By Andy Patterson, Tutor, ADL- Academy for Distance Learning
A Walipini is a type of passive solar greenhouse underground. It is an Aymara Indian word for a "place of warmth." First developed over 20 years ago for the cold mountainous regions of South America, this method can allow growers to maintain a productive garden year-round, even in the coldest of climates. Image in the public Domain.
Controlling temperature in a conventional glass greenhouse can be a real problem, and opening ventilation hatches at the top of a greenhouse might not be enough to prevent heat damage to plants in hot weather. It is very easy to ‘overcook’ things. And whilst the growing season is extended, greenhouses tend to be limited in winter as they lose heat to the surroundings quickly. As a solution to this, some permaculturalists house animals such as chickens adjacent to a solar hothouse to act as a thermal buffer, manure source, and a carbon dioxide generator.
The Walipini works on the same principles as a greenhouse, but it is more like a cold frame embedded and sheltered in the earth. In its simplest terms, is a rectangular hole in the ground 6 ‛ to 8’ deep covered by plastic sheeting. Sometimes they are called Sun Pits, which indicates quite accurately the notion of a hole in the ground, with a transparent top, that soaks up Sun in order to stay warm.
Walipinis make use of the fact the ground is thermally stable below the frost line. An underground greenhouse (of any type) is a much more energy-efficient greenhouse, that stays warmer and can grow more and longer- providing year-round source of food without having to heat and cool. It can be -23oC at the surface, yet a metre below this level underground is a toasty +10 oC to +15oC.
Source: Ceres Greenhouse Solutions[4]
The angle of the roof should depend on latitude. The light entry to the system is at its most efficient when light strikes the glass at an angle of 90 degrees. This is preferable at the winter solstice when the light is weakest. Use of plastic is preferable to glass to facilitate this. . At the summer solstice this angle will have the opposite effect and maximize reflection and minimize penetration. This angle can be varied, but will change the basic design of maximizing heat during a winter solstice and minimizing it during the summer solstice.
There are several factors to consider in Walipini design which will determine how well it will work; (i) location, aspect, slope and latitude; (ii) Drainage and ventilation (for example, sunken walkways will conveniently act as cold air pits; (iii) Soil type and structural integrity of the build; (iv) Water table and water seepage can be problematic unless designed out; (v) Thermal mass and heat retaining walls/ sandbags; (vi) Control of pests such as burrowing mammals.
Using nature to design simple sustainable but efficient food cultivation systems is becoming a necessity for many. More can be found out by studying with ADL on a variety of horticulture, permaculture and agriculture courses.
References
[1] What's a Walipini? Seasons Unity Project Online. Author Unknown, 2015. http://bit.ly/2bA798L
[2] Build a $300 underground greenhouse for year-round gardening (Video). Treehugger Online. Kimberley Mok, Feb 2013. http://bit.ly/2bE5ScC
[3] Walipini Style Greenhouses. Resiliant Life Online. Brandon Garrett, Mar 2014. http://bit.ly/2cptBmm
[4] The Walipini Low-Down. Ceres Greenhouse Solutions. Author unknown. Sept 2014
http://bit.ly/2cpsYJy
