Thermo shutters: Perhaps the easiest method
available to maintain winter, night-time heat in the greenhouse
is the use of thermo shutters (night insulation). Thermo shutters
are merely insulation devices that are placed over the glass at
night, and removed during the day. Their benefit is because the
glazing necessary to generate adequate heat during the day also
allows the escape of that same heat at night. Thermo shutters prevent
the escape of much of that heat. Installing and removing them each
day lends credence to the dictum, "passive solar requires active
people", but it is an activity for active people which is well
worth the effort. However, most growers are unwilling to utilise
Thermo shutters. Fortunately, a properly designed, passive solar
greenhouse will perform satisfactorily without them.
E. Thermal mass: Thermal mass is any material
that in mass, acts like a storage heater. Thermal mass stores the
heat from the day and releases the stored heat back during the night.
Typical examples of high thermal mass materials are concrete, rock,
brick, iron, soil and water. Large barrels filled with water are
an excellent source of greenhouse thermal mass. The soil in the
containers which hold the palms is a good form of thermal mass.
A large cold frame with many large pots of soil will absorb more
heat during the night than one with only a few. That's why a cold
frame works better as the number of palms in containers in it increases.
In order to be most effective, the pots should be black, and hit
by direct sunlight. Accordingly, it is best to put the largest,
potted palms in the front, southerly facing row so that they receive
unimpeded, direct sunlight.
F. Venting: A passive solar greenhouse must
be vented. The most practical vent openers are those operated by
a wax cylinder. They require no electricity and cost about $50.00.
The correct location for an exhaust vent is at the highest point
of the greenhouse. Otherwise you will have a pocket of hot air.
At the floor level you need intake vents. This enables the entry
of fresh air containing carbon dioxide to permeate the greenhouse
and perpetuate the growing cycle. Intake vents should be the same
square footage as exhaust vents. This promotes convection.
G. Air circulation: Air circulation is beneficial.
If you follow the above formula, your greenhouse will heat up quickly
and on a normal day, voluminous amounts of excess, hot air will
be exhausted through your ceiling vent via natural convection. The
greater the convection, the greater the air circulation.
Summary: Regardless of your climate, you
can have an effective, passive solar greenhouse, heated by the generosity
of the sun. And it will bring you unbelievable success in terms
of quickly growing palms to the optimum, plantable, substantially
rootbound, five gallon size. Something that you probably, have never
For a brochure on: "The Diamond Lane
Guide to Passive Solar Greenhouses" Write to Don Tollefson,
599 California Avenue, Venice, California, USA. 90291. Phone +1