Greenhouses and high tunnels
give vegetable farmers a jump on the growing season in
the spring and protect against cold temperatures in
the fall. In northern climates, extending the season
significantly for warm-season crops comes at a cost:
some kind of a heating system. The vast majority of
such systems burn fossil fuels like heating oil or
propane. However, in recent years, more and more
farmers have been experimenting with renewable fuels
such as wood, wood chips, used vegetable oil or shell
corn.
The
Intervale Community Farm uses this corn furnace to
heat its
greenhouse. When you switch to a new heating
system that uses biomass
fuel, it's a good idea to keep your old fossil fuel
system in
place until you work out the kinks.
Photos
by Vern Grubinger.
In Vermont, Massachusetts
and elsewhere, cooperative extension has obtained and
provided some cost share funds for growers to help
them try out renewable energy heating systems. The
ultimate goal is to help growers save money on heating
costs while at the same time reducing reliance on
fossil fuels. In response, some growers have installed
shell corn furnaces, in part because there are nearby
farms that produce that fuel at a reasonable cost.
However, as is often the case with new technologies,
there can be a pretty steep learning curve associated
with switching heating systems.
"For the first couple months
we thought this was a huge lemon," said Andy Jones,
farm manager at the Intervale Community Farm (ICF) in
Burlington, Vt. The ICF grows 25 acres of mixed
vegetables for their 525-member CSA. They start
transplants for many of their vegetable crops in a
30-by-100-foot double-poly greenhouse, firing up the
furnace in mid-March. Until a couple of years ago, the
greenhouse was heated with propane. Then, as part of
the University of Vermont Extension biomass furnace
project for greenhouses, they installed an LDJ
A-Maize-Ing Heat furnace. The unit is rated at up to
165,000 Btu per hour and comes with a 14-bushel hopper
from which corn is augured into the combustion
chamber.
"Our first year we had a lot
of challenges getting the unit set up so it was
burning right. We had the chimney installed according
to spec in the owner's manual, but it didn't end up
working well in a greenhouse environment, so there was
a lot of tinkering to make the system run properly. By
the next year it was working great, and now we
couldn't be more excited to have it," Jones explained.
"Fuel quality is just as important with biomass
heating systems as it is with conventional furnaces.
To operate properly, corn furnaces require fuel that
has been cleaned and dried down to the proper moisture
level for optimum combustion."
"The lessons we learned that first year were: buy
good-quality fuel with low 'fines' content; route a
straight chimney inside the greenhouse using double-wall
stovepipe and outside the greenhouse use triple-wall
chimney pipe; and finally, be sure to set the greenhouse
ventilation louvers to open prior to the exhaust fan
switching on in order to prevent back drafting of flue
gasses into the greenhouse," he said.
"By using the corn furnace
we are now reducing our propane use by 80 percent or
so. We used to heat the greenhouse with a couple
propane unit heaters. We've kept one in place since
the corn furnace doesn't like to idle in pilot mode,
which any furnace has to do when the sun is out a lot
and the days are relatively warm. So late in the
heating season we shut off the corn furnace and burn
propane when it's needed," Jones said. "Still, the 80
percent reduction in propane use is significant,
especially when you look at the cost of propane versus
the cost of other fuels. Shell corn is about half the
cost of propane on a Btu basis, so we end up shaving
40 percent off our fuel cost, and that's pretty
attractive."
If you are considering a
change in fuels for heating your greenhouses, be sure
to compare the true costs, which should account not
only for the Btu content per dollar of fuel, but also
for the typical combustion efficiency of different
fuels. In the case of corn or wood fuels, you also
have to account for burning off the portion that is
water. Penn State University has an easy-to-use
calculator online (http://energy.cas.psu.edu/EnergySelector.html)
that can help you make true cost comparisons.
Penn State also has a lot of
useful information about using shell corn as a fuel,
located at http://energy.cas.psu.edu/shellcorn.html.
Topics include: shopping for a corn stove (or
furnace), locating a corn supplier, quality and
storage considerations, and disposing of the corn ash.
Apparently corn ash has some modest value as a
fertilizer and as a liming agent, with no evidence of
heavy metals or any other contaminants.
According to the Penn State
site: "Burning shelled corn as a fuel can be a
feasible way of dealing with the high prices of more
conventional fuels such as fuel oil, propane, natural
gas, coal and firewood. Using corn as a fuel does not
compete with the food supply needed for nourishment
throughout the world. While it is recognized that
malnutrition is a serious global problem, the world is
not experiencing a food production problem. Instead,
the world faces political challenges associated with
providing infrastructure systems for food distribution
and storage."
Jones is heating his
greenhouse with shell corn specifically grown and
processed to be used as fuel. That means it is
thoroughly cleaned and dried down to the appropriate
moisture content, which is about 12 or 13 percent.
It's supplied by Vermont Golden Harvest Biofuels, a
family farm in adjacent Addison County. Other farmers
participating in the biomass furnace project with the
same type of furnace have successfully used wood
pellets instead of shell corn or a mix of the two
fuels. Both fuels must be stored properly to prevent
them from absorbing moisture, and shell corn must also
be sealed well to protect against hungry rodents and
birds. In addition, materials handling is more of an
issue with biomass fuels than fuels that are pumped
into your tank. For example, it takes 15 pounds of
shell corn to provide the same amount of heat as one
gallon of propane, so more storage space is needed.
"The biomass unit here at
the Intervale Community Farm cost around $6,000
installed" said Jones. "That's three times what a
similar propane unit would cost. It's a lot more
money, but consider that fossil fuel prices have about
doubled in the last few years, so the payback is a lot
faster than it would have been in the past."
In addition to reducing your
fuel costs, working with a local supply of biomass
fuel can provide some measure of security about future
fuel costs and availability. Your farm could also gain
a "green" marketing benefit if your customers are
excited about the effort to use less fossil fuel. For
farmers like Jones, these things all come together in
a package that has multiple benefits, despite some
extra hassles compared to simply setting the
thermostat and letting the gas company fill the tanks.
The author is vegetable and berry specialist
with University of Vermont Extension based at the
Brattleboro office.
This article is reprinted with the permission of the
publisher.