Australian greenhouse consultant Graeme Smith explains how Temperature Integration could be considered in the battle against fast-rising energy costs. He explains how tracking the 24hour temperature can help a grower do so by maintaining an optimum 24t sum.
"The cost of energy is fast rising globally that I suspect is due to ever-dwindling supplies, poor chain management and certainly some profiteering, and is affecting a wide range of industries with our protected cropping industry not immune," says Graeme Smith. "It has strong impacts on our cost of production and viability that is already significant in greenhouse, especially semi‐closed, and vertical farm systems. Our modern controlled production systems, even with tighter management of energy consumption, are also affected by rising costs therefore it is prudent to consider alternate solutions that are practical, reliable, controllable, and achieve a significant reduction in energy with little to no effect on crop yield." According to Graeme, TI (temperature integration) could be considered.
Conventional 24hour temperature control
Conventional greenhouse control systems normally allow for a wide range of time periods over a typical 24hour day, with many allowing ramping up and down into and out of these periods and their target setpoints can be influenced by many variables to steer our crops for enhanced yield, quality and produce uniformity. "However in a challenging paradigm of increasing energy costs, we should turn to the basic crop production principles on the integration of plant physiology (how crops grow and what affects their growth), with environmental management: a growth blueprint."
24hour temperature sum (24t)
A key principle for all growers is to track their 24hour temperature (24t) to ensure it closely matches the amount of light energy received by the plants each day, the so‐called radiation sum or DLI. Along with CO2 levels, these parameters are very important in terms of plant growth and development by following a well‐known ‘blueprint for growth’ profile in terms of these measured values, Graeme explains. "Instantaneous temperature or temperature of a plant at any given moment is important in terms of sugar production (photosynthesis) or transpiration rates, whereas the 24hour temperature sum influences the development rates and architecture of a plant (e.g. producing 3 leaves, then a flower truss, then 3 leaves, etc, in a tomato plant) n.b."
"For plant development, the average temperature is generally more important than the instantaneous temperature Both humans and plants respond to circadian rhythms and plants have a special function whereby they adapt to an average 24t sum over an extended period and they typically respond to periods of around 7days."
So what's the use of this in real life growing? "The practical application of this average 24t sum could allow a grower to repair a broken boiler that is down for say 2 or 3 days, therefore the 24t sum is lower, increase the 24t sum for the next 2 or 3 days to fill in the lost temperature profile, and the plant will continue as if nothing happened in terms of plant development as the 24t sum is normal and on target over a 7‐day period. n.b. there are bandwidth limits as to how cold or hot the plants can get over this period!" Graeme says. "TI can exploit this plant development profile by varying the daily and nightly temperature highs and lows yet maintain an optimum 24t sum resulting in maintaining plant development rates with no decrease in production."
Conventional daily temperature management
The following chart describes a typical daily heating and ventilation temperature profile a greenhouse grower may follow to steer their crops using 4 time periods and some ramping with various influences on temperature setpoints based on accumulated light or other climate factors
Or in a far simpler way, could look like the following;
TI daily temperature management TI temperature control simply introduces a fixed day/night maximum and minimum temperate target and may deliver the following example temperature profile;
Employing a TI strategy, we target the 24t sum and in a more sophisticated scenario, a grower may deliver the following example temperature profile with TI compared to a conventional strategy
TI allows a higher bandwidth of maximum and minimum temperatures yet results in exactly the same 24t sum to maintain consistent plant development rates.
TI has no fixed heating temperature per period, has an adjustable deviation range that results in less energy demand (lower night heating), less day ventilation (higher CO2 efficiency), reduces any energy peaks, and improves production scheduling.
To optimize TI, a climate screen (preferably energy type) and scheduled weather forecasting is recommended with a climate computer to track your 24t sum on a continual basis to target an adjustable temperature bandwidth (low to high) of 4–8C.
Potential energy savings
In practical use, a bandwidth of 4C can deliver an energy saving of ~5 ‐ 10%, and a bandwidth of 8C, can deliver an energy saving of ~10 ‐ 20%. "All with no harmful effects on the crop!", Graeme emphasizes.
To summarise TI – temperature integration,
• For plant development, the average temperature is generally more important than the instantaneous temperature
• Crops respond to the average temperature sum of ± 7 days • Temperature can deviate more than 200 degree‐hours
• TI has no fixed heating temperature per period
• Lower heating demand at night (energy savings), higher ventilation temperatures during the day (higher CO2 efficiency)
• Temporary temperature deviations can be accepted (adjustable deviation range 40 ‐ 80C)
• A screen and scheduled weather forecasting is recommended with a climate computer to track and target 24t sum to match radiation sum
• Modern climate computers have a ‘TI’ software setting to automate this tracking and control process (requires setpoint programming)
• TI has no harmful effects on the crop!
"Temperature Integration (TI) has the significant ability to save growers from 5 – 20% energy to improve viability, increase CO2 efficiency to lift yield and not adversely affect the crop," Graeme summarises. "Therefore could be considered by growers as part of their enhanced ‘blueprint for growth’ pathway to improved production and provide a buffer against rising energy costs!"