In the 13th century, greenhouses were built in Italy to house the exotic plants that explorers brought back from the tropics. They were originally called giardini botanici (botanical gardens).
‘Active’ greenhouses, in which it is possible for the temperature to be increased or decreased manually, appeared much later. Sanga yorok written in the year 1450 AD in Korea, contained descriptions of a greenhouse, which was designed to regulate the temperature and humidity requirements of plants and crops. One of the earliest records of the Annals of the Joseon Dynasty in 1438 confirms growing mandarin trees in a Korean traditional greenhouse during the winter and installing a heating system of Ondol.
The concept of greenhouses also appeared in Netherlands and then England in the 17th century, along with the plants. Some of these early attempts required enormous amounts of work to close up at night or to winterize. There were serious problems with providing adequate and balanced heat in these early greenhouses. Today, the Netherlands has many of the largest greenhouses in the world, some of them so vast that they are able to produce millions of vegetables every year.
The French botanist Charles Lucien Bonaparte is often credited with building the first practical modern greenhouse in Leiden, Holland during the 1800s to grow medicinal tropical plants. Originally only on the estates of the rich, the growth of the science of botany caused greenhouses to spread to the universities. The French called their first greenhouses orangeries, since they were used to protect orange trees from freezing. As pineapples became popular, pineries, or pineapple pits, were built.
Experimentation with the design of greenhouses continued during the 17th century in Europe, as technology produced better glass and construction techniques improved. The greenhouse at the Palace of Versailles was an example of their size and elaborateness; it was more than 500 feet (150 m) long, 42 feet (13 m) wide, and 45 feet (14 m) high.
The golden era of the greenhouse was in England during the Victorian era, where the largest glasshouses yet conceived were constructed, as the wealthy upper class and aspiring botanists competed to build the most elaborate buildings. A good example of this trend is the pioneering Kew Gardens. Joseph Paxton, who had experimented with glass and iron in the creation of large greenhouses as the head gardener at Chatsworth, in Derbyshire, working for the Duke of Devonshire, designed and built The Crystal Palace in London, (although the latter was constructed for both horticultural and non-horticultural exhibition).
Other large greenhouses built in the 19th century, included the New York Crystal Palace, Munich’s Glaspalast and the Royal Greenhouses of Laeken (1874–1895) for King Leopold II of Belgium.
In Japan, the first greenhouse was built in 1880 by Samuel Cocking, a British merchant who exported herbs.
In the 20th century, the geodesic dome was added to the many types of greenhouses. Notable examples are the Eden Project, in Cornwall, The Rodale Institute in Pennsylvania, the Climatron at the Missouri Botanical Garden in St. Louis, Missouri, and Toyota Motor Manufacturing Kentucky.
Greenhouse structures adapted in the 1960s when wider sheets of polyethylene film became widely available. Hoop houses were made by several companies and were also frequently made by the growers themselves. Constructed of aluminum extrusions, special galvanized steel tubing, or even just lengths of steel or PVC water pipe, construction costs were greatly reduced. This resulted in many more greenhouses being constructed on smaller farms and garden centers. Polyethylene film durability increased greatly when more effective UV-inhibitors were developed and added in the 1970s; these extended the usable life of the film from one or two years up to 3 and eventually 4 or more years.
Gutter-connected greenhouses became more prevalent in the 1980s and 1990s. These greenhouses have two or more bays connected by a common wall, or row of support posts. Heating inputs were reduced as the ratio of floor area to roof area was increased substantially. Gutter-connected greenhouses are now commonly used both in production and in situations where plants are grown and sold to the public as well. Gutter-connected greenhouses are commonly covered with structured polycarbonate materials, or a double layer of polyethylene film with air blown between to provide increased heating efficiency.
Greenhouses are usually glazed structures, but are typically expensive to construct and heat throughout the winter. A much more affordable and effective alternative to glass greenhouses is the walipini (an Aymara Indian word for a “place of warmth”), also known as an underground or pit greenhouse. First developed over 20 years ago for the cold mountainous regions of South America, this method allows growers to maintain a productive garden year-round, even in the coldest of climates.
Here’s a video tour of a walipini that even incorporates a bit of interior space for goats:
It’s a pretty intriguing set-up that combines the principles of passive solar heating with earth-sheltered building. But how to make one?From American sustainable agriculture non-profit Benson Institute comes this enlightening manual on how a walipini works, and how to build it:
The Walipini utilizes nature’s resources to provide a warm, stable, well-lit environment for year-round vegetable production. Locating the growing area 6’- 8’ underground and capturing and storing daytime solar radiation are the most important principles in building a successful Walipini.
The Walipini, in simplest terms, is a rectangular hole in the ground 6 ‛ to 8’ deep covered by plastic sheeting. The longest area of the rectangle faces the winter sun — to the north in the Southern Hemisphere and to the south in the Northern Hemisphere. A thick wall of rammed earth at the back of the building and a much lower wall at the front provide the needed angle for the plastic sheet roof. This roof seals the hole, provides an insulating airspace between the two layers of plastic (a sheet on the top and another on the bottom of the roof/poles) and allows the sun’s rays to penetrate creating a warm, stable environment for plant growth.
This earth-sheltered greenhouse taps into the thermal mass of the earth, so that much less energy is needed to heat up the walipini’s interior than an aboveground greenhouse. Of course, there are precautions to take in waterproofing, drainage and ventilating the walipini, while aligning it properly to the sun — which the manual covers in detail.
Best of all, according to the Benson Institute, their 20-foot by 74-foot walipnifield model out in La Paz cost around $250 to $300 only, thanks to the use of free labour provided by owners and neighbours, and the use of cheaper materials like plastic ultraviolet (UV) protective sheeting and PVC piping.
to take my mind off my life at the moment, so on the net I play
The Crown Land Use Policy Atlas
The Crown Land Use Policy Atlas (the Atlas) is the source of area-specific land use policy for Crown lands in a large part of central and northern Ontario. The area covered by the Atlas (area in yellow on inset map) includes more than 39 million hectares of Crown land and waters or about 45 per cent of the province. In time, the Atlas will be expanded to include southern Ontario and the community based land use plans in the Far North.
The Atlas contains land use policies consolidated from a variety of planning documents such as District Land Use Guidelines (1983 as revised); local land use area plans; Ontario’s Living Legacy Land Use Strategy (1999) and the Guide to Crown Land Use Planning (2011).
The Atlas has three components:
If you’re a hiker, camper, bird-watcher, angler or hunter, Ontario’s natural resources provide a wealth of opportunities for activities of all kinds.
- The Map Browser – allows users to view the boundaries of Crown land use areas
- The Policy Report Search Tool – allows users to search for and retrieve information on individual land use areas
- The Land Use Amendment Search Tool – allows users to search for and retrieve information on individual land use amendments.
Because of the limitations of mapping data, the Atlas cannot be used to precisely identify on-the-ground locations of features such as privately-owned land, roads or other locations. Some Crown land use designations may appear to overlap onto private and federal land. These designations do not apply to such lands.
Radiant barriers are installed in homes — usually in attics — primarily to reduce summer heat gain and reduce cooling costs. The barriers consist of a highly reflective material that reflects radiant heat rather than absorbing it. They don’t, however, reduce heat conduction like thermal insulation materials.
HOW THEY WORK
Heat travels from a warm area to a cool area by a combination of conduction, convection, and radiation. Heat flows by conduction from a hotter location within a material or assembly to a colder location, like the way a spoon placed in a hot cup of coffee conducts heat through its handle to your hand. Heat transfer by convection occurs when a liquid or gas — air, for example — is heated, becomes less dense, and rises. As the liquid or gas cools, it becomes denser and falls. Radiant heat travels in a straight line away from any surface and heats anything solid that absorbs its energy.
Most common insulation materials work by slowing conductive heat flow and — to a lesser extent — convective heat flow. Radiant barriers and reflective insulation systems work by reducing radiant heat gain. To be effective, the reflective surface must face an air space. Dust accumulation on the reflective surface will reduce its reflective capability. The radiant barrier should be installed in a manner to minimize dust accumulation on the reflective surface.
When the sun heats a roof, it’s primarily the sun’s radiant energy that makes the roof hot. Much of this heat travels by conduction through the roofing materials to the attic side of the roof. The hot roof material then radiates its gained heat energy onto the cooler attic surfaces, including the air ducts and the attic floor. A radiant barrier reduces the radiant heat transfer from the underside of the roof to the other surfaces in the attic.
A radiant barrier works best when it is perpendicular to the radiant energy striking it. Also, the greater the temperature difference between the sides of the radiant barrier material, the greater the benefits a radiant barrier can offer.
Radiant barriers are more effective in hot climates than in cool climates, especially when cooling air ducts are located in the attic. Some studies show that radiant barriers can reduce cooling costs 5% to 10% when used in a warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system. In cool climates, however, it’s usually more cost-effective to install more thermal insulation than to add a radiant barrier.
TYPES OF RADIANT BARRIERS
Radiant barriers consist of a highly reflective material, usually aluminum foil, which is applied to one or both sides of a number of substrate materials such as kraft paper, plastic films, cardboard, oriented strand board, and air infiltration barrier material. Some products are fiber-reinforced to increase durability and ease of handling.
A radiant barrier’s effectiveness depends on proper installation, so it’s best to use a certified installer. If you choose to do the installation yourself, carefully study and follow the manufacturer’s instructions and safety precautions and check your local building and fire codes. The reflective insulation trade association also offers installation tips.
It’s easier to incorporate radiant barriers into a new home, but you can also install them in an existing home, especially if it has an open attic. In a new house, an installer typically drapes a rolled-foil radiant barrier foil-face down between the roof rafters to minimize dust accumulation on the reflective faces (double-faced radiant barriers are available). This is generally done just before the roof sheathing goes on, but can be done afterwards from inside the attic by stapling the material to the bottom of the rafters.
When installing a foil-type barrier, it’s important to allow the material to “droop” between the attachment points to make at least a 1.0 inch (2.5 cm) air space between it and the bottom of the roof. Foil-faced plywood or oriented strand board sheathing is also available.
Note that reflective foil will conduct electricity, so workers and homeowners must avoid making contact with bare electrical wiring. If installed on top of attic floor insulation, the foil will be susceptible to dust accumulation and may trap moisture in fiber insulation, so it is strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation.