Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2007
Publication Date: 6/1/2008
Citation: Kimball, B.A., Conley, M.M., Wang, S., Xingwu, L., Morgan, J.A., Smith, D.P. 2008. Infrared heater arrays for warming ecosystem field plots. Global Change Biology, (14):309-320.
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 commercial heaters with adequate power emit their thermal radiation in non-uniform pattern. However, by assembling arrays of six heaters pointed toward the center of a circular 3-meter-diameter plot and tilted at an angle of 45° from vertical, uniform heating was achieved. Such arrays were tested for periods lasting more than a month over grazing land at Haibei, Qinghai, China and Cheyenne, WY. Good performance was observed at both sites. Thus, we conclude that these hexagonal arrays of ceramic infrared heaters can be a successful T-FACE system for warming ecosystem field plots. This research will benefit all consumers of food and fiber.
Technical Abstract: TThere is a need for methodology to warm open-field plots in order to study the likely effects of global warming on ecosystems in the future. Herein, we describe the development of arrays of more powerful and efficient infrared heaters with ceramic heating elements. By tilting the heaters at 45 degrees from horizontal and combining six of them in a hexagonal array, good uniformity of warming was achieved across 3-m-diameter plots. Moreover, there do not appear to be obstacles (other than financial) to scaling to larger plots. The efficiency [nh (%); thermal radiation out per electrical energy in] of these heaters was higher than that of the heaters used in most previous infrared heater experiments and can be described by: nh = 10 + 25exp(-0.17 u), where u is wind speed at 2m height (ms-1). Graphs are presented to estimate operating costs from degrees of warming, two types of plant canopy, and site windiness. Four such arrays were deployed over plots of grass at Haibei, Qinghai, China and another at Cheyenne, Wyoming, USA, along with corresponding reference plots with dummy heaters. Proportional integral derivative systems with infrared thermometers to sense canopy temperatures of the heated and reference plots were used to control the heater outputs. Over month-long periods at both sites, about 75% of canopy temperature observations were within 0.5 degrees C of the set-point temperature differences between heated reference plots. Electrical power consumption per 3-m-diameter plot averaged 58 and 80kWh day -1 for Haibei and Cheyenne, respectively. However, the desired temperature differences were set lower at Haibei (1.2 degrees C daytime, 1.7 degrees C night) than Cheyenne (1.5 degrees C daytime, 3.0 degrees C night), and Cheyenne is a windier site. Thus, we conclude that these hexagonal arrays of ceramic infrared heaters can be a successful temperature free-air-controlled enhancement (T-FACE) system for warming ecosystem field plots.