Small Scale Green House...
Part # 2 (Solar Chimney & HVAC)...
The
aluminum framed screen door was found out in the barn, though appears to be
brand new after washing off over 20 years of bird crap, feathers and hay.
The
door has been cut to size and still feels quite solid. It has the typical 2
sliding windows and a screen.
Given
I know "Shit" about solar chimney's and even less about basic
construction, you can imagine that the pause between the door pictured above and
the framing shown to the left was several days.
Ultimately
I opted for a simple 12" by 12" box that is 96" tall. The frame
has support frames located at either end and one in the middle.
The
lower 48" have support legs with a 16" overlap screwed through.
It
sounds flimsy but it's heavy as hell and was a bastard to position as
construction is now a solo effort.
The
center of the 8ft run is secured as well to the rafters, so don't think that
it's a "free-standing structure", as well the base will be secured to
the decking once I run the duct work.
The
images above are predictably the Up & Down views of the chimney once the top
was painted flat black, had a light backing applied to the northern exterior,
and was tightly wrapped in heavy clear vinyl... (still from the same quantity of
vinyl that was purchased to "skin" the green house.)
The
basic premise that I hope holds true is that the upper (clear/black) portion
heats the air, that would create a slight draft that will start extracting the
air out of the green house.
The
turbine was initially added as a weather cap, a) because I've had one
sitting in my shop for about 15 years (and was too lazy to install it) and b)
because I needed the shelf space.
The
turbine does appear to catch a lot of air and with even a slight breeze, will
spin-up and actively start drawing air out of the greenhouse.
You
may be as surprised as I was in the direction that things went over the few days
that the chimney was under development.
A few
days of above average temps (mid Apr 2006) between 5C at night & 20C during
the day with lots of sunshine. Since I had the DS1615 temperature data
collectors working, I thought I may as well place one under eaves inside the
green house and monitor a high location (6ft, 5 in) that was shaded.
The
green house was doing something, the day time temps fluctuated between 55F at
night up to 85F during the day (for no particular reason I have the DS1615 set
to the F scale, and can't be bothered to set it C), the trend peaked once the
solar chimney was completely enclosed as it reached a high of 110.3F and killed
3 trays of seedlings.
This
was when I realized how little I knew about greenhouses, and their purposes
(perhaps it's the subliminal brainwashing of the word "green" that
makes them a good idea), regardless I learned the absolute minimum to resolve my
current problem.
The
only additional information that I've added to my blank lexicon of greenhouse
lore is that "they provide a REGULATED environment that offers the OPTIMAL
combination of heat & humidity for an average of the biomass under
production"
Did I
say "Biomass" rather than "Plants"? and was the word
"Production" supposed to mean "Growing"? Yes, and yes...
Don't make the mistake of getting too attached to your biomass, as it may
influence your judgment when it comes to hard decisions that need to be made
regarding production.
Green
House HVAC System
After
looking quickly on the web for some way to regulate the green house I started to
stumble on the acronym HVAC (high voltage alternating current? No... Heating
Ventilation Air Conditioning).
I
also was finding lots of systems that ranged from $1,000 through to $40, 000
systems that were controlled by a computer (a Computer!!! all hail the
silicon god...) in all fairness much of the price was for industrial
grade hardware ie; pumps, compressors & monster blowers for huge
installations.
Certainly
I could cobble together some sort of passable HVAC system (and quick, if we keep
losing trays of seedlings the wife will just stop using the green house and this
becomes a real failure)
To
the left is as bare-bones a system that I could muster and still not leave the
farm to buy anything extra.
I cannibalized
the digital thermostat from out Oil furnace that hasn't been used in years, 2
fans scavenged from "Computers", a recovered UPS battery
and bits of wire.
Once
I proved to myself that I could actually turn 2 fans on & off independently
via the thermostat, I started to go into super scavenger mode and started hauling
out parts and hardware that has been just itching to be used.
This
is the finished unit...
The
enclosure is light steel with a hinge and a spacious interior.
The basic
idea is that the thermostat can be programmed either as a "Heating"
source, where the fan(s) can be turned on to draw air from the machine shop
below a specified temperature, or as a "Cooling" source, where the
fan(s) are blowing hot air up the chimney, and/or drawing hot air out of the
machine shop and on up out the chimney.
To
the left is the assembled kit ready of installation, the solar panel was one a
chum dropped out as the positive wire had broken free from the panel.
As an
aside, I've started to adopt the use of Computer power-supply connectors for any
inter-connect points that require +5V, and/or +12V lines, the female connectors
are scavenged from dead Hard disks, floppy's or CD-Rom drives.
The
schematic below hopefully clarifies the images above...
Given
the simple arithmetic that would typically be used to size components
appropriately, resulting in a stable system ie; solar panel keeps battery
charged relative to the load being demanded on sunny days, bear in mind that I'm
simply using as many parts as possible from what is on hand.
If I
have to start charging the battery more than 2 or 3 times per season, I'll
either get a bigger panel or go with smaller fans (if possible)... For all I
know at this point I may need to go with larger fans and an even larger
battery.
The
image to the right is the air hardware that will connect the green house and the
machine shop.
All
material was recovered from a scrap yard for free, or donated by MacDonald
Construction (a strong supporter of theworkshop.ca) except 2 dryer vents that
offered 8 ft of flex ducting, and a light plastic one-way air baffle all for
$9.00 each.
Given
that the day time temps have plummeted back down to +10C with evening lows close
to -5C in the evening, I'd better start installing this stuff...