Copyright (c) 2012 All rights reserved. http://works.bepress.com/iyildiz Recent documents in Ilhami Yildiz en-us Sat, 24 Nov 2012 12:26:58 PST 3600 http://works.bepress.com/iyildiz/10 http://works.bepress.com/iyildiz/10 Fri, 02 Oct 2009 11:26:39 PDT The purpose of this study was to determine and compare the performances of conventional and heat pump systems for cooling open and closed loop (confined) greenhouse systems. A dynamic simulation model was developed and validated to predict energy and mass exchanges in a greenhouse as a function of dynamic environmental factors. The model has options to evaluate the effects of location, time of the year, orientation, single and double polyethylene glazings, conventional and heat pump heating and cooling systems, CO₂ enrichment, ventilation, variable shading, and the use of night curtains in open and confined greenhouse environments. Variable shading, ventilation and evaporative cooling provided cooling in the conventional system. In the heat pump systems, however, gas fired heat pump units provided cooling. Outputs of the simulation model included both temporal and vertical distribution of air, leaf, floor and cover temperatures, CO₂, relative humidity, solar radiation, and photosynthetically active radiation in addition to the dynamics of photosynthesis, respiration, transpiration, energy and CO₂ use and fixation in the greenhouse. This study concluded that the heat pump system performed very well with a variable shading system meeting the cooling requirements of both open and confined greenhouse systems.

]]> Ilhami Yildiz et al. Articles http://works.bepress.com/iyildiz/9 http://works.bepress.com/iyildiz/9 Fri, 02 Oct 2009 11:26:38 PDT The degree-day method is commonly used to estimate energy consumption for heating and cooling in residential, commercial and industrial buildings, as well as in greenhouses, livestock facilities, storage facilities and warehouses. This article presents monthly and yearly averages and spatial distributions of heating, cooling, and industrial degree-days at the base temperatures of 18 °C and 20 °C, 18 °C and 24 °C, and 7 °C and 13 °C, respectively; as well as the corresponding number of days in Turkey. The findings presented here will facilitate the estimation of heating and cooling energy consumption for any residential, commercial and industrial buildings in Turkey, for any period of time (monthly, seasonal, etc.). From this analysis it will also be possible to compare and design alternative building systems in terms of energy efficiencies. If one prefers to use set point temperatures to indicate the resumption of the heating season would also be possible using the provided information in this article. In addition, utility companies and manufacturing/marketing companies of HVAC systems would be able to easily determine the demand, marketing strategies and policies based on the findings in this study.

]]> Ilhami Yildiz et al. Articles http://works.bepress.com/iyildiz/8 http://works.bepress.com/iyildiz/8 Fri, 02 Oct 2009 11:26:38 PDT The purpose of this study was to determine and compare the performances of conventional and heat pump systems for energy and water conservation in open and confined greenhouse systems. Conventional gas furnaces and evaporative cooling, respectively, provided heating and cooling in the conventional system. In the heat pump systems, gas-fired heat pump units provided both heating and cooling. The greenhouse with heat pump units also had an option to be operated as a completely confined system, using one of the heat pump units as a dehumidifier. Average energy consumption in winter was 56.9, 23.5, and 11.3 MJ/day.m² in the conventional, open, and closed loop (confined) heat pump systems, respectively. In spring, the same greenhouse systems averaged 20.6, 8.8, and 5.3 MJ/day.m², respectively. In summer, energy consumption was considerably less than those predicted for winter and spring. The major portion of the total energy consumption was for heating. Daily transpiration rates averaged for winter, spring, and summer were 2.09, 2.02, and 1.02 kg H₂O/day.m² in the conventional, open, and closed loop heat pump systems, respectively. In the closed loop system, almost all the transpired water was recovered on the cooling coils, making the overall water consumption in this system essentially zero. This study concluded that greenhouse operation with the heat pump system has a great potential for enormous energy, water, and CO₂ savings, as well as cooling and dehumidification. A confined greenhouse with a heat pump system would make it easier to control the humidity and keep high CO₂ levels, while reducing the risk of insects and diseases. A combination of open and closed loop systems would be the most energy conserving system, operating the system as a closed loop system in winter, spring and fall, and as an open system in summer.

]]> Ilhami Yildiz et al. Articles http://works.bepress.com/iyildiz/7 http://works.bepress.com/iyildiz/7 Fri, 02 Oct 2009 11:26:37 PDT The purpose of this study was to develop and validate a dynamic simulation model to be employed in accurate prediction of microclimate in a greenhouse as a function of dynamic environmental factors. The model has options to evaluate the effects of location, time of the year, orientation, single and double polyethylene glazings, conventional and heat pump heating and cooling systems, open and confined greenhouse systems, CO₂ enrichment, variable shading, and the use of night curtains. Conventional gas furnace and evaporative cooling, respectively, provided heating and cooling in the conventional system. In the heat pump systems, gas-fired heat pump units provided both heating and cooling. The heat pump systems were operated both as an open and a completely confined system. Outputs of the simulation model included both temporal and vertical distribution of air, leaf, floor and cover temperatures, CO₂, relative humidity, solar radiation, and photosynthetically active radiation in addition to the dynamics of photosynthesis, respiration, transpiration, energy and CO₂ use and fixation. Comparison of experimental and predicted results showed that the compared microclimatological parameters were in fairly good agreement. The greenhouse model developed in this study is useful for ecologists, plant scientists, and engineers to evaluate individual or combined effects of various forcing functions on the enclosed environment and plant responses; and to develop control strategies for different parameters.

]]> Ilhami Yildiz et al. Articles http://works.bepress.com/iyildiz/6 http://works.bepress.com/iyildiz/6 Wed, 30 Sep 2009 16:52:38 PDT Considerable effort is expended to conserve energy and water in current greenhouse systems, and look for alternative energy sources, especially passive heating and cooling strategies. Proper environmental management systems can significantly change the energy and moisture dynamics of greenhouse production systems. In this study, specifically, influences of dynamic row spacing on energy and water conservation were investigated. A dynamic computer simulation model was used to compare different row spacings, plant heights, and leaf dimensions to draw a conclusion about energy and water conservation. The results showed that using smaller spacings between cucumber crop rows (for instance, 0.5 m instead of 0.75 m) reduced energy consumption per unit floor area in average of 14.4%. With a decrease in row spacing, the total amount of surface for radiation exchange decreases, and plant canopy shading within the canopy increase consequently. This leads to less radiational and evaporative cooling in smaller row spacings, hence lower heating requirements during the heating season. By changing the row spacing from 0.75 m to 0.5 m, average water savings (adjusted to the whole greenhouse area) of 27.8% occurred. A complete system analysis is necessary to be able to make a viable conclusion in total energy and water conservation.

]]> A. Moya et al. Articles http://works.bepress.com/iyildiz/5 http://works.bepress.com/iyildiz/5 Wed, 30 Sep 2009 16:52:37 PDT In addition to the labor, energy and water consumption are the two main cost drivers in current greenhouse systems. Consequently, considerable effort is expended to conserve energy and water, and look for alternative energy sources. Greenhouses in hot and arid regions also require large quantities of water for irrigation. Proper environmental management systems can significantly change the energy and moisture dynamics of greenhouse production systems. This study aims to focus on reducing energy and water consumption in semi-arid California greenhouses. Influences of mulch (having different reflectivities) on energy and water conservation were investigated. The reflectivity of mulch used as a floor cover affects the radiation distribution within the canopy stand, eventually affecting the overall energy and water consumption. A dynamic computer simulation model was used to compare different mulch reflectivities, plant heights, and leaf dimensions to draw a conclusion about energy and water conservation. The results showed that using mulch with less reflectivity (for instance, 20% instead of 80%) reduced energy consumption by as much as 4.2%. With a decrease in reflectivity, the absorptivity of the mulch increases consequently. A high absorptivity results in higher rates of solar energy being absorbed during the day, and released during the night. The mulch functions as a collection device, while the floor itself being the thermal mass. By increasing the reflectivity from 20% to 80%, water savings of up to 8.6% occurred. The savings in energy consumption, therefore, always have to be seen in conjunction with the water consumption. Also, the effect of reflective mulch fades away as shade from canopy stand increases. A complete system analysis is necessary to obtain a complete energy and water balance and to be able to make a viable conclusion.

]]> T. Mehlitz et al. Articles http://works.bepress.com/iyildiz/4 http://works.bepress.com/iyildiz/4 Wed, 30 Sep 2009 16:52:36 PDT In addition to the labor, energy and water consumption are the two main cost drivers in current greenhouse systems. Consequently, considerable effort is expended to conserve energy and water, and look for alternative energy sources, especially environmentally friendly renewable energy sources and technologies. Greenhouses in hot and arid regions also require large quantities of water for irrigation. Using proper technologies and environmental management systems can significantly change the energy and moisture dynamics of greenhouse production systems. This study aims to focus on reducing natural gas, electricity, and water consumption in semi-arid California greenhouses introducing renewable energy heat pump technologies to both open and confined greenhouses in California. The confined system has no external aeration and has no need for further water supply. It has a great potential to reduce the demand for natural gas, the load on the power grid, and the demand for irrigation water in greenhouse operations. It also allows plant protection without using chemical insecticides and the accumulation of carbon dioxide without aeration losses.

]]> C. Hardin et al. Articles http://works.bepress.com/iyildiz/3 http://works.bepress.com/iyildiz/3 Wed, 30 Sep 2009 16:52:35 PDT At Cal Poly the motto is “Learn by Doing”. In the College of Agriculture, this is especially true and many of the labs provide an opportunity for students to implement this philosophy. Updated climate controls were installed in a series of greenhouses on the top floor of the Agricultural Science building that are used for student and faculty research projects. A Programmable Logic Controller (PLC) was installed to actuate the various vents, shading, heating, cooling and irrigation. A control program was developed to control and log temperatures and other operating parameters to monitor the greenhouse. An easy to use computer program was developed that is able to be accessed from a network web site. Implementation of this interface allows students and faculty to carry out projects and to keep accurate records of the environmental conditions affecting their research. The program emulates the previous control system so that it will be easy to use, but also offers other options not available before. This greenhouse allows for engineering students to develop additional control programs and gives them hands on experience and insight into their operation and function.

]]> G. Diaz et al. Articles http://works.bepress.com/iyildiz/1 http://works.bepress.com/iyildiz/1 Wed, 30 Sep 2009 16:52:34 PDT The objective of this study was to evaluate the effects of relative humidity, light management levels, minimum ventilation rates, CO₂ enrichment and canopy size on energy consumption in three different greenhouse systems (conventional, open-loop heat pump, and confined heat pump) in winter, spring, and summer months. No difference was observed in energy consumption with relative humidity set point levels in winter due to the already low relative humidity levels. Some differences were observed in spring and summer due to extra dehumidification required to maintain the inside relative humidity at lower levels. Energy consumption in summer was reduced up to 25.5% by using an 80% relative humidity set point instead of 70% in the open heat pump system. Using a 250 W/m² light management level instead of 350 W/m2 resulted in a 5% reduction in energy consumption in summer, but the energy used for ventilation and heating did not change in summer. The only change was observed in the energy required for cooling. However, the energy consumption was significantly affected by the minimum ventilation rate. A 50% reduction (using 0.005 m³/s.m² instead of 0.01 m³/s.m²) in the minimum ventilation rate resulted in 26%, 21%, and 1.5% decreases in total energy consumptions in winter, spring, and summer, respectively. Using a CO₂ enrichment level of 1000 ppm compared to an enrichment level of 350 ppm resulted in a slight decrease in leaf temperatures during the day. This decrease caused a decrease in the air temperature resulting in slightly higher energy consumption for heating the greenhouse. This small increase in the energy consumption was about 1.7%. The partial canopy (0.4 m) systems had more energy consumption than the full canopy (2.0 m) greenhouse systems.

]]> Ilhami Yildiz et al. Articles http://works.bepress.com/iyildiz/2 http://works.bepress.com/iyildiz/2 Wed, 30 Sep 2009 16:52:34 PDT The objective of this study was to evaluate the effects of relative humidity, light management, minimum ventilation rates, CO₂ enrichment and canopy size on water consumption in three different greenhouse systems (conventional, open heat pump, and confined heat pump) in winter, spring, and summer months. Using different relative humidity set points resulted in almost the same relative humidity regimes within the confined greenhouse system, resulting in similar transpiration rates. No difference was observed in transpiration rates in the open system in winter either, because the inside relative humidity levels never reached the 70% and 80% set points. Some differences were observed in spring and summer. Up to a 5.1% reduction was observed in transpiration rates by going from a 70% set point to an 80%. Maintaining an average solar radiation level of 250 W/m² instead of 350 W/m² inside the greenhouse reduced the transpiration rate approximately 12.5% at both relative humidity set points. Using a minimum ventilation rate of 0.005 m³/s.m² instead of 0.01 m³/s.m² reduced the transpiration rates about 16%, 11%, and 3% in winter, spring, and summer, respectively. The higher decrease in winter was caused by the increase in inside relative humidity when lower ventilation rate was used. Using a CO₂ enrichment level of 1000 ppm compared to an enrichment level of 350 ppm resulted in transpiration rates that were predicted to be slightly lower in all the three greenhouse systems used. This decrease was 14% in the confined system, and by about 5% in both the conventional and open heat pump systems. The partial canopy stands (0.4 m) had approximately 7%, 5%, and 6% higher transpiration rates than the full canopy stands (2.0 m) in the conventional, open heat pump, and confined heat pump systems, respectively.

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