The Passive Solar Greenhouse

(page 3)

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 done before.

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 (310) 392-7806

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