Rob’s Modified Walipini

 In Built Environment, Design, Featured, Greenhouse

When a friend of mine told me that they wanted to build a walipini, my first reaction was, of course, “what the heck is a walipini?”. The answer was simple: a walipini is an underground passive solar style greenhouse. It’s an innovative and potentially inexpensive way to grow food in our cold northern climate. When I checked out the pinterest photo though,  I noticed some major flaws in the design that would minimize it’s potential and efficiency. So I went about writing this micro-blog, to demonstrate how I would go about optimizing this innovative growing system.

 

What Works With The Original Design:

  1. The walipini is underground so it benefits from the low energy geothermal heat that we get at about 6 ft (or 2 meters) below ground.  The earth down there is about 6 degrees C so it will help keep the space warm.
  2. Because it is built underground, if the walls are buttressed properly, you can avoid the most of the cost of building materials. Really the only cost for this greenhouse is the truss system on top, the glazing material and the excavation.
  3. Because it is underground you avoid the high energy loss associated with cold winds.

 

Suggested  Design Improvements:

  1.  The underground nature of the walipini means that cold air will collect in the bottom of the structure. Unfortunately this is where the majority of your produce is growing. In the blog, the walipini is glazed with poly which has almost no insulative value. Therefore, as the glazing looses heat from the growing space, cold air will migrate down to the ground and create a frost pocket around your vegetables. To resolve this, I would raise my garden beds up and dig below the paths to create a cold sink. Basically wherever your pathways are, dig them deeper and then build a board walk over them. The cold air will then sink to these lowest points, instead of around the plants. (And since the space below the board walk is valuable, why not use it for something useful, like cold storage?)
  2. I would build my walipini into a south facing slope and use a shed style roof instead of a gable style roof as depicted in the photo. Shed roof’s are easy to build, cheap, and take advantage of the southern aspect of the sun. These roofs are also easier to glaze (you can cover them in polycarbonate), and if the right slope is chosen the snow will shed on its own. In addition, the shed style roof has less corners. The more corners we have in a structure, the more heat loss and infiltration we have to deal with. The glazing surface is where the majority of heat loss is going to occur. Finally, with a shed style roof, it’s much easier to deploy an insulative blanket at night than with a gable roof. This is important as using an insulating blanket at night can reduce your heat loss by up to 75%! For your insulation cover. you can just use an insulated construction tarp. They are cheap and have eyelets which make them easy to install on high tensile wire.
  3. Rescue rigid insulation from construction sites and use it to create a shallow insulation skirting all the way around the perimeter of the greenhouse. Even though it’s underground, heat is still going to migrate out of the space until the pit is in equilibrium with the soil around it. This insulative barrier will prevent frost from migrating into the space.
  4. I would build a rocket mass heater with a giant thermal storage bank within the space. These heaters are not perfect, but they are inexpensive and will burn whatever you give them. They store heat in their thermal mass, allowing them to burn only once every 12 – 24 hours, depending on how well your space is insulated, how cold it is outside and how big of a mass you are using.
  5. On the entrance, I would borrow a design strategy from indigenous building traditions: Make the entrance go much further down into the ground than the growing surface inside the greenhouse. In essence you have to go down and then climb back up again. Cold air sinks and this depression in the ground will be your airlock. It will prevent all the warm air inside from leaving the building.
  6. Keep the greenhouse longer on the east – west axis and shorter on the north – south access to maximize solar gain.
  7. Use a polycarbonate panel if you can afford it. They last a lot longer and they are more efficient. If you can’t afford it, use to layers of poly, one on the outside and one on the inside. Then take a bathroom fan and inflate the glazing wall for maximum insulation.
  8. On the low end of the shed-style roof, install an eaves trough to harvest the rain water. Store the rainwater inside the structure for additional thermal mass, and on the north wall of the space to capture maximum solar gain.

Overall I think this design is pretty awesome. If you take these recommendations, send me some photos – I would love to see what you build!

Helpful Links:

A free PDF with additional instructions – http://www.the-meal.net/graph/manuel_walipina_benson.pdf

Different Designs To Consider:

http://zombiehunters.org/forum/viewtopic.php?f=39&t=108526

http://www.inspirationgreen.com/pit-greenhouses.html

 

Resources on Rocket Mass Heaters:

https://www.youtube.com/watch?v=BoW-ICO83hM

https://www.youtube.com/watch?v=Sqznv5GDSWc

 

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Showing 43 comments
  • umq

    Hi,
    I am masters student and I am currently researching on walipini and I need to know how much would building a walipini cost? I need the bill of materials besides the total cost. Any size is acceptable. Do you think you can provide me such details?
    I appreciate any help you can provide me on this matter.

    Thank You,
    Umer.M.Qureshi

    • rob avis
      rob avis

      I have not built one so I am not sure. However I do not think it is as cheap as they say it is if you build it safe.

      Regards,

      R

  • es9836

    Hello,

    I am looking for a specialist in underground greenhouses to speak to my class about the subject. I have been randomly googling and have stumbled across this site. Rob would you be interested in doing something like this via video chat? You seem very knowledgable! We are doing a class project of making some mini versions of the underground greenhouses for our school. Please let me know as soon as you can!

    Thank you!

  • Brian Huntley

    Hello, I would like to know the answer to Joaquin’s question as well! I am in Nova Scotia and I am planning to build a Walipini this summer. Not sure if it will work, but I would like to combine an Aquaponics system as well. I am looking into different heating options as well. If I build this Walipini near our manure shed, I am wondering about circulating the heat from the manure into the Walipini for cheap heat. Any thoughts on this from anyone?

    Thanks

  • Kathy

    Rob – the link for the walipini.pdf took me to a totally different website – which totally confused me!! ??? Help please?? I sent an email as well so responding either way is appreciated.
    Thanks
    Kathy

  • Joaquin

    Hi there. I am very interested in your post, because I am planing to build a Walipini this days. I have read the manual of the Walipini of La Paz, Bolivia, which is very complete, and with your ideas mixed, would be perfect. But I have only one problem, the inclination od the roof. It will be build in Serbia, but the manual speaks of the souther hemisphere, and the formula is your latitude plus 23 degrees. I dont know if this applies for the north hemisphere. What do you think about this?
    Thanks, and looking forward for your answer.

  • Jay

    If interested in adding suplementary light you can consider hydro generators made of old washing machines check out google lots of info. Having a woodstove with fan system will help in northern geographic.
    Aswell building your retaining walls out of tires similar to earthship concepts will give you much more thermal mass. Having a thermal break on exterior of retaining walls underground and speration from outside ground temperatures will help with heat retention .As for the groud water situation a sump pump is a verry inexpensive soloution. Looking into trying this out myself.

    • rob avis
      Rob Avis

      Thanks Jay,

      Here are a couple of things to think about.

      1) Sump pumps fail and it is energy expensive to pump water.
      2) Earthship tire walls do not add any additional thermal mass as they are filled with the same parent materials. They may change the albedo which will change how much they absorb, not store.
      3) A wood stove is a good option as long as you have diurnal thermal insualtion for the glazing surface. Making these spaces work here is all about reducing night time thermal heat loss.

      Thanks for your comments.

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