Submitted to: Journal of Theoretical and Applied Climatology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2011
Publication Date: 10/1/2011
Citation: Kimball, B.A., Conley, M.M., Lewin, K.F. 2011. Performance and energy costs associated with scaling infrared heater arrays for warming field plots from 1 to 100 m. Journal of Theoretical and Applied Climatology. 108:247-265.
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, which has previously been demonstrated to work at a plot scale of 3 meters in diameter. However, in order to accommodate large stature vegetation, as well as to provide more treated plant sample material, it is desired to increase plot size, but costs will also up by an unknown amount. In this paper methodology is developed to account for both the efficiency of larger heaters and of smaller thermal radiation loses outside the plot area. Going from 3 to 100 meter scale plots for 4 degrees C (7 degrees F) of warming, electrical power costs are estimated to increase from about $6,800 to $2,300,000 per plot. However, there is an economy of scale such that the costs would be about $960 and $290 per m2 for the 3- and 100-m plots, respectively. This research will benefit all consumers of food and fiber.
Technical Abstract: To study the likely effects of global warming on open-field vegetation, hexagonal arrays of infrared heaters are currently being used for low-stature (<1 m) plants in small (=3 m) plots. To address larger ecosystem scales, herein we show that excellent uniformity of the warming can be achieved using nested hexagonal and rectangular arrays. Energy costs depend on the overall efficiency (useable infrared energy on the plot per electrical energy in), which varies with the radiometric efficiency (infrared radiation out per electrical energy in) of the individual heaters and with the geometric efficiency (fraction of thermal radiation that falls on useable plot area) associated with the arrangement of the heaters in an array. Overall efficiency would be about 26% at 4 ms-1 wind speed for a single hexagonal array over a 3-m-diameter plot and 67% for a 199-hexagon honeycomb array over a 100-m-diameter plot, thereby resulting in an economy of scale.