Designing Your Own Passive Solar Greenhouse, Part 1
Recently, I took part in a webinar with Curtis Stone and Small Farm Academy on designing passive solar greenhouses and growing crops for profit. In this series of articles, I want to summarize what we explored in that webinar and tell you how you can design your own greenhouse that can extend the planting season, enhance growing conditions, and provide a cheery space for those dark winter days. Let’s get started!
Step 1: Set Your Goals
The best way to set your goals so they will translate into actionable design is to ask yourself the following main question: What climate are you trying to mimic?
If you know the USDA zone you would like to garden in (I’m using USDA because most gardeners are familiar with the classification system), you already have a concrete guideline for your design – Simply create a space that brings that zone to you. The great thing with USDA zones are that they are based on extreme minimum winter temperatures, which as a mechanical engineer, tells me everything I need to know about things like insulation requirements, heating costs, glazing types, and so forth. For those of you who are not mechanical engineers, here’s a handy design tool that you can use to calculate the right R-values to create your desired USDA growing zone:
Other features you may wish to include in your passive solar greenhouse might include the following:
- Canning Kitchen
- Root Cellar
- Rainwater Storage Area
- Sunbathing Deck for Seasonal Affective Disorder (SAD)
- Hammock, Hot Tub, Sauna (Gotta dream big, right?)
Step 2: Select Your Site
This is obviously a key step, if not THE key step. A passive solar greenhouse is essentially a collector for solar radiation and photosynthetic energy. The optimal orientation in our part of the world is going to be around 15 degrees east of South. This maximizes morning sun and heat when the greenhouse is coldest. That said, if you have limited options, you can also go to up to 45 degrees off South and still achieve good results.
Select a location that gives you good sun access year-round. I highly recommend getting a solar pathfinder; it’s a fantastic tool you can use to calculate the amount of solar resources of a site. Here’s a video I made to show off how to use it:
If you want a digital version, you can find good apps for both Android and iOS. (I like Sunseeker myself)
Another tip: Make sure that your site is clear of excess shading from buildings or trees (which in the case of the latter can vary seasonally) You want as much sun as you can get!
Step 3: Figure Out Your Aspect Ratio
The aspect ratio determines your greenhouse’s general footprint. Your goal here is to maximize solar gain while minimizing heat loss; this usually means long and narrow buildings. Obviously this will depend on your site, so this element can be a bit flexible. Here are some aspect ratios that work well:
Step 4: Determine the Shape or Cross-Section
This is an extension of Step 3, but the shape or cross-section goes a bit further and determines how the greenhouse will look in three-dimensional space. Many shapes are possible, so here are some of the questions you want to ask yourself when design the right space for you:
- How high are the crops you want to grow?
- Where do you want the upper and lower vent walls?
- Are there any clearance issues on your site?
- Will the functions and features of your greenhouse require certain shapes?
- Do you have any ergonomic and accessibility requirements to ensure optimal usage?
Got your aspect ratio and your cross-section nailed down? Congratulations, you’ve basically designed your greenhouse’s shell! In the next articles of this series, we’ll go over the next key steps to designing your very own passive solar greenhouse: Foundation, Kneewall, Ventilation, and Glazing. Stay tuned!
Interested in learning more? Click the banner below to get more information on our Advanced Passive Solar Greenhouse Design 5-Week Intensive: