re: solar panels/turbines/electric radiant heaters SOLAR.KnowledgePublications.com

re: solar panels/turbines/electric radiant heaters
20 mar 1999
dave_martens@my-dejanews.com wrote:

>i have a commercial poultry operation and are looking for economical ways
>to heat my farm, if possible, i would like use renewable energy sources...

how about a greenhouse? 

they'll bulldoze my front lawn sunday morning, two greenhouse kits
will be delivered on monday, and my farmer friend and i hope to have
them assembled and filled with 500 tomato plants already started
in other houses by april 15.

standard labor to put up a 30 x 96' greenhouse in a field from scratch
is 3 people, 1 day (if they know what they are doing :-) putting the
single 28 x 100' pieces of plastic film on these 14' wide x 9' tall
x 96' long houses should take 2 people an hour or so, on a calm day. 

the house nearer the road will be covered with bayer's new clear
10-year dureflex urethane film (tres elegant, non?), and the one
behind it will have a $120 piece of standard 4-year cloudy greenhouse
polyethylene film with uv inhibitors.

assembling these houses is fairly simple, like a large erector set,
more like a tent than a building...

pound the 50" "ground sleeve" pipes into the ground on 4' centers, making
the tops all the same level, then slip the single-piece bent hoop pipes
into them, and attach the ridge pipe purlin with clamps. then add 1x4 hip
purlin boards to the hoops with u-clamps to secure the plastic film at
the top of the roll up sides, about 4' above the ground, and bolt a 1x8
perimeter skirtboard to the ground sleeves (we aren't sure we need this,
but we'll probably do it anyway.)

the endwalls will be plastic film over 2x4 framing on 4x8' centers,
with 1 or 2 plastic-film-covered 4x8' doors. 

(we'll put up the houses running ew with a 14' space between them, and
at some point we may add another arch between them to make them into a
single 42' x 96' 4,032 ft^2 gutter-connected greenhouse with 3 arches
and a little more post bracing under the gutters, like, 2x4s u-clamped 
to the vertical part of those pipes to prevent buckling, and maybe a
soaker hose in each seamless gutter for snow melting, with the plastic
films lapped over the center arch.) 

the next step is to stretch the large piece of plastic film over
the frame squarely and secure it to the hip boards with deck screws
and another 1x4 batten board, then lay the bottom edge of the film
out flat on the ground about a foot on each side of the house, slide
together each 100' thinwall swedged pipe roller, attach a t-handle
with a right angle clamp at one end, and duct tape (the universal
solution :-) the plastic to the roller pipe every 2'.

the roller pipe ends up hanging from the film as it's rolled up, so
as i understand this, it only needs a handle at one end. the high tunnel
ap note from ag prof otho wells at u new hampshire says one person can
roll up an entire 96' side from one end in about 20 seconds (about
10 turns on the crank.)

it might be fun to mechanize this with thermostatic control. we might
slowly rotate another ridge purlin with a gearmotor, with some strings
attached to that axle that loop under both side rollers from the inside
of the house, with the other ends of the strings joining in a loop over
the outside of the house between the bows, which would also serve to
reduce wind flutter and plastic film fatigue. 

bubblewalls are another option for shading and insulation.

the hoops are 21' lengths of standard schedule 40 3/4" galvanized
water pipe, (1.05" od) bent into a gothic arch shape (3 bends, like
the outline of a typical house) by 2 people using a large outdoor
plywood table with some simple 2x4 guides nailed to it as a jig.

the manufacturer mike schwarz (302) 656-0276 is a low-overhead
wholesale pipe vendor in wilmington de who got into the greenhouse
business when he realized that he was selling a lot of his pipe
with cosmetic defects to large local growers who were bending it
into greenhouses.

he doesn't know much about the greenhouse business yet, and doesn't
realize that he's in the solar heating business, and hasn't applied
for any million solar roof grants yet, so his prices are quite low,
at 42 cents per square foot of "solar collector," or about 0.4 cents
per peak watt, about a hundred times less than photovoltaic power. 

happy spring!

nick