CEA Basics: Sustainability

Energy is needed to power greenhouse equipment used for heating and cooling, lighting, irrigation, and other support systems and buildings. Net zero grid energy use can be achieved by reducing greenhouse energy consumption and demand, and offsetting the remaining energy use with on-site renewable energy production. 

Efficiency
Energy use can represent a large operating cost if the greenhouse is not designed for energy efficiency.   Energy use  is impacted by greenhouse location, orientation, and covering materials, all of which impact the need for climate control systems.  Energy use can be minimized by selecting right-sized equipment with high efficiency ratings, commissioning the systems once installed, optimizing equipment operation based on actual need, and conducting regular maintenance on equipment.  For existing greenhouses, an energy audit can be conducted by a qualified engineer or energy specialist to identify opportunities for saving energy and increasing efficiency.   ​

Renewable Energy Production
Once energy efficiency is maximized, the next step to achieving net-zero energy grid use is on-site renewable energy production. Renewable energy can be an alternative source of electricity or fuel combustion for producing heat energy, generating electricity, or operating vehicles. Solar panels (photovoltaics) and wind turbines are the most common systems used for generating electricity. Solar energy is especially useful for powering cooling equipment, as peak cooling typically occurs simultaneously with peak solar radiation.  Wind turbines are most effective in areas where winds speeds and directions are consistent and reliable.  Alternative biofuels derived from plants can be produced on-site or delivered.  Ethanol and biodiesel are the most common sources of biofuel, and have a wide range of applications.  Methane can also be used, and is most readily available from manure and landfills. ​

Water is required for irrigating plants, evaporative cooling, and other operational processes.  Several strategies can be employed to both decrease the need for water and alleviate the environmental burden on water supplies.

Efficiency
Water is required to irrigate plants and provide evaporative cooling, when used.  Water use can be minimized by growing tomatoes hydroponically, which can reduce irrigation water use by more than 50% relative to field tomato production.  Even greater reductions in irrigation water use can be achieved with recirculating irrigation systems. Evaporative cooling can utilize large quantities of water, which can be mitigated by not over-ventilating the greenhouse and by employing control strategies that do not add excessive water.  Drought-resistant tomato varietals, which require lower water supplies, can also be selected, if they meet market expectations.  Regular maintenance of the irrigation and evaporative cooling system will ensure that water is not wasted due to leaks or plugs in the system. 

Water Collection
Traditionally, irrigated agriculture acquires water from a nearby lake or river, from a canal that delivers water long distances from faraway water sources, or directly from wells on site,   Water can also be acquired from a nearby utility, when available. To reduce the burden on these water supplies and the relative environmental impact, alternative sources of water can be used, including rainwater harvesting and recirculating systems, such as condensate capture, and waste water reuse and treatment.  Rainwater harvesting is most often used as a supplementary supply of water, and water availability is highly dependent on climate and annual rainwater volumes.  Systems that are designed to reuse water vapor (condensate), irrigation drainage, or other "waste" water can be effective, but their complexity requires a skilled engineer to design.

Humans and food crops rely on each other for evolutionary success. We humans consume what plants produce and/or discard, including fruits, vegetables, and oxygen.  In turn, plants rely on animal species for nutrients, carbon dioxide, and species propagation.  Together, we form a synergistic relationship, interdependent on the success of the other.  Controlled environment agriculture provides us the opportunity to facilitate that relationship through co-integrated systems: those designed for human shelter and those designed for food production.  In many cases, the "waste" stream from one environment is exactly what the other environment needs, and visa versa.  By integrating urban agriculture projects into building operations, greater environmental sustainability and crop yields can be achieved.  Building-Integrated Greenhouse systems can reduce resource demands of both the greenhouse and building; limit waste production and discharge through capture and re-use; help produce healthy conditions for humans and plants; and create a unique experience for occupants.