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Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/4/2005 Publication Date: 11/1/2005 Citation: Kimball, B.A. 2005. Theory and performance of an infrared heater for ecosystem warming. Global Change Biology 11:2041-2056. Interpretive Summary: In order to study the likely effects of global warming on future ecosystems, including agricultural fields, a method for applying a heating treatment to open-field plant canopies [i.e., a temperature free-air controlled enhancement (T-FACE) system] is needed which will warm vegetation as expected by the future climate. One method which shows promise is infrared heating, but a theory of operation was lacking for predicting the performance of infrared heaters. Therefore, a theoretical equation was derived to predict the thermal radiation required to warm a plant canopy, expressed as the amount of power required to heat a unit land area by one degree. It proved to have good accuracy, as was determined by comparing the theoretical performance against actual data obtained from an experimental infrared heating system. This research will benefit all consumers of food and fiber. Technical Abstract: In order to study the likely effects of global warming on future ecosystems, a method for applying a heating treatment to open-field plant canopies [i.e., a temperature free-air controlled enhancement (T-FACE) system] is needed which will warm vegetation as expected by the future climate. One method which shows promise is infrared heating, but a theory of operation is needed for predicting the performance of infrared heaters. Therefore, a theoretical equation was derived to predict the thermal radiation power required to warm a plant canopy per degree rise in temperature per unit of heated land area. Another equation was derived to predict the thermal radiation efficiency of an incoloy rod infrared heater as a function of wind speed. An actual infrared heater system was also assembled which utilized two infrared thermometers to measure the temperature of a heated plot and that of an adjacent reference plot and which used proportional-integrative-derivative control of the heater to maintain a constant temperature difference between the two plots. Provided that it was not operated too high above the canopy, the heater system was able to maintain a constant set-point difference very well. Furthermore, there was good agreement between the measured and theoretical unit thermal radiation power requirements when tested on a Sudan grass (Sorghum vulgare) canopy. One problem that has been identified for infrared heating of experimental plots is that the vapor pressure gradients from inside the leaves to the air outside would not be the same as would be expected if the warming were done by heating the air everywhere, i.e. by global warming. Therefore, a theoretical equation was derived to compute how much water an infrared-warmed plant would lose in normal air compared to what it would have lost in air which had been warmed at constant relative humidity, as is predicted with global warming. On an hourly or daily basis, it proposed that this amount of water could be added back to plants using a drip irrigation system as a first order correction to this vapor pressure gradient problem. |
