An Affordable Window Greenhouse
The capstone project for Queen’s University 4th Year Mechanical Engineering Class,"Engineering for Sustainable Development", is to design and construct an Appropriate Technology with a quantifiable engineering result (to see other class projects, click here). I have chosen to construct a greenhouse, review the heat requirement on the system for the whole year; then, based on the materials and conditions selected, review costs associated with this and build a scaled model.
This project is the first step to easy community greenhouse development - the goal of the affordable greenhouse is to:
- Improve greenhose design and awareness for residential application.
- Demonstrate the feasibility (i.e costs) of a greenhouse in the winter months and determine the best time to install such a system for optimal crop yield.
Due to the materials selected and the cold Canadian Spring, it is not effective to construct until late April. But with better material selection and innovative greenhouse designs, I am hopeful that constructing miniature greenhouses will become common practice.
The blueprints for the construction of an affordable greenhouse are below; for this greenhouse a single pane Polyinyl chloride (PVC) covered greenhouse was reviewed. Heat losses and calculations were done in MatLab using constants from the Canadian Climate Normals website and sunlight radiation from Queen's University Living Building.
Measure Window Parameters
Measure the perimeter of the window.
I used measuring tape and a piece of paper to record the area of the window in relation to the window sill.
You could use a piece of string and mark size on string, cut piece and label so it can be identified later.
Determine Greenhouse Size
Draw out the greenhouse and label dimensions. Keep in mind, the relation to your window area or surface area you are building around. Minimize the height, as it just increases the surface area of heat loss.
- My total height = half of the total window pane height.
- Total length = width of 1 window.
- Total depth = 2 pots deep.
Build the greenhouse to size of window or surface area you need - including out in the open if you prefer!
Assemble the frame
Cut the structural pieces (the wood) to match the dimensions specified. Use hammer and nails to fasten them together. I found a stability brace bar to be helpful. The stability brace bar helped during installation after the structure was built because it gave extra stability to the greenhouse frame.
You don't have to use wood to build the frame. You could use PVC or anything else that's handy. You just need to build a structure that plastic will fit tight around.
Gather a team of people as the film step is a delicate art. Place double sided tape around the frame, outward facing so it will stick to the plastic film. Next unroll the plastic sheeting and pull it taught, then put it on the frame where the tape should hold it tight.
You could use a different type of plastic film, and you could screw on, maybe glue or staple the plastic to the frame.
Attach Remaining Film
Greenhouse with film attached.
Structural drawing of greenhouse frame with film attached on all external sides.
Repeat the previous step for all external sides of the greenhouse frame. Be delicate.
Install the Greenhouse
This is the structural brace I used to hoist the greenhouse into place.
View of the greenhouse about to be attached and window crack filler (sealant) sprayed on.
Install the brace bar as seen above in Step 3 and use it to hoist the platform into place. The brace bar is a convenient place to tie a rope or fasten another material for green house transportation (to and from construction site).
The rope made this straight forward. Push it up if you don't have a rope.
Fill Window Cracks
Make sure to fill any gaps between the house and the newly designed greenhouse structure. If major holes remain, a draft will be felt and obviously greatly decrease heat retention (so the greenhouse is colder!). Use spray foam filler to fill the gaps.
The first few days I did not have this done properly and the greenhouse was not retaining the heat.
Let the foam dry overnight. It is not healthy for you or the plants to be breathing the fumes. Mud, styrofoam, caulk, putty, or most materials that can be packed tightly will work as sealants!
Blow-dry the film tight
This type of PVC is designed so that as it is heated it will tighten and become taught to the greenhouse so it doesn't flap in the wind and wear out.
You could use metal pots filled with hot coals fr radiant heat, could use steam from camp fire.
Apply Duct Tape
Use duct tape on any last cracks. Be sure to fill all visible cracks, especially when it is colder outside, or else greenhouse will be rendered virtually useless. The 'roof' blew off as it wasn't secured enough by the first duct taping - so double the duct tape.
If you don't have duct tape, use any tape that you have. If there's no tape around, ensure that the top surface can be connected with twine or nails. Ours was half way up a window, so we needed to tape it to the glass.
Add Pots and Soil
Put in pots and soil. Make sure the soil layer is deep enough to allow the plants to grow - ROT 1 foot every 5 months the plant will be in there.
If the greenhouse is built right out of a window sill at ground level (like from a basement window), it could just cover plants already in ground.
When installing a greenhouse, it is important to consider your region - the shading, the climate,the location, etc.
|Shading Consideration||Climate Considerations||Location Considerations|
|pick a sunny greenhouse location - if you are in the northern hemisphere this likely means a south facing spot||There needs to be good weather, approximately 10 C and above for a lengthy period of time (~4 month minimum)||For appropriate technology use, place in a window location or sectioned off cube|
|careful to pick a sunny location - with no overhangs, that will decrease heat transfer and plant growth, especially in the start of the season||before you embark on your greenhouse adventure, ensure your selected spot has substantial light - not always overcast||'Know your area' - check the minimum required temperature for your plants|
|dangers: housemates, footballs, squirels and anything that can could 'accidentally' damage your 'Affordable Greenhouse'||for a low cost greenhouse such as the one proposed, you'll see that at minimum 10 C is require for optimal conditions.||place in an open area, like a courtyard, wide open front yarc or window sill - some place where you see it everyday helps (trust me, I wake up to mine)
Acknowledgments, Credits, and Bibliography