Indoor Agriculture

 The importance of temperature control:

    The science and practice of producing high quality, high quantity plants and veggies indoors is better understood and precisely controlled more today, than ever in the past.  I’ve been reading quite a bit on controlled environment agriculture (CEA) or hydroponically-based agriculture.  Although it may seem unnatural to grow plants in a such a manipulated manner, there are irrefutable advantages to hydroponics.  


   In a CEA, food, flowers, and medicinal plants can be grown free of chemicals, pests, bacteria and fungi.  It creates work in the the agricultural industry all year, not regulated by outside temperatures, and can be located within communities and urban areas.  

    In hydroponics, air temperatures need to be between 72-76 degrees F.  Ideal temperatures for the nutrient water are 65-70 degrees F.  Anymore than 10 to 15 degrees F difference between day and night temperatures can stress plants and have adverse effects.  The recommended temperatures for root zone heating in greenhouses are 70-75 degrees F.  Accurately managing these temperatures can produce optimal crop, speed up biological processes, and play an important role in starting seeds and cutting roots. It can have the opposite effect, if temperature is not well controlled, causing rise in bacteria, pests, molds and affecting overall, plant health and yield.

   If temperature control is so important in indoor agriculture, then it brings up the question of energy consumption and cost.  According to Cornell University, studies suggest the non-solar, energy required to grow and transport fresh food at least 1000 miles, is equivalent to the energy required for local production in CEA facilities in cold, US climates.  Unless, its hydroponics in Antarctica or settlements in outer space, most hydroponics are raised in greenhouses that require heating and cooling.  

   For decades now, greenhouse hobbyists and professionals have been trying to harness the sun’s heat by storing it in various thermal mass and utilizing electric, mechanical, and advanced solar thermal equipment. Many argue that using solar energy systems is not economical because of collection and storage costs.  This is where phase change materials made from salt hydrates can largely reduce and minimize energy consumption and cost in the CEA and greenhouse industry.

   Phase change material or PCM made from salt hydrates are non-toxic and non-flammable, making it an ideal material to implement indoors.  PCM maintains specific temperatures for a specific period of time.  For example, PCM 22P holds temps between 70-73 degrees F and PCM 24P holds temps from 73-77 degrees F.   Most greenhouses and all CEAs have some sort of energy source to heat and cool their space.  PCM stores heat or cold and stabilizes temperatures for ideal growing conditions.  

    How does PCM work in a greenhouse heated by passive solar?  Just replace what thermal mass you currently have with PCM bottles/profiles of appropriate temperature.  The quantity of PCM required will be much less than water or rock and will stabilize indoor temperatures.

How does PCM work in a greenhouse heated by active solar?  Incorporate encapsulated PCM of appropriate temperature into the storage tank (or add another storage tank to an existing system) to utilize the heat of the sun collected during the day for use at night.   

How would PCM work in a greenhouse heated by electrical or mechanical equipment that is fueled otherwise?  Strategically place PCM of appropriate temperature in the greenhouse as thermal mass (as in the passive solar) and the heating equipment will operate much less than normally.  The PCM is storing and releasing heat, maintaining warm temperatures for much longer than without the PCM.  When the PCM solidifies, heating equipment will run again to recharge PCM.

     Cooling works in the same manner except the PCM changes phase from a solid to a liquid acting as a heat sink and provides temperature control for thermal storage systems.


Calculations for PCM temperatures and quantity depend on the type of plants, square footage of space, and average outdoor temperatures.http://www.rgees.com/technology.php