored heat to the room...
    SLOWLY, Over Night...

    In the morning, the thermal mass is cold, the room stayed warm, and the solar collector and solar PV panel heats the thermal mass up again for the next night!

    It's all free heat and energy, it's self timing (on & off), and it's virtually maintinance free since the 'Anti-freeze' is in a close circuit in tubing, there is no evaporation losses.
    It simply continues to work from sun up to sun down until you turn the pump off in the late spring or early summer.
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    If you use nothing more than a tank of water, you can use an old car radiator or two (plumbed in series) in the water tank to heat it up!
    Radiators work good for about anything but drinking water!
    The long, thin kind from early '70's cars seem to work best around here...

    Look into simple solar water heating, and you will learn just how easy it is to heat water with the sun!
     
    Last edited: Oct 13, 2008