A.J. Both

Controlling greenhouse light to a consistent daily integral

Lettuce growth data are presented that show the importance of the daily light integral for predictable vegetative growth. Dry mass accumulation is shown to be proportional to the light integral, and a consistent daily light integral is proposed to be central to consistent production. Supplemental lighting control rules are defined and described and a computer implementation is used in conjunction with ten years of hourly weather data to test (by simulation) adequacy of the rules to control supplemental lights and movable shades in greenhouses to achieve a consistent daily integral of Photosynthetically Active Radiation (PAR), mol-m –2 -day –1 , on days of either insufficient or excess solar irradiation, which are most days. The rules require neither historical data bases of weather characteristics nor daily weather forecasts. Control decisions are suggested to be made hourly, based on the current day’s accumulating solar PAR integral inside the greenhouse. The model is sensitive to time-of-day electricity rates, changing seasons, weather, greenhouse and component characteristics, and greenhouse location (latitude and longitude). The rules contain parameters with values suggested for northeastern United States solar conditions but which may be adjusted for local solar climates that are significantly different.

Guidelines for measuring and reporting environmental parameters for experiments in greenhouses

BackgroundThe importance of appropriate, accurate measurement and reporting of environmental parameters in plant sciences is a significant aspect of quality assurance for all researchers and their research. There is a clear need for ensuring research across the world can be compared, understood and where necessary replicated by fellow researchers. A common set of guidelines to educate, assist and encourage comparativeness is of great importance. On the other hand, the level of effort and attention to detail by an individual researcher should be commensurate with the particular research being conducted. For example, a researcher focusing on interactions of light and temperature should measure all relevant parameters and report a measurement summary that includes sufficient detail allowing for replication. Such detail may be less relevant when the impact of environmental parameters on plant growth and development is not the main research focus. However, it should be noted that the environmental experience of a plant during production can have significant impact when subsequent experiments investigate plants at a molecular, biochemical or genetic level or where species interactions are considered. Thus, researchers are encouraged to make a critical assessment of what parameters are of primary importance in their research and these parameters should be measured and reported.ContentThis paper brings together a collection of parameters that the authors, as members of International Committee on Controlled Environment Guidelines (ICCEG) in consultation with members of our three parent organizations, believe constitute those which should be recorded and reported when publishing scientific data from experiments in greenhouses. It provides recommendations to end users on when, how and where these parameters should be measured along with the appropriate internationally standardized units that should be used.

A Natural Ventilation Model for Open-Roof Greenhouses

A computer simulation model for natural ventilation in open-roof greenhouses was developed to predict the ventilation performance. The model predicts ventilation rate and the temperature differences between inside and outside, based on the weather and structural conditions including internal net radiation, wind velocity, and height and area of the roof openings. The ventilation rate was calculated from thermal buoyancy and wind forces. A sensible heat balance was incorporated to calculate the ventilation rate and the temperature difference simultaneously. A four-span open-roof greenhouse with roof sections hinging at the gutters and opening at the ridge, constructed on the Rutgers University campus, was used for data collection. Measurements of climate conditions in the direct vicinity of the greenhouse were conducted. Using the observed outdoor and greenhouse conditions, the model parameters were calibrated statistically. The accuracy of the model and the modifications to the model are discussed by comparing the predicted and observed greenhouse temperatures. It is shown that the internal temperature rise depends on the roof configuration as well as solar radiation and wind velocity. The resulting simulation model can be used to implement new environment control strategies for open-roof greenhouses.

Effect of temperature perturbations on tomato (Lycopersicon esculentum Mill.) quality and production scheduling

Summary Controlled environment experiments were conducted to evaluate the effect of a 2-week change in air temperature imposed after first fruit-set on tomato production scheduling and on the quality of vine-ripened fruit. Experiments were conducted with hydroponically-grown tomato (Lycopersicon esculentum Mill., cv. ‘Laura’). Air temperature was altered from control day/night temperature values of 23°/18°C for a 2-week period starting 10 d after fruit-set. Plants were returned to the 23°/18°C temperature and a minimum of eight fruits per treatment were harvested at three ripening stages, breaker (when 25% of the fruit skin had acquired a red tint), breaker plus 3 d, and breaker plus 6 d. A perturbation of ± 5°C (28°/23°C and 18°/13°C) was used in two Experiments (E1 and E2) and ± 7°C (30°/25°C and 16°/11°C) was used in a third Experiment (E3). Fruits were more responsive to an increase than to a decrease in temperature. Reductions in days to harvest (from 3.1 – 8.5 d) and fruit fresh weight at later stages of vine-ripening were observed for the high temperature treatments. Colour indices, soluble solids contents (SSC), acidity and viscosity at each ripening stage were significantly affected by high temperature treatments. The results indicate that short-term temperature perturbations following first fruit-set can influence the rates at which changes occurred in the external appearance of fruit (colour) and in their internal characteristics. The results can be used to improve environmental control and management strategies for tomato growers.

Evaluating Energy Savings Strategies Using Heat Pumps and Energy Storage for Greenhouses

As energy costs are increasing, many greenhouse operators are re-evaluating energy consumption and savings strategies. In most cases, updating older heating systems to more efficient units in addition to the use of double layer glazing, insulation materials, and energy curtains significantly reduces fuel consumption. Insulating greenhouses must not conflict with the need for high light transmission through the structure. Since solar radiation loads often significantly exceed the instantaneous heat requirement of a greenhouse, many ideas have been proposed to capture this excess heat and store it for later greenhouse heating. Heat pumps are promising for use in an integrated cooling and heating system. In the study described in this paper, a simple spreadsheet approach was used to evaluate the performance of a system utilizing a heat pump and water storage. The evaluation bases its calculations on historic hourly weather data to determine hourly cooling and heating rates and storage status. The calculations allow for evaluations of the appropriate size of the heat pump, storage device, and heat exchangers. The calculations are used to investigate storage capacities that are sized for one to a few days harvest of surplus heat from the greenhouse for a range of percentages of peak cooling requirement. The model includes the option of utilizing a geothermal source for the heat pump to charge the storage during periods when greenhouse cooling is not required. The first study presented examines the impact of increasing thermal storage capacity on heat utilization from a generic co-generation system. The second considers a specific, natural gas fired, fuel cell system for various sizes of greenhouse at two different locations and includes the utilization of CO2 from the reformer section. The heat pump study looks at the relationships between capacities of the heat pump and storage for two different locations. Provided hourly weather data are available for other sites, the spreadsheet approach can be used for other locations across the world.

Open-roof Greenhouse Design with Heated Ebb and Flood Floor

An open-roof greenhouse production system with a heated ebb and flood floor irrigation system is being developed and evaluated. In addition to continuous roof vents, the greenhouse is equipped with sidewall vents to allow for ventilation during windy and rainy conditions. This paper discusses the design details as well as the instrumentation used for the evaluation. Preliminary data, collected over a 2.5-month period, of light and temperature conditions are presented. The greenhouse temperature closely followed outside temperature conditions for the entire measurement period when the inside temperature exceeded the set point. The inside light conditions were significantly affected by the greenhouse structure, and inside light intensities around solar noon could exceed outside light intensities due to reflection from the opened roof segments.

Numerical Modeling of Greenhouse Floor Heating

A numerical simulation model of a greenhouse floor heating system was developed and validated using data collected in a research greenhouse located at Cook College, Rutgers University, New Brunswick, New Jersey. The model was then modified and used to evaluate two different heat pipe diameters and spacings that are typical in the greenhouse industry today: 13 mm (0.5 in.) diameter pipe placed on 22.9 cm (9 in.) centers, and 19 mm (0.75 in.) diameter pipe placed on 30.5 cm (12 in.) centers. Two heat pipe elevations within the solid concrete floor system were also simulated, and the effects of the pipes vertical position, diameter, and spacing on surface heat flux, surface temperature, and surface temperature uniformity were evaluated. The simulation results showed that the smaller diameter pipe placed closer together and at a lower elevation provided the best temperature uniformity without compromising other performance criteria. The model was then further modified to simulate flats with growing media placed on the floor surface. Model simulations were conducted for six different supply water temperatures ranging from 32.2°C (90°F) to 60°C (140°F), while maintaining a target ambient greenhouse air temperature of 15.6°C (60°F). The simulation outputs showed that using the smaller diameter pipe placed closer together resulted in a higher surface heat flux, a higher growing media temperature, and greater temperature uniformity within the growing media, for each supply water temperature simulated.

Proposed product label for electric lamps used in the plant sciences

Electric lamps are widely used to supplement sunlight (supplemental lighting) and daylength extension (photoperiodic lighting) for the production of horticultural crops in greenhouses and controlled environments. Recent advances in light-emitting diode (LED) technology nowprovide the horticultural industrywith multiple lighting options. However, growers are unable to compare technologies and LED options because of insufficient data on lamp performance metrics. Here, we propose a standardized product label that facilitates the comparison of lamps across manufacturers. This label includes the photosynthetically active radiation (PAR) efficacy, PAR conversion efficiency, photon flux density output in key wave bands, as well as the phytochrome photostationary state (PSS), red/far red ratio, and graphs of the normalized photon flux density across the 300–900 nm wave band and a horizontal distribution of the light output.

Creating a master plan for greenhouse operations

Changes in the greenhouse industry during the past decades have increased greenhouse construction and operation costs significantly. This makes it necessary to carefully plan the overall design of the facilities in order to avoid costly retrofits at a later stage. A comprehensive master plan is required that reflects how the owner/operator intends the completed facility to function. A key component of the plan is the careful integration of all the systems and buildings comprising the entire greenhouse operation.

Manipulation of Tomato Fruit Quality Through Temperature Perturbations in Controlled Environments

Quality factors such as size, color, taste, and nutritional content are important criteria for marketing of greenhouse tomato fruit. While the majority of the research on fruit quality factors focuses on effects of post-harvesting and storage conditions, the environmental conditions during plant growth and the time for which the fruit is allowed to ripen on the vine also influence fruit quality. Growth chamber experiments were performed with tomato (cv. Laura) aiming to study the influence of air temperature perturbations during fruit set on fruit quality at maturity, the time to harvest, and the harvest window. Plants were grown in 6” pots and pruned to the 2nd true leaf above the first fruit cluster. Nutrients were provided through a drip irrigation system. All plants were grown under the same environmental conditions except for a two week period beginning 10 days after fruit-set during which plants were assigned to one of three day/night temperature treatments, 28/23°C, 23/18°C, and 18/13°C. Five tomato fruits were harvested from each plant at three distinct physiological ages; breaker stage (taken as the point at which 25% of the fruit begins to turn red), breaker stage plus three days, and breaker stage plus six days. Harvested fruits were analyzed for mass, size, color, soluble solids content, pH, acidity, viscosity, and other quality parameters. Initial results show significant temperature effects on fruit size, mass, developmental rate, and fruit processing characteristics. The results are applicable towards the development of more efficient plant production strategies for greenhouse growers and for NASA’s advanced life support research program.