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Finding the balance to improve crop performance maintaining high energy efficiency levels

Annually, indoor and greenhouse growers produce significantly more lbs/ft3 of canopy compared to open field. It is a fact that we have learned how to improve crop productivity over the years and we are still expecting an exponential increase in this area. Now the most important challenge is to find the most energy efficient way to keep increasing crop productivity.

It is clear that growers will start to incorporate new management techniques, products, and technologies that allow them to increase profitability in projects in a more efficient way. In addition, nowadays growers experience a huge pressure to improve the use of energy and natural resources to produce food.

Product selection and system management 
When speaking about energy efficiency there are a lot of approaches we can take. However, we need to recognize two key aspects that have a great impact on energy efficiency. System management and the selected components.

The capability of our systems to create a more energy-efficient production will depend a lot on our system management for different environmental variables. In addition, the capability to have more control over system management will also depend on our product selection. The grower's last decision will be crucial to reach better results when working on the design of a system and selecting the components used to operate the facility. 

Consistency is the first step towards energy-efficient projects 
In order to optimize system management we first need to understand our system and crop requirements. Secondly, we need to find a balance point where environmental variables and, as consequence, production can maintain consistency. Once we know the spot where we need to be, it’s time to explore how to maximize energy efficiency when creating those conditions. By understanding each of the most common environmental variables, their interaction, and the components in our system used to control the environmental variables, we can improve energy efficiency.

Let’s focus on the questions to approach when working in increasing efficiency by working with the most common environmental variables

Light is directly related to crop performance and yield. Efficiency is all about high yields and lower resources consumed.

  • Is natural light enough to maximize productivity? Is supplemental lighting necessary?
  • If artificial lighting is used: Are my lamps efficient (1.81 μmol/J or higher)? Is my light spectrum maximizing development for my specific crop? Can I improve harvest index with a specific spectrum?  
  • Are my lights impacting the expenses of management to control other environmental variables (e.g. temperature, humidity, VPD) in my system? Can I select a better lamp?
  • Which is the most efficient way to deliver light? Which is my priority: Create a photoperiod or to reach a specific DLI? Can I reduce output at specific periods without affecting my goals?

Air flow
Airflow can have an impact on plant gas exchanges including CO2 intake for photosynthesis and transpiration. Bad airflow can affect our yield by reducing crop performance or even causing nutrient deficiencies.

  • Do I have a good design that allows good air circulation? Bad design can increase the demand of ventilation in the system.
  • Do I have enough fans? Is the fan capacity enough to move the volume of air required?
  • Is my air velocity uniform? Can I do something to improve uniformity? 

Humidity can increase expenses in growing system management, promote diseases and increase irrigation when it’s not under good management.

  • Is humidity uniform in my system? Can I improve uniformity?
  • Is there a specific area promoting more or less relative humidity? (e.g. light, leaks, wet walls, fogger systems, fans etc.)  
  • Can I make any changes to improve uniformity and consistency in relative humidity around my growing system?

When speaking about the temperature in growing systems, we can work with air temperature, rootzone temperature and leaf temperature. All of them will have a strong impact on our plant metabolism affecting product quality and even harvest time. Temperature can also have an effect on humidity, transpiration rate and VPD. Therefore, it’s one of the most important variables to control when looking to improve consistency in our growing system.

  • Was the design of my system done with the purpose of maximizing the energy balance to reach the desired temperature? Glazing material, shade cloths, insulation of indoor facilities, volume and more aspects can be crucial to reduce cost of cooling and heating systems. Are there any changes that can be done to reduce electric costs for heating and cooling?
  • Can I reduce natural radiation in the greenhouse without affecting daily requirements of light in my crop to reduce overheating and demand of a cooling system?
  • Is my system oversized? Could it be more efficient to heat roots instead of air?
  • Can I spot any component negatively impacting temperature consistency in my system? (Light, fans, fogging systems, etc.)
  • Do I know about the variety of products available to reduce overheating in greenhouses?

VPD is the amount of vapor that can still be stored in the air until the saturation point is reached, under the same temperature. This variable is measured in kPa and is a result of interaction between relative humidity and temperature. It can provide information about crop transpiration and risk for fungal development. In order to maintain consistency in growing systems, the track of VPD can be a really useful tool. 

  • Do I need a VPD calculator? Check Dr. Greenhouse webpage using the following link
  • Do I know VPD requirements for my crop? This number will be crop / stage of development specific but a common range is 0.8 – 1.2 kPa.
  • Can I improve humidity or temperature management to keep the consistency in VPD levels?

All plants need water and nutrients to improve performance. However, plants can show an increased demand of water when environmental variables in our systems are not well managed. Excess of transpiration can increase irrigation demand. Some variables related to transpiration are temperature, relative humidity, rootzone humidity, air flow and VPD. Some components in the greenhouse affecting transpiration can be lamps, fans, shade clothes, exhaust fans, fogging systems etc.

  • Are my lamps affecting transpiration significantly? HPS requires additional ventilation equipment to maintain a proper grow room temperature. The reduced leaf temperature under LED fixtures would decrease transpiration by 17% compared to HPS fixtures (Nelson and Bugbee, 2015).
  • Is the use of exhaust fans efficient enough to keep relative humidity balanced without increasing transpiration rate?
  • Can I reduce natural radiation in the greenhouse without affecting daily requirements of light in my crop to reduce transpiration?

Another important aspect that should not be ignored when managing growing systems is maintenance! All the equipment used must keep working in their best condition to avoid situations that can increase energy consumption in the system. It is recommended to keep your team trained well enough to be able to recognize any maintenance issues on time. 

Remember, resource use efficiency is equal to yield divided by the resources consumed. Every project can work to reduce resources. It’s all about a good design, good selection of components, good management and maintenance. 

For more information:
Hort Americas

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