Original papers
Control of greenhouse-air energy and vapor pressure deficit with heating, variable fogging rates and variable vent configurations: Simulated effectiveness under varied outside climates

https://doi.org/10.1016/j.compag.2020.105515Get rights and content

Highlights

  • Strategy kept setpoints when either cooling or heating was needed in the greenhouse.

  • Fogging lowered VPD and ventilation lowered enthalpy while heating increased it.

  • Transpiration cooled the greenhouse air by adding up to 84.5% of the water vapor.

  • Control not effective when it wasn’t psychrometrically possible to reach setpoints.

Abstract

Climate in greenhouses is continuously influenced by the outside environmental conditions. Outside conditions are always variable, especially in locations with extreme climates. Under non-extreme climates, greenhouses equipped with natural ventilation systems coupled with on–off controllers may be sufficient to effectively maintain appropriate climate conditions for plant growth. However, additional and flexible climate control systems, such as variable frequency drive (VFD) controllers, may be needed under extreme environments. In this study, the performance of a greenhouse climate control strategy, which considers plant transpiration, includes heating, operates variable vent configurations and a fogging system on a VFD basis, was tested by computer simulations. The strategy uses a set point of air specific enthalpy (55.8 kJ kg−1) to control the heaters and vents while a set point of Vapor Pressure Deficit (VPD) of 1.0 kPa is used to control the fogging system. Simulations were performed for two locations with different climates to test the strategy’s capabilities. Set points were effectively maintained whenever cooling demands existed in the greenhouse. For that, the crop played a key role by adding to the atmosphere on average 55.14 and 84.53% of the water vapor by means of plant transpiration for the first and second locations, respectively. When demands for heating existed, the set points were maintained whenever it was psychrometrically possible. When the outside air is at high humidity levels, the set points cannot be achieved under this approach. Under such conditions, the set points may be continuously and simultaneously kept if a dehumidification action is added to the strategy.

Introduction

Outside conditions are always variable, especially in locations with extreme environments. Climate in greenhouses is continuously influenced by the outside conditions. Thus greenhouse climate control is needed to maintain desired setpoints. Under non-extreme conditions, natural ventilation (NV), the most common method used worldwide aiding to maintain suitable climate conditions for plant production (Kittas et al., 1997, Katsoulas et al., 2006), together with on–off control logics, may be sufficient to effectively maintain appropriate climate conditions for plant growth. However, when the outside climate is extreme, as it is in arid and semiarid regions, other control systems such as cooling (Sethi and Sharma, 2007), heating (van Beveren et al., 2019), and flexible controllers (Pahuja et al., 2015), such as variable frequency drives (VFD) (Teitel et al., 2004), may be used to enhance the capabilities of the greenhouse climate control systems. Hybrid systems, such as the aforementioned, must be accompanied with effective control strategies and should be aligned with local climates to ensure appropriate greenhouse environmental conditions (Ghoulem et al., 2019).

In the case of greenhouse cooling, previous experimentation with fogging has proven good results (Sase et al., 2006, Villarreal-Guerrero et al., 2013). Fogging systems operate with a lower water use (López et al., 2012) and a higher environmental uniformity than pad-fan (Toida et al., 2006), improving plant productivity (Leyva et al., 2013, Lu et al., 2015). Evaporative cooling, such as fogging systems, simultaneously used with NV and shading could potentially reduce greenhouse energy requirements (Ghoulem et al., 2019), and operation costs, instead of coupling it with mechanical ventilation. Furthermore, fogging systems could also be used for applying crop-protection products (Sánchez-Hermosilla et al., 2013).

Several climate control strategies employing fogging systems coupled with NV have been developed and experimented (Baille et al., 2006, Sase et al., 2006, Handarto et al., 2007, Li, 2007, Perdigones et al., 2008, Garcia et al., 2011, Villarreal-Guerrero et al., 2012a, Lu et al., 2015). However, the control of cooling with fog and NV is complex due to the interaction of various environmental factors (Merril et al., 2016). In addition, when the outside climate gets too cold and cooling control is not needed, the use of heating may be required to be psychrometrically able to reach appropriate set points for plant growth. Thus, there is still a need for more research on how to effectively control the climate of greenhouses under varied outside conditions.

In the past years, a strategy for NV coupled with fogging systems and its control algorithm was developed (Villarreal-Guerrero et al., 2012a) and validated (Villarreal-Guerrero et al., 2013) for a semiarid greenhouse. During validation, the strategy performed satisfactorily. Moreover, the capabilities of the strategy to maintain a desired greenhouse climate under different outside climatic conditions were tested afterwards (Villarreal-Guerrero et al., 2014). The strategy showed a good performance when cooling was needed in the greenhouse. However, since the strategy was primarily developed for cooling, a tight control on the set points was not possible during night and early in the morning when increasing the greenhouse internal energy was required.

Therefore, the original strategy was improved and the algorithm modified by including a heating component with the same principle originally used for cooling. The present study presents results from computer simulations of the strategy under two locations with varied outside climates. An analysis was made on the capabilities of the strategy on maintaining desired climate conditions. In addition, recommendations for further improvements on the algorithm are stated.

Section snippets

The climate control strategy

In this study, we evaluated the capabilities of a greenhouse climate control strategy, which considers the cooling and humidification effects from crop transpiration. The strategy operates with variable vent configurations, a fogging system operated on a VFD basis and proportional heating (100 and 200 W m−2). The strategy uses set points of air enthalpy to take actions on the vent configurations and the heating system. Likewise, it uses set points of air VPD to control the fogging rate. These

Results and discussion

To find out about the capabilities of the new strategy to maintain the greenhouse climate around the set points, seven days were simulated. Four days corresponded to the first location while three were measured at the second one. Table 1 shows some descriptive values prevailing during such days. In general, SLP has a hotter and a drier climate than Chapingo. Thus, the strategy would normally have to perform more cooling in SLP than in Chapingo while more heating may be needed in Chapingo than

Conclusions

The performance of a strategy to control the greenhouse climate was tested for two locations with different climates using numerical simulations. The strategy equipped with cooling showed a good performance whenever cooling requirements were present. When conditions were cold and humid, the addition of a heating component to the strategy allowed achieving the desired set points. However, when the water vapor present in the air was excessive, the heating component of the strategy was not capable

CRediT authorship contribution statement

Federico Villarreal-Guerrero: Conceptualization, Methodology, Software, Writing - original draft. Alfredo Pinedo-Alvarez: Data curation, Writing - review & editing. Jorge Flores-Velázquez: Investigation, Visualization, Supervision, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors deeply thank the ‘Universidad Autónoma Chapingo’ (UACh), for the help and the opportunity provided to access the data collected from the weather station installed at its facilities. Likewise, the authors thank the personnel at the 'Facultad de Agronomía y Veterinaria, UASLP', for allowing us to collect the weather data needed to perform the simulations for this location.

References (31)

Cited by (15)

  • Effects of vent opening, wind speed, and crop height on microenvironment in three-span arched greenhouse under natural ventilation

    2022, Computers and Electronics in Agriculture
    Citation Excerpt :

    Natural ventilation is an important factor affecting greenhouse production, which is greatly influenced by ventilation configuration. Appropriate ventilation mode is conducive to guiding external air flow into the room, forming a better airflow field, and improving the cooling and dehumidification effect of the greenhouse (Bournet et al., 2007; He et al., 2015b; McCartney et al., 2018; Villarreal-Guerrero et al., 2020). There are three main factors that impact natural ventilation: greenhouse factors (greenhouse type, size and internal crops), external factors (wind cases, solar radiation and local environment), and human factors (ventilation configuration, wet curtain and sunshade).

  • Feasibility study of wind turbine system integrated with insulated Greenhouse: Case study in Tunisia

    2021, Sustainable Energy Technologies and Assessments
    Citation Excerpt :

    Besides, the energy optimization efficiency of greenhouses is significantly enhanced thanks to the control strategy, including PID, Fuzzy Logic Controller FLC, predictive, and optimal controls, etc. Villarreal-Guerrero [4] tested by simulations the performance of a variable frequency drive control, which is applied to the vents, heaters, and fogging systems to control the air energy and vapor pressure of greenhouse under different climates. The disadvantage of this command is that the set-points cannot be attained with a high level of ambient humidity.

  • Design and construction of bioclimatic wooden greenhouses 4: Architectural integration and quantitative analyses

    2023, Design and Construction of Bioclimatic Wooden Greenhouses 4: Architectural Integration and Quantitative Analyses
View all citing articles on Scopus
View full text