Greenhouse energy may be conserved
By Doris Henrique
Asst. Agricultural
Editor
University of Delaware
NEWARK, Del. - Com
mercial nurserymen and
homeowners with hobby
greenhouses are both faced
with a critical problem today
. the conservation of energy
in greenhouse operation. The
best way to do this is with
better insulation, says Dr.
David Mears, an
agricultural engineer at
Rutgers University who has
been working for several
'years on ways to solve the
problem. He has developed
some simple techniques
which can cut fuel con
sumption in the average
greenhouse by as much as
one half.
Mears talked about some
of these techniques recently,
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during the Delaware Nur
serymen’s Short Course in
Dover, Del This is an annual
event sponsored jointly by
the Delaware Cooperative
Extension Service and the
Delaware Association of
Nurserymen.
He told his audience there
that it’s irrelevant to talk
about how much longer fossil
fuel supplies are going to
last. “The fact is, these are
limited and running out.
Whether it’s a matter of five
years or fifty, we’d better get
crackin’ oh some answers.”
The engineer and his
colleagues at Rutgers have
been tackling the knotty
problem of energy con
servation in greenhouses
from two directions; im
proved insulation to cut heat
loss, and improved heat
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sources, including the use of
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By far the easiest way to
save energy in a greenhouse
is to find a way to cut heat
loss, be explains. Insulation
isn’t as glamorous a subject
as solar energy or nuclear
power plants or windmills,
but it’s far more practical.
This is largely because
greenhouses are notoriously
poor in design from this
standpoint.
In one of their first efforts
at improving insulation, the
Rutgers team came up with
a procedure which they say
can reduce fuel oil con
sumption by 33 per cent. The
idea is simple - you just take
two sheets of polyethylene,
seal them together, blow air
inside and use this “pillow"
to cover your greenhouse
frame. For every 100 units of
fuel oil you’d bum in a fairly
tight single covered house,
you’ll use only about 67 with
this treatment, states Mears.
This is because of the in
sulating effect of the dead air
space between the sheets of
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plastic. The idea is adap
table to many types of
greenhouse and is currently
being used by one com
mercial nursery operation in
central New Jersey on a
structure that covers six
acres.
Another insulation
treatment being studied is
the use of curtains which can
be raised at night inside the
greenhouse. The material
used doesn’t matter - clear
polyethylene, black
polyethylene, aluminized
mylar, fabric or something
else. What is important is the
dead air space that’s
created. When Mears and his
colleagues installed such
curtains inside a greenhouse
with the plastic pillow
treatment, they were able to
further reduce fuel con
sumption to half of what it
would have been in a con
ventional house.
Greenhouse Operators can
also economize on fuel by
improving the method of
heat distribution in their
buildings. The Rutgers team
Lancaster Farming. Saturday, March 12.1977-
is now working on an ex
perimental design where
heat is provided by warm
water under the floor of a
house insulated in the ways
described above. This water
can be heated either by
conventional fuel or by solar
means.
The idea is to spread a
vinyl swimming pool liner
over a three-quarter inch
cushion of slab styrofoam
and partially fill this liner
with crashed rock. This is
then capped wittua layer of
porous concrete to provide a
surface to walk on. Warm
(75-80 degrees F.) water is
then circulated through the
crushed rock. The result is
equivalent to having a large,
warm lake under the floor of
the house. The entire in
stallation costs about 80
cents a square foot, says
Mears, and it distributes
heat much more evenly than
systems where water pipes
are buried under regular
concrete.
In the prototype design
being developed at Rutgers,
the water for this heating
system is warmed most of
the time by a nearby solar
collector which stores heat
on sunny days. An oil burner
provides backup heat for
cloudy weather when not
enough solar heat is
collected. The collector used
is a simple one built of wood
and plastic for about $1 a
square foot. Though not as
efficient as more expensive
commercial types, the unit
provides adequate heat for
the needs of the greenhouse.
A further refinement of the
heating system is to in
troduce what might best be
referred to as a temporary
“warming wall” inside the
greenhouse. To do this, a
clothesline is strung across
an aisle. A piece of per
forated plastic tubing is
attached to this and a large
sheet of plastic is then
draped over the line so that it
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hangs down to the floor on
both sides. Warm water is
next pumped through the
perforated tubing. This runs
down inside the plastic sheet
and drains through the
porous concrete floor back
into the water stored there.
The effect is to warm the
air space around the plastic
“wall” to the same tem
perature as the water
flowing inside, without
saturating the atmosphere of
the house with humidity, as
would happen were the
warm water to be simply
sprayed into the air. When
the warmer is not needed,
the clothesline is simply
lowered to the floor.
Some of the devices being
developed by Mears and his
associates to reduce fuel
consumption may remind
the reader of the once
famous inventions of Rube
Goldberg. But the fact is,
these ideas really work.
Between September 1 and
January 3, using all the
above procedures and in
spite of extremely low
temperatures and a record
number of degree days, the
researchers succeeded in
heating their experimental
greenhouse with about one
fifth the fossil fuel they
would have had to use in a
conventional, single glazed
structure of the same size.
Lest commercial nur
serymen and home
greenhouse buffs think that
all these energy saving ideas
must wait for some future
application, along with the
solar energy, it is well to
remember Mear’s initial
point - that half of their
overall fuel savings resulted
from insulation im
provements alone. Solar
energy may someday
become the routine fuel in
greenhouse operations, but
for the present there’s a big
savings to be made just by
locking in the heat, no
matter what its source.
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