Submitted to: Acarology International Congress Proceedings
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. Acarology International Congress Proceedings. 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: There is a need to study the likely effects of global warming on ecosystems with experimental treatments as representative as possible of future environmental conditions. One approach that shows much promise is the use of hexagonal arrays of infrared heaters to warm canopies of vegetation. This approach is currently being used in several experiments on low-stature plants (<1 m) in 3-m-diameter plots (and smaller). However, in order to approach more realistic ecosystem scales, it is necessary to greatly increase plot size. By nesting hexagonal arrays in a honeycomb pattern, we show that excellent uniformity of the warming treatment can theoretically be achieved across the plots. Switching from heaters with a characteristic dimension of 60 mm to larger heaters with a characteristic dimension of 1220 mm would increase the theoretical heater radiometric efficiency (percentage of input electrical power emitted as thermal radiation) from about 69% to 82% at a wind speed of 4 m s-1, and the theoretical geometric efficiency (percentage of thermal radiation that falls within the useable plot area) would increase from about 37% to 84% as plot diameter increases from 3 to 100 m. The overall efficiency is the product of the radiometric and geometric efficiencies, which would be about 26% at the 4 m s-1 wind speed for a single hexagon of the smaller heaters over a 3-m-diameter plot and 69% for a 199-hexagon honeycomb over a 100-m-diameter plot. Assuming that 4°C is the desired degree of warming and that electricity costs US$0.1 per kWh, under Konza Prairie, KS conditions, annual energy costs would be about $8,500 for a 3-m-diameter plot and $3,300,000 for a 100-m-diameter plot. However, there is an economy of scale such that the costs would be about $1,200 and $410 per square meter for the 3- and 100-m plots, respectively.