The availability of solar radiation in a bow-type, air-inflated, double polyethylene covered greenhouse was studied. Solar total radiation (0.285 to 2.8 μm waveband) transmittance and the transmittance of photosynthetically active radiation (solar PAR, 0.4 to 0.7 μm) were compared. The comparisons were reported for measurements made both at the glazing and the plant canopy levels. A relationship was previously determined for the available solar total radiation (W m-2) and solar PAR (μmol s-1 m-2), transmitted through the atmosphere. This report focuses on the effects of glazing and structure on transmitting ambient solar radiation and the development of a relationship for transmittance of solar total radiation (W m-2) versus solar PAR (μmol s-1 m-2) between the two wavebands.
Previous studies on high pressure fogging have shown their capability for maintaining temperature and humidity in acceptable ranges most of the year in greenhouses located in semiarid regions. The heat load, and therefore cooling demand, inside the greenhouse vary during the day and throughout the seasons. Thus, it may be advantageous to use a variable pressure fogging (VPF) system, where specific fog rates can be supplied based on the cooling demand. However, the absence of effective cooling strategies is one of the drawbacks limiting the extensive use of these systems. A well defined control strategy should account for plant's contribution on cooling and humidification in the control algorithm. This study compared the accuracy of three evapotranspiration models using measured values from greenhouse grown pepper plants. The results showed that Stanghellini model (R2=0.93) predicted measured evapotranspiration rates slightly better than Penman-Monteith (R2=0.84) and Takakura models (R2=0.79). Furthermore, a computer simulation was developed to compare a proposed control algorithm for VPF to a typical on/off fixed pressure fogging system based on vapor pressure deficit (VPD). Results showed that VPD based fixed pressure fogging strategy consumed more water and energy compared to the VPF system. Cycling of the pump was smaller and higher stability of temperature and relative humidity were achieved by the operation of the VPF system.
A mission aboard a space vehicle to other planets takes time. To sustain life, the space crew's three basic needs including air, water and food need to be replenished. Today, researchers are studying alternatives to meet these needs considering the special circumstances related to space travel. Efforts to develop bioregenerative life support systems (BLSS) are underway. Over the years, NASA has been providing leadership in developing BLSS.
Simulated performance of a greenhouse cooling control strategy with natural ventilation and fog cooling. Villarreal-Guerrero, F., M. Kacira, e. Fitz-Rodriguez, R. Linker, C. Kubota, G. giacomelli, A. Arbel. 2011. Simulated performance of a greenhouse cooling control strategy with natural ventilation and fog cooling. Biosystems Engineering. Published.
Information acquisition is the foremost requirement for the control and continued operation of any complex system. This is especially true when a plant production system is used as a major component in a sustainable life support system. The plant production system not only provides food and fiber but is a means of providing critically needed life supporting elements such as O2 and purified H2O. The success of the plant production system relies on close monitoring and control of the production system. Machine vision technology was evaluated for the monitoring of plant health and development and showed promising results. Spectral and morphological characteristics of a model plant were studied under various artificially induced stress conditions. From the spectroscopic studies, it was found that the stresses can be determined from visual and non-visual symptoms. The development of the plant can also be quantified using a video image analysis base approach. The correlations between the qualities of the model plant and machine vision measured spectral features were established. The success of the research has shown a great potential in building an automated, closed-loop plant production system in controlled environments.