Search Results

You are looking at 21 - 30 of 120 items for :

  • "evaporative cooling" x
  • All content x
Clear All
Free access

Jack W. Buxton and John N. Walker

Natural-light growth chambers constructed within a greenhouse compartment were equipped with a ventilation/circulation system, two stages of heating, and evaporative cooling. Air drawn from the greenhouse compartment continuously ventilated the chambers; the air was heated or cooled to the set-point temperature. A computer-controlled environmental system maintained uniform temperatures within the chambers and maintained the temperature within ±1C of the set point at night and during periods of low solar radiation; during higher solar radiation periods, control was not as precise. Carbon dioxide concentration was accurately maintained, and the photosynthetic photon flux from supplemental high-pressure sodium lamps was ≈200 μmol·m-2·s-1. The natural-light growth chambers provide a means for studying the interactive effects of temperature, light, and other environmental variables in experiments to increase production efficiency.

Free access

Matthew Rogoyski, Alvan Gaus, Byron McNew, Israel Broner, and Thomas Mourney

A simulator of a control system for evaporative cooling of crop canopies was developed. This development, prior to implementation of an irrigation/cooling system, allowed for experimentation before committing resources to the field system. The project provided insight into problems of modeling interaction between biological, mechanical, and digital systems and demonstrated how specialists from diverse areas can solve these problems. The object orientation methodology and the C++ programming language were tools for development of this simulator. A communication mechanism was devised to facilitate interactions between software entities representing both concrete and abstract objects corresponding to the problem domain. The object-oriented approach to the system development allowed for better communication between team members, irrespective of their background in software engineering. The modular and polymorphic nature of the object-oriented code made it possible to plan for code reuse in future projects. Simulator development using the object-oriented paradigm was found to be preferable over the procedural model used by team members in other projects in the past.

Free access

Marvin P. Pritts

Manipulating light, temperature, moisture, and nutrients to favor plant growth and productivity is an important component of horticulture. The technology required to achieve such manipulation ranges from inexpensive, basic practices to elaborate, costly approaches involving the latest engineering advances. For example, pruning and mulching are relatively low-tech methods for improving light interception and soil moisture status in small fruit plantings. At the opposite extreme are glass houses with supplemental lighting, CO2 enrichment, and nutrient film hydroponic systems Of greatest value to small fruit growers, however, is technology that ran be applied in field situations, such as the use of overhead irrigation for maintaining soil moisture status, frost protection, and evaporative cooling. One of the greatest challenges to small fruit growers and rcsearchers is integrating new technology into production systems. The introduction of a new technique for environmental modification usually has indirect effects on other aspects of management, which may require additional technology to compensate for adverse changes while maintaining the favorable change. In addition, unique macro- and microclimates demand and market opportunities, specific solutions, and the result is a dynamic, diverse collage of production systems used by growers throughout the world.

Free access

Thomas G. Ranney

Leaf gas exchange and chlorophyll fluorescence measurements were used as indices for evaluating heat tolerance among five species of birch: paper (Betula papyrifera), European (B. pendula), Japanese (B. platyphylla var. japonica `Whitespire'), Himalayan (B. jacquemontii), and river (B. nigra). Measurements were conducted on individual leaves at temperatures ranging from 25C to 40C. Carbon exchange rates (CER) were depressed for all species at 40C. However, there was considerable variation in both absolute and relative (percent of maximum) CER among species at 40C; river birch maintained the highest absolute and relative CER while CER of paper birch was reduced the most. Although stomatal conductance of paper birch decreased at higher temperatures, internal leaf CO2 increased indicating that reduced stomatal conductance was not responsible for decreased CER. Stomatal conductance of river birch increased at higher temperatures which provided for enhanced uptake of CO2 and greater evaporative cooling. Variable chlorophyll fluorescence decreased similarly for both species with increasing temperatures. Measurements of dark respiration rates over the range of 25C to 40C suggested that the primary factor influencing variation in CER at higher temperatures was due to variation in respiration rates at higher temperatures.

Free access

James E. Faust, Sven Verlinden, and Royal D. Heins

Rapid reduction in temperature for two to three hours starting at sunrise reduces stem elongation compared to elongation of plants maintained under constant temperatures during the day. This experiment was designed to determine if syringing plants with water at sunrise would substitute for a reduction in air temperature or enhance the response to the drop in temperature. Easter lily (Lilium longiflorum Thumb.) plants were exposed to constant 20°C or to 20°C and then 16°C for a 3-hr period following sunrise. Half the plants in each temperature regime were syringed at 30-minute intervals with 20°C water for 3 hr starting 20 minutes before sunrise. Shoot-tip temperature during the three-hr pulse time averaged 20.0 and 17.3°C for the dry plants and 17.3 and 14.7°C for the syringed plants. Total elongation for the dry plants at 20°C was 30 cm and for the temperature-pulsed plants, 4.8 cm less; for the syringed plants, 3.3 and 5.8 cm less, respectively. While shoot-tip temperature of dry plants averaged 0.9°C above air temperature during the remaining hours of the day, syringed plants averaged 1.0°C cooler than the same air temperature even though plants had dried. The data indicate the reduction in stem elongation from a low-temperature pulse at sunrise can be enhanced by evaporative cooling.

Free access

A. Erez, Z. Yablowitz, and R. Korcinski

Fresh fruits of stone fruit species are either lacking or in short supply in the months of March and April on the world market. This results from the absence of late-maturing cultivars in most of these species and from their poor storage capabilities. In March–April, supply from the Southern Hemisphere is dwindling or finished, while supply from the Northern Hemisphere has not started yet. A horticultural system was developed in Israel to get early fruit ripening of stonefruit species. The system developed is based on early completion of dormancy requirements followed by greenhouse tree growing. The system uses the following elements: 1) Improve chilling accumulation in winter by using evaporative cooling, to prevent chilling negation by high day temperatures. 2) Monitor salt accumulation level to prevent damage to branches and buds. 3) Monitor bud temperature and evaluate dormancy development according to the dynamic model. 4) Use dormancy breaking chemicals to compensate for part of the chilling not applied. 5) Cover of the trees with polyethylene having the appropriate characteristics of light filtering. 6) Keep the temperature in the greenhouse lower than the maximal temperature allowed, at every specific stage of development by ventilation. By using this system, fruit ripening was advanced by 4 to 6 weeks in peaches and nectarines (harvested from late March) and by 4 weeks in sweet cherries (harvested from April 11). Yields of 20 to 30 tons/ha were obtained in both species with high fruit quality.

Free access

Y. Zhang, J.L. Shipp, and T.J. Jewett

Overhead fogging or misting is an essential technique applied in modern greenhouses for cooling and humidifying. This technique can be used to promote yield and quality of greenhouse crops either by providing favorable environment for the plant growth or by increasing the efficiency of greenhouse pest and disease control. In this study, the effect of high-pressure overhead misting on greenhouse climate and leaf surface microclimate conditions for cucumber crops in a glass greenhouse was investigated. It was found that the temperature of the greenhouse air was lowered by 5-6 °C and relative humidity was increased by 20% to 30% during misting. The temperature of sunlit leaves was slightly reduced in the morning (2-3 °C), and leaf wetness duration was significantly extended by misting. Leaf wetness duration under misting was predominately influenced by light intensity at the leaf level and was modelled as a function of misting period and average radiation intensity. Results of this study can be used to improve the predictions of pest and disease breakout and the efficiency of their control measures. The empirical model developed in this study can be integrated with leaf surface microclimate models to correctly predict surface moisture conditions and evaporative cooling from water films at the leaf surface.

Free access

Robert W. Langhans and Mauricio Salamanca

With the primary objective of assuring food safety at the production level, a HACCP (Hazard Analysis and Critical Control Point) plan was developed and implemented in an 8000-ft2 greenhouse producing 1000 heads of lettuce per day in Ithaca, N.Y. The plan was developed following the HACCP principles and application guidelines published by the National Advisory Committee on Microbiological Criteria for Foods (1997). The CEA glass greenhouse uses both artificial high-pressure sodium lamps and a shade curtain for light control. Temperature is controlled via evaporative cooling and water heating. Lettuce plants are grown in a hydroponic pond system and are harvested on day 35 from day of seeding. Known and reasonable risks from chemical, physical, and microbiological hazards were defined during the hazard analysis phase. Critical control points were identified in the maintenance of the pond water, the operation of evaporative coolers, shade curtains, and during harvesting and storage. Appropriate prerequisite programs were implemented before the HACCP plan as a baseline for achieving minimum working conditions. Proper critical limits for some potential hazards were established and monitoring programs set up to control them. Postharvest handling was setup in an adjacent head house that was adapted as a food manufacturing facility according to New York State Dept. of Agriculture and Markets standards. Potential applications will be discussed.

Free access

Thomas L. Davenport, Stanley P. Burg, and Thomas L. White

U.S. regulations prevent importation of fresh horticultural commodities that have not received an approved quarantine treatment assuring 100% mortality of potentially invasive insect pests. Because imported mangoes are likely to be infested by the Caribbean fruit fly (Anastrepha suspensa Loew) and other tropical fruit flies such as A. ludens Loew, A. striata, A. distincta, A. fraterculus, A. serpentina, or A. oblique, they must be hot-water treated prior to shipment in order to satisfy quarantine requirement. Hot water treatment often damages the fruit, especially if it is not fully mature. Hypobaric (low pressure = LP) intermodal shipping containers developed by the VacuFreshSM Corp. preserve fresh commodities, such as horticulturally mature mangoes, far longer than is possible using other technologies. We tested the ability of over 70,000 Caribbean fruit fly eggs and larvae to survive a simulated optimal hypobaric condition for shipment of mangoes (15 mm Hg, 98% RH, at the lowest, safe non-chilling temperature, 13 °C). A. suspensa eggs or larvae were maintained on agar media, flushed with one air change per hour at the storage pressure, and shielded with Mylar to prevent radiant heat uptake and limit evaporative cooling. Nearly 98% of the eggs and larvae were killed within 1 week at 15 mm Hg in eight replicated experiments. All eggs were killed at that pressure by 11 days, whereas a significant number survived at ambient pressure. Shipment of fresh produce using this technology promises to provide quarantine control while preserving the freshness of fully mature tropical fruits and vegetables.

Free access

Thayne Montague, Roger Kjelgren, and Larry Rupp

Research was conducted to investigate how energy balance of bark mulch and turf surfaces influence gas exchange and growth of recently transplanted trees. On several occasions over a 3-year period, stomatal conductance and leaf temperature were measured throughout the day on `Emerald Queen' Norway maple (Acer platanoides L.) and `Greenspire' littleleaf linden (Tilia cordata Mill.) trees growing over each surface. Tree water loss was estimated using a general transport flux equation applied to the tree crown apportioned between sunlit and shade layers. Microclimate variables were measured over each surface with a permanent weather station. Tree growth data were collected at the end of each growing season. Soil heat flux data revealed that a greater portion of incoming radiation was prevented from entering the soil below mulch than below turf. Due to this insulating effect, and consequent lack of evaporative cooling, mulch surface temperature was greater, and emitted more longwave radiation, than turf. Leaves over mulch intercepted more longwave radiation, had greater leaf temperature, and greater leaf-to-air vapor pressure difference than leaves over turf. As a result, leaves over mulch had greater stomatal closure than leaves over turf. Estimated tree water loss varied between surface treatments and with climatic conditions. Trees over turf had greater shoot elongation and leaf area than trees over mulch. These data suggest that gas exchange and growth of recently transplanted trees in an arid climate may be reduced if planted over nonvegetative, urban surfaces.