Whether Indoor cultivation or greenhouse cultivation energy consumption is a major expense, and consideration. Each locale has its own challenges in the form of temperature, humidity, growing season, need for additional lights, the availability of electricity, natural gas, and latitude of operation. Geothermal power in its different forms can provide a solution to heating and even cooling, certain areas like Iceland and other hot spot can even use the super-heated water to provide electricity.
The earth has a temperature gradient from the extraordinarily hot core out to the cold vacuum of space. The insulation properties of magma, rock of different types, dissolved water, and atmosphere acts as a lid to keep that heat trapped. In the near underground the high thermal inertia (tendency to resist heat release or gain) tends towards the average yearly temperatures in a given region. In temperate regions, while it may be 2C outside, 2.5m deep the temp may be a warmer 15C until you reach about 25m when the temperature starts to stay at 22C and is resistant to any atmospheric temperature fluctuations. While in the same location summer temperature underground stays that 12-14C while the outside temperature may be as high as 35C. This temperature differential can be used to perform work and provide power in the form of heating and cooling.
We have a variety of high-tech and low tech means of exploiting the temperature differentials to achieve our ultimate aim of providing an ideal environment to our year-round cultivation spaces. We can even add extra devices to increase the productivity of the systems.
Heat Pumps- Heat pumps move energy by absorbing energy from a colder space to a warmer one, as this is opposite the normal heat flow rules, a small amount of energy must be used to accomplish this task. Heat pumps require a refrigerant (fluid/gas medium), and four main components a compressor, a condenser, and expansion valve, and an evaporator. Your refrigerator and air conditioners is a heat pump, but using the reverse setup can provide heating and ventilation as well. Heat pumps can use reversal valves to provide heat OR cooling depending on need. In general heat pumps for heating are 3-4 times more efficient than electrical resistance heaters. The source of the heat in heat pumps may be air or water. Water has a higher thermal inertia and can carry more heat per unit volume than air and may be more applicable in larger installations. The near constant water temperatures under the ground from 2.5m to 25m allow a great heat sink or source of heat depending on the application and season of operation. Additionally, one may use other means of heating the water used in heat pumps such as boilers, solar reflectors, or enclosed pipes cooling engines. If cool water is needed cooling towers or other means of chilling can be added to the system.
How it works: the refrigerant is compressed on one side of the exchanger to make it hotter, while the pressure is released on the other side to where the heat is absorbed (resulting in cooling). The hot and pressurized fluid is cooled in a heat exchanger (the condenser) to lower the pressure slightly and the temperature a great deal. This condensed liquid then passes through a device to greatly lower the pressure (the expansion valve) which then enters another heat-exchanger where it absorbs more heat and boils. This boiling gas is then recycled to the condenser where the cycle repeats. Work, cooling or heating can be provided depending on the setup of where each side of the devices are located (think of the hot air your air conditioner expels outside, that hot air is the heat absorbed from the rooms you want cooled!)
For large scale greenhouse structures, geothermal heat pump utilizes the near constant underground temperatures(10C-16C) and an underground pipe looped water system to provide cooling or heating depending on the time of the year. In combination with other sources of heating or cooling (heat pumps included!) this system in conjunction greatly expands the ability to heat or cool your facility efficiently. While these systems have a higher upfront cost the saving in energy usage can pay the initial investment off in a few to several years, while the lifetime of the facility can be 3-4 times the payoff period.
Due to the various efficiencies and set-ups, geothermal heat pumps can provide cost saving through lower electricity or natural gas usage, a stable environment that allows for your crops to mature with less issues, and the stability and long-lasting nature of the system due to the relative simplicity.
While our goals of cultivating Pharmaceutical-grade cannabis are the same there are many paths to get there, spending time and money with a competent engineer and professional HVAC companies to explore the set of systems that provide energy, cost savings, as well as an optimal environment is key. Before settling on a cookie-cutter system, please explore the length you expect to operate and all alternatives available to make your facility rise above the rest.
by Damon Lippert