CO2 monitoring is all but necessary for indoor farmers and greenhouse cultivators looking to optimize yield, time to harvest, and energy consumption, however carbon dioxide concentration is difficult to measure in practice. Most CO2 detection techniques are difficult to optimize for battery life, and sensor equipment often uses fans and non-waterproof enclosures to let air into the sensing elements. Further, calibration procedures must be followed for accurate CO2 sensing. For these reasons and others, most CO2 sensors require wired installation, limiting their use in a greenhouse or indoor farm.

GrowFlux’s CO2 Microclimate Sensor was born out of the frustrations of many growers and farmers who have tried and failed to use CO2 sensors originally designed for applications outside of agriculture. GrowFlux’s CO2 Microclimate Sensor brings several new features we developed based on our experience working with indoor growers, including cloud connectivity and cloud based datalogging, a splash resistant enclosure that lets gases into the detector while maintaining a 5 minute response time, and wire free installation with high reliability GrowFlux Mesh wireless connectivity. These key features allow growers to place the sensors anywhere among the plant canopy, zeroing in on the microclimate variations that are affecting their crops.

Detection technique

There are two basic types of carbon dioxide sensing techniques, and not all detection techniques are equal.

Capacitive sensing - also known as CMOS gas sensing - this technique uses a small semiconductor chip inside the sensor that is coated in a specialized coating and layered with a micro heating plate. This low cost sensor detects gases such as CO2, carbon monoxide, alcohols, volatile organic compounds (VOCs), and other gases by measuring the change in capacitance of the coating on the chip as it absorbs these gases. This type of sensor responds primarily to VOCs as well as hundreds of other compounds in the air, and is generally not well suited for horticultural use.

Non-dispersive infrared (NDIR) - this technique uses an infrared light source and an infrared detector to measure CO2 in the air; the optics and precision of these devices are highly engineered to only measure CO2 - NDIR detectors do not respond to other gases and VOCs in the air.

Not only does GrowFlux’s CO2 Microclimate Sensor use NDIR detection, it also compensates the measurement for atmospheric pressure and relative using a separate pressure sensor, giving optimal accuracy in varying conditions.

Wireless reliability

Wireless CO2 sensors can be placed closer to crops and across large areas. Wireless CO2 sensors can also be re-positioned easily to develop a better understanding of microclimates in your cultivation space. The wireless technology within the sensor can affect monitoring practices.

Response time

CO2 sensors typically use a permeable housing to protect sensitive detector elements from dust. The design of these protective housings greatly affects how fast air permeates into the detector, and in turn how fast a carbon dioxide sensor responds to changes in CO2 concentration in the air. Some sensors on the market can take up to an hour to stabilize to an accurate reading.

For horticulture applications using carbon dioxide supplementation, relatively fast response times are necessary to capture surges in CO2 concentration

Battery Life

Engineering NDIR CO2 detectors for long battery life is a complex challenge; up until 2020, very few battery powered CO2 sensors even existed.

Data

Sending the data directly to the cloud in real time unlocks the full potential of the data; cloud based data logging makes the sensor data visible in real time, opening up integrations with other applications and systems. In our experience, logging devices which store sensor data locally lead to poor data collection practices - personnel lose data, get lazy and stop consistently gathering data, and often don’t budget the time to manage the data with spreadsheets.

As with any cloud connected sensor, be sure to select a sensor that allows for raw data download and integration with other systems with a software API.

Calibration

All CO2 sensors drift in accuracy slowly over time. Look for a sensor with a robust and easy to perform calibration procedure. We have even seen some sensors marketed for horticulture use that entirely lack calibration methods. Some CO2 sensors on the market are built first for indoor air quality sensing in buildings, where the CO2 concentration typically drops to outdoor ambient levels at some point each 24 hours - these sensors often use autocalibration techniques based on this diurnal rhythm. Such autocalibration methods will lead to inaccurate data when used in horticulture.

GrowFlux’s CO2 Microclimate Sensor can be calibrated outdoors in minutes without any specialized equipment.

The GrowFlux team recently returned from Indoor Ag-Con Asia in Singapore. With the conference in its fourth year in Asia, established indoor farms, tech companies, researchers, entrepreneurs, and government officials gathered to share the latest developments in indoor ag-tech. Here is a summary of our key take-aways.

Sensing

Sensors play a critical role in indoor farms - especially indoor vertical farms challenged with thermal stratification, causing different micro-climates throughout the controlled environment. Going beyond conventional sensors, hyperspectral cameras and biosensors for plant hormones - both methods to directly detect plant responses- were featured by researchers developing new technologies for the industry.

Scalability

Automation, artificial intelligence, robotics, and IoT were discussed heavily at Indoor Ag-Con Asia - all technologies that are key to scaling and are currently used in profitable indoor farms, and all technologies indoor farms must master to achieve scalability.

IoT

With many sessions touching on IoT in established indoor farms as though it was an afterthought, it is clear the role of connected devices in indoor farming is firmly rooted in the industry. GrowFlux discussed the importance of using robust IoT technology - such as time series database technology, standards, and scalable technologies - to enable an AI powered future of indoor farming.

Lighting

Lighting was among the most discussed topics at Indoor Ag-Con Asia, with speakers from Sananbio, National Taiwan University, Signify, GrowFlux, and others giving talks focused on lighting, spectrum, and controls. The significance of crop specific spectral control was highlighted throughout many presentations, underscoring the impact GrowFlux’s tunable lighting technology in the industry.

Seeds for Indoor Ag

Several presenters discussed the emergence of new seed developed for indoor cultivation which holds the promise of higher profitability, considering most of the conventional seed available today is adapted for the challenges that come with outdoor cultivation, such as disease and pest resistance.

When planning a large scale Controlled Environment Agriculture (CEA) facility such as a hybrid lit greenhouse or indoor cultivation space, network resilience, network set up time, and installation cost are important factors to consider in selecting a horticultural lighting solution. Some lighting solutions on the market require zone controllers and data cables, which adds labor and cost to the installation process. Most wireless lighting control solutions require a multi step network setup process for each fixture, which adds up to a significant amount of time for facilities requiring hundreds or thousands of fixtures. 

For wireless control solutions, network resilience is an important factor to consider for large scale facilities. Unreliable lighting network connectivity can grind a large facility to a halt, sucking up time and resources to troubleshoot network issues all while the lighting solution is not performing as designed.

Only GrowFlux offers AetherMesh wireless controls on all of its products. AetherMesh was designed specifically for large scale CEA facilities and solves the issues discussed above:

Network resilience:

• AetherMesh communicates on Sub 1-GHz frequencies and utilizes a high efficiency, high gain antenna, ensuring that wireless signals easily penetrate through dense buildings, multiple walls, concrete, and warehouses containing dense arrays of shelving.

• Line of sight range of 1+ mile (1.6+ km) is possible between AetherMesh devices; indoor range through walls is typically upwards of 500ft (150+ m).

• AetherMesh wireless mesh links self heal. If a device has trouble routing a message through one route, the mesh automatically finds another path through which to route messages. All network nodes maintain multiple network paths through which to route messages, choosing the most power and traffic efficient route in real time.

• AetherMesh splits the 902-928 MHz band into 50 channels; the network automatically channel hops communication across these channels to avoid interference.

• When we communicate lighting settings to a zone of fixtures, we send up to 90 days of scheduled control. This ensures that fixtures know exactly what they should be doing in the event of communication failure. Fixtures immediately get back to the correct scheduled control after any power failures.

Network setup time:

• GrowFlux products incorporating AetherMesh wireless control set up rapidly out of the box - simply power on the device for the first time within 10 feet of your Access Point, and the device will securely join and remember the network within 30 seconds. AetherMesh network setup does not involve passwords, codes, IP address, or any other complicated network setup steps.

• Connecting hundreds or thousands of fixtures happens as fast as the units are unpacked. Unpacking and initial power on occurs near an Access Point prior to hanging the fixture in the grow space.

• Zone definition is entirely software based with our browser based interface - zones are not defined through network settings.

Installation cost:

• One Access Point can support networks upwards of 1000 devices, significantly reducing cost

• Zone definition is entirely software based, so hardware zone controllers are eliminated.

• Every fixture on the network operates as a full power wireless mesh node (battery powered sensors perform limited extension of the mesh network to conserve battery life). This means repeaters and additional gateways are not required for large networks.

• Since GrowFlux products are fully wireless, the installation labor and cost associated with data cables and controllers is eliminated.

Coefficient of Utilization (CU) is a measure of how much light exiting the fixture will fall on a canopy area of a certain size; CU is an important factor to consider in designing an energy efficient Controlled Environment Agriculture (CEA) facility. CU is expressed as a ratio of the total light emitted by the fixture to the light that falls on an area of canopy of a defined size. It is important to note that the light that does not fall on the canopy directly under the fixture may either be wasted (to walls or floor), or may fall on canopy area adjacent to the fixture, depending on the design of the facility.

The American Society of Agricultural and Biological Engineers (ASABE) published the first of three standards for the horticulture lighting industry on August 8, 2017, bringing much needed codification to horticulture lighting technology. ANSI/ASABE Standard S640 titled "Quantities and Units of Electromagnetic Radiation for Plants (Photosynthetic Organisms)" establishes quantities and units used to describe light in relation to plants. Standards are important to the industry because they help everyone get on the same page with regard to the language used to describe the technology, the units of measure for lighting, metrics used to market products, and methods of bench-marking performance. 

The first of three standards, ANSI/ASABE S640, covers units of measure used to describe horticulture lighting. We took a look a the standard and summarized some key points:

1. PAR (photosynthetic active radiation) is a unit of measure of radiation relevant to plant growth, falls in the wavelength range of 400-700nm, and is expressed in two terms:

• PPF - Photosynthetic Photon Flux - PAR emitted by a source, measured in units of micromoles

• PPFD - Photosynthetic Photon Flux Density - PAR that falls on a unit of surface area

2. There are several ways to describe the wavelength portion of a PAR measure; these include Photosynthetic (400-700nm), UV (100-400nm), Far Red (700-800), and spectral (100-800nm). This results in terms such as Far Red Photon Flux Density, UV Photon Flux Density, or Spectral Photon Flux Density - in addition to Photosynthetic Photon Flux Density (PPFD). 

3. A measure may use two high level types of units to describe radiation: Radiate units (a quantity of energy) or Quantum units (a quantity of photons). This means Photosynthetic Photon Flux and Photosynthetic Radiant Flux both describe the same thing, however the first is expressed in micromoles (or µmol, a quantity of photons) and the latter is expressed in watts (W, a unit of energy). 

4. Far red light falls between 700 and 800nm

5. UV light is divided into three bands:

• UVA - 315-400nm

• UVB - 280-315nm

• UVC - 100-280nm

6. There are two distinct ways to plot a PAR spectrum:

• SPD, Spectral Power Distribution, a plot of PAR against wavelength, expressed in the units of radiant watts

• SQD, Spectral Quantum Distribution, a plot of PAR against wavelength, expressed in the units of micromoles

7. Daily Light Interval is a measure of PPFD over a 24 hour period

Discussion

The standard discusses rationale behind several decisions, and notes that there is currently no accepted interpolation of bands across the PAR spectrum (as is the case with the UV spectrum). We have provided a brief summary of key components of the standard; we suggest readers purchase and read the full standard for a comprehensive overview of the units used to describe PAR. 

Whats next?

• The Design Lights Consortium (DLC) will publish draft policy for energy efficiency in horticultural lighting in September 2018. This will create uniform requirements for energy rebates and incentives among utility providers

• ASABE will publish the next horticulture lighting standard some time in 2018

Further reading:

• Horticultural Lighting Metrics, Urban Ag News, blog post by Ian Ashdown, P. Eng., FIES

• ASABE Publishes First of Three Horticultural LED Lighting Standards, ASABE News