What is the future of agriculture? There is a large network of people to feed and now some limit on resources such as water. How do we continue to grow and improve. I believe the future is automation. I know that would also be the sentiment of many others as well. We can see automation impact the rest of the world in front our eyes. It is the next frontier for agriculture.
I believe that paired with the indoor growing we will see the agricultural revolution. If you look at the desire for locally grown food and growing concerns about the preservatives used in our foods, you can see the shift in thought about agriculture and where food comes from. To get food fresh and close to the source the answer is to leverage Agri-tech and our ability to harness power. You can take what is a very complex logistical problem and turn it into a much more manageable one. Think if each major city had a large or several large greenhouses that could supply food for the whole city. And they did and could grow anything you could ever want? I believe this is possible! The limit is us only.
Today I want to discuss an important concept for greenhouse construction. It is that of R value. Some may of heard of this because it is a term that is used in housing for insulation. For those who have not heard of R value, it is defined as the capacity of insulating material to resist hit flow.(thanks Google :)). For those that enjoy the technical side of it like myself here is how R value is calculated. For those of you who don’t care about that stuff please skip the italicized part and I will jump back into why it matters for a greenhouse.
R Value Calculation
The R value calculation starts with the K-value which is measure of thermal conductivity of a material. According to insulation.org:Thermal conductivity, n: the time rate of steady state heat flow through a unit area of a homogeneous material induced by a unit temperature gradient in a direction perpendicular to that unit area. Essentially meaning that thermal conductivity is based on not only rate of thermal energy transfer but also unit of area and direction of the heat transfer. Again according to insulation.org the ATSM definition of k- value in units of measure is Btu-inch/hour per sq ft per degrees F. K values of course can be found on tables or simply looked up. So no need to do the calculations on your own.
If you have the K value getting the R Value is not difficult. It is simply the thickness of the material in inches divided by the k value. This again is a measure of how much insulation a material provides. The higher the value the more the material will resist heat transfer. R values are also in tables so not something that would need to be calculated.
Why is R value important?
In a greenhouse it is important to understand the R value of the materials you build with so you can ensure that the right temperature is maintained inside for proper plant growth. This also factors in what kind of heating you need to maintain said temperature level. There are obviously many ways to keep a greenhouse at the right temperature. Since we have been looking at Passive Solar Greenhouses we will continue down the path to do it in that way. The better the insulator you have the less you will need to spend on ways to heat your greenhouse. In some climates it might even prevent the need for a heating system!
A book a mentioned earlier gives a good idea of how to calculate Heat Loss = (1/Rvalue)x(surface area)x(difference in temperature between inside and outside)(The Year-Round Solar Greenhouse:How to Design and Build a Net Zero Energy Greenhouse). This is also not a linear relationship. The increase of R value gives a fairly exponential decrease of heat loss. So getting the right balance if insulating materials and transparent materials for light transmission. The thing to think about is your greenhouse layout. Focus on materials for light transmission on the south side since that is where your light will come in and more insulation on the north side. Adding glazing will reduce the light transmission but increase R value. The key for you is to find the mix between that will work for your greenhouse in the climate you are in.