re: greenhouse passive heater SOLAR.KnowledgePublications.com

re: greenhouse passive heater
12 may 2004
33a6pa001@sneakemail.com wrote:
 
>i am building a small greenhouse (gh).

what are the dimensions of your gh?

>i want to include a passive heating system for those cold winter nights.

i guess you just want to keep the plants from freezing.

>my idea is to line the back wall of the gh (facing south) with 4 inch
>black abs pipe filled with water.  obviously, i want the tubes of water
>to collect heat during the day and release it at night to warm the
>greenhouse.  the back wall of the gh will be insulated from the north
>winds while the south wall will be windows -- the roof will be glazed
>with corrugated polycarbonate panels.  the location gets full sun in
>winter -- some shade in the summer -- which seems ideal.

roger williams used to have a 200' tomato gh like this in new brunswick.
his pipes were long and thin and black and horizontal. he says the plants
liked being watered with warmer water in wintertime. i put 200 55 gallon
water drums into one 100' pa gh. it never freezes.

>the other wrinkle in this is that i have a pond (approximately 8x10)
>which extends about two feet (2x10) into the greenhouse.  i've
>attached a site plan of the greenhouse/pond which i hope helps clarify
>my description.  (the drawing is not to scale.)

i don't see it. i don't think usenet does attachments.

>my questions:
>
>1.  does my passive solar heater make sense?  will it be worth the bother?

it sorta makes sense. it seems to me there are better ways. how about dark
plastic vertical 55 gallon drums?

>2.  if i stand the pipes on end filled with h2o and the ends capped,
>how much airspace should be left in the pipes for the h2o to expand --
>or will the h2o get hot enough to expand?

you might leave an inch.

>3.  given that i am located in jackson, ms and rarely get hard freezes
>and that even if we do get a hard freeze it  is usually accompanied by
>clear skies (ergo, a full day of full sun before the freeze), how much
>should i worry about the pipes freezing?

not much. nrel says january is the worst-case month for solar heating, when
830 btu/ft^2 of sun falls on the ground and 1070 falls on a south wall on
an average 44.1 f day. the average daily min is 32.7. the record low is 2 f. 
 
>4.  what effect will the pond have on the greenhouse -- or vice versa?
>the front wall of the gh will go across the length of the pond and
>extending below the water surface though not to the bottom of the
>pond.  the pond water will continually circulate through filters and
>the waterfall.

that alone might keep the gh from freezing. you might trickle some pond
water between two layers of glazing on a cold night to avoid freezing.
 
>5.  any other comments or recommendations would be welcome.

or fill the space between two layers of plastic film with air during
the day and soap bubble foam at night.

nick

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